Preparation of Room-temperature Self-healing Recyclable Polyurethane Elastomers Based on Multiple Hydrogen/Nitrogen Coordination Boro-oxygen Bonds System

Preparation of Room-temperature Self-healing Recyclable Polyurethane Elastomers Based on Multiple Hydrogen/Nitrogen Coordination Boro-oxygen Bonds System | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Preparation of Room-temperature Self-healing Recyclable Polyurethane Elastomers Based on Multiple Hydrogen/Nitrogen Coordination Boro-oxygen Bonds System 雨辰 焦, Ming Zhou, Bo Pu, Xiaoling Yang, Chenyiting Li, Liangliang Xia, and 7 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8014090/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 10 Mar, 2026 Read the published version in Journal of Polymer Research → Version 1 posted 5 You are reading this latest preprint version Abstract Polyurethane elastomers have excellent tensile properties and elastic recovery properties, but traditional polyurethane elastomers are often broken and irreparable due to wear, so the research on high strength self-healing polyurethane elastomers has broad application prospects. In this study, based on the concept of intrinsic self-healing, multiple hydrogen bonds and boroxane rings with N-B coordination bonds were designed into the molecular. A novel polyurethane elastomer was prepared by four-step addition of polytetrahydrofuranediol, isophorone diisocyanate, 4,4'-methylene bis(2-chloroaniline), 2-formylphenylboric acid, toluene, N, N-dimethylacetamide and 2, 6-pyridinediol. The prepared elastomers exhibit strain-induced strengthening and have excellent self-healing properties as well as excellent mechanical properties. When the molar ratio of PDM/MOCA is 60/40(PU HB-60/40 ), the tensile strength of the material is 18.8 MPa (self-healing efficiency 94.7%), and elongation at break is 2132% (self-healing efficiency 91.7%), and toughness is 117.0 MJ·m -3 (self-healing efficiency 86.7%). Synchronous self-healing efficiency exceeds 86%. In addition, the elastomer also has the ability to be recyclable, and the change of mechanical properties are slightly before and after dissolution and reshaping. This study provides beneficial ideas for preparing room temperature self-healing recyclable polymers with high strength. polyurethane elastomers dynamic covalent/non-covalent bonds strength room-temperature self-healing recyclable Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1 Introduction Polyurethane (PU) elastomer materials are widely used in scientific research and engineering applications due to their good chemical stability, wear resistance and molecular designability [ 1 – 4 ] . However, owing to external factors such as heat and machinery, the traditional PU elastomer will cause micro-cracks in the material and fail to heal itself, resulting in deterioration of physical and chemical properties and shortening of service life. Moreover, the inability to self-healing makes PU materials disposable, which does not meet the international requirements of environmental protection and low-carbon environmental protection. A good deal of PU elastomers currently on the market are crosslinked by irreversible covalent bonds and do not have self-healing properties [ 5 ] . Therefore, PU elastomers are endowed with multiple functions (such as self-healing properties, high strength, etc.) through molecular design to obtain multifunctional materials [ 6 – 13 ] , which are favored by researchers [ 14 ] . According to the self-healing mechanism, self-healing materials can be divided into extrinsic aid type and intrinsic type [ 15 – 16 ] . Extrinsic self-healing usually needs to promote the self-healing process through external AIDS such as repair agents. But once the repair agents are released, they cannot be replenished. So, it has the feature of one-time repair. This feature leads to the fact that materials prepared with an external self-healing mechanism can only heal once at the same injury location [ 17 ] . Compared with external self-repair, intrinsic self-repair is derived from polymer crack repair theory [ 18 ] . Based on the characteristics of reversible chemical molecular recombination, the intrinsic self-healing ability of the material is endowed by introducing dynamic network structure into the material body structure. Since intrinsic self-healing depends on reversible dynamic bonds within the molecular chain, the same fracture location can be repaired repeatedly [ 19 ] . Dynamic bonds can be divided into reversible covalent bonds [ 20 – 21 ] and reversible non-covalent bonds [ 22 ] . Xiang et al. [ 23 ] obtained a kind of cross-linked silicone elastomer using PDMS (polydimethylsiloxane)as the main material and silane containing disulfide bond as the crosslinking agent. The tensile strength of the elastomer can recover to 78% of the initial strength when self-healing at 120 ℃. Xu et al. [ 24 ] prepared a kind of polyurea-semi carbazone-graphite carbon nitride nanosheet material. The hydrogen bond in the matrix makes the material self-healing at room temperature, and the artificial scratches on the surface of the material disappear after 10min of repair. However, these materials do not have both excellent mechanical properties and self-healing properties. It is challenge to prepare polymer materials with good room temperature self-healing properties and high strength [ 25 ] . Generally, materials with higher mechanical strength have more strict self-healing conditions [ 26 ] . To realize the self-healing of materials, two necessary processes are required:(a) the amorphous structure and the motion between polymer chains;(b) polymer dynamic network and rapid intermolecular recombination at damaged sites. However, most current room temperature self-healing polymers generally have great difficulty carrying high loads (≤ 15 MPa). Recently, the formation of dynamic networks based on the interaction of dynamic non-covalent bonds [ 27 – 28 ] and dynamic covalent bonds [ 29 – 34 ] has become a hot topic. Through the intermolecular interaction, the dynamic reversible equilibrium between the polymer molecules is established respectively, and the polymer network with good dynamic effect is obtained. In this study, based on the characteristics of rapid recombination of multiple hydrogen bonds and reversible cross-linked covalent bonds to improve the cross-linking density of polymers, the reversible dynamic non-covalent bonds-multiple hydrogen bonds and reversible dynamic covalent bonds-nitrogen coordination boroxane six-member ring structure was introduced into the molecular, and the high strength room temperature self-healing recyclable PU elastomers were prepared by stepwise polycondensation. In addition, the elastomer exhibits “strain enhancement”, which is attributed to the rational network design of the elastomer. The synthesis and structural analysis of PU elastomer were carried out and confirmed as the target product. At the same time, the mechanics, film properties, self-healing properties of the material were tested, and the recycle of the material was studied to investigate the practical application ability of the material. 2 Experimental Section 2.1 Materials Polytetrahydrofuranediol (PTMEG-2000, Mn = 2000g/mol, f = 2), isophorone diisocyanate (IPDI), 2, 6-pyridinediol (PDM), 98% or higher), 4, 4 '-methylene double (2-chloro aniline) (MOCA, 98% or higher), 2-formyl benzene boric acid (FBA, 98% or higher), toluene (AR), N, N - dimethyl acetamide (10-channel DMAc), molecular sieve (4 a, 80–100 mesa) and dibutyltin dilaurate (DBTDL) were purchased from Shanghai Aladdin Biochemical Technology Co., LTD. It can be used without further purification. 2.2 Synthesis of materials The synthesis was divided into two parts, namely the synthesis of prepolymer and product. PU elastomers were synthesized by stepwise polycondensation using polytetrahydrofuranediol (PTMEG-2000) as crystallizing agent. 20 g PTMEG was placed in a three-necked flask, stirred under vacuum at 120°C (pressure below − 0.09 MPa), dehydrated for 30min, and then cooled to 80°C. Then, 8.40 g R = 3.8 IPDI (R is the molar ratio of IPDI isocyanate group to PTMEG-2000 hydroxyl group) and 0.01 g DBTDL were added to the three-neck flask, and the reaction was continued for 3 h at 80°C. Then 3.40 g PDM was added to the reaction system and the reaction was continued for 3 h in 25 mL toluene solution at 80°C. Finally, 1.59 g MOCA and 10 mL DMAc were added to the system for reaction for 3 h, and the primary amino-NH 2 terminated PU prepolymer was obtained. A series of PU prepolymers with the same R value and different PDM/MOCA molar ratio n (n = 90/10, 80/20, 70/30, 60/40, 50/50, 30/70, 10/90) were synthesized by the same process and were primary amino-NH 2 terminated. The -NH 2 terminated PU prepolymer was reacted with 0.82 g FBA and 20 mL toluene in 4A molecular sieve (5 g) for 3 h with Schiff base, and the light-yellow viscous product is obtained (all reaction processes were carried out in N 2 atmosphere). The liquid product was poured into the polytetrafluoroethylene mold and placed in a vacuum oven (80°C) for 48 h to remove the solvent, and a transparent PU elastomer film was obtained finally. The synthesized product was named PU PIPMB in the order of raw materials reaction. Then products were labeled as PU HB−90/10 , PU HB−80/20 , PU HB−70/30 , PU HB−60/40 , PU HB−50/50 , PU HB−30/70 and PU HB−10/90 according to different n values respectively. 2.3 Characterization Fourier transform infrared spectroscopy (FTIR) was tested by Nico-let iN10(Thermo Fisher Scientific). The test temperature was 30°C ~ 70°C, and one point was tested every 10°C. The 1 H NMR of the product was measured by Bruker Avance 400 MHz NMR spectrometer. For FTIR and 1 H NMR, a sample was tested due to the same process and raw material. The degree of polymerization was measured by gel permeation chromatography (GPC) using Waters 1515 gel chromatograph. The polymer structure was analyzed by DSC 214 (Netzsch, Germany) analyzer. The test temperature was − 80°C ~ 200°C. The elastomer film was analyzed by wide-angle X-ray diffraction (WXAD) with Bruker D8 ADVANCE X. Ultraviolet-visible spectrophotometer was used to measure the visible light transparency of elastomer film sample (20 mm × 20 mm × 0.5 mm). Atomic force microscopy (AFM) was used to measure AFM images. 2.4 Mechanical test Mechanical tests were performed on the LAB SANS tensile testing machine (with a 500 N load cell) and under standard conditions (25°C ± 2°C and 60% ± 2% relative humidity (RH)). The puncture test was carried out under compression mode at the rate of 50 mm/min on the tensile testing machine. The sample size was 60 mm × 6 mm × 1 mm, and the fracture energy was represented by the fracture work. To evaluate self-healing efficiency, the broken sample was reconstructed and healed at 25°C ± 2°C for a period of time at an ambient relative humidity of 60% ± 2%. The self-healing η of the sample is expressed by the recovery of tensile strength and elongation at break, as shown in Eq. 1 : $$\:\eta\:\left(100\%\right)={E}_{after}/{E}_{pristine}\times\:100\%$$ 1 In the above equation, E after and E pristine were the elongation at break of file samples. The cyclic tensile test was carried out on the LAB SANS tensile tester under the conditions of 25°C ± 2°C and relative humidity of 50% ± 10%, and the tensile rate was 100mm/min. The strain is set to 100% and 1000% respectively, stretched to the specified strain and unloaded at the same rate to complete a cycle. Wait for 180 s, and then proceed to the next stretching cycle. The thermal and mechanical properties were tested by DMA Q800 analyzer, and the energy storage modulus G 'and loss factor were obtained (frequency: 1Hz, test temperature: -100℃~150℃, heating rate: 3℃/min). The stress relaxation experiment was carried out by DMA Q800, where the sample was placed at 100% strain for 1000 seconds and the change of stress over time was recorded. 2.5 Quantum chemistry calculation All calculations in this study were performed using the Gaussian 16 program package. Full geometric optimization was performed by B3LYP-D3/6-311 + G (d, p) to locate all stationary points. Meanwhile, dispersion-corrected density functional theory (DFT-D3(BJ)) was used to obtain the single-point energy of all optimized structures with 6-311 + G (d, p) basis sets. The quantum theory of atoms-in-molecules (QTAIM) descriptors and other H-bonds were calculated based on high quality density functional theory wave functions using Multiwfn software. The DFT calculation in this paper have been done on the supercomputing system in the High-Performance Computing Center of Southwest Petroleum University. 3 Results and discussion 3.1 Molecular structure design The PU elastomers in this study were synthesized by prepolymer method (Fig. 1 a). PTMEG, IPDI, DBTDL, PDM, toluene, MOCA and DMAc were reacted in turn to obtain the primary amino-NH 2 terminated prepolymers. The -NH 2 terminated prepolymer was reacted with FBA by Schiff base in toluene solution, and the target product was obtained after solvent removal (the reaction process was carried out in N 2 atmosphere). Finally, the transparent PU elastomer film was obtained, and the product monomer was shown in Tables S1. According to the characterization of FTIR (Fig. S1 and Tables S2), 1 H NMR (Fig. S2) and GPC (Tables S3) (PU HB−60/40 was used for FTIR and 1 H NMR characterization), PU elastomers were successfully synthesized. They were labeled as PU HB−90/10 , PU HB−80/20 , PU HB−70/30 , PU HB−60/40 , PU HB−50/50 , PU HB−30/70 and PU HB−10/90 with different n values respectively. DSC indicated that the glass transition temperature T g of PU HB-60/40 was lower than − 58°C (Tables S4), and only a single glass transition was observed on the DSC curve at the test temperature of (-80°C ~ 200°C) (Fig. S3), which preliminarily indicated that the PU PIPMB had amorphous structure. WXAD further confirmed the amorphous structure, and the spectrogram has only fairly wide “spikes” at 2θ = 10°~30°/35°~50° without sharp small angular peaks (Fig. S4). The XRD pattern of the polymer was accompanied by a diffuse “rise peak”, which shows a short-range amorphous state. Very small T g and amorphous structures were extremely important for achieving high self-healing efficiency at room temperature. Moreover, PU HB-60/40 could withstand 2732 MJ of large displacement needle puncture (Fig. 1 b), and its rupture energy can reach 100.75 kJ‧m -2 (Fig. 1 c). PU HB-60/40 film was transparent under visible light, and the transmittance to visible light (λ = 400 nm-780 nm) reached 93.3% (Fig. 1 d). AFM images showed (Fig. 1 e, S3a, b) that the PU HB-60/40 has nanoscale and loosely packed hard domains in the micro/nano scale range, and its hard phase (dispersed phase) was disordered in the soft phase (continuous phase), showing microphase separation and amorphous state, which was also of great significance for room temperature self-healing. 3.2 Mechanical properties Figure 2 a showed the stress-strain curve of PU PIPMB , and the data were shown in Tables S5. The graph showed “strain enhancement”, that was, the stress increased with the increase of strain, and there was no obvious stress yield point on the curve. The tensile strength of PU HB−70/30 , PU HB−60/40 , PU HB−30/70 and PU HB−10/90 exceeded 10 MPa. The percentage of elongation at break of most samples exceeded 2000%; The toughness of PU HB−70/30 , PU HB−60/40 and PU HB−30/70 samples exceeded 100 MJ·m − 3 ; The tensile strength of PU HB−60/40 was 18.8 MPa; The elongation at break was 2132%, and the toughness was 117.0 MJ·m − 3 . Thus, the PU HB−60/40 showed excellent mechanical properties and significantly exceeded previously reported [ 35 – 43 ] (Fig. 2 a, Table S6). The dynamic disintegration and recombination of multiple hydrogen bonds, the unentanglement and orientation arrangement of polymer segments are two important factors of strain strengthening. In the elastomer molecular structure (in the case of PU HB−60/40 ), the carbamate(-NH-CO-), urea(-NH-CO-NH-) and pyridine(-N=) groups formed the hydrogen bonds of the hierarchy (Fig. 2 c). Quantum chemical calculations showed that the hydrogen bonding energies of pyridine-carbamate, pyridine-urea, carbamate-carbamate, carbamate-urea and urea-urea were 6.73, 10.8, 8.85, 10.9 and 13.9 kcal mol − 1 respectively (Table 1 ). This difference in the type, number and binding energy of dynamic hydrogen bond interactions is crucial for the formation of different aggregation states within elastomers. The inter-hard segment binding energy was very important for the formation of different aggregation states in the structure, and the inter-hard segment binding energy was different significantly, and most of the binding energy was relatively low. AFM indicated that the PU HB−60/40 has a hard segment phase with nanometer scale and loose packing. The amorphous loose structure was a prerequisite for the formation of dynamic hard segment structure, and the low binding energy between the hard segment phases was an important basis for realizing the dynamic activity and an important feature of the dynamic network recombination at room temperature. Multiple hydrogen bonds, as dynamic sacrificial bonds, could maintain the crystal configuration through hierarchical fracture dissipation stress during tensile process. In the initial stage of the curve (strain: 0%~800%), the hydrogen bonds formed by carbamate and pyridine with low energy was used as a dynamic sacrifice bond, which was conducive to energy dissipation during large deformation. As the strain increases, the strong hydrogen bonds formed between the groups acts as the dynamic sacrifice bonds, and the PTMEG chain was oriented along the tensile direction. Thus, the strength increases, and a new crystalline phase was formed. The stretching continued, the molecular chain was gradually normalized, and the crystallinity was enhanced. Table 1 Bonding energy of individual H-bonds in PU HB−60/40 Type Bonding energy of an individual H-bond (kcal mol − 1 ) A-B 6.73 A-C 10.8 B-B 8.85 B-C 10.9 C-C 13.9 3.3 Room temperature self-healing properties To evaluate the self-healing efficiency of PU elastomers, a completely broken sample was self-healed at 25°C ± 2°C for 48h (without special instructions, the ambient relative humidity was 60%±2%). Figure 3 a-g and Tables S7 showed the results of room temperature self-healing. Because of the excellent effect of disintegration and recombination of multiple hydrogen bonds in PU HB-70/30 , PU HB-60/40 and PU HB-30/70 , the curves still showed “strain enhancement”. Additionally, this was a further proof of excellent mechanical properties. The self-healing efficiency of tensile strength, elongation at break and toughness of elastomer exceeded 70%, 80% and 79% respectively. For the PU HB-60/40 with excellent initial mechanical properties, the self-healing efficiency of tensile strength, elongation at break and toughness were 94.7%, 91.7% and 86.7% respectively, and the synchronous self-healing efficiency exceeded 86%, indicating that PU HB-60/40 achieved an excellent combination of self-healing efficiency and mechanical properties. Since the motion and dynamic network of polymer chains were the necessary conditions for the material to achieve self-healing, self-healing may result from the full interpenetration of polymer chains across the broken surface of the connection and the rearrangement of the hierarchical hydrogen bond network [ 44 – 46 ] . The variation trends of room temperature self-healing effect and efficiency over time of PU HB-60/40 were shown in Fig. 4 a and Tables S8 respectively. With the extension of time, the molecular chain segment and its diffusion and entanglement motion tended to be stable, and the reversible dynamic chemical bonds rearrangement and self-healing efficiency of the fracture increased significantly. The relative humidity of the restoration environment had a significant impact on the results (Fig. 4 b, Tables S9). When the relative humidity increased from 60% to 90%, the tensile strength, elongation at break and self-healing efficiency of the toughness of PU HB-60/40 at room temperature showed a decreasing trend. The donor/acceptor at the fracture site had formed hydrogen bonds with water molecules before recombination. Solvent effect reduced the strength of hydrogen bonds and the self-healing efficiency. Ring-opening reaction occurred in the nitrogen coordination boroxane six-member ring at the cross section, thus the crosslinking density and mechanical strength decreased. However, even if the relative humidity is 90%, the room temperature self-healing efficiency of the tensile strength was still more than 65%. Therefore, it had good water resistance. After soaking PU HB-60/40 in water and conventional treatment, it was self-healed in a drying vessel at room temperature for 48h respectively (Fig. 4 c, Tables S10). After water immersion, the nitrogen coordination boroxane six-member ring at the cross section was hydrolyzed and ring-opened to phenylboronic acid, and the fracture of nitrogen coordination boro-oxygen bonds and hydrogen bonds increased the motion activity of chain segment. As damaged surface contacted and surface water evaporated, nitrogen coordination boro-oxygen bonds and hydrogen bonds gradually repaired, and mechanical properties recovered. Although there was chemical crosslinking structure in PU HB-60/40 , the number of nitrogen coordination boro-oxygen bonds was small, so the multiple hydrogen bonds were the main reversible structure of the system. The rapid rearrangement of multiple hydrogen bonds resulted in healing, while the nitrogen coordination boro-oxygen bonds gradually rearranged in the later stage, and finally realized high strength self-healing. Figure 4 d showed the DMA test curve, which transformed at about − 100°C, and the storage modulus G' begins to decline. Because the internal friction resistance of the motion of molecular chain segments under the influence of heat or external force mainly came from the binding energy between the hard segments of its molecular structure, the hydrogen bonds force decreases with the temperature increased, resulting in binding energy decreased [ 47 – 48 ] . In addition, the nitrogen coordination boroxane six-member ring opened that caused the crosslinking degree decreased. Therefore, the rigidity of the molecular chain segment decreased and the activity increased. The loss factor (Tan δ) first increased, then decreased and then increased again. This was due to the molecular chain segment changed from freezing to motion and from glassy state to high elastic state with the increase of temperature, so the chain segment moved slowly. As the temperature gradually increased, the motion of the chain segment caught up with the external force and the internal friction was small. The temperature continued to rise (about 25°C) to the viscoelastic state, the complete motion of the chain segment produced irreversible permanent deformation, large internal friction, and the hard phase rearrangement. The variable temperature FTIR spectra was shown in Fig. 4 e. The hydrogen bonds were greatly affected by temperature, and the absorption strength of PU HB-60/40 at wave number 1704 cm -1 , 1530 cm -1 and 1241 cm -1 gradually decreased from 30°C to 70°C, indicating that the intermolecular hydrogen bonds were gradually dissociated with increasing temperature [ 49 – 50 ] , and the intermolecular distance became larger, showing a free state, and the intermolecular hydrogen bonds cannot be formed. Moreover, the absorption frequency of the groups forming hydrogen bonds decreased significantly, indicating that dynamic hydrogen bonds existed between the molecules of the elastomers. At wave number 675 cm -1 , the absorption intensity decreased gradually, and the nitrogen coordination boroxane six-member ring gradually opened, indicating that dynamic hydrogen bonds also existed in the molecule. Figure 4 (f) showed the stress-strain curve of PU HB-60/40 . With the extension of time, the stress gradually decreased, and the ratio of tensile stress σ to initial maximum stress σ 0 after 1000s σ/σ 0 = 0.45. When the same stress was tested at 40 and 55°C, σ/σ 0 after 1000s were 0.36 and 0.16 respectively, and the stress reduction was more obvious. Under the action of external force, the molecular chain segment stretched along the direction of external force, resulting in internal stress which counterbalanced with external force. The molecular conformation changed with the motion of the chain segment to produce relative slip and gradually returned to the curled state, and the internal stress and external force gradually attenuated and eliminated to maintain constant deformation. Since the internal friction resistance of the molecular chain segment of elastomer PU HB-60/40 and its motion was mainly due to the intermolecular multiple hydrogen bonds, the hydrogen bonds with weak bond energy broke and restructured to maintain the molecular configuration when the strain was low, which caused stress relaxation. The binding energy of intermolecular hydrogen bonds was weakened with the increase of temperature, and the hydrogen bonds were more likely to break and recombine. PU HB-60/40 showed faster stress relaxation, which once again indicated that dynamic hydrogen bonds existed between polymer molecules. The energy dissipation of multiple hydrogen bonds was investigated by cyclic tensile test. The hysteresis energy was 0.35 MJ·m -3 after one tensile cycle at 100% strain. The hysteresis loop showed that the elastomer could dissipate energy effectively during the stretch-contraction process (Fig. 4 g, Table S11). After 5 times of cyclic stretching, hysteresis energy could still reach 0.3 MJ·m -3 . When the low strain was 100%, the weak hydrogen bonds in the dynamic hard phase underwent rapid reversible dissociation and recombination, and the hysteresis zone recovered after 180s, with no residual strain and elastic recovery. When the strain increased to 1000%, the hysteresis energy increased significantly (hysteresis energy 15.78 MJ·m -3 ) during the first load-to-unload cycle (Fig. 4 h). This suggested that breaking of weak hydrogen bonds can dissipate energy efficiently. The hysteresis area decreased (hysteresis energy 2.19 MJ·m -3 ) after 8 cycles at an interval of 180s, but the degree of decrease gradually decreased, and there was always a certain residual strain after each cyclic stretching. The results showed that the retraction process caused by weak hydrogen bonds was an important factor for the accelerated recovery of elasticity, while the kinetics of strong hydrogen bonds was weak and the change rate was slow. In conclusion, the above series of relevant experimental results show that further indicated that the motion of polymer chains and reversible dynamic networks played a significant role. In addition, the molecular segments move well at room temperature, which is also an important prerequisite for the polymer to have excellent room temperature self-healing properties. 3.4 Recyclable properties Interestingly, although the PU HB−60/40 film had a partial chemical cross-linked structure, it could still be recovered by redissolution and drying in solvent, such as DMF or DMAc. This may be due to the good dynamic properties of the internal network structure of PU HB−60/40 [ 51 ] , which conferred dissolution plasticity on PU HB−60/40 . This indicated that the internal molecular structure of PU HB−60/40 extended the service life, and the mechanical properties remain almost unchanged (Fig. 5 a). It was further proved that PU HB−60/40 had excellent tensile strength and excellent room temperature self-healing efficiency and had practical application potential. In addition, the transparent PU HB−60/40 film could be effectively bonded to the surface of objects (such as wood and metal products), and scratches on the film could be self-healing at room temperature (Fig. 5 b-d). This was because the multiple hydrogen bonds that provided reversible dynamic network during the repair process were broken and quickly rearranged to achieve healing, which showed good recyclable properties. Therefore, this performance will meet the requirement of international green and sustainable development. 4 Conclusion In this study, five monomers (PTMEG, IPDI, PDM, MOCA and FBA) were reacted sequentially, then DBTDL and DMAc were introduced for chain extension, and finally PU PIPMB elastomers were obtained through stepwise polycondensation. FTIR, 1 H NMR and GPC tests showed that the PU elastomers were successfully synthesized. The PU PIPMB had excellent mechanical properties, and its stress-strain curve showed “strain enhancement”. When the PDM/MOCA molar ratio was 60/40(PU HB-60/40 ), the tensile strength, elongation at break and toughness were 18.8 MPa, 2132% and 117.0 MJ·m -3 respectively. The puncture energy was 2732 MJ and the fracture energy was 100.75 kJ·m -2 , showing excellent strength and toughness. AFM, WXAD and DSC tests showed that PU PIPMB had amorphous structure and room temperature self-healing ability. For PU HB-60/40 with excellent mechanical properties, the self-healing efficiency of tensile strength, elongation at break and toughness after 48 h of room temperature self-healing were 94.7%, 91.7% and 86.7% respectively, showing excellent room temperature self-healing properties. However, the balance between the performance of this polyurethane elastomer and its practical application still needs to be further improved to ensure that it can function effectively in real-world applications. In addition, PU PIPMB elastomers had decent reuse performance, and the mechanical properties of PU HB-60/40 were not significantly reduced after recycling. Therefore, this study provided a useful idea for preparing sustainable high strength room temperature self-healing polymers. Declarations Acknowledgements This work was supported by The Key Projects of Sichuan Province Natural Foundation (Projects No. 2023NSFSC0027) and the Project of the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Projects No. PLN2022-03) and the Open Fund (PLN2023-23) of National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Southwest Petroleum University). Conflicts of interest We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted. All authors declare that all data in this study are available. The authors have no relevant financial or non-financial interests to disclose. The authors have no competing interests to declare that are relevant to the content of this article. All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript. The authors have no financial or proprietary interests in any material discussed in this article. All authors whose names appear on the submission 1) made substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data; or the creation of new software used in the work; 2) drafted the work or revised it critically for important intellectual content; 3) approved the version to be published; and 4) agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. Affiliation Yuchen Jiao is studying at the School of New Energy and Materials at Southwest Petroleum University as a graduate student (2023 Grade). He is majoring in Materials Engineering. E-mail: [email protected] Ming Zhou received his B.Sc., M.Sc., and Ph.D. from the Southwest Petroleum University in Chengdu of the PR China and worked at the School of New Energy and Materials at Southwest Petroleum University as a research chemist in 2002. He is a professor and a doctoral tutor at the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation. His research fields are Oilfield materials. E-mail: [email protected] , Tel: +8613880947076. QQ: 106747878 Address: No.8, Xindu Avenue, Xindu District, Chengdu City. He is corresponding author Bo Pu is working in the safety and environmental protection quality supervision and testing Institute of CNPC Chuanqing Drilling Engineering Co., LTD. He is majoring in chemical engineering and process related research. Email: [email protected] Xiaoling Yang is studying at the School of New Energy and Materials at Southwest Petroleum as a doctoral student (2021 Grade). She is majoring in Materials Science and Engineering. E-mail: [email protected] Chenyiting Li is studying at the School of New Energy and Materials at Southwest Petroleum as a graduate student (2021 Grade). She is majoring in Materials Engineering. E-mail: [email protected] Liangliang Xia is working at the School of New Energy and Materials at Southwest Petroleum University, Chengdu, 610500, China. E-mail: [email protected] Guilin Deng is studying at the School of New Energy and Materials at Southwest Petroleum University as a graduate student (2023 Grade). She is majoring in Materials Science and Engineering. E-mail: [email protected] Yunyao Wei is studying at the School of New Energy and Materials at Southwest Petroleum University as a graduate student (2023 Grade). He is majoring in Materials Science and Engineering. E-mail: [email protected] Jing Zhong is studying at the School of New Energy and Materials at Southwest Petroleum University as a graduate student (2023 Grade). He is majoring in Materials Science and Engineering. E-mail: [email protected] Zheng Wu is studying at the School of New Energy and Materials at Southwest Petroleum University as a graduate student (2023 Grade). He is majoring in Materials Engineering. E-mail: [email protected] Shi Chen is studying at the School of New Energy and Materials at Southwest Petroleum University as a graduate student (2023 Grade). He is majoring in Materials Science and Engineering. E-mail: [email protected] Jian Wang is working at the School of College of Food and Biological Engineering, Chengdu University, Chengdu 610106, China. E-mail: [email protected] Yujun Zhou is studying at the College of Chemistry and Chemical Engineering at China West Normal University as an undergraduate student (2023 Grade). She is majoring in Chemistry. 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09:24:06","extension":"png","order_by":21,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":33806,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinegroupimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8014090/v1/36ed8ae1664dcc26077bec55.png"},{"id":96598075,"identity":"25daffb9-0801-4e41-8b9a-578f27faaa41","added_by":"auto","created_at":"2025-11-24 08:01:59","extension":"png","order_by":22,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":18984,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinegroupimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8014090/v1/910d3cc85300e41024cd09ab.png"},{"id":96598073,"identity":"378abef0-4709-4940-bb4d-fcdbc4e9ec9a","added_by":"auto","created_at":"2025-11-24 08:01:59","extension":"xml","order_by":23,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":141520,"visible":true,"origin":"","legend":"","description":"","filename":"JPOLD25017660structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8014090/v1/6268dd75bad6b2775d1da07e.xml"},{"id":96598076,"identity":"6dbc8f06-bc0c-43e5-9eac-ea8c5b984ffd","added_by":"auto","created_at":"2025-11-24 08:01:59","extension":"html","order_by":24,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":150740,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8014090/v1/bba4550d1fc018798fc1f332.html"},{"id":96598051,"identity":"2f2dcc0b-0040-489b-a709-c8fe4974bc86","added_by":"auto","created_at":"2025-11-24 08:01:58","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":340319,"visible":true,"origin":"","legend":"\u003cp\u003eCharacteristics of PU\u003csub\u003ePIPMB\u003c/sub\u003e room temperature self-healing elastomers: (a) Synthesis route and method of PU elastomers; (b) Membrane puncture force-displacement curve of PU\u003csub\u003eHB-60/40\u003c/sub\u003e; (c) Stress-strain curves of membrane fracture energy (from top to bottom: initial state, after cutting) of PU\u003csub\u003eHB-60/40\u003c/sub\u003e; (d) Transparency spectrum of PU\u003csub\u003eHB-60/40\u003c/sub\u003e sample (20mm×20mm×0.5mm); (e) AFM 2D phase diagram of PU\u003csub\u003eHB-60/40\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8014090/v1/0eac7ad83b0a4d22c25b329f.png"},{"id":96598057,"identity":"75ef19b2-9901-4358-aef0-121861d1880c","added_by":"auto","created_at":"2025-11-24 08:01:59","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":369105,"visible":true,"origin":"","legend":"\u003cp\u003eMechanical properties of PU\u003csub\u003ePIPMB\u003c/sub\u003e: (a) Stress-strain curves ;(b) Comparison of mechanical properties between PU\u003csub\u003eHB-60/40\u003c/sub\u003e and recently reported relevant materials; (c) Hierarchical hydrogen bonds formed between carbamate, urea and pyridine of PU\u003csub\u003eHB-60/40\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8014090/v1/0066c92ca7fb8ad9e7c0ba33.png"},{"id":96598052,"identity":"b7bb1c0c-804d-49e5-be1d-90d657145d36","added_by":"auto","created_at":"2025-11-24 08:01:58","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":503540,"visible":true,"origin":"","legend":"\u003cp\u003eStress-strain curves of PU\u003csub\u003ePIPMB\u003c/sub\u003e before and after healing: (a)PU\u003csub\u003eHB-90/10\u003c/sub\u003e; (b)PU\u003csub\u003eHB-80/20\u003c/sub\u003e; (c)PU\u003csub\u003eHB-70/30\u003c/sub\u003e; (d)PU\u003csub\u003eHB-60/40\u003c/sub\u003e; (e)PU\u003csub\u003eHB-50/50\u003c/sub\u003e; (f)PU\u003csub\u003eHB-30/70\u003c/sub\u003e; (g)PU\u003csub\u003eHB-10/90\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8014090/v1/68cbfd248115a942ae63ef6d.png"},{"id":96598056,"identity":"82e95bec-bf98-439d-9c32-2445ad3db61c","added_by":"auto","created_at":"2025-11-24 08:01:59","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":427439,"visible":true,"origin":"","legend":"\u003cp\u003eCharacteristics of PU\u003csub\u003eHB-60/40\u003c/sub\u003e :(a) The trend of room temperature self-healing effect over time; (b)\u003c/p\u003e\n\u003cp\u003eonship between energy storage modulus G' and loss factor Tan δ and temperature; (e) FTIR spectra at variable temperature; (f) Stress relaxation curves at different temperatures (100% strain, held 1000 s); (g, h)PU\u003csub\u003eHB-60/40\u003c/sub\u003e cyclic tensile test (from left to right: the sample is loaded with 100% strain and then unloaded, and then loaded and unloaded after 180 s; The sample is loaded with 1000% strain and then unloaded, and then loaded and unloaded after 180 s. Loading and unloading rates are 100 mm/min).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8014090/v1/7eb415b7be081c2badc712d8.png"},{"id":96598058,"identity":"08712b73-29ef-47ba-8107-dc9ffac8c0e8","added_by":"auto","created_at":"2025-11-24 08:01:59","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":570299,"visible":true,"origin":"","legend":"\u003cp\u003eRecyclable properties of PU\u003csub\u003eHB-60/40\u003c/sub\u003e: (a) Stress-strain curve after cyclic preparation (b) Initial scratch status; (c) Scratch self-healing at 25 °C±2 °C, 60%±2%RH for 24 h; (d) Scratch self-healing 36 h at 25 °C±2 °C, 60%±2%RH.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8014090/v1/c1f4119db0fc83cf40509813.png"},{"id":104739575,"identity":"9a7e3f31-7497-48f8-a8a5-198ca6ec22b7","added_by":"auto","created_at":"2026-03-16 16:09:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2572923,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8014090/v1/33b0107c-be1c-4166-85a7-3aac86bb3e9f.pdf"},{"id":96598053,"identity":"1ecc9ce6-7b43-4413-ac6f-0edfa650bd47","added_by":"auto","created_at":"2025-11-24 08:01:58","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":192003,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.docx","url":"https://assets-eu.researchsquare.com/files/rs-8014090/v1/b78d6df16bc1a3049dd44ea5.docx"},{"id":96598062,"identity":"8691de57-32f0-424a-a4e3-7055e2123397","added_by":"auto","created_at":"2025-11-24 08:01:59","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":2062922,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-8014090/v1/522739f9826e3d459ba6875c.docx"}],"financialInterests":"","formattedTitle":"Preparation of Room-temperature Self-healing Recyclable Polyurethane Elastomers Based on Multiple Hydrogen/Nitrogen Coordination Boro-oxygen Bonds System","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003ePolyurethane (PU) elastomer materials are widely used in scientific research and engineering applications due to their good chemical stability, wear resistance and molecular designability \u003csup\u003e[\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. However, owing to external factors such as heat and machinery, the traditional PU elastomer will cause micro-cracks in the material and fail to heal itself, resulting in deterioration of physical and chemical properties and shortening of service life. Moreover, the inability to self-healing makes PU materials disposable, which does not meet the international requirements of environmental protection and low-carbon environmental protection. A good deal of PU elastomers currently on the market are crosslinked by irreversible covalent bonds and do not have self-healing properties \u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e. Therefore, PU elastomers are endowed with multiple functions (such as self-healing properties, high strength, etc.) through molecular design to obtain multifunctional materials \u003csup\u003e[\u003cspan additionalcitationids=\"CR7 CR8 CR9 CR10 CR11 CR12\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e, which are favored by researchers \u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eAccording to the self-healing mechanism, self-healing materials can be divided into extrinsic aid type and intrinsic type \u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e. Extrinsic self-healing usually needs to promote the self-healing process through external AIDS such as repair agents. But once the repair agents are released, they cannot be replenished. So, it has the feature of one-time repair. This feature leads to the fact that materials prepared with an external self-healing mechanism can only heal once at the same injury location \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e. Compared with external self-repair, intrinsic self-repair is derived from polymer crack repair theory \u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e. Based on the characteristics of reversible chemical molecular recombination, the intrinsic self-healing ability of the material is endowed by introducing dynamic network structure into the material body structure. Since intrinsic self-healing depends on reversible dynamic bonds within the molecular chain, the same fracture location can be repaired repeatedly \u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. Dynamic bonds can be divided into reversible covalent bonds \u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e and reversible non-covalent bonds \u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e. Xiang et al. \u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e obtained a kind of cross-linked silicone elastomer using PDMS (polydimethylsiloxane)as the main material and silane containing disulfide bond as the crosslinking agent. The tensile strength of the elastomer can recover to 78% of the initial strength when self-healing at 120 ℃. Xu et al. \u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e prepared a kind of polyurea-semi carbazone-graphite carbon nitride nanosheet material. The hydrogen bond in the matrix makes the material self-healing at room temperature, and the artificial scratches on the surface of the material disappear after 10min of repair. However, these materials do not have both excellent mechanical properties and self-healing properties.\u003c/p\u003e\u003cp\u003eIt is challenge to prepare polymer materials with good room temperature self-healing properties and high strength \u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e. Generally, materials with higher mechanical strength have more strict self-healing conditions \u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e. To realize the self-healing of materials, two necessary processes are required:(a) the amorphous structure and the motion between polymer chains;(b) polymer dynamic network and rapid intermolecular recombination at damaged sites. However, most current room temperature self-healing polymers generally have great difficulty carrying high loads (\u0026le;\u0026thinsp;15 MPa). Recently, the formation of dynamic networks based on the interaction of dynamic non-covalent bonds \u003csup\u003e[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e and dynamic covalent bonds \u003csup\u003e[\u003cspan additionalcitationids=\"CR30 CR31 CR32 CR33\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e has become a hot topic. Through the intermolecular interaction, the dynamic reversible equilibrium between the polymer molecules is established respectively, and the polymer network with good dynamic effect is obtained.\u003c/p\u003e\u003cp\u003eIn this study, based on the characteristics of rapid recombination of multiple hydrogen bonds and reversible cross-linked covalent bonds to improve the cross-linking density of polymers, the reversible dynamic non-covalent bonds-multiple hydrogen bonds and reversible dynamic covalent bonds-nitrogen coordination boroxane six-member ring structure was introduced into the molecular, and the high strength room temperature self-healing recyclable PU elastomers were prepared by stepwise polycondensation. In addition, the elastomer exhibits \u0026ldquo;strain enhancement\u0026rdquo;, which is attributed to the rational network design of the elastomer. The synthesis and structural analysis of PU elastomer were carried out and confirmed as the target product. At the same time, the mechanics, film properties, self-healing properties of the material were tested, and the recycle of the material was studied to investigate the practical application ability of the material.\u003c/p\u003e"},{"header":"2 Experimental Section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials\u003c/h2\u003e\u003cp\u003ePolytetrahydrofuranediol (PTMEG-2000, Mn\u0026thinsp;=\u0026thinsp;2000g/mol, f\u0026thinsp;=\u0026thinsp;2), isophorone diisocyanate (IPDI), 2, 6-pyridinediol (PDM), 98% or higher), 4, 4 '-methylene double (2-chloro aniline) (MOCA, 98% or higher), 2-formyl benzene boric acid (FBA, 98% or higher), toluene (AR), N, N - dimethyl acetamide (10-channel DMAc), molecular sieve (4 a, 80\u0026ndash;100 mesa) and dibutyltin dilaurate (DBTDL) were purchased from Shanghai Aladdin Biochemical Technology Co., LTD. It can be used without further purification.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Synthesis of materials\u003c/h2\u003e\u003cp\u003eThe synthesis was divided into two parts, namely the synthesis of prepolymer and product. PU elastomers were synthesized by stepwise polycondensation using polytetrahydrofuranediol (PTMEG-2000) as crystallizing agent. 20 g PTMEG was placed in a three-necked flask, stirred under vacuum at 120\u0026deg;C (pressure below \u0026minus;\u0026thinsp;0.09 MPa), dehydrated for 30min, and then cooled to 80\u0026deg;C. Then, 8.40 g R\u0026thinsp;=\u0026thinsp;3.8 IPDI (R is the molar ratio of IPDI isocyanate group to PTMEG-2000 hydroxyl group) and 0.01 g DBTDL were added to the three-neck flask, and the reaction was continued for 3 h at 80\u0026deg;C. Then 3.40 g PDM was added to the reaction system and the reaction was continued for 3 h in 25 mL toluene solution at 80\u0026deg;C. Finally, 1.59 g MOCA and 10 mL DMAc were added to the system for reaction for 3 h, and the primary amino-NH\u003csub\u003e2\u003c/sub\u003e terminated PU prepolymer was obtained. A series of PU prepolymers with the same R value and different PDM/MOCA molar ratio n (n\u0026thinsp;=\u0026thinsp;90/10, 80/20, 70/30, 60/40, 50/50, 30/70, 10/90) were synthesized by the same process and were primary amino-NH\u003csub\u003e2\u003c/sub\u003e terminated. The -NH\u003csub\u003e2\u003c/sub\u003e terminated PU prepolymer was reacted with 0.82 g FBA and 20 mL toluene in 4A molecular sieve (5 g) for 3 h with Schiff base, and the light-yellow viscous product is obtained (all reaction processes were carried out in N\u003csub\u003e2\u003c/sub\u003e atmosphere). The liquid product was poured into the polytetrafluoroethylene mold and placed in a vacuum oven (80\u0026deg;C) for 48 h to remove the solvent, and a transparent PU elastomer film was obtained finally. The synthesized product was named PU\u003csub\u003ePIPMB\u003c/sub\u003e in the order of raw materials reaction. Then products were labeled as PU\u003csub\u003eHB\u0026minus;90/10\u003c/sub\u003e, PU\u003csub\u003eHB\u0026minus;80/20\u003c/sub\u003e, PU\u003csub\u003eHB\u0026minus;70/30\u003c/sub\u003e, PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e, PU\u003csub\u003eHB\u0026minus;50/50\u003c/sub\u003e, PU\u003csub\u003eHB\u0026minus;30/70\u003c/sub\u003e and PU\u003csub\u003eHB\u0026minus;10/90\u003c/sub\u003e according to different n values respectively.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Characterization\u003c/h2\u003e\u003cp\u003eFourier transform infrared spectroscopy (FTIR) was tested by Nico-let iN10(Thermo Fisher Scientific). The test temperature was 30\u0026deg;C\u0026thinsp;~\u0026thinsp;70\u0026deg;C, and one point was tested every 10\u0026deg;C. The \u003csup\u003e1\u003c/sup\u003eH NMR of the product was measured by Bruker Avance 400 MHz NMR spectrometer. For FTIR and \u003csup\u003e1\u003c/sup\u003eH NMR, a sample was tested due to the same process and raw material. The degree of polymerization was measured by gel permeation chromatography (GPC) using Waters 1515 gel chromatograph. The polymer structure was analyzed by DSC 214 (Netzsch, Germany) analyzer. The test temperature was \u0026minus;\u0026thinsp;80\u0026deg;C\u0026thinsp;~\u0026thinsp;200\u0026deg;C. The elastomer film was analyzed by wide-angle X-ray diffraction (WXAD) with Bruker D8 ADVANCE X. Ultraviolet-visible spectrophotometer was used to measure the visible light transparency of elastomer film sample (20 mm \u0026times; 20 mm \u0026times; 0.5 mm). Atomic force microscopy (AFM) was used to measure AFM images.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Mechanical test\u003c/h2\u003e\u003cp\u003eMechanical tests were performed on the LAB SANS tensile testing machine (with a 500 N load cell) and under standard conditions (25\u0026deg;C\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C and 60% \u0026plusmn; 2% relative humidity (RH)). The puncture test was carried out under compression mode at the rate of 50 mm/min on the tensile testing machine. The sample size was 60 mm \u0026times; 6 mm \u0026times; 1 mm, and the fracture energy was represented by the fracture work. To evaluate self-healing efficiency, the broken sample was reconstructed and healed at 25\u0026deg;C\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C for a period of time at an ambient relative humidity of 60% \u0026plusmn; 2%. The self-healing \u003cem\u003eη\u003c/em\u003e of the sample is expressed by the recovery of tensile strength and elongation at break, as shown in Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\eta\\:\\left(100\\%\\right)={E}_{after}/{E}_{pristine}\\times\\:100\\%$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eIn the above equation, \u003cem\u003eE\u003c/em\u003e\u003csub\u003eafter\u003c/sub\u003e and \u003cem\u003eE\u003c/em\u003e\u003csub\u003epristine\u003c/sub\u003e were the elongation at break of file samples. The cyclic tensile test was carried out on the LAB SANS tensile tester under the conditions of 25\u0026deg;C\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C and relative humidity of 50% \u0026plusmn; 10%, and the tensile rate was 100mm/min. The strain is set to 100% and 1000% respectively, stretched to the specified strain and unloaded at the same rate to complete a cycle. Wait for 180 s, and then proceed to the next stretching cycle. The thermal and mechanical properties were tested by DMA Q800 analyzer, and the energy storage modulus G 'and loss factor were obtained (frequency: 1Hz, test temperature: -100℃~150℃, heating rate: 3℃/min). The stress relaxation experiment was carried out by DMA Q800, where the sample was placed at 100% strain for 1000 seconds and the change of stress over time was recorded.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5 Quantum chemistry calculation\u003c/h2\u003e\u003cp\u003eAll calculations in this study were performed using the Gaussian 16 program package. Full geometric optimization was performed by B3LYP-D3/6-311\u0026thinsp;+\u0026thinsp;G (d, p) to locate all stationary points. Meanwhile, dispersion-corrected density functional theory (DFT-D3(BJ)) was used to obtain the single-point energy of all optimized structures with 6-311\u0026thinsp;+\u0026thinsp;G (d, p) basis sets. The quantum theory of atoms-in-molecules (QTAIM) descriptors and other H-bonds were calculated based on high quality density functional theory wave functions using Multiwfn software. The DFT calculation in this paper have been done on the supercomputing system in the High-Performance Computing Center of Southwest Petroleum University.\u003c/p\u003e\u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Molecular structure design\u003c/h2\u003e\u003cp\u003eThe PU elastomers in this study were synthesized by prepolymer method (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). PTMEG, IPDI, DBTDL, PDM, toluene, MOCA and DMAc were reacted in turn to obtain the primary amino-NH\u003csub\u003e2\u003c/sub\u003e terminated prepolymers. The -NH\u003csub\u003e2\u003c/sub\u003e terminated prepolymer was reacted with FBA by Schiff base in toluene solution, and the target product was obtained after solvent removal (the reaction process was carried out in N\u003csub\u003e2\u003c/sub\u003e atmosphere). Finally, the transparent PU elastomer film was obtained, and the product monomer was shown in Tables S1. According to the characterization of FTIR (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e and Tables S2), \u003csup\u003e1\u003c/sup\u003eH NMR (Fig. S2) and GPC (Tables S3) (PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e was used for FTIR and \u003csup\u003e1\u003c/sup\u003eH NMR characterization), PU elastomers were successfully synthesized. They were labeled as PU\u003csub\u003eHB\u0026minus;90/10\u003c/sub\u003e, PU\u003csub\u003eHB\u0026minus;80/20\u003c/sub\u003e, PU\u003csub\u003eHB\u0026minus;70/30\u003c/sub\u003e, PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e, PU\u003csub\u003eHB\u0026minus;50/50\u003c/sub\u003e, PU\u003csub\u003eHB\u0026minus;30/70\u003c/sub\u003e and PU\u003csub\u003eHB\u0026minus;10/90\u003c/sub\u003e with different n values respectively.\u003c/p\u003e\u003cp\u003eDSC indicated that the glass transition temperature T\u003csub\u003eg\u003c/sub\u003e of PU\u003csub\u003eHB-60/40\u003c/sub\u003e was lower than \u0026minus;\u0026thinsp;58\u0026deg;C (Tables S4), and only a single glass transition was observed on the DSC curve at the test temperature of (-80\u0026deg;C\u0026thinsp;~\u0026thinsp;200\u0026deg;C) (Fig. S3), which preliminarily indicated that the PU\u003csub\u003ePIPMB\u003c/sub\u003e had amorphous structure. WXAD further confirmed the amorphous structure, and the spectrogram has only fairly wide \u0026ldquo;spikes\u0026rdquo; at 2θ\u0026thinsp;=\u0026thinsp;10\u0026deg;~30\u0026deg;/35\u0026deg;~50\u0026deg; without sharp small angular peaks (Fig. S4). The XRD pattern of the polymer was accompanied by a diffuse \u0026ldquo;rise peak\u0026rdquo;, which shows a short-range amorphous state. Very small T\u003csub\u003eg\u003c/sub\u003e and amorphous structures were extremely important for achieving high self-healing efficiency at room temperature. Moreover, PU\u003csub\u003eHB-60/40\u003c/sub\u003e could withstand 2732 MJ of large displacement needle puncture (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), and its rupture energy can reach 100.75 kJ‧m\u003csup\u003e-2\u003c/sup\u003e(Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). PU\u003csub\u003eHB-60/40\u003c/sub\u003e film was transparent under visible light, and the transmittance to visible light (λ\u0026thinsp;=\u0026thinsp;400 nm-780 nm) reached 93.3% (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). AFM images showed (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee, S3a, b) that the PU\u003csub\u003eHB-60/40\u003c/sub\u003e has nanoscale and loosely packed hard domains in the micro/nano scale range, and its hard phase (dispersed phase) was disordered in the soft phase (continuous phase), showing microphase separation and amorphous state, which was also of great significance for room temperature self-healing.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Mechanical properties\u003c/h2\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea showed the stress-strain curve of PU\u003csub\u003ePIPMB\u003c/sub\u003e, and the data were shown in Tables S5. The graph showed \u0026ldquo;strain enhancement\u0026rdquo;, that was, the stress increased with the increase of strain, and there was no obvious stress yield point on the curve. The tensile strength of PU\u003csub\u003eHB\u0026minus;70/30\u003c/sub\u003e, PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e, PU\u003csub\u003eHB\u0026minus;30/70\u003c/sub\u003e and PU\u003csub\u003eHB\u0026minus;10/90\u003c/sub\u003e exceeded 10 MPa. The percentage of elongation at break of most samples exceeded 2000%; The toughness of PU\u003csub\u003eHB\u0026minus;70/30\u003c/sub\u003e, PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e and PU\u003csub\u003eHB\u0026minus;30/70\u003c/sub\u003e samples exceeded 100 MJ\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e; The tensile strength of PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e was 18.8 MPa; The elongation at break was 2132%, and the toughness was 117.0 MJ\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e. Thus, the PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e showed excellent mechanical properties and significantly exceeded previously reported \u003csup\u003e[\u003cspan additionalcitationids=\"CR36 CR37 CR38 CR39 CR40 CR41 CR42\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, Table S6). The dynamic disintegration and recombination of multiple hydrogen bonds, the unentanglement and orientation arrangement of polymer segments are two important factors of strain strengthening. In the elastomer molecular structure (in the case of PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e), the carbamate(-NH-CO-), urea(-NH-CO-NH-) and pyridine(-N=) groups formed the hydrogen bonds of the hierarchy (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). Quantum chemical calculations showed that the hydrogen bonding energies of pyridine-carbamate, pyridine-urea, carbamate-carbamate, carbamate-urea and urea-urea were 6.73, 10.8, 8.85, 10.9 and 13.9 kcal mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e respectively (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). This difference in the type, number and binding energy of dynamic hydrogen bond interactions is crucial for the formation of different aggregation states within elastomers. The inter-hard segment binding energy was very important for the formation of different aggregation states in the structure, and the inter-hard segment binding energy was different significantly, and most of the binding energy was relatively low. AFM indicated that the PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e has a hard segment phase with nanometer scale and loose packing. The amorphous loose structure was a prerequisite for the formation of dynamic hard segment structure, and the low binding energy between the hard segment phases was an important basis for realizing the dynamic activity and an important feature of the dynamic network recombination at room temperature. Multiple hydrogen bonds, as dynamic sacrificial bonds, could maintain the crystal configuration through hierarchical fracture dissipation stress during tensile process. In the initial stage of the curve (strain: 0%~800%), the hydrogen bonds formed by carbamate and pyridine with low energy was used as a dynamic sacrifice bond, which was conducive to energy dissipation during large deformation. As the strain increases, the strong hydrogen bonds formed between the groups acts as the dynamic sacrifice bonds, and the PTMEG chain was oriented along the tensile direction. Thus, the strength increases, and a new crystalline phase was formed. The stretching continued, the molecular chain was gradually normalized, and the crystallinity was enhanced.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eBonding energy of individual H-bonds in PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eType\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eBonding energy of an\u003c/p\u003e\u003cp\u003eindividual H-bond (kcal mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eA-B\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e6.73\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eA-C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e10.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eB-B\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e8.85\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eB-C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e10.9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eC-C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e13.9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Room temperature self-healing properties\u003c/h2\u003e\u003cp\u003eTo evaluate the self-healing efficiency of PU elastomers, a completely broken sample was self-healed at 25\u0026deg;C\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C for 48h (without special instructions, the ambient relative humidity was 60%\u0026plusmn;2%). Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea-g and Tables S7 showed the results of room temperature self-healing. Because of the excellent effect of disintegration and recombination of multiple hydrogen bonds in PU\u003csub\u003eHB-70/30\u003c/sub\u003e, PU\u003csub\u003eHB-60/40\u003c/sub\u003e and PU\u003csub\u003eHB-30/70\u003c/sub\u003e, the curves still showed \u0026ldquo;strain enhancement\u0026rdquo;. Additionally, this was a further proof of excellent mechanical properties. The self-healing efficiency of tensile strength, elongation at break and toughness of elastomer exceeded 70%, 80% and 79% respectively. For the PU\u003csub\u003eHB-60/40\u003c/sub\u003e with excellent initial mechanical properties, the self-healing efficiency of tensile strength, elongation at break and toughness were 94.7%, 91.7% and 86.7% respectively, and the synchronous self-healing efficiency exceeded 86%, indicating that PU\u003csub\u003eHB-60/40\u003c/sub\u003e achieved an excellent combination of self-healing efficiency and mechanical properties. Since the motion and dynamic network of polymer chains were the necessary conditions for the material to achieve self-healing, self-healing may result from the full interpenetration of polymer chains across the broken surface of the connection and the rearrangement of the hierarchical hydrogen bond network \u003csup\u003e[\u003cspan additionalcitationids=\"CR45\" citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe variation trends of room temperature self-healing effect and efficiency over time of PU\u003csub\u003eHB-60/40\u003c/sub\u003e were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and Tables S8 respectively. With the extension of time, the molecular chain segment and its diffusion and entanglement motion tended to be stable, and the reversible dynamic chemical bonds rearrangement and self-healing efficiency of the fracture increased significantly.\u003c/p\u003e\u003cp\u003eThe relative humidity of the restoration environment had a significant impact on the results (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, Tables S9). When the relative humidity increased from 60% to 90%, the tensile strength, elongation at break and self-healing efficiency of the toughness of PU\u003csub\u003eHB-60/40\u003c/sub\u003e at room temperature showed a decreasing trend. The donor/acceptor at the fracture site had formed hydrogen bonds with water molecules before recombination. Solvent effect reduced the strength of hydrogen bonds and the self-healing efficiency. Ring-opening reaction occurred in the nitrogen coordination boroxane six-member ring at the cross section, thus the crosslinking density and mechanical strength decreased. However, even if the relative humidity is 90%, the room temperature self-healing efficiency of the tensile strength was still more than 65%. Therefore, it had good water resistance.\u003c/p\u003e\u003cp\u003eAfter soaking PU\u003csub\u003eHB-60/40\u003c/sub\u003e in water and conventional treatment, it was self-healed in a drying vessel at room temperature for 48h respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, Tables S10). After water immersion, the nitrogen coordination boroxane six-member ring at the cross section was hydrolyzed and ring-opened to phenylboronic acid, and the fracture of nitrogen coordination boro-oxygen bonds and hydrogen bonds increased the motion activity of chain segment. As damaged surface contacted and surface water evaporated, nitrogen coordination boro-oxygen bonds and hydrogen bonds gradually repaired, and mechanical properties recovered. Although there was chemical crosslinking structure in PU\u003csub\u003eHB-60/40\u003c/sub\u003e, the number of nitrogen coordination boro-oxygen bonds was small, so the multiple hydrogen bonds were the main reversible structure of the system. The rapid rearrangement of multiple hydrogen bonds resulted in healing, while the nitrogen coordination boro-oxygen bonds gradually rearranged in the later stage, and finally realized high strength self-healing.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed showed the DMA test curve, which transformed at about \u0026minus;\u0026thinsp;100\u0026deg;C, and the storage modulus G' begins to decline. Because the internal friction resistance of the motion of molecular chain segments under the influence of heat or external force mainly came from the binding energy between the hard segments of its molecular structure, the hydrogen bonds force decreases with the temperature increased, resulting in binding energy decreased \u003csup\u003e[\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]\u003c/sup\u003e. In addition, the nitrogen coordination boroxane six-member ring opened that caused the crosslinking degree decreased. Therefore, the rigidity of the molecular chain segment decreased and the activity increased. The loss factor (Tan δ) first increased, then decreased and then increased again. This was due to the molecular chain segment changed from freezing to motion and from glassy state to high elastic state with the increase of temperature, so the chain segment moved slowly. As the temperature gradually increased, the motion of the chain segment caught up with the external force and the internal friction was small. The temperature continued to rise (about 25\u0026deg;C) to the viscoelastic state, the complete motion of the chain segment produced irreversible permanent deformation, large internal friction, and the hard phase rearrangement.\u003c/p\u003e\u003cp\u003eThe variable temperature FTIR spectra was shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee. The hydrogen bonds were greatly affected by temperature, and the absorption strength of PU\u003csub\u003eHB-60/40\u003c/sub\u003e at wave number 1704 cm\u003csup\u003e-1\u003c/sup\u003e, 1530 cm\u003csup\u003e-1\u003c/sup\u003e and 1241 cm\u003csup\u003e-1\u003c/sup\u003e gradually decreased from 30\u0026deg;C to 70\u0026deg;C, indicating that the intermolecular hydrogen bonds were gradually dissociated with increasing temperature \u003csup\u003e[\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]\u003c/sup\u003e, and the intermolecular distance became larger, showing a free state, and the intermolecular hydrogen bonds cannot be formed. Moreover, the absorption frequency of the groups forming hydrogen bonds decreased significantly, indicating that dynamic hydrogen bonds existed between the molecules of the elastomers. At wave number 675 cm\u003csup\u003e-1\u003c/sup\u003e, the absorption intensity decreased gradually, and the nitrogen coordination boroxane six-member ring gradually opened, indicating that dynamic hydrogen bonds also existed in the molecule.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(f) showed the stress-strain curve of PU\u003csub\u003eHB-60/40\u003c/sub\u003e. With the extension of time, the stress gradually decreased, and the ratio of tensile stress σ to initial maximum stress σ\u003csub\u003e0\u003c/sub\u003e after 1000s σ/σ\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.45. When the same stress was tested at 40 and 55\u0026deg;C, σ/σ\u003csub\u003e0\u003c/sub\u003e after 1000s were 0.36 and 0.16 respectively, and the stress reduction was more obvious. Under the action of external force, the molecular chain segment stretched along the direction of external force, resulting in internal stress which counterbalanced with external force. The molecular conformation changed with the motion of the chain segment to produce relative slip and gradually returned to the curled state, and the internal stress and external force gradually attenuated and eliminated to maintain constant deformation. Since the internal friction resistance of the molecular chain segment of elastomer PU\u003csub\u003eHB-60/40\u003c/sub\u003e and its motion was mainly due to the intermolecular multiple hydrogen bonds, the hydrogen bonds with weak bond energy broke and restructured to maintain the molecular configuration when the strain was low, which caused stress relaxation. The binding energy of intermolecular hydrogen bonds was weakened with the increase of temperature, and the hydrogen bonds were more likely to break and recombine. PU\u003csub\u003eHB-60/40\u003c/sub\u003e showed faster stress relaxation, which once again indicated that dynamic hydrogen bonds existed between polymer molecules.\u003c/p\u003e\u003cp\u003eThe energy dissipation of multiple hydrogen bonds was investigated by cyclic tensile test. The hysteresis energy was 0.35 MJ\u0026middot;m\u003csup\u003e-3\u003c/sup\u003e after one tensile cycle at 100% strain. The hysteresis loop showed that the elastomer could dissipate energy effectively during the stretch-contraction process (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg, Table S11). After 5 times of cyclic stretching, hysteresis energy could still reach 0.3 MJ\u0026middot;m\u003csup\u003e-3\u003c/sup\u003e. When the low strain was 100%, the weak hydrogen bonds in the dynamic hard phase underwent rapid reversible dissociation and recombination, and the hysteresis zone recovered after 180s, with no residual strain and elastic recovery. When the strain increased to 1000%, the hysteresis energy increased significantly (hysteresis energy 15.78 MJ\u0026middot;m\u003csup\u003e-3\u003c/sup\u003e) during the first load-to-unload cycle (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh). This suggested that breaking of weak hydrogen bonds can dissipate energy efficiently. The hysteresis area decreased (hysteresis energy 2.19 MJ\u0026middot;m\u003csup\u003e-3\u003c/sup\u003e) after 8 cycles at an interval of 180s, but the degree of decrease gradually decreased, and there was always a certain residual strain after each cyclic stretching. The results showed that the retraction process caused by weak hydrogen bonds was an important factor for the accelerated recovery of elasticity, while the kinetics of strong hydrogen bonds was weak and the change rate was slow. In conclusion, the above series of relevant experimental results show that further indicated that the motion of polymer chains and reversible dynamic networks played a significant role. In addition, the molecular segments move well at room temperature, which is also an important prerequisite for the polymer to have excellent room temperature self-healing properties.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Recyclable properties\u003c/h2\u003e\u003cp\u003eInterestingly, although the PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e film had a partial chemical cross-linked structure, it could still be recovered by redissolution and drying in solvent, such as DMF or DMAc. This may be due to the good dynamic properties of the internal network structure of PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e \u003csup\u003e[\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]\u003c/sup\u003e, which conferred dissolution plasticity on PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e. This indicated that the internal molecular structure of PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e extended the service life, and the mechanical properties remain almost unchanged (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). It was further proved that PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e had excellent tensile strength and excellent room temperature self-healing efficiency and had practical application potential. In addition, the transparent PU\u003csub\u003eHB\u0026minus;60/40\u003c/sub\u003e film could be effectively bonded to the surface of objects (such as wood and metal products), and scratches on the film could be self-healing at room temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb-d). This was because the multiple hydrogen bonds that provided reversible dynamic network during the repair process were broken and quickly rearranged to achieve healing, which showed good recyclable properties. Therefore, this performance will meet the requirement of international green and sustainable development.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eIn this study, five monomers (PTMEG, IPDI, PDM, MOCA and FBA) were reacted sequentially, then DBTDL and DMAc were introduced for chain extension, and finally PU\u003csub\u003ePIPMB\u003c/sub\u003e elastomers were obtained through stepwise polycondensation. FTIR, \u003csup\u003e1\u003c/sup\u003eH NMR and GPC tests showed that the PU elastomers were successfully synthesized. The PU\u003csub\u003ePIPMB\u003c/sub\u003e had excellent mechanical properties, and its stress-strain curve showed \u0026ldquo;strain enhancement\u0026rdquo;. When the PDM/MOCA molar ratio was 60/40(PU\u003csub\u003eHB-60/40\u003c/sub\u003e), the tensile strength, elongation at break and toughness were 18.8 MPa, 2132% and 117.0 MJ\u0026middot;m\u003csup\u003e-3\u003c/sup\u003e respectively. The puncture energy was 2732 MJ and the fracture energy was 100.75 kJ\u0026middot;m\u003csup\u003e-2\u003c/sup\u003e, showing excellent strength and toughness. AFM, WXAD and DSC tests showed that PU\u003csub\u003ePIPMB\u003c/sub\u003e had amorphous structure and room temperature self-healing ability. For PU\u003csub\u003eHB-60/40\u003c/sub\u003e with excellent mechanical properties, the self-healing efficiency of tensile strength, elongation at break and toughness after 48 h of room temperature self-healing were 94.7%, 91.7% and 86.7% respectively, showing excellent room temperature self-healing properties. However, the balance between the performance of this polyurethane elastomer and its practical application still needs to be further improved to ensure that it can function effectively in real-world applications.\u003c/p\u003e\u003cp\u003eIn addition, PU\u003csub\u003ePIPMB\u003c/sub\u003e elastomers had decent reuse performance, and the mechanical properties of PU\u003csub\u003eHB-60/40\u003c/sub\u003e were not significantly reduced after recycling. Therefore, this study provided a useful idea for preparing sustainable high strength room temperature self-healing polymers.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by The Key Projects of Sichuan Province Natural Foundation (Projects No. 2023NSFSC0027) and the Project of the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Projects No. PLN2022-03) and the Open Fund (PLN2023-23) of National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Southwest Petroleum University).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.\u003c/p\u003e\n\u003cp\u003eAll authors declare that all data in this study are available.\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003eThe authors have no competing interests to declare that are relevant to the content of this article.\u003c/p\u003e\n\u003cp\u003eAll authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript.\u003c/p\u003e\n\u003cp\u003eThe authors have no financial or proprietary interests in any material discussed in this article.\u003c/p\u003e\n\u003cp\u003eAll authors whose names appear on the submission\u003c/p\u003e\n\u003cp\u003e1) made substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data; or the creation of new software used in the work;\u003c/p\u003e\n\u003cp\u003e2) drafted the work or revised it critically for important intellectual content;\u003c/p\u003e\n\u003cp\u003e3) approved the version to be published; and\u003c/p\u003e\n\u003cp\u003e4) agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAffiliation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYuchen Jiao is studying at the School of New Energy and Materials at Southwest Petroleum University as a graduate student (2023 Grade). He is majoring in Materials Engineering. E-mail: [email protected]\u003c/p\u003e\n\u003cp\u003eMing Zhou received his B.Sc., M.Sc., and Ph.D. from the Southwest Petroleum University in Chengdu of the PR China and worked at the School of New Energy and Materials at Southwest Petroleum University as a research chemist in 2002. He is a professor and a doctoral tutor at the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation. His research fields are Oilfield materials. E-mail: [email protected], Tel: +8613880947076. QQ: 106747878 Address: No.8, Xindu Avenue, Xindu District, Chengdu City. He is corresponding author\u003c/p\u003e\n\u003cp\u003eBo Pu is working in the safety and environmental protection quality supervision and testing Institute of CNPC Chuanqing Drilling Engineering Co., LTD. He is majoring in chemical engineering and process related research. Email: [email protected]\u003c/p\u003e\n\u003cp\u003eXiaoling Yang is studying at the School of New Energy and Materials at Southwest Petroleum as a doctoral student (2021 Grade). She is majoring in Materials Science and Engineering. E-mail:\u0026nbsp;[email protected]\u003c/p\u003e\n\u003cp\u003eChenyiting Li is studying at the School of New Energy and Materials at Southwest Petroleum as a graduate student (2021 Grade).\u0026nbsp;She\u0026nbsp;is\u0026nbsp;majoring\u0026nbsp;in\u0026nbsp;Materials\u0026nbsp;Engineering.\u0026nbsp;E-mail:\u0026nbsp;[email protected]\u003c/p\u003e\n\u003cp\u003eLiangliang Xia is working at the School of New Energy and Materials at Southwest Petroleum University, Chengdu, 610500, China. E-mail: [email protected]\u003c/p\u003e\n\u003cp\u003eGuilin Deng is studying at the School of New Energy and Materials at Southwest Petroleum University as a graduate student (2023 Grade). She is majoring in Materials Science and Engineering. E-mail: [email protected]\u003c/p\u003e\n\u003cp\u003eYunyao Wei is studying at the School of New Energy and Materials at Southwest Petroleum University as a graduate student (2023 Grade). He is majoring in Materials Science and Engineering. E-mail: [email protected]\u003c/p\u003e\n\u003cp\u003eJing Zhong is studying at the School of New Energy and Materials at Southwest Petroleum University as a graduate student (2023 Grade). He is majoring in Materials Science and Engineering. E-mail: [email protected]\u003c/p\u003e\n\u003cp\u003eZheng Wu is studying at the School of New Energy and Materials at Southwest Petroleum University as a graduate student (2023 Grade). He is majoring in Materials Engineering. E-mail: [email protected]\u003c/p\u003e\n\u003cp\u003eShi Chen is studying at the School of New Energy and Materials at Southwest Petroleum University as a graduate student (2023 Grade). He is majoring in Materials Science and Engineering. E-mail: [email protected]\u003c/p\u003e\n\u003cp\u003eJian Wang is working at the School of College of Food and Biological Engineering, Chengdu University, Chengdu 610106, China. E-mail: [email protected]\u003c/p\u003e\n\u003cp\u003eYujun Zhou is studying at the College of Chemistry and Chemical Engineering at China West Normal University as an undergraduate student (2023 Grade). She is majoring in Chemistry. E-mail: [email protected]\u003c/p\u003e\n\u003cp\u003eAbove authors are all come from China.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eD. K. Chattopadhyay, K. V. S. N. Raju, Structural engineering of polyurethane coatings for high performance applications, Prog. Polym. Sci. 32(3) (2008), 352-418. https://doi.org/10.1016/j.progpolymsci.2006.05.003.\u003c/li\u003e\n\u003cli\u003eS. Y. Kang, Z. X. Ji, L. F. Tseng, Design and synthesis of waterborne polyurethanes, Adv. 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J. 466(2023), 143179. https://doi.org/10.1016/j.cej.2023.143179.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"polyurethane elastomers, dynamic covalent/non-covalent bonds, strength, room-temperature self-healing, recyclable","lastPublishedDoi":"10.21203/rs.3.rs-8014090/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8014090/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePolyurethane elastomers have excellent tensile properties and elastic recovery properties, but traditional polyurethane elastomers are often broken and irreparable due to wear, so the research on high strength self-healing polyurethane elastomers has broad application prospects. In this study, based on the concept of intrinsic self-healing, multiple hydrogen bonds and boroxane rings with N-B coordination bonds were designed into the molecular. A novel polyurethane elastomer was prepared by four-step addition of polytetrahydrofuranediol, isophorone diisocyanate, 4,4'-methylene bis(2-chloroaniline), 2-formylphenylboric acid, toluene, N, N-dimethylacetamide and 2, 6-pyridinediol. The prepared elastomers exhibit strain-induced strengthening and have excellent self-healing properties as well as excellent mechanical properties. When the molar ratio of PDM/MOCA is 60/40(PU\u003csub\u003eHB-60/40\u003c/sub\u003e), the tensile strength of the material is 18.8 MPa (self-healing efficiency 94.7%), and elongation at break is 2132% (self-healing efficiency 91.7%), and toughness is 117.0 MJ·m\u003csup\u003e-3\u003c/sup\u003e(self-healing efficiency 86.7%). Synchronous self-healing efficiency exceeds 86%. In addition, the elastomer also has the ability to be recyclable, and the change of mechanical properties are slightly before and after dissolution and reshaping. This study provides beneficial ideas for preparing room temperature self-healing recyclable polymers with high strength.\u003c/p\u003e","manuscriptTitle":"Preparation of Room-temperature Self-healing Recyclable Polyurethane Elastomers Based on Multiple Hydrogen/Nitrogen Coordination Boro-oxygen Bonds System","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-24 08:01:54","doi":"10.21203/rs.3.rs-8014090/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-11-12T06:56:05+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-11-12T06:47:56+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Journal of Polymer Research","date":"2025-11-11T20:39:19+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-11-07T13:00:12+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymer Research","date":"2025-11-06T22:06:23+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"021b6819-dbcf-4643-9963-08fa5ca3a052","owner":[],"postedDate":"November 24th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-03-16T16:04:57+00:00","versionOfRecord":{"articleIdentity":"rs-8014090","link":"https://doi.org/10.1007/s10965-025-04746-w","journal":{"identity":"journal-of-polymer-research","isVorOnly":false,"title":"Journal of Polymer Research"},"publishedOn":"2026-03-10 15:59:32","publishedOnDateReadable":"March 10th, 2026"},"versionCreatedAt":"2025-11-24 08:01:54","video":"","vorDoi":"10.1007/s10965-025-04746-w","vorDoiUrl":"https://doi.org/10.1007/s10965-025-04746-w","workflowStages":[]},"version":"v1","identity":"rs-8014090","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8014090","identity":"rs-8014090","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}