Mechanism of Effect of Non-Reactive Polyhedral Oligomeric Silsesquioxane Nanostructures on HTPB-Based Polyurethane Network Formation: A Rheokinetic Analysis

Abstract This study explored the influence of non-reactive POSS nanostructures (Octa isobutyl silsesquioxane (OIBS) and Octa phenyl silsesquioxane (OPS)) on polyurethane (PU) from Hydroxyl-terminated polybutadiene (HTPB) resin and various curing agents (Toluene diisocyanate (TDI), Hexamethylene diisocyanate (HDI), Isophorone diisocyanate (IPDI), and Dimeryl-diisocyanate (DDI)). Contrary to previous expectations, POSS nanostructures enhanced the initial viscosity of HTPB resin. The Chemo-rheological method and Arrhenius and Eyring equations were employed to determine the reaction kinetics of PU synthesis. It was found that POSS nanostructures modulated the reaction kinetics between isocyanate and diol depending on the curing agent and POSS type. For instance, POSS accelerated the reaction in IPDI and TDI systems but slowed it down in the DDI system. In the HDI system, the POSS effect varied with its type and concentration, which were analyzed in detail. Besides the type of POSS, the nanostructure concentration also affected the PU synthesis's kinetics. Different concentrations of OIBS and OPS in each system were compared, and the possible reasons for the observed patterns were discussed. These results were explained by considering the interactions between POSS nanostructures and PU components. A plausible mechanism for the role of non-reactive POSS in PU synthesis kinetics was proposed.