Melt-Polymerization of Acrylamide Initiated by Nucleophiles: A Route Towards Highly Branched and Amorphous Polyamide 3

The melt-polymerization of acrylamide initiated by nucleophiles allows for the preparation of polyamide 3 (PA 3) with a branching factor of about 1.5. The high share of branching units imparts a fully amorphous morphology featuring a low glass transition temperature of 67 °C and renders the polymer water soluble. The disclosed method provides an easy, resource-efficient and green access to a polymer interesting for applications in biological and biomedical systems. The obtained PA 3 was characterized by several NMR-techniques, MALDI-TOF mass spectrometry, size-exclusion chromatography, thermal analyses and powder-X-ray diffractometry. Preparation and characterization of a 15N-marked polymer complemented the elucidation of the polymers structure. Mechanistically, the polymerization can be considered as an aza-Michael polymerization of acrylamide involving zwitter-ionic species as the key intermediates being responsible for the high degree of branching.