Functionalized electron-rich pyridines as initiators for the epoxy homopolymerization

A simple and modular dialkylation of two electron-rich pyridine derivatives, namely 4-aminopyridine or 1,2,3,4-tetrahydropyrido[3,4-b]pyrazine, is achieved by aza-Michael reactions with electron-poor olefins (ethyl acrylate and acrylonitrile). Reducing the ester groups in the ethyl acrylate-derived compounds yielded the corresponding hydroxyl-containing derivatives. Subsequently, homopolymerization of phenyl glycidyl ether as well as an epoxy-alcohol polyaddition were catalyzed using the introduced compounds. As a reference catalyst, 4-dimethylaminopyridine was used. We found that in all cases an irreversible termination of the polymerization at temperatures above 100°C occurred. The decomposition was particularly rapid in the case of pyridine derivatives containing hydroxyl groups. In contrast, at a constant temperature of 100 °C, the latter compounds gave the fastest phenyl glycidyl ether homopolymerization and high conversions were found for all electron-rich pyridine derivatives. However, testing the catalysts at high alcohol concentrations at temperatures higher than 100 °C resulted in similarly moderate conversions in all cases.