Homopolymerization of epoxy monomers initiated by 4-(Dimethylamino)pyridine

Abstract

The anionic epoxy homopolymerization initiated by tertiary amines, imidazoles, and ammonium salts is a complex reaction exhibiting two undesired characteristics for practical applications: (a) slow reaction rates with long induction periods, and (b) short primary chains due to the high rate of chain transfer reactions. Therefore, these systems have not found an important place in commercial applications. In this study, it is shown that using 4-(dimethylamino)pyridine (DMAP) as initiator of the polymerization of phenyl glycidyl ether (PGE) or diglycidyl ether of bisphenol A (DGEBA) enables to obtain high polymerization rates and longer primary chains than those generated using typical initiators. A critical molar ratio DMAP/epoxy groups was necessary to attain complete conversion. Networks resulting from the DMAP-initiated homopolymerization of DGEBA exhibited a high crosslink density and corresponding high values of the glass transition temperature (Tg = 160°C) and of the rubbery elastic modulus (higher than 100 MPa). An intense brown color of reaction products, associated with an absorption band with a maximum at 360 nm, was ascribed to the presence of initiator fragments with conjugated double bonds in chain ends. These results might revalorize the anionic homopolymerization of epoxy monomers for commercial applications.