A Paradigm for the Mechanisms and Products of Spontaneous Polymerizations

In spontaneous vinyl and ring-opening copolymerizations, polar and resonance effects on the intermediates from bond-forming initiation offer a continuous spectrum of reactivities and polymer structure. In bond-forming initiation, an electron-rich donor monomer forms a bond to an acceptor monomer. The donor monomer may be a vinyl monomer with O, N, or aryl substituent or it may be an aza- or oxacycle. The acceptor monomer may be a vinyl monomer carrying CN, COOR, or SO(2)R substituent or it may be a cyclic anhydride or malcimide. Beyond this, the donor may have a pi-like strained single bond, whereas the acceptor may be an electrophilic quinodimethane. Lewis acids may be used to enhance the electrophilicity of acceptor monomer. Reactions rates and polymer composition are determinded by systematically varying the stability of the first intermediate designated P (for polymethylene). The nature of the intermediate will vary from a highly reactive trans biradical, Which initiates chain alternating copolymerization, to a cis/gauchezwitterion, which can initiate chain ionic homopolymerization, to an extremely stablized zwitterion, which cannot add monomer, but builds up in concentration, forming alternating copolymer. This model embraces the existing literature for a wide variety of monomers and possesses predictive power. (C) 2009 Wiley Periodicals. Inc J Polym Sci Part A Polym Chem 47 6735-6749. 2009