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 structures. 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 SO₂R substituent or it may be a cyclic anhydride or maleimide. Beyond this, the donor may have a π‐like strained single bond, whereas the acceptor may be an electrophilic quinodimethane. Lewis acids may be used to enhance the electrophilicity of acceptor monomers. Reaction rates and polymer composition are determined 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/gauche zwitterion, which can initiate chain ionic homopolymerization, to an extremely stabilized zwitterion, which cannot add monomer, but builds up in concentration and terminates by combination, forming alternating copolymer. This model embraces the existing literature for a wide variety of monomers and possesses predictive power. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009