AbstractA systematic investigation of the polymerization of crotonaldehyde was carried out. It was found that certain tertiary phosphines, whose pKa is greater than 8.0, were active catalysts for this polymerization. The experimental data were most consistent with a polymer structure resulting from a vinyl type polymerization of crotonaldehyde with a simultaneous cyclization of some vicinal, pendent aldehyde groups. The rate of polymerization was a sensitive function of the temperature, monomer concentration, catalyst concentration, and the dielectric constant of the solvent while the molecular weight was rather insensitive to these variables. The latter effect indicated that the predominant termination step was through chain transfer to monomer with a reinitiation by monomer anions. A charge separation mechanism involving the direct interaction of a tertiary phosphine with the monomer in the initiation step was proposed for this polymerization.