Activated monomer mechanism in the cationic polymerization of cyclic ethers

Abstract

AbstractCationic polymerization of oxiranes proceeds in the presence of hydroxyl groups containing compounds by activated monomer (AM) mechanism, competing with active chain end (ACE) mechanism. According to the AM mechanism, propagation involves reaction of activated (e.g. protonated) monomer molecules with nucleophilic sites in the growing macromolecules. Active species are located on the monomer, and growing macromolecule is neutral; thus side‐reactions, typical for active chain‐ end mechanism, are suppressed. In the polymerization of ethylene oxide (EO) ether oxygen atoms along the chain are more exposed to the attack than in the polymers of substituted oxiranes and also react with protonated monomer. The contribution of these reactions, in comparison with propagation involving hydroxyl end groups, is analysed. The participation of the polymer units is highly restrained for chains with bulky substituents. In the AM polymerization of propylene oxide (PO) and epichlorohydrin (ECH), chain growth proceeds predominantly on the terminal hydroxyl groups. Syntheses of telechelic oligomers and macromonomers, applying the AM mechanism with protonated monomers, are described.