CATIONIC POLYMERIZATION OF GLYCIDOL - COEXISTENCE OF THE ACTIVATED MONOMER AND ACTIVE CHAIN-END MECHANISM

Cationic polymerization of glycidol ((hydroxymethyl)oxirane) may invol ve two competing propagation mechanisms: active chain end (ACE) mechan ism (nucleophilic attack of the monomer on the tertiary oxonium ion ac tive species) and activated monomer (AM) mechanism (an attack of the h ydroxyl group of the polymer on the protonated monomer). The first mec hanism should lead to polymers containing exclusively primary hydroxyl groups. Propagation by the AM mechanism leads on the other hand to po lymers containing both primary and secondary (mostly) hydroxyl groups, depending on the direction of the opening of the protonated oxirane r ing. Analysis of the microstructure of polymers of glycidol of relativ ely high molecular weights (($) over bar M(n) = 10(3)-10(4)) by C-13 N MR spectroscopy as well as by Si-29 NMR spectroscopy of the silylated samples shows the presence of the secondary hydroxyl groups. The signi ficant fraction (up to 50%) of the secondary hydroxyl groups in the po lymer indicates the important contribution of the AM mechanism of prop agation.