R. Tokar et al., CATIONIC POLYMERIZATION OF GLYCIDOL - COEXISTENCE OF THE ACTIVATED MONOMER AND ACTIVE CHAIN-END MECHANISM, Macromolecules, 27(2), 1994, pp. 320-322
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.