P. Cancouet et al., Functional polysiloxanes. II. Neighboring effect in the hydrosilylation ofpoly(hydrogenmethylsiloxane-co-dimethylsiloxane)s by allylglycidylether, J POL SC PC, 38(5), 2000, pp. 837-845
Citations number
23
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY
Polysiloxanes bearing epoxy groups as lateral substituents were prepared by
the hydrosilylation of 1-allyloxy-2,3-epoxypropane (allylglycidylether) wi
th poly(hydrogenmethylsiloxane-co -dimethylsiloxane)s (D-H-D copolymers) of
various compositions. To determine the optimal conditions of the hydrosily
lation catalyzed by hexachloroplatinic acid, the kinetics of the reaction w
ere investigated for the poly(hydrogenmethylsiloxane) homopolymer. The reac
tion was first order in platinum, first order in double bonds, and 0.5 in S
iH. This kinetic law was consistent with the hypothesis that hydrogenmethyl
siloxane dyads are much more reactive than isolated units, which may be exp
lained by the simultaneous insertion of two vicinal SiH's in a binuclear co
mplex of platinum. This peculiar type of neighboring effect was investigate
d further by comparison of the kinetics of the hydrosilylation of D-D-H cop
olymers of various compositions and D-H block lengths and was confirmed by
the microstructure of a D-D-H copolymer (50/50) before and after partial hy
drosilylation. Triad analysis by Si-29 NMR showed that the resulting copoly
mer was not statistical but contained a high proportion of isolated SiH. Th
is explains why hydrosilylation proceeded in two steps: a fast reaction of
D-H-D-H dyads and a slow reaction of the remaining isolated D-H units. (C)
2000 John Wiley & Sons, Inc.