P. Cancouet et al., Functional polysiloxanes. I. Microstructure of poly(hydrogenmethylsiloxane-co-dimethylsiloxane)s obtained by cationic copolymerization, J POL SC PC, 38(5), 2000, pp. 826-836
Citations number
21
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY
Poly(hydrogenmethylsiloxane-co-dimethylsiloxane)s of various compositions h
ave been prepared by cationic ring-opening polymerization of octamethylcy-c
lotetrasiloxane (D-4) and 1,3,5,7-tetramethylcyclotetrasiloxane (D-4(H)) in
the presence of hexamethyldisiloxane as end-blocker or by rearrangement of
poly(hydrogenmethylsiloxane) in the presence of D-4. These copolymers were
examined by high resolution IPI NMR (500.13 MHz) and Si-29 NMR (99.37 MHz)
spectroscopies. Triad effects were observed by H-1 and up to heptad effect
s by Si-29 NMR. The chemical shifts were assigned for these stereosequences
. The intensities of the triad signals were used to calculate the quantitat
ive parameters describing the microstructure of the copolymer chains: numbe
r-average block length (L) and persistence ratio (eta) The values of these
parameters for copolymers prepared in various experimental conditions show
that the time necessary for redistribution reactions (backbiting) is much l
arger than the time required to establish the equilibrium between linear po
lymer and cyclic oligomers. However, redistribution is fast enough to preve
nt the formation of block copolymers even in the case of the rearrangement
of poly(hydrogenmethylsiloxane) in the presence of D-4. (C) 2000 John Wiley
& Sons, Inc.