MICROSTRUCTURAL ANALYSIS OF POLYSILAPROPYNYLENE COPOLYMERS BY C-13 AND SI-29 NUCLEAR-MAGNETIC-RESONANCE

The sequence distribution of poly(dimethylsilapropynylene-co-diphenylsilapropynylenes) [[(Me2SiC≡C-)x(Ph2SiC≡C-)y]n] has been studied by NMR spectroscopy. It is shown that the silylethynyl units are randomly distributed within the copolymer cyclic and linear chains at equilibrium. The distributions of triad and pentad sequences in the29Si NMR and of diad and tetrad sequences in the13C NMR have been determined theoretically and compared with experimental spectra. Rearrangement reactions leading to the randomized products occur and have been shown to compete with condensation reactions. This randomization process is independent of the nature of substituents on the silicon atom and temperature. The ratio of specific copolymerization equilibrium constants has been calculated, and the whole process of copolymerization is shown to be entropy driven. © 1990, American Chemical Society. All rights reserved.