A structural study of silicon-based interpenetrating polymer networks by solid state 1H and 13C NMR spectroscopy

Abstract

High-resolution solid-state 13C CP/MAS NMR spectra and two-dimensional (2D) 13C– 13C and 1H– 1H exchange NMR spectra of cured ladder silsesquioxane oligomer (LDS)/polycarbosilane (PCS) system which forms interpenetrating polymer networks (IPN) have been measured, in order to elucidate the phase structure and miscibility. From the 13C CP/MAS NMR experimental results on cured LDS/PCS IPN samples with various mixture weight ratios, it was found that the 1 HT 1ρ value of cured LDS/PCS IPN with mixture weight ratio=8/2[LDS/PCS(8/2)] sample was smaller than the 1 HT 1ρ values of cured LDS/PCS IPN samples with other mixed weight ratios. This suggests that in the cured LDS/PCS(8/2), the intermolecular dipole–dipole interaction most effectively contributes to the 1 HT 1ρ because of the shortest intermolecular distance between LDS and PCS chains. Further, from the 2D 13C– 13C and 1H– 1H exchange NMR results, it was found that the intramolecular spin diffusion occurs in all the samples, and intermolecular spin diffusion occurs in cured LDS/PCS(8/2). This shows that the miscibility of LDS/PCS(8/2) is higher compared to that in cured LDS/PCS samples with the other mixed weight ratios, and in cured LDS/PCS(8/2) the interchain distance between LDS and PCS portions is within the order of several 10 nm.