Solid-state NMR study of structure, size and dynamics of domains in hybrid siloxane networks

Structure, size and dynamics of domains of hybrid siloxane networks prepared by copolymerization of tetraethoxysilane (TEOS) and dimethyl(diethoxy)silane (DMDEOS) were studied by several techniques of solid-state H-1 and Si-29 NMR spectroscopy as well as by ab initio quantum chemical calculations. T-1 rho(H-1) relaxation times, dipolar dephasing and spin diffusion experiments confirmed the existence of nano-heterogeneous system with random, bicontinuous morphology. The size of domains of TEOS homopolymer is about 1.3-2.8 nm, the size of copolymer phase bring larger, ca. 4.0-6.8 nm. Quantum chemical ab initio calculations of geometry and the principal values of Si-29 NMR chemical shift tensor and the isotropic chemical shift confirmed our structural predictions that copolymers with polycyclic structure units are formed. The accord of calculated values with those experimentally determined was sufficiently good. (C) 2000 Elsevier Science Ltd. All rights reserved.