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

Structure, size and dynamics of domains of hybrid siloxane networks prepare d by copolymerization of tetraethoxysilane (TEOS) and dimethyl(diethoxy)sil ane (DMDEOS) were studied by several techniques of solid-state H-1 and Si-2 9 NMR spectroscopy as well as by ab initio quantum chemical calculations. T -1 rho(H-1) relaxation times, dipolar dephasing and spin diffusion experime nts confirmed the existence of nano-heterogeneous system with random, bicon tinuous 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 che mical ab initio calculations of geometry and the principal values of Si-29 NMR chemical shift tensor and the isotropic chemical shift confirmed our st ructural predictions that copolymers with polycyclic structure units are fo rmed. The accord of calculated values with those experimentally determined was sufficiently good. (C) 2000 Elsevier Science Ltd. All rights reserved.