Synthesis and structure of ladder polymethylsilsesquioxanes from sila-functionalized cyclotetrasiloxanes

Highly regulated ladder-structured polymethylsilsesquioxanes soluble in solvents with high molecular weight were synthesized from sila-functionalized tetramethylcyclotetrasiloxanes [MeSiXO]4 (X = H, OEt, NCO) by the dehydrogenative condensation of [MeSiHO]4 with water in the presence of N,N-diethylhydroxylamine or the hydrolytic polycondensation of [MeSiXO]4 (X = OEt, NCO). Formation of a siloxane-ladder structure was confirmed based on the appearance of two absorption bands and a signal due to Si–O–Si linkage in the infrared spectra and a silsesquioxane unit in 29Si nuclear magnetic resonance spectra, respectively. The narrow half-peak width of the 29Si nuclear magnetic resonance spectra suggested the formation of a highly regulated ladder structure for polymethylsilsesquioxanes.