Synthesis and characterization of alkylene-bridged silsesquicarbodiimide hybrid xerogels

Hybrid polymers consisting of flexible organic chains within an inorganic silsesquicarbodiimide network of the type [(NCN)1.5Si-(CH2)x-Si(NCN)1.5]n (where x=2, 6, and 8) were prepared by mild sol–gel polycondensation reactions of bis(trichlorosilyl)alkanes and bis(trimethylsilyl)carbodiimide. The presence of the NCN groups in xerogel structures was identified by FTIR spectra. The composition and molecular structures were characterized by elemental analysis, solid-state 13C CP MAS- and 29Si CP MAS-NMR spectroscopies, and XRD. Scanning as well as transmission electron microscopies were used to examine the morphology of the xerogels. In addition, the pore structure of the materials was examined by the gas adsorption (BET) method and it is found that the surface area decreased with increasing length of the alkylene spacing group.