Dynamic-mechanical thermal analysis of aramid-silica hybrid composites prepared in a sol-gel process

Several types of nonbonded and chemically bonded composites of silica with linear and linear-nonlinear aramid polymers were prepared using the sol-gel process. The linear polyamide chains were synthesized by the reaction of a mixture of m- and p-phenylene diamines and terephthaloyl chloride in dimethyl acetamide. The nonlinear chains were prepared using 1,3,5-benzenetricarbonylchloride along with tereph-thaloyl chloride, thereby significantly increasing the average functionality of the monomers. These increased functionality chains were then endcapped with aminophenyl-trimethoxysilane. Silica networks chemically bonded to the polyamide chains were produced by the addition of tetramethoxysilane to the aramid solution and its subsequent hydrolysis and condensation. The films cast from these solutions were yellow, and those containing up to 25 wt % silica were also transparent. Dynamic-mechanical thermal analysis was carried out to characterize interfacial bonding and interactions, in particular through the use of values of the glass transition temperatures Tg of the polymers. The presence of the silica caused increases in Tg, with the increases being largest for the composites in which there was strong interfacial bonding between the polymer chains and the ceramic silica phase.