COMPATIBILITY OF POLYIMIDE-SILICATE CERAMERS INDUCED BY ALKOXYSILANE SILANE COUPLING AGENTS

A hybrid material incorporating silica networks in polyimide films was produced using the sol-gel technique from solution mixtures of polyamic acid and partially polymerised tetraethoxysilane (TEOS) containing small amounts of a functionalised alkyl trimethoxysilane. These were converted into films by solvent evaporation, followed by imidisation and condensation reactions through temperature increases to a maximum of 350 degrees C. Depending on the alkoxysilane solution composition and mixing parameters, different morphologies were obtained, varying from semi-interpenetrating networks of linear polyimide within highly crosslinked silica chains, to finely dispersed heterogeneous systems exhibiting either co-continuous or particulate microstructure. Gelation studies revealed that in the presence of amine catalysts, the tetraethoxysilane solutions modified with gamma-glycidyloxypropyltrimethoxysilane had the shortest gelation times, indicating that the epoxy groups become involved in the formation of the network by reactions with the carboxylic acid groups of the polyamic acid and through homopolymerisation. At the maximum temperature allowable for the imidisation reactions (400 degrees C) small amounts of residual SiOH groups were detected within the silicate network. The tensile strength of ceramers was found to go through a maximum with increasing curing time at 400 degrees C, whereas the elongation at break decreased monotonically and then remained constant.