Effect on the thermal resistance and thermal decomposition properties of thermally cross-linkable polyimide films obtained from a reactive acetylene

Homopolyimides are prepared by 4,4′-(ethyne-1,2-diyl)diphthalic anhydride as dianhydride monomer and several diamine monomers. The copolyimides are prepared with 4,4′-oxydianiline as an amine monomer， 3,3′,4,4′-oxydiphthalic anhydride as an anhydride monomer with the addition of 4,4′-(ethyne-1,2-diyl)diphthalic anhydride as another anhydride monomer. The structure of polyimides is characterized by Fourier transform infrared spectroscopy and X-ray diffraction. Thermogravimetric analysis, thermomechanical analysis and thermo-oxidative degradation kinetics analysis are used to investigate the properties of polyimides. The homopolyimide show the best thermal stability in both nitrogen and air atmosphere by 4,4′-oxydianiline and 4,4′-(ethyne-1,2-diyl)diphthalic anhydride. The results also indicate that the thermally cross-linkable copolyimide films not only enhance the thermal stability behaviors of polyimide by controlling the addition of dianhydride, but also improve substantially the upper limit temperature of thermal aging by undergoing chemical cross-linking reaction of the diphenylethynylene structures and providing multifarious naphthalene ring groups and biphenyl structures. Diphenylacetylene crosslinking merging to the long-chain of polyimide is a useful conversion for enhancing the thermal stability and the thermal degradation stability of aromatic polymers.