PHOTOCROSSLINKING OF POLYIMIDE CONTAINING BENZOPHENONE UNIT - INTRAMOLECULAR AND INTERMOLECULAR REACTIONS IN SOLUTION

The photocrosslinking, using a high-pressure Hg lamp at 30°, of a polyimide from 3,3′-diethyl-4,4′-diamino-diphenylmethane with benzophenonetetracarboxylic dianhydride in aerated and degassed solutions was studied by i.r. spectroscopic, viscosity and light-scattering measurements. The quantum yields for intermolecular reactions are φAirinter/[C]0 = 0.68 l mol-1 and φVacinter/[C]0 = 1.8 l mol-1, and the quantum yields for intramolecular reactions, including some side reaction with the solvent, are φAirintra = 0.96 × 10-2 and φVacintra = 1.8 × 10-2 in the presence and absence of oxygen, respectively; they were calculated from the initial concentration dependence on the rate of decrease of benzophenone groups in the polymer. The magnitudes of Mw and 〈s2〉 1 2 are governed by the competition between intra- and intermolecular crosslinking; the contraction ratio, g = 〈s2〉cr/〈s2〉1, of a polymer coil because of intramolecular crosslinking becomes 0.02 at the onset of gelation in a degassed dilute solution. The polyimide in dichloromethane behaves like a flexible polymer which forms many intramolecular crosslinks during photocrosslinking. © 1990.