Preparation of Transparent Polyimides and Their Photoinduced Charge Transfer

Abstract

Polyamide acids (PAA) were prepared from aromatic dianhydrides and aliphatic diamines, which ordinary give high molecular weight polymer due to salt formation during polymerization. Addition of tertiary amines to the PAA solution improves the polymerization reaction due to restriction of the salt formation. Resulting polyimide (PI) was photoirradiated in the presence of tetraphenylporphirine (TPP) as electron donor which transferred electrons to PI, since the partially aliphatic polyimide consists of pyromellitic moieties as strong electron acceptor. The active species generated during the electron transfer process was identified as radical cation of TPP by the laser flash photolysis, whose lifetime is much higher than that in solution. The charge separation by the stabilization of the radical cation is due to strong electron affinity of pyromellitic anhydride moieties of transparent polyimides.