Photocrosslinking of polymers bearing epoxy or epithio groups by quinones in the solid state

Abstract

AbstractPhotocrosslinking of poly(glycidyl methacrylate) (PGMA) and a copolymer of 2,3‐epithiopropyl methacrylate and methyl methacrylate [P(ETMA‐co‐MMA)] was studied in the solid state in the presence of various quinones. The efficiency of photocrosslinking was strongly dependent upon the structures of quinones and the kinds of polymers. For example, the alkyl‐substituted quinones such as 2‐ethyl‐p‐benzoquinone (EQ), 2‐tert‐butyl‐p‐benzoquinone (tBQ) and 2,5‐di‐tert‐butyl‐p‐benzoquinone (2,5‐dtBQ) did not induce photocrosslinking of poly(methyl methacrylate) (PMMA), whereas they acted as efficient photocrosslinking agents in PGMA and P(ETMA‐co‐MMA). The formation of charge transfer complexes did not play a principal role in this effective photocrosslinking, because the order of the photocrosslinking efficiency [EQ > tBQ > 2,5‐dtBQ > p‐benzoquinone (Q)] was not in agreement with that of the magnitude of the electron affinities of quinones, i.e., Q > EQ > tBQ > 2,5‐dtBQ. Photopolymerization of propylene sulfide (PS) in the presence of tBQ or Q was also investigated. The presence of tBQ induced polymerization of PS upon UV irradiation. From these results, it was deduced that the photocrosslinking of P(ETMA‐co‐MMA) film containing tBQ proceeds via a cationic polymerization of epithio groups. A similar mechanism should be applicable to the photocrosslinking of PGMA film containing tBQ.