Stabilizing ion pairs in poly(methyl methacrylate)

Decay of ions trapped in gamma-irradiated poly(methyl methacrylate) (PMMA)-containing ion scavengers was examined. Cations in PMMA migrate through diffusion and by a hopping transfer of the charge. They encounter anions, combine, and thereby decay. The diffusion of cations was confirmed by a comparison of decay of ions in PMMA-containing pyrene and that in a copolymer of methyl methacrylate and I-pyrenylmethyl metbacrylate. Cations in the former sample decay faster than those in the latter sample. The ions in the copolymer are chemically bonded to the polymer chains, preventing the diffusion of the ions. However, the dependence of the decay of the ions on the concentration of pyrenyl groups indicated that the ions decay through a hopping transfer of the charge on pyrenyl groups. The hopping transfer was suppressed by triphenylamine. The suppression is ascribed to structural difference in neutral triphenylamine and its cation. Anions in PMMA are ketyl-type anions at the side chains of the polymer. Their migration is suppressed, since they are connected to the polymer chains and the structures of the neutral state and its anion are different.