Nanosecond Pulse Radiolysis of Polystyrene and Poly(methylmethacrylate)

Polystyrene and poly(methylmethacrylate) (PMMA) containing diphenyl and naphthalene as solutes have been studied by nanosecond pulse radiolysis. Solute negative ions were detected in PMMA but not in polystyrene. Solute triplet states were formed in times short compared with the lifetimes of the solute excited singlet states, whose presence was observed via their fluorescence. G (triplet) values of 0.2M samples of naphthalene and diphenyl in polystyrene were estimated to be 1.7 and 1.3, respectively. It is also shown that for high concentrations of solute less than 25% of the solute triplet states is derived from ion neutralization inside the spur. No evidence of intersystem crossing from solute excited singlet states was observed. Triplet yields in PMMA were smaller than those in polystyrene by a factor of 2 or more and were strongly affected by other transient species accumulated in previous irradiations. This latter quenching mechanism appears to involve the precursor, rather than the solute triplet states themselves. Possible modes of solute triplet-state formation are discussed, and it is concluded that triplet energy transfer from the solvent is the most probable mechanism.