Molecular mobility of poly(methyl methacrylate): a time-resolved electron spin resonance study with photoexcited triplet-state phenazine as a probe

Molecular mobilities of poly(methyl methacrylate) (PMMA) doped with phenazine as a probe were investigated by employing a time-resolved electron spin resonance (ESR) technique. Amplitudes of the transient ESR responses from photoexcited triplet phenazine molecules were monitored immediately after a pulse from an excimer laser (308 nm). The amplitudes were measured at several microwave powers with the probes in PMMA matrices of different average molecular weights. The transient ESR data are found to correlate with the relative molecular mobilities of host matrices as reflected by the differences in their glass transition temperatures. The time scale of motion detected by this method is in the range of 10 exp --4 -10 exp --6 s. 34 ref.--AA