Dynamics Of Polystyrene Probed By Muon Spin Spectroscopy

Muon spin spectroscopic measurements were made on atactic low-molecular-weight (LMW) (1.3 kg mol(-1)) and high-molecular-weight (HMW) (202 kg mol(-1)) polystyrene. Muoniated cyclohexadienyl radicals, which are formed by muonium addition to the phenyl side groups, are used as local probes of bulk dynamics. Muon spin relaxation is caused by the secondary gamma-relaxation process, which involves motion of the phenyl rings, and is sensitive to the glass transition. The activation energy of the gamma-relaxation process in the rubbery state is 0.60(2) eV in the HMW sample and 0.37(3) eV in the LMW sample.