Dynamics of polystyrene probed by muon spin spectroscopy

Abstract 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 γ -relaxation process, which involves motion of the phenyl rings, and is sensitive to the glass transition. The activation energy of the γ -relaxation process in the rubbery state is 0.60(2) eV in the HMW sample and 0.37(3) eV in the LMW sample.