Abstract
AbstractThis paper reports the first measurements of macromolecular segmental relaxation times by phosphorescence depolarization. Steady‐state phosphorescence polarization experiments were performed on samples of poly(methyl acrylate) incorporating 0.5 wt % copolymerized acenaphthylene or 1‐vinyl naphthalene as phosphorescent probes over the temperature range 77 to 310°K. Depolarization of phosphorescence occurs with the onset of segmental motion of the polymer at ca. 278°K. Motion of either probe is characterized by an activation energy of 195 (±5) kJ mole−1, which is in fair agreement with the mean value of 230 kJ mole−1 estimated for the segmental relaxation of poly(methyl acrylate) by dielectric and mechanical relaxation techniques. Transient depolarization measurements confirm the absence of probe motion below the glass transition temperature. Phosphorescence intensity and triplet state lifetime data are capable of detection of a second transition in the polymer in accord with observations using more conventional techniques.
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