VISCOSITY DEPENDENCE OF THE LOCAL SEGMENTAL DYNAMICS OF ANTHRACENE-LABELED POLYISOPRENE IN DILUTE-SOLUTION

The local segmental dynamics of anthracene-labeled polyisoprene in dilute solution have been studied using time-correlated single photon counting. Nine solvents covering more than 2 decades in viscosity were utilized. The shape of the observed orientation autocorrelation functions was independent of solvent, temperature, and viscosity. Correlation times (r(c)) were determined as a function of temperature in all solvents. Contrary to the prediction of Kramers' theory in the high-friction limit, it was found that tau(c) is-proportional-to eta(0.76) at constant temperature. An apparent power law dependence was also observed in a recent C-13 NMR study of polyisoprene dynamics in dilute solution. These results are consistent with the idea that the friction opposing conformational transitions is frequency dependent.