LOCAL DYNAMICS OF POLYISOPRENE IN TOLUENE

Local dynamics of polyisoprene in dilute solution with toluene are examined through C-13 NMR relaxation measurements. The variations of T1 and NOE with Larmor frequency are analyzed over a wide temperature range, including both the extreme narrowing region and the T1 minima. A frequency-temperature superposition of the data demonstrates that the distribution of motional time constants does not change shape with temperature and has a temperature and viscosity dependence consistent with that in nine other solvents. The data are analyzed in terms of eight motional models. Only those models that invoke motion on two well-separated time scales are successful. The slower, conformational motions correspond to activated torsional dynamics. The faster motions are librations within potential energy wells. Local dynamics in toluene are believed to exemplify polyisoprene dynamics in other solvents. Some similarities to local dynamics in bulk polymers are also expected.