CONCENTRATION AND TEMPERATURE-DEPENDENCE OF LOCAL MOTIONS IN POLYISOPRENE TETRAHYDROFURAN

The fluorescence anisotropy decay method is used to measure the rotational diffusion of 9,10-diphenylanthracene and the segmental motion of anthracene-labeled polyisoprene in tetrahydrofuran solutions of polyisoprene. The concentration dependences of these two measures of local motion are reported from pure solvent to bulk polymer at 4.5, 25.0, and 45.5-degrees-C. These results are compared to previously reported measurements of the translational diffusion of methyl red in the same system. The translational and rotational diffusion measurements have the same concentration and temperature dependence. A somewhat weaker concentration and temperature dependence is observed for the labeled chain motions. The differences between the rigid probe and segmental motions are tentatively attributed to a decrease in the size of the motional unit for local chain dynamics at high concentrations and low temperatures. This explanation is consistent with recent dielectric relaxation results on a related system.