ROTATIONAL-DYNAMICS OF ANTHRACENE AND 9,10-DIMETHYLANTHRACENE IN POLYISOPRENE

Singlet and triplet transient grating experiments have been used to measure rotational correlation functions for anthracene and 9,10-dimethylanthracene in cis-polyisoprene from Tg + 120 °C to Tg + 20 °C. Over this temperature range, the rotational correlation time varies by seven decades and follows the temperature dependence of the bulk viscosity. The observed correlation functions are not consistent with predictions of the anisotropic rotational diffusion model. The observed correlation functions for anthracene are consistent with a change in the predominant axis for rotational diffusion as a function of temperature. At high temperatures, in-plane rotation occurs most rapidly, while at low temperatures rotation about the long axis predominates. © 1990 American Institute of Physics.