Fluorescence Depolarization Study of Local Motions in Polymers at the ϑ Temperature

Abstract

The mean relaxation times, Tm's, of four different polymers measured by the fluorescence depolarization method were compared at their ϑ temperatures. These polymers, i.e., cis-polyisoprene (cis-PI), polystyrene (PS), poly(α-methylstyrene) (PαMS), and syndiotactic poly(methyl methacrylate) (s-PMMA), were labeled with anthracene in the middle of the main chain by living anionic polymerization. The ϑ temperature is a standard point without an excluded volume effect, and the ϑ temperature of these four polymers are almost the same, 34−35 °C. Therefore, the comparison of the Tm's at the ϑ temperature enables us to clarify the relationship between the chain local motion and the chemical structure. The order of the reduced relaxation times, Tm/η, was Tm/η(cis-PI) < Tm/η(PS) < Tm/η(PαMS) < Tm/η(s-PMMA), and the order of activation energies, E*, was E*(cis-PI) < E*(PS) < E*(PαMS) < E*(s-PMMA). From a molecular standpoint, the relaxation times depend on both the substituents attached to the main chain and the stereoregularity of the polymer chains. In consideration of the stereoregularity of the polymer chains, the relaxation time of atactic PαMS is estimated to be not much different from the relaxation time of atactic PMMA.