Local Chain Dynamics of Poly(N-vinylcarbazole) Studied by the Fluorescence Depolarization Method

Abstract

The local segmental motion at the center of the main chain of poly(N-vinylcarbazole) (PVCz) in dilute solutions was examined by the time-resolved fluorescence depolarization method. Anthracene-labeled PVCzs with various molecular weights were synthesized by living cationic polymerization. The relaxation time and the activation energy of the local motion were evaluated through the fluorescence anisotropy decay. The molecular weight dependence of the relaxation time could not be explained merely from the viewpoint of segment density, suggesting that the local potential for the rotational motion is an important factor governing the local dynamics of the polymer chain. The local motion of PVCz was compared with those of other polymers. Both the relaxation time and the activation energy were larger than those of other polymers. Moreover, PVCz had a larger critical molecular weight which is defined as the molecular weight where the reduced relaxation time reaches the saturation value. This is attributed to the fact that the bulky side chain suppresses the conformational transition of the polymer backbone.