Local chain dynamics of Poly(N-vinylcarbazole) studied by the fluorescencedepolarization method

The local segmental motion at the center of the main chain of poly(N-vinylc arbazole) (PVCz) in dilute solutions was examined by the time-resolved fluo rescence depolarization. method. Anthracene-labeled PVCzs with various mole cular weights were synthesized by living cationic polymerization. The relax ation time and the activation energy of the local motion were evaluated thr ough the fluorescence anisotropy decay. The molecular weight dependence of the relaxation time could not be explained merely from the viewpoint of seg ment 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 th e relaxation time and the activation energy were larger than those of other polymers. Moreover, PVCz had a larger critical molecular weight which is d efined as the molecular weight where the reduced relaxation time reaches th e saturation value. This is attributed to the fact that the bulky side chai n suppresses the conformational transition of the polymer backbone.