ABSTRACT:Polystyrene (PS) labeled with anthracene in the middle of the main chain was prepared, and the relaxation time of their local motion in the solvents with various viscosities was examined by the fluorescence depolarization technique. We measured the relaxation time of emission anisotropy, Tm, in four kinds of mixed solvents of diethylphthalate (DEP) and cyclohexanone (CHO). These are good solvents for PS and have different viscosities. With the addition of DEP to cyclohexanone, i.e., with the increase in solvent viscosity, the activation energy of Tm, E*, obtained by using the reaction rate theory of Kramers in the high friction (diffusion limit) changed from a positive value to a negative value. The value of E* was also negative in the case of tripropionin, which is a poor solvent for PS and has a high viscosity. Therefore, we conclude that the negative E* does not depend on the quality of the solvent, i.e., whether the solvents are good or poor, but on the viscosity of the solvent. Then, we evaluated E* on the basis of Grote-Hynes' equation and of the Robinson's equation. The analysis by the Robinson's equation gave positive values of E*. The anomaly of the activation energies of the local motions may be explained by the movement of the polymer chains in an ordered solvent of strong intermolecular interaction.