The local motion of polystyrenes in dilute solutions was examined by the fluorescence depolarization technique. The samples, polystyrene (PS), poly(a-methylstyrene) (PaMS), and poly(pmethylstyrene) (PpMS), were labeled with the fluorescent probe anthracene in the middle of the main chain. The relaxation time of their local motion in dilute solutions was examined by fluorescence anisotropy measurement. The activation energy of the relaxation time of the polymer chain, E*, was also evaluated by the theory of Kramers' diffusion limit. There was a close correlation between the reduced relaxation time, TJ , or its activation energy and the chain expansion factor; i.e., both the reduced relaxation time and the activation energy decrease as the solvent quality becomes better. The reduced relaxation time and the activation energy depended on the local segment density of the polymer chain in the solution. The local motion for each polymer was compared in a solvent. The relaxation time and the activation energy of PaMS were larger than those of PS. This indicated that the barrier height of the local motion for a disubstituted polymer chain is higher than that for a monosubstituted one. Furthermore, the relaxation time and the activation energy of the PpMS chain were larger than those of PS.

ABSTRACT:Activation energies of local conformational transItIOns in polymers were investigated by the fluorescence depolarization method. The mean relaxation time related to the local conformational transitions was measured for dilute solutions of the anthracene-labeled polystyrene (PS), and anthracene-labeled polY(IX-methylstyrene) (PIXMS) in various solvents. The obtained data were successfully analyzed by use of the generalized formula of Helfand based on the reaction rate theory of Kramers. The results showed that the activation energy is larger in poor solvents than in good solvents which reflects the chain expansion effect. It is clear that the apparent activation energy is influenced by two types of polymer-solvent interactions, i.e., the frictional interaction (short-range interaction) and the chain expansion effect (long range interaction), and that the former can also be evaluated roughly by the present analysis.

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.