THIRD VIRIAL-COEFFICIENTS OF POLYSTYRENE IN DIFFERENT THETA-SOLVENTS

Third virial coefficients (A(3)) are reported for a series of high mol ecular weight, narrow molecular weight distribution polystyrenes (PS) in benzene, a good solvent, and three Theta solvents: cyclohexane (CH) , 1-chloroundecane (CUD), and diethyl malonate (DEM). A(3) values meas ured in benzene and cyclohexane are in good agreement with previously reported results for these polymer/solvent systems. A(3) values measur ed in CUD and DEM are consistently much smaller than values measured i n CH for the same sample. This specific solvent effect is also reflect ed in larger Theta condition intrinsic viscosity ([eta]) values for PS in CH, as compared to PS in CUD or DEM. These results demonstrate a c orrelation between larger repulsive three-body interactions under Thet a conditions and larger Theta condition [eta] values. However, the rad ii of gyration of PS samples in these three Theta solvents were identi cal within experimental error. These results suggest that hydrodynamic properties are more sensitive to residual ternary interactions than a re thermodynamic properties. Furthermore, our results indicate that th e Flory hydrodynamic parameter phi can have different values in differ ent Theta solvents. Similar results were reported recently by Yamakawa and co-workers for poly(methyl methacrylate) in two different Theta s olvents.