The mean-square radius of gyration and intrinsic viscosity were determined for isotactic poljKmethyl methacrylate) (i-PMMA) with the fraction of racemic diads fT *» 0.01 in acetone at 25.0 °C and in chloroform at 25.0 °C in the range of weight-average molecular weight Mw from 6.58 x 102 to 1.93 x 106. The results for the gyration-and viscosity-radius expansion factors Os and a, for i-PMMA along with those previously obtained for atactic poly(methyl methacrylate) (a-PMMA) with fT = 0.79 in the same solvents are found to become functions only of the scaled excluded-volume parameter z defined in the Yamakawa-Stockmayer-Shimada theory on the basis of the helical wormlike chain. Here, a, for i-PMMA has been calculated as before by taking account of the dependence on solvent of the Flory-Fox factor in the unperturbed state. Thus the present results along with the previous ones for atactic polystyrene (a-PS), polyisobutylene, and a-PMMA lead to the conclusion that the quasi-two-parameter scheme is valid for Os and a, for a variety of polymer-solvent systems irrespective of the differences in chain stiffness, local chain conformation, and solvent condition. This also indicates that there is no draining effect on a, at least for these systems. It is found that the effects of chain stiffness on as and remain appreciable even for Afw > 106 for i-PMMA as well as for a-PS and a-PMMA. The effects are smaller for i-PMMA than for a-PMMA both in acetone and in chloroform, reflecting the fact that the former chain is less stiff than the latter. It is also found that the values of the binary-cluster integral ß between beads (segments) for the two PMMAs in the same solvent are almost identical with each other, indicating that ß is independent of the stereochemical structure of the polymer chain.

The mean-square radius of gyration

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