Excluded-volume effects on the mean-square radius of gyration and intrinsic viscosity of oligo- and poly(methyl methacrylates)

Abstract

The mean-square radius of gyration and intrinsic viscosity were determined for isotactic poly(methyl methacrylate) (i-PMMA) with the fraction of racemic diads f r ≃ 0.01 in acetone at 25.0 °C and in chloroform at 25.0°C in the range of weight-average molecular weight M w from 6.58 x 10 2 to 1.93 x 10 6 . The results for the gyration- and viscosity-radius expansion factors αs and α η for i-PMMA along with those previously obtained for atactic poly(methyl methacrylate) (a-PMMA) with f r = 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, α η for i-PMMA has been calculated as before by taking account of the dependence on solvent of the Flory-Fox factor Φ o 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 αs and α η 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 α η at least for these systems. It is found that the effects of chain stiffness on αs and α η remain appreciable even for M w > 10 6 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 β between beads (segments) for the two PMMAs in the same solvent are almost identical with each other, indicating that β is independent of the stereochemical structure of the polymer chain.