Excluded-volume effects in star polymer solutions: Six-arm star polystyrene in cyclohexane near the Theta temperature

Anionically polymerized six-arm star polystyrene samples with weight-averag e molecular weights M-w of 5.6 x 10(4)-3.2 x 10(6) were studied by light sc attering and viscometry in cyclohexane at different temperatures to determi ne their z-average mean-square radii of gyration ([S-2](z)) second and thir d virial coefficients (A(2) and A(3)), and intrinsic viscosities ([eta]) Th e values of A(3) at the Theta point (34.5 degrees C), where those of A(2) w ere essentially zero for M-w > 10(6), were about 5 x 10(-4) cm(6) mol g(-3) and yielded 4 x 10(-45) cm(6) for the ternary cluster integral. The data f or [S-2](z) and A(2) at Theta were in line with previous perturbation calcu lations taking into account ternary cluster interactions, but the (residual ) ternary effects on these properties were not very significant, at least, for M-w > 10(6). The expansion factor alpha(S)(2) for [S-2] and that for [e ta] plotted against the conventional excluded-volume parameter for M-w > 1 x 10(6) came close to the known relations for both Linear and four-arm star polystyrenes of high molecular weight in cyclohexane. On the other hand, t he relation between Psi (the interpenetration function) and alpha(S)(2) for the six-arm star polymer appeared far above that for the linear chain and appreciably above that for the four-arm star chain at temperatures above Th eta. These experimental results for alpha(S)(2) and Psi were quantitatively described by the interpolation formulas constructed in previous work.