Excluded-Volume Effects in Star Polymer Solutions. Six-Arm Star Polystyrene in Benzene

Abstract

Seven narrow-distribution samples of six-arm star polystyrene ranging in weight-average molecular weight Mw from 6.1 x 10 4 to 3.4 x 10 6 in benzene at 25°C have been studied by light scattering and viscometry to determine their z-average radii of gyration, second and third virial coefficients, and intrinsic viscosities. The ratios of the respective properties to those of linear polystyrene in the same solvent are established for high Mw. Data analysis shows that the relation between the radius expansion factor and the conventional excluded-volume parameter z comes close to the known relations for four-arm star and linear polystyrenes of high molecular weight and is described fairly satisfactorily by the previously proposed interpolation formula. On the other hand, the viscosity expansion factor vs. z curve appears slightly below that for linear polystyrene though almost superimposed on that for the four-arm star polymer. Thus the difference in this expansion factor between the linear and star chains remains to be explained theoretically. The experimental interpenetration function for the six-arm star polymer gradually decreases to about 0.6, a value close to recent Monte Carlo data, with increasing Mw. Its comparison with the previously constructed interpolation expression suggests that, as was the case for linear flexible polymers, the effect of chain stiffness on the second virial coefficient needs to be considered for Mw below 10 6 •

Monte Carlo calculation of second and third virial coefficients of linear and star polymers on lattice

“…9 The experimental results for linear polymers are available for polystyrene in benzene 10 and polyisobutylene in cyclohexane. 11 Again, our data are in good agreement with these data in the case of linear polymers.…”

Light Scattering and Phase Separation Studies on Cyclohexane Solutions of Six-Arm Star Polystyrene†

“…13,14 These samples, synthesized by a coupling reaction of anionically polymerized living polystyrene, were well fractionated and their weight to number-average molecular weight ratios were less than 1.04. The ratio of M w of each sample to that for its arm was 6 AE 0:3, ensuring that each molecule has almost exactly six arms with very narrow length distribution.…”

“…The ratio of M w of each sample to that for its arm was 6 AE 0:3, ensuring that each molecule has almost exactly six arms with very narrow length distribution. 13,14 The chosen samples were dried for more than 24 h in vacuo and dissolved into cyclohexane, which had been dried over sodium metal, refluxed for 4 h, and fractionally distilled. Solutions for light scattering measurements were optically clarified with a Teflon filter of 0.5 mm pore size.…”

Monte Carlo calculation of second and third virial coefficients of small-scale comb polymers on lattice

“…24,25 Finally, we plot the comb polymers' gyration radii, A 2 and A 3 , as a function of comb length in Figs. Such a topological dependence has already been reported in experiments, but for star polymers.…”