## Abstract

Tracer diffusion coefficients, D, for two 3-arm star (M_{w}= 3.79 X 10^{5}and 1.19 X 10^{6}) and for four 12-arm star (M_{w}= 5.5 x 10^{4}, 4.67 X 10^{5}, 1.11 X 10^{6}, and 1.69 X 10^{6}) polystyrenes (PS) have been measured in solutions of poly (vinyl methyl ether) (PVME)/o-fluorotoluene, by dynamic light scattering. PVME matrix concentrations ranged up to 0.30 g/mL, with molecular weights P_{w}= 1.4 X 10^{5}, 6.3 X 10^{6}, and 1.3 x 10^{6}. The PS radii of gyration were also measured by static light scattering, for one linear (M_{w}= 1.05 X 10^{6}), one 3-arm star (M_{w}= 1.19 X 10^{6}), and one 12-arm star (M_{w}= 1.69 X 10^{6}) PS in PVME (P_{w}= 2.5 X 10^{5}) solutions, over the concentration range 0 < c < 0.05 g/mL. The mobility of the stars has been compared to that for the linear polymers reported in the preceding article, under identical solution conditions. The ratio D_{star}/D_{linear}for^{a}given set of solution conditions was computed in two ways, either at constant arm molecular weight (i.e., viewing a linear molecule as a 2-arm star) or at constant total molecular weight. In the former case, above concentrations that scale approximately as c_{e}, the entanglement concentration for the PVME, the ratio D_{star}/D_{linear}decreases substantially with increasing concentration, for both 3-arm and 12-arm stars. This observation indicates that in entangled solutions, the mechanism(s) for diffusion depends on diffusant architecture. At constant total molecular weight, for 12-arm stars, the ratio D_{star}/D_{linear}increases slightly with increasing concentration, due to the earlier onset of entanglement effects for the spatially larger linear molecules. The measured PS radii of gyration decrease with increasing matrix concentration in a manner that is independent of PS architecture. These data were directly comparable to those reported for PS in PS/toluene by small-angle neutron scattering, indicating that in this ternary system the small, negative PS-PVME interaction parameter has little effect on macroscopic chain properties.

Original language | English (US) |
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Pages (from-to) | 3409-3418 |

Number of pages | 10 |

Journal | Macromolecules |

Volume | 22 |

Issue number | 8 |

DOIs | |

State | Published - Aug 1 1989 |