MELT RHEOLOGY OF 4-ARM AND 6-ARM STAR POLYSTYRENES

The dynamic moduli of linear, four-arm and six-arm star polystyrene melts were measured over a wide range of frequencies and temperatures by the eccentric rotating disk method. The zero-shear viscosities of the star polystyrenes were less than those linear polystyrenes of the same molecular weight (M < 106). However, viscosities of the high molecular weight stars were larger when comparisons were made at a constant radius of gyration. The observed enhancements agree with those found in polybutadiene stars when compared on the basis of the parameter Z(Mbr/Me), where Z and Me are constants characteristic of each polymer, and Mbr is the molecular weight of the arm. The zero-shear recoverable compliance of the star polymers is well-described by the Rouse-Ham formula Je0 = 0.4g2pRT/M The plateau modulus GN0 appears to be the same for linear and star polystyrenes. The frequency dependence of the dynamic moduli was examined for the possible presence of a second relaxation mechanism in high molecular weight stars, giving rise to viscosity enhancement, which is absent in the terminal spectrum of linear polymers. © 1979, American Chemical Society. All rights reserved.