Rheological properties of polystyrene blends with rigid ladderlike polyphenylsilsesquioxane

Polystyrene (PS) blends with rigid ladderlike polyphenylsilsesquioxane (PPSQ) were prepared by solution casting followed by hot pressing. The rheological properties of these blends were studied under dynamic shear and uniaxial elongation conditions. The loss modulus (G") and dynamic shear viscosity (eta*) of the 95/5 PP/PPSQ blend were slightly lower than those of pure PS at low frequencies (<= 10(-2) rad/s). However, the storage modulus (G'), G", and eta* of the other blends (90/10, 85/15, and 80/20) were higher than those of pure PS and increased with PPSQ content. The eta(E) data demonstrated that PS/PPSQ blends exhibited slightly weaker (5% PPSQ) or much weaker (10% PPSQ) strain hardening than PS. In contrast, the 85/15 and 80/20 PP/PPSQ blends showed strain softening, and the extent of strain softening increased with PPSQ content. PS entanglements might have been reduced by the specific interactions between PS and PPSQ, which locally ordered some PS molecules in the 95/5 blend sample, because most of the PPSQ might have been well dispersed in the PS continuous phase, and only a few small PPSQ particles (similar to 1.3 mu m) were formed because of good miscibility. However, at high PPSQ contents (>= 10%), many larger hard PPSQ particles were formed, which acted as fillers during, the rheological measurements. (c) 2005 Wiley Periodicals, Inc.