Rheological properties of branched polystyrenes: linear viscoelastic behavior

Oscillatory shear measurements on a series of branched graft polystyrenes (PS) synthesized by the macromonomer technique are presented. The graft PS have similar molar masses (Mw between 1.3×105 g/mol and 2.4×105 g/mol) and a polydispersity Mw/Mn around 2. The molar masses of the grafted side chains Mw,br range from 6.8×103 g/mol to 5.8×104 g/mol, which are well below and above the critical entanglement molar mass Mc of linear polystyrene. The average number \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\ifmmode\expandafter\bar\else\expandafter\fi{p}}$$\end{document} of side chains per molecule ranges from 0.6 to 6.7. The oscillatory measurements follow the time–temperature superposition principle. The shift factors do not depend on the number of branches. The zero-shear viscosities of all graft PS are lower than those of linear PS with the same molar mass, which can be attributed to the smaller coil size of the branched molecules. It is shown that the influence of branching on the frequency dependence of the dynamic moduli is weak for all graft PS that were investigated, which can be explained by the low entanglement density.