Uniaxial extensional flow behavior of comb-shaped poly(methyl methacrylate)

Comb-shaped poly(methyl methacrylate)s (PMMAs) with various mass fractions and various molecular weights of the side chains were prepared by free-radical polymerization followed by atom transfer radical polymerization (ATRP). The rheological properties were characterized in linear-viscoelasticity and in uniaxial extensional flow. Due to branching and thereby slow relaxation of the backbone, significant strain hardening was observed and well analyzed by the molecular stress function (MSF) model. The model parameter fmax2 increased with increasing Mn,bb at almost constant Mn,br and p¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{p} $$\end{document}, and with increasing p¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{p} $$\end{document} at almost constant Φn,br, where Mn,bb and Mn,br are the number-average molecular weights of the backbone and the branched chains, and p¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{p} $$\end{document} and Φn,br are the average number per backbone and the number-average mass fraction of the branched chains, respectively. These results provide guidelines for the polymer design with the aim of enhancing strain hardening in elongational flow.