The viscosity slope constant k′—ternary systems: Polymer–polymer–solvent

Abstract

AbstractThe viscosity slope constant k′, i.e., \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\lim }\limits_{c \to 0} \frac{{d\left( {{{\eta _{sp} } \mathord{\left/ {\vphantom {{\eta _{sp} } c}} \right. \kern-\nulldelimiterspace} c}} \right)}}{{dc}}\frac{1}{{[\eta ]^2 }} $\end{document}, is shown to be of increasing significance in polymer science as a molecular‐weight‐independent criterion of solvent power and as a parameter sensitive to various changes in polymer structure, such as long‐chain branching. Ideally, it is a dimensionless parameter, independent of molecular size, which arises only from the mutual hydrodynamic interaction of polymer molecules and depends, therefore, on the intrinsic flexibility of the polymer chain and on the polymer density in the coiled molecule. In real systems, however, other interactions may contribute, sometimes very significantly, to k′. For such real systems, the general expression: is suggested. In ternary systems, polymer–polymer–solvent, ideal expressions for ηsp/c and k′ are developed, that for k′ being: It is proposed that deviations from ideal behavior so defined are due to nonhydrodynamic polymer‐polymer interactions and might be used to detect and measure the strength of such interactions. Some preliminary data for the system polystyrene–poly(methyl methacrylate)–m‐xylene are presented and discussed.