Correlation between the crossover modulus and the molecular weight distribution using the Doi-Edwards theory of reptation and the Rouse theory

Abstract

The crossover modulus in the dynamic mechanical spectrum was linked with the molecular weight distribution (MWD) over a wide range of polydispersity ( $${{\bar M_w } \mathord{\left/ {\vphantom {{\bar M_w } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }}$$ = 1 to 6). Reasonable agreement was obtained between theory and experiment for near monodisperse and narrow MWD polymers using the Doi-Edwards theory of reptation. For broad MWD polymers, the Doi-Edwards theory was found to be inapplicable. Using the Doi-Edwards theory for the shorter chains and a Rouse type mechanism for the longer chains, a good fit was obtained between the calculated and experimentally measured crossover modulus values.