The effect of microstructure on polyisoprene melt dynamics*

cis-1,4 polyisoprene (PI) has been studied exhaustively due to being a major component of natural rubber and as a model system to interrogate fundamental mechanisms in polymer dynamics. Synthesis of polyisoprene (PI), a primary commercial polymer, typically results in a mixture of predominantly cis-1,4 but also trans-1,4 and 3,4 isomer repeat units. trans-1,4 PI melts have not been well characterized; a limited number of reports emphasized features that are distinct relative to isomers of similar well-studied elastomers such as polybutadiene. In this study, we systematically investigate the properties of PI random copolymers using detailed all-atom molecular dynamics simulations.  We examine the role of composition and temperature on the thermodynamic, conformational, dynamic and rheological properties providing data on the role of microstructure in a significant class of elastomers.