Polyisoprene (PI) melts have been studied, with most reports focusing on systems with high 1,4-cis content. In contrast, 1,4-trans PI homopolymers or random copolymers have seldom been examined, despite a handful of investigations suggesting a distinct dynamic behavior. Herein, we employ all-atom simulations to investigate the effect of chemical architecture on the dynamics of cis and trans-PI homopolymers, as well as copolymers. We examine the thermodynamic, conformational, and structural properties of the polymers and validate the performance of the models. We probe chain dynamics, revealing that cis-PI presents accelerated translation and reorientation modes relative to trans as recorded by the mean square displacement of the chain center-of-mass as well as by the characteristic times of the lower modes in a Rouse analysis. Interestingly, progressing to higher modes, we observe a reversal with trans units exhibiting faster dynamics. This was further confirmed by calculations of local carbon–hydrogen vector reorientation dynamics, which offer a microscopic view of segmental mobility. To obtain insight into the simulation trajectories, we evaluate the intermediate incoherent scattering function that supports a temperature-dependent crossover in relative mobility that extends over separations beyond the Kuhn-length level. Finally, we analyzed the role of non-Gaussian displacements, which demonstrate that cis-PI exhibits increased heterogeneity in dynamics over short-timescales in contrast to trans-PI, where deviations persist over times extending to terminal dynamics. Our all-atom simulations provide a fundamental understanding of PI dynamics and the impact of microstructure while providing important data for the design and optimization of PI-based materials.

In this research work, we provide a detailed investigation of the structural and viscoelastic properties of crosslinked styrene butadiene rubber (SBR) networks that are studied using atomistic molecular dynamics simulations.

The behavior and properties of polymer–resin blends are critical for the design of advanced polymeric systems in a wide range of applications. In this work, we present an atomistic molecular dynamics study of the effects of hydrogenated dicyclopentadiene (H-DCPD) resin on the structural, dynamical, and viscoelastic properties of polymer matrices. Two different systems are examined: linear 1,4-cis polyisoprene (PI) and a four-component styrene–butadiene rubber (SBR) copolymer. The results reveal lower miscibility of H-DCPD resin in PI compared to that in SBR, as evidenced by the formation of resin-rich domains, revealed by the magnitude of local peaks in resin–resin radial distribution functions. Temperature-dependent analysis shows that structural and dynamical properties are most sensitive at ambient conditions (T = 300 K, P = 1 atm), with PI exhibiting significantly reduced molecular mobility due to its proximity to the glass transition temperature. This restricted dynamics directly influences the viscoelastic response, leading to increased structural rigidity upon resin addition. Furthermore, the effect of resin concentration is systematically assessed, demonstrating that, while 17 vol% resin has a negligible impact on both systems, increasing the concentration to 34 vol% in PI, results in pronounced changes in its structural and viscoelastic behaviors. Overall, this study highlights atomistic molecular dynamics simulations as powerful predictive tools for the rational design of resin–elastomer blends.

Chain relaxation in melts of moderately entangled macromolecules presents the first signs of topological constraints that are commonly manifested in the rheology of long commercial- grade polymers. In this study, we employ multiscale molecular dynamics simulations to examine the relaxation characteristics of model polyisoprene (PI) melts through the transition from the Rouse regime to entangled systems. We probed the impact of molecular weight and stereochemistry, and we evaluated the accuracy of theory in modeling the end-to-end relaxation. Our results support that trans-PI dynamics is distinct, with entanglements forming at a lower degree of polymerization than other compositions due to differences in the characteristic ratio and packing of this polymer. For all moderately entangled systems, modeling the end- to-end relaxation with the original Likhtman-McLeish theory with contour-length fluctuations presents deviations from recorded data both in the early-time and terminal regime. We propose numerical modifications that significantly improve the model for all systems studied without introducing additional parameters. Our approach allows accurate predictions for long macromolecules based on data from detailed simulations with moderately entangled polyisoprene systems.