Long-Chain Branched Polypentenamer Rubber: Topological Impact on Tensile Properties, Chain Dynamics, and Strain-Induced Crystallization

In this work, the effect of long-chain branching (LCB) on the tensile properties of sulfur-cured, unfilled, polypentenamer rubber (PPR) was investigated. Branched PPR, prepared by ring-opening metathesis copolymerization of cyclopentene (CP) and dicyclopentadiene (DCPD), showed improved mechanical strength, demonstrating more than 3 times higher tensile stress at 500% strain compared to its linear counterpart (a homopolymer of CP). In situ wide-angle X-ray scattering showed that branching units caused significant changes in the strain-induced crystallization (SIC). At low temperatures, linear PPR underwent rapid SIC after a critical stretch was reached, while branched PPR crystallized more slowly. However, SIC is not the cause of the enhanced mechanical strength. Elevated temperature experiments confirmed that even in the absence of SIC, LCB PPR exhibits a stiffer stress–strain response. We propose that the stiffer behavior of branched PPR is caused by a reduction in the chain mobility. The origins of reduced chain mobility are likely from topological constraints imposed by the LCB architecture and also from an unintended nanofiller effect created by microphase separation of DCPD-rich domains. The work described here is the initial investigation of adding branching units to PPR to improve the elastomer performance.