Transformation of semicrystalline polymer mechanics by cyclic polymers†

Cyclic polymers, lacking chain ends and featuring unique topological constraints, offer distinctive mechanical and thermal behaviors. This study synthesizes and compares semicrystalline linear and cyclic polycyclooctene (PCOE), with linear PCOE produced via ring-opening metathesis polymerization (ROMP) and cyclic PCOE via ring-expansion metathesis polymerization (REMP). Mechanical, thermal, and crystalline properties were evaluated through tensile testing, dynamic mechanical analysis (DMA), and wide-angle X-ray scattering (WAXS). Findings reveal that crosslinked cyclic PCOE exhibits lower tensile strength but greater stretchability than its linear counterpart, indicating enhanced network softness. DMA results show cyclic PCOE has a lower glass transition temperature T_g and rubbery plateau modulus

, while WAXS indicates lower crystallinity in cyclic PCOE < 25%, stabilizing at approximately 15% under a tensile strain of 100%. These differences suggest that polymer topology, not crystallinity, primarily dictates the mechanical response. Molecular dynamics simulations, using a crystallizable model of polyethylene, replicate the lower stress and higher stretchability observed experimentally, highlighting more compact cyclic polymer conformations with fewer entanglements. The results align with past studies on amorphous cyclic polymers, providing deeper insights into how cyclic architectures affect semicrystalline polymer mechanics. This combined experimental and simulation approach advances understanding of cyclic polymer architectures and their transformative impact on polymer properties.