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 G_rubbery^', 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 structures affect semicrystalline polymer mechanics. This combined experimental and simulation approach advances understanding of cyclic polymer architectures and their transformative impact on polymer properties.

中文翻译：

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环状聚合物对半结晶聚合物力学的转化


环状聚合物没有链端，具有独特的拓扑约束，具有独特的机械和热性能。本研究合成并比较了半结晶线性和环状聚环辛烯 （PCOE），与通过开环复分解聚合 （ROMP） 产生的线性 PCOE 和通过扩环复分解聚合 （REMP） 产生的环状 PCOE。通过拉伸测试、动态机械分析 （DMA） 和广角 X 射线散射 （WAXS） 评估机械、热和晶体性能。研究结果表明，交联环状 PCOE 比线性 PCOE 表现出更低的拉伸强度但更大的拉伸性，表明网络柔软度增强。DMA 结果表明，环状 PCOE 具有较低的玻璃化转变温度T_g和橡胶状平台模量 G_rubbery^'），而 WAXS 表明环状 PCOE < 25% 的结晶度较低，在 100% 的拉伸应变下稳定在约 15%。这些差异表明，聚合物拓扑结构，而不是结晶度，主要决定了机械响应。使用聚乙烯的可结晶模型进行分子动力学模拟，复制了实验中观察到的较低应力和较高拉伸性，突出了更紧凑的循环聚合物构象和更少的缠结。该结果与过去对无定形环状聚合物的研究一致，为循环结构如何影响半结晶聚合物力学提供了更深入的见解。这种实验和仿真相结合的方法促进了对循环聚合物结构及其对聚合物特性的变革性影响的理解。