Controlling thermomechanical behavior of semicrystalline hydrogenated polynorbornene through the cis‐ to trans‐cyclopentylene ratio

Abstract

Though polynorbornene synthesized by ring‐opening metathesis polymerization has an intrinsically all‐cis configuration of the cyclopentylene backbone rings, a fraction of these rings can be epimerized to the trans configuration during hydrogenation over suitable catalysts. By varying the method of hydrogenation, semicrystalline hydrogenated polynorbornenes (hPNs) with trans levels between 0 and 36% were obtained. With increasing trans content, the glass transition temperature, melting point, and enthalpy of melting decrease modestly. By contrast, the temperature at which the hPN crystal transitions into a rotationally disordered polymorph varies strongly with trans content, ranging from 126 °C (all‐cis) to 71 °C at 27% trans; at trans contents of 34% and above, no rotationally‐ordered phase is observed at any temperature. The room‐temperature Young's modulus shows no dependence on trans content, while the yield stress drops by 20% at 1% trans content and slowly decreases further with additional epimerization. The temperature dependence of the Young's modulus differs for trans‐containing versus all‐cis polymers, while the temperature dependence of the yield stress is set by the polymorph type (rotationally ordered vs. disordered).