Controlling the Mechanical Behavior of Hydrogenated Polynorbornene

Hydrogenated polynorbornene (hPN) synthesized via ring-opening metathesis polymerization is a semi-crystalline polymer even while atactic, as it is able to accommodate stereodefects within the crystal. We have previously shown control over phase behavior in hPN via epimerization of the cyclopentylene ring in the backbone structure. The polymorphic transition temperature into a rotationally-disordered state, T_cc, is strongly affected by epimerization, while epimerization has only a minor effect on the melting temperature, T_m, and no appreciable effect on the total crystallinity (J. P. Klein and R. A. Register, J. Polym. Sci. B, 57, 1188 (2019)). In this talk, the effect of epimerization on both the stress-strain behavior and dynamic mechanical thermal properties are discussed. Epimerization causes a decrease in both the Young’s modulus and the yield strength of the polymer, and it also reduces the breadth of the modulus-vs.-T plateau region (above T_g) significantly, in line with the decrease in T_cc. hPN-based polymers with a pyrene endgroup show a strong fluorescence sensitivity to melting/crystallization, and work is underway to evaluate their utility in probing other hPN transitions.