Hydrogenated polynorbornene (hPN) synthesized by ring-opening metathesis polymerization (ROMP) exhibits a thermoreversible change in crystal polymorph at a temperature T-cc below its melting point, T-m. The polymorphic transition corresponds to a sharp increase in rotational disorder around the chain axis as the temperature is increased above T-cc. Saturation of ROMP polynorbornene (PN) to hPN can be achieved through both catalytic and noncatalytic approaches. Here, three different hydrogenation routes were employed on the same precursor polymer: catalytic routes over either supported Pd-0 or a Ni/Al complex, and noncatalytic saturation with diimide. The different hydrogenation routes result in hPNs with varying degrees of epimerization of the cyclopentylene ring (from cis to trans); these epimerized units are included in the hPN crystals. The crystal structure of the rotationally ordered hPN polymorph, observed below T-cc, changes sharply at low levels of epimerization and then is weakly influenced by further increases in trans content. The stability of the rotationally ordered hPN polymorph decreases with increasing epimerization, as reflected in a reduction of T-cc from 134 degrees C to 92 degrees C at 22% epimerization. T-cc is less affected by epimerization than by the inclusion of a similar content of 5-methylnorbornene units, reflecting the smaller size of the trans defect. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1188-1195