Ring-opening metathesis polymerization (ROMP) was used to synthesize novel ring-opened poly[ 5 - (2-phenylethylnorbornene)]. Hydrogenation can produce two different saturated derivatives, with the phenyl groups either preserved or saturated to cyclohexyl groups. These two different hydrogenated products allowed us to compare the effect of replacing the pendant phenyl groups with cyclohexyl groups on properties such as the glass transition temperature (T-g). We found that Tg decreased by only 2 degrees C (from 28 to 26 degrees C) upon replacement of the phenyl groups. This contrasts with the effect of saturating the phenyl groups in the addition polymer of 5-(2-phenylethylnorbornene), where the Tg increased by 34 degrees C, from 215 to 249 degrees C, a remarkable difference in magnitude and direction compared with the ROMP polymers.