We report on the synthesis of poly (homo-isobutylene) and poly(homo-alpha-methylstyrene) and the thermal properties of these new polymers. Based on the ring-opening metathesis polymerization (ROMP) of 3,3-dimethylcyclopropene and 3-methyl-3-phenyl-cyclopropene, the respective ring-opened polymers were generated. Several catalytic systems (first-generation (1), second-generation (11), third-generation Grubbs-type (IV) and the Schrock-type initiator Mo(N-2,6-iPr(2)C(6)H(3))(CHCMe2Ph)(OCMe3)(2) (III) were used. Particularly II, III and IV offered access to living polymerization reactions in the case of 3-methyl-3-phenyl-cyclopropene, however, not with 3,3-dimethylcyclopropene. The obtained ROMP-polymers were hydrogenated using tosylhydrazide, furnishing poly(homo-isobutylene) and poly(homo-alpha-methylstyrene) in high yields. Thermal-measurements (DSC-measurements) revealed T-g- and T-m-values located between those of poly (isobutylene), poly(styrene), and high-density poly(ethylene).