Cationic ring-opening copolymerizations of various cyclic ether compounds with volume expanding monomers bearing norbornene backbones [norbornene-spiro orthocarbonate (N-SOC) and norbornene-cyclic carbonate (N-CC)] were carried out in the presence of a thermally latent initiator 1. The 10% weight loss decomposition temperatures (T-d10) and the volume changes on the copolymerizations were measured for these resultant products. In the comparison between copolymerizations of bifunctional epoxide 2 with N-SOC and with N-CC, it was found that N-CC served as a more useful volume controllable comonomer than N-SOC. The copolymerizations with N-CC yielded the products with a decrease in the volume change (volume shrinkage) and with an increase in the monomer feed ratio of N-CC; T-d10 was relatively similar to the homopolymer of epoxide 2 and was observed except when the proportion of N-CC was more than 20% in the monomer feed ratio of N-CC. In contrast, similar copolymerizations with N-SOC did not exhibit such tendencies, probably because of the low efficiency of the copolymerization derived from the low miscibility of N-SOC for the epoxide. The other copolymerization systems of other bi- and monocyclic ether compounds (3-6 and phenyl glycidyl ether) with N-CC also indicated an almost similar tendency toward that of the copolymerization with epoxide 2. (C) 2004 Wiley Periodicals, Inc.