Copolymerizations of a six-membered ring spiro-orthocarbonate bearing adamantane backbones (AD-SOC, 1) and a monofunctional epoxide, PGE, in the presence of cationic initiators such as Sc(OTf)(3) were carried out under various reaction conditions. As a result, instead of the anticipated poly(ether-ether-carbonate) 11, two types of copolyethers (12 and 18) consisting of two or three types of ether components having different substituent groups were unusually formed along with the evolution of carbon dioxide gas, in which AD-SOC efficiently acted as the corresponding oxetane equivalent monomers 3 and 4. Furthermore, the copolymerization behavior, including the formation of copolyethers 12 and 18, unexpectedly and significantly depended on the reaction conditions, such as the concentration of the initiator. For example, the copolymerizations with 5 mol % of Sc(OTf)(3) mainly afforded copolyether 18, while those with 1 mol % mainly gave copolyether 12. In addition, treatments with 5 mol % of Sc(OTf), also yielded CH2Cl2, THF, and DMF-insoluble networked products, indicating relatively higher thermal stability compared with a common polyether. (c) 2005 Wiley Periodicals, Inc.