ABSTRACT:Six-membered spiro orthocarbonates with methyl substituents were prepared from cyclic dibutylstannyl glycolates and carbon disulfide, then polymerized using boron trifluoride etherate as the catalyst in l,2-dichloroethane at 30°C. The methyl substituent caused a decrease in the polymer yield. The 2,8-dimethyl and 2,4,8,10-tetramethyl spiro monomers were polymerized by a l,10-transfer reaction to bring about polyethercarbonates analogously to the unsubstituted spiro monomer. The spiro-monomer having 3,3,9,9-tetramethyl substituents underwent a 1,10-transfer polymerization at 30°C accompanied with the formation of polycarbonate segment which was partially depolymerized to the corresponding cyclic carbonate monomer at refluxing temperature of 1,2-dichloroethane. Contrary to the above, no polymer was obtained from the 2,2,4,8,8,10-hexamethyl spiro monomer.KEY WORDS Spiro Orthocarbonate / Cationic Polymerization / Transfer Polymerization / Substituent Effect / Polyethercarbonate /