New polymers containing spiroorthocarbonate units on the main chain were synthesized and characterized. The polymers were prepared by using redox or free-radical catalysts in solution polymerization of 3,9-dimethylene-1,5,7,11-tetraoxaspiro [5,5] undecane [or simply called bimethylenespiroorthocarbonate (BMSOC)] and dithiols at lower temperatures. Their spiroorthocarbonate units could undergo hydrolysis in acidic conditions at room temperature. The structure of polymers was investigated by nuclear magnetic resonance (1H- and 13C-NMR) and Fourier transform infrared (FTIR) spectroscopy. The kind of dithiols had a remarkable effect on properties of the polymers. Block polymers obtained from BMSOC and dithiols could result in a better combination of properties. © 1993 John Wiley & Sons, Inc.