New polymers containing ortho ester and thioether moieties in the polymer backbone were synthesized by radical polyadditions using 2,4-dimethylene-1,3-dioxolane (1). Alcohols added to the 2-methylene group of 1 selectively to afford vinyl ethers 3 having an ortho ester structure, especially diols gave divinyl ortho esters 2 for the polyaddition. Thiol added to the vinyl ether 3 in good yield in the presence of azobis(isobutyronitrile) at 60-degrees-C in benzene, and hence the radical polyadditions of dithiols to 2 were carried out under the same conditions to obtain polysulfides bearing ortho ester moieties in the backbone. Ortho ester units in the polymer could easily undergo hydrolysis in water-tetrahydrofuran at 65-degrees-C, and the structure of the compounds obtained was speculated by the hydrolysis of the model compounds 3.