Pure 1,2-addition polymers, poly(2-methylene-1,3-dioxolane), Ib, poly(2-methylene-1 ,3-dioxane), 2b, and poly(2-methylene-5, Ei-dimethyl-l,3-dioxane), 3b, were prepared using the cationic initiators H2SO4, TiCl4, BF3, and also Ru(PPh3)(3)Cl-2. Small ester carbonyl bands in the IR spectra of Ib and 2b were observed when the polymerizations were performed at 80 degrees C (Ib) and both 67 and 138 degrees C (2b) using Ru(PPh3)3(C)l(2). The poly( cyclic ketene acetals) were stable if they were not exposed to acid and water. They were quite thermally stable and did not decompose until 290 degrees C (Ib), 240 degrees C (2b), and 294 degrees C (3b). Different chemical shifts for axial and equatorial H and CH3 on the ketal rings were found in the H-1 NMR spectrum of 3b at room temperature. High molecular weight 3b ((M) over bar(n) = 8.68 x 10(4), (M) over bar(w) = 1.31 x 10(5), (M) over bar(z) = 1.57 x 10(5)) was obtained upon cationic initiation by H2SO4. Poly(2-methylene-1,3-dioxane), 2b, underwent partial hydrolysis when Ru(PPh3)(3)Cl-2 and water were present in the polymer. The hydrolyzed products were 1,3-propanediol and a polymer containing both poly( 2-methylene-1,3-dioxane) and polyketene units. The percentages of these two units in the hydrolyzed polymer were about 32% polyketene and 68% poly(2-methylene-1,3-dioxane ). No crosslinked or aromatic structures were observed in the hydrolyzed products. The molecular weight of hydrolyzed polymer was (M) over bar(n) = 5740, (M) over bar(w) = 7260, and (M) over bar(z) = 9060.