Plant oil-derived a,?-diacetals are polycondensated to the novel polyacetals [OCH2O(CH2)y]n (y = 19 and 23) with molecular weight of ca. Mn = 2 x 104 g mol-1. The long methylene sequences provide substantial melt and crystallization temperatures (Tm = 88 degrees C and Tc = 68 degrees C for y = 23), and rates of hydrolytic degradation are dramatically lower for the long-chain polyacetals versus a shorter chain analogue (y = 12) studied for comparison.