The asymmetric lactone (3S,4R)-3-methyl-4-benzyloxycarbonyl-2-oxetanone (6) was anionically polymerized to give an insoluble, crystalline, highly isotactic polymer with (2S, 3S)-benzyl beta-3-methylmalate repeating units. Solubility was achieved by copolymerization of 6 with the racemic (R, S)-butyl malolactonate (7). The semicrystalline copolymer was characterized ((M) over bar(n) = 107000, T-g = 29,6 degrees C, T-m = 161 degrees C, [alpha] = 1,5 deg . dm(-1). g(-1). cm(-1)) and its stereosequence investigated by C-13 NMR.