SYNTHESIS AND CHARACTERIZATION OF POLY(1,5-DIOXEPAN-2-ONE-CO-L-LACTICACID) AND POLY(1,5-DIOXEPAN-2-ONE CO-D,L-LACTIC ACID)

Copolymers of L- or D,L-dilactide with 1,5-dioxepan-2-one (DXO) have b een investigated. Statistical copolymers were obtained using stannous- 2-ethylhexanoate (Sn(oct)(2)) as catalyst in bulk. Reactivity ratios w ere r((DXO)) = 0.1 and r((dilactide)) = 10 C-13-NMR spectroscopy indic ated a more extensive block structure than expected in a totally rando m copolymer. Transesterification takes place and shortens the average sequence length with increased temperature. The ability of the L-lacti c acid (L-LA)/DXO copolymer to crystallize seems to be retained despit e substantial amounts of 1,5-dioxepan-2-one in the composition. Proper ties, like glass transition temperature, crystallinity, and mechanical properties, are strongly dependent on the molar composition of the co polymer. The mechanical properties of a copolymer (molar ratio: DXO/L- LA, 25/ 75), measured in tension, indicated a flexible, soft material. This copolymerization seems to be initiated by impurities like water present in monomers and/or Sn(oct)(2), giving the tin compound the rol e of a catalyst.