Ring-opening polymerization of degradable polyesters

Medium to high molecular weight random copolymers of 1,5-dioxepan-2-one (DXO) and L-lactide (L-LA) or epsilon-caprolactone (epsilon-CL) of different compositions have been investigated. Polymerization was conducted in bulk at 110 degrees C using stannous 2-ethylhexanoate as catalyst. Poly(DXO-co-L-LA) is a hydrolysable material with a glass transition temperature (T-g) ranging from -36 up to 58 degrees C depending on the molar composition. The material exhibited crystallinity as long as the amount of DXO did not exceed 50 weight%. Reactivity ratios were determined to r(L-LA)=10 and r(DXO)=0.1, giving a more blocky structure than expected in a random copolymer. The copolymer between epsilon-CL and DXO was shown to be a truly random copolymer by C-13 NMR as expected from the reactivity ratios, r(DXO)=1.6 and r(epsilon). (CL)=0.6. T-g of the material was ranging from -64 up to -39 degrees C. The ability of the poly(DXO-co-epsilon-CL) to crystallize was retained up to a DXO content of 40 weight%. The melting temperature and crystallinity of both copolymers decrease with increasing amount of DXO. Incorporation of semicrystalline comonomers, L-LA or epsilon-CL, into the amorphous poly(DXO) creates materials with adjustable properties depending on the molar composition.