Mechanical Properties and Biodegradation of Poly(L-lactic acid-co-succinic acid-co-1,4-butene diol)

초록

Direct condensation polymerization of LA in bulk state yields only low-molecular-weight polymers due to low reaction equilibrium constant.High-molecular weight PLLA is produced either by direct condensation polymerization of LA in solution state or by ring-opening polymerization through the lactide intermediate. In the first route, solvent with high boiling point is used to remove the dissociated water by means of azeotropic distillation technigue.2 Disadvantage of this route are relatively large reactor and purification facility for the used solvent7. The second route also requires multi-step processes. Recently, Mitsui chemical, succeeded in producting of high-molecularweight PLLA by solid state polycondensation of PLLA oligomer obtained from liquid state polycondensation of LA. Helminen et al.4 introduced triethoxysilane end group to DL-lactide oligomers and Synthesized high-molecular-weight polymers based on lactic acid units through intermolecular linking reaction. In this study, LA was copolymerized with succinic acid (SA) and 1,4- butene diol (1,4-BED) using TNBT as a catalyst Bulk condensation polymerization of L-lactic acid produced PLLA homopolymer with weight average molecular weight (Mw) of 4.0×104. Addition of SA and 1.4-BED to LA (0.25 mole each per 100 mole of LA) increased Mw and polydispersity of PLASBED to 1.4×105 and 3.7 respectively. However further increase of SA and 1,4-BED concentration in the copolymerization reaction medium to 1.0 mole each per 100 mole of LA decreased Mw of PLASBED down to 7.6×104. PLLA homopolymer obtained from the bulk condensation polymerization was too brittle to prepare specimens for the tensile test. In contrast, PLASBED tensile properties comparable with those of a commercially produced high-molecular-weight PLLA purchased from Shimadzu Co.(Japan). PLASBED was chain extended by intermolecular linking reaction through the unsaturated bonds of 1.4-BED units in PLASBED using benzoyl peroxide (BPO).