Synthesis, characterization and degradability of the comb-type poly(4-hydroxyl-ε-caprolactone-co-ε-caprolactone)-g-poly(L-lactide)

The novel comb-type biodegradable graft copolymers based on epsilon-caprolactone and L-lactide were synthesized. Firstly, 2-oxepane-1,5-dione (OPD) was synthesized by the Baeyer-Villiger oxidation of 1,4-cyclohexanedione, and was subsequently copolymerized with E-caprolactone (CL) to produce poly(2-oxepane-1,5-dione-co-epsilon-caprolactone) (POCL) catalyzed by stannous(II) 2-ethylhexanoate in toluene. Then, POCL was converted into poly(4-hydroxyl-epsilon-caprolactone-co-epsilon-caprolactone) (PHCL) using sodium borohydride as reductant. Finally, poly(4-hydroxyl-epsilon-caprolactone-co-epsilon-caprolactone)-g-poly(L-lactide) (PHCL-g-PLLA) were prepared successfully by bulk ring-opening polymerization of L-lactide using PHCL as a macro-initiator. All the copolymers have been characterized by H-1 and C-13 NMR, DSC, and GPC. Compared with the random copolymer of poly(CL-co-LA), the elongation is highly increased. And the thermal analysis showed that the crystallization rate of the PCL backbone in the graft copolymers was greatly reduced compared to the PCL homopolyrner. The hydrolytic degradation of the copolymer was much faster in a phosphate buffer (pH = 7.4) at 37 degrees C, which is confirmed by the weight loss and change of intrinsic viscosity. (C) 2009 Elsevier Ltd. All rights reserved.