Synthesis and properties of photocurable biodegradable multiblock copolymers based on poly(ε-caprolactone) and poly(L-lactide) segments

Photocurable biodegradable multiblock copolymers were synthesized from poly(epsilon-caprolactone) (PCL) diol and poly(L-lactide) (PLLA) diol with 4,4'-(adipoyldioxy)-dicinnamic acid (CAC) dichloride as a chain extender derived from adipoyl chloride and 4-hydroxycinnamic acid, and they were characterized with Fourier transform infrared and H-1 NMR spectroscopy, gel permeation chromatography, wide-angle X-ray diffraction, differential scanning calorimetry, and tensile tests. The copolymers were irradiated with a 400-W high-pressure mercury lamp from 30 min to 3 h to form a network structure in the absence of photoinitiators. The gel concentration increased with time, and a concentration of approximately 90% was obtained in 90-180 min for all the films. The photocuring hardly affected the crystallinity and melting temperature of the PCL segments but reduced the crystallinity of the PLLA segments. The mechanical properties, such as the tensile strength, modulus, and elongation, were significantly affected by the copolymer compositions and gel concentrations. Shape-memory properties were determined with cyclic thermomechanical experiments. The CAC/PCL and CAC/PCL/PLLA (75/25) films photocured for 30-120 min showed good shape-memory properties with strain fixity rates and recovery rates of approximately 100%. The formation of the network structure and the crystallization and melting of the PCL segments played very important roles for the typical shape-memory properties. Finally, the degradation characteristics of these copolymers were investigated in a phosphate buffer solution at 37 degrees C with proteinase-k and Pseudomonas cepacia lipase. (c) 2005 Wiley Periodicals, Inc.