AB- and ABC-type di- and triblock copolymers of poly[styrene-block-(ε-caprolactone)] and poly[styrene-block-(ε-caprolactone)-block-lactide]: synthesis, characterization and thermal studies

摘要

Polystyrene terminated with benzyl alcohol units was employed as a macroinitiator for ring-opening polymerization of s-caprolactone and L-lactide to yield AB- and ABC-type block copolymers. Even though there are many reports on the diblock copolymers of poly(styrene-block-lactide) and poly(styrene-block-lactone), this is the first report on the poly(styrene-block-lactone-block-lactide) triblock copolymer consisting of two semicrystalline and degradable segments. The triblock copolymers exhibited twin melting behavior in differential scanning calorimetry (DSC) analysis with thermal transitions corresponding to each of the lactone and lactide blocks. The block derived from ε-caprolactone also showed crystallization transitions upon cooling from the melt. In the DSC analysis, one of the triblock copolymers showed an exothermic transition well above the melting temperature upon cooling. Thermogravimetric analysis of these block copolymers showed a two-step degradation curve for the diblock copolymer and a three-step degradation for the triblock copolymer with each of the degradation steps associated with each segment of the block copolymers. The present study shows that it is possible to make pure triblock copolymers with two semicrystalline segments which also consist of degradable blocks.