Stereocomplex formation of poly(l-lactide)-poly(ε-caprolactone) multiblock copolymers with Poly(d-lactide)

Abstract

Stereocomplex formation is known to increase the melting temperature of poly(l-lactide) (PLLA). In this study, we investigate the stereocomplex formation of poly(l-lactide)-poly(ε-caprolactone) multiblock copolymers (PLLA-PCL MBCs) with poly(d-lactide) (PDLA). The stereocomplexed PLLA-PCL MBCs were readily synthesized by adding PDLA into PLLA-PCL MBCs solutions. X-ray diffraction and differential scanning calorimetry measurements indicate the preferential formation of stereocomplexes. Tensile moduli of PLLA-PCL MBCs increased after stereocomplex formation; however, they conserved their large elongation at break values even when the composition of hard segments (PLLA and PDLA) in the sample increased. The combination of high Young's modulus (>400 MPa) and large elongation (>400%) is high level reported for biodegradable thermoplastic elastomers. Dynamic mechanical analysis measurements suggest improved thermal-deformation stability in the stereocomplexes. Stereocomplex formation of PLLA-PCL random multiblock copolymers synthesized by the copolymerization of PLLA and PCL oligomers with PDLA also effectively increased the melting temperature and the Young's modulus. This simple strategy of adding PDLA into PLLA-segmented copolymers may be a useful method for the synthesis of any other stereocomplexed PLLA-segmented block copolymer.