Stereocomplexation of Poly(l-lactide) and Random Copolymer Poly(d-lactide-co-ε-caprolactone) To Enhance Melt Stability

Abstract

■ INTRODUCTION Stereocomplex polylactide (s-PLA) is a polylactide based macromolecule which has been known as one of the choices to enhance the properties of polylactides which is formed from an enantiomeric polymer blend of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA). The s-PLA has melting temperature (Tm) approximately 50 °C higher than the Tm of either PLLA or PDLA. There are so many reports about s-PLA macromolecules development using linear PLLA and PDLA homopolymers. Moreover, there are also s-PLA macromolecules developments using block copolymer, starshaped, and cyclic based polylactide. The melt processing is regular material processing in industry. Unfortunately, s-PLA from linear high-molecularweight polylactide has weakness due to limitation of memory to re-form s-PLA after melted (melt stability). Biela et al. reported the star-shaped s-PLA with has 13 arms or more able to completely melt and perfectly reversible due to hardlock-type interactions. The melt stable star-shaped s-PLA requires starshaped PDLA and PLLA with 13 arms or more. Otherwise, commercial polylactide is mostly in the linear form. Consequently, the star-shaped s-PLA concept is not suitable to apply for commercial polylactide. For these reasons, it is necessary to find a new concept for making melt stable s-PLA which can be applied to the commercial polylactide. Therefore, we studied about the stereocomplexation of PLLA and random copolymer of poly(D-lactide-co-e-caprolactone) (PDLCL) with small content of e-caprolactone (CL). The addition of small amount of caprolactone in the PDLCL is addressed as soft fragment to accelerate the chain movement of PDLA fragments to interact with PLLA chain after melted and “re-assemble” sPLA. In this report, we demonstrated for the first time that small caprolactone content in the PDLCL can enhanced the melt stability of s-PLA.