Non-Covalent PS-SC-PI Triblock Terpolymers via Polylactide Stereocomplexation: Synthesis and Thermal Properties

Polylactide (PLA) stereocomplexes (SCs) containing amorphous block copolymers have gained enormous interest due to their unique properties and wide range of potential applications. In this work, we report the synthesis and properties of non-covalent triblock terpolymers: polystyrene-SCPLA-polyisoprene (PS-SC-PI) via the stereocomplexation of PS-b-PDLA with PI-b-PLLA diblock copolymers through the solution-precipitation method. The diblock copolymers were prepared by combining the anionic polymerization high-vacuum technique with ring-opening polymerization (ROP). First, several well-defined ω-hydroxyl polystyrenes and polyisoprenes (PS-OH and PI-OH) with varied molecular weights were synthesized by anionic polymerization using sec-BuLi as the initiator. PS-OH and PI-OH were used as the macroinitiators for the ROP of DLA and LLA catalyzed by tin(II) 2-ethyl hexanoate to afford PS-b-PDLA and PI-b-PLLA. PS-SC-PIs were prepared by mixing PS-b-PDLA and PI-b-PLLA solutions (in dichloromethane) and precipitated into methanol. The molecular characteristics of the block copolymers were determined by 1H NMR spectroscopy and size exclusion chromatography. The formation of PS-SC-PIs was evidenced by differential scanning calorimetry, X-ray diffraction, and Fourier-transform infrared, and circular dichroism spectroscopies. A preliminary study by atomic force microscopy reveals the thin-film phase behavior and the supramolecular organization of the PS-SC-PI.