Structure–property modulation in multiblock Poly(l-lactide-co-ethylene brassylate) copolymers and their stereocomplexed blends with Poly(d-lactide)

Abstract

Copolymerization offers an effective alternative to physical blending for modulating polylactide (PLA) stereocomplexation and thermomechanical properties, primarily due to its ability to suppress microphase separation. In this study, we investigate the impact of ethylene brassylate (EB) incorporation in multiblock poly(l-lactide-co-ethylene brassylate) copolymers (PLEBs) across a range of LLA:EB ratios (100:0 to 60:40), as well as their stereocomplexed blends with poly(d-lactide) (SC-PLEBs). Comprehensive structural, thermal, and mechanical characterization was performed using nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimetry, X-ray diffraction, thermal gravimetric analysis, tensile and dynamic mechanical analysis. We demonstrate that EB copolymerization significantly influences stereocomplex crystal formation and thermomechanical performance. Notably, the PLEB60/PDLA blend (SC60), containing about 50 % EB segments, achieved a stereocomplexation degree above 80 %, resulting in a 75 % increase in modulus compared to its corresponding copolymer (PLEB60), and an additional 500 MPa over the SC100 (PLLA/PDLA) blend allowing us to control the mechanical properties from ductile (copolymer) to rigid (stereocomplexed copolymer). Furthermore, SC60 exhibited a ∼10 K increase in glass transition temperature (T_g) relative to PLEB60, highlighting the structural reinforcement imparted by stereocomplexation. Our results underscore the importance of copolymerization in modulating stereocomplexation and thus the final material properties of polylactide enantiomeric blends for a wide range of applications, from soft to rigid.