Semicrystalline-Glassy Multiblock Copolymers via Mechanochemical Synthesis toward Tough Poly(lactide)

A series of semicrystalline-glassy (poly(amide11)–poly(lactide))n (PA11–PLA)n multiblock copolymers with >97% renewable carbon content were developed for tough PLA. The resulting copolymers exhibited superior mechanical performance, comparable to those of commercial PA11 and PLA. Amine-terminated PA11 with a Mn,NMR of 12 kg mol–1 was prepared by bulk self-condensation and subsequently capped with only one LA molecule through mechanochemical ball milling, to produce HO–LA–PA11–LA–OH. After adding Sn(Oct)2, unreacted LA was propagated in one-pot by ring-opening polymerization to make PLA–PA11–PLA with a fPLA of 0.5–0.8. The hydroxyl-telechelic triblocks were also coupled with diisocyanate by ball milling to manufacture (PA11–PLA)n multiblocks. The well-defined molecular structures demonstrated controlled PA11 and PLA lengths. Thermal analysis determined the phase separation of PA11 and PLA based on Tg,PLA (48–56 °C) and Tm,PA11 (183–186 °C) and confirmed the two transitions of thermal degradation (Td). SAXS profiles of the multiblocks also verified their microphase-separated morphologies. The temperature dependence of χ for the PA11–PLA system, χPA11–PLA = (426.00 ± 4.81)/T – (0.90 ± 0.01), simply represented as 0.24 and 0.13 at 100 and 140 °C, was estimated using the TODT values obtained from the DMA of three symmetric PLA–PA11–PLA triblocks with a fPLA of 0.5. The resulting semicrystalline-glassy multiblocks showed superior tensile characteristics, merging PLA-originated initial modulus and yield stress (E = 758–903 MPa and σyield = 57–63 MPa), and a PA11-derived toughening even with strain hardening (εb = 380–500%, σb = 40–51 MPa, and γ = 124–171 MJ m–3). These results show promising potential for polymeric materials with sustainability and strength-toughness balance.