Multiblock Thermoplastic Elastomers Derived from Biodiesel, Poly(propylene glycol), and <scp>l</scp>-Lactide

Abstract

A series of [poly(l-lactide)–poly(dimer acid methyl ester-alt-poly(propylene glycol))–poly(l-lactide)]n (PLLA–PDP–PLLA)n multiblock copolymers was synthesized in a three-step procedure: PLLA–PDP–PLLA (LDPL) triblock copolymers were synthesized using ring-opening polymerization of l-lactide with PDP macroinitiators, which was prepared via step-growth melt polycondensation based on biodiesel and macro-diol, followed by chain extension of the LDPL triblock with 4,4′-methylenebis(phenyl isocyanate). Molecular characterization revealed that the synthetic procedures yielded the desired triblock and multiblock copolymers (fPLLA = 0.22–0.27). The relationship between thermal behavior and morphology indicated microphase separation into two domains in both the triblocks and multiblocks. Compared to previously reported triblocks with a high molar mass and PLLA hard blocks with inaccessible order–disorder transition temperature (TODT) values, the multiblock architectures in this study were found to become disordered at much lower temperatures (TODT = 82–128 °C). To prepare (LDPL)n multiblocks, coupling low-molar-mass LDPL triblocks without free-standing thin films led to dramatically enhanced tensile properties. The self-adhesive performance of the pressure-sensitive adhesive (PSA) system including the multiblocks was evaluated, showing a peel strength of 3.1 N cm–1, a probe tack of 1.9 N, and static shear strength of >50 000 min, which are values comparable to those of current PSAs. These biodiesel-based thermoplastic elastomers hold promise for sustainability and high value-added economy.