Synthesis and properties of biodegradable supramolecular polymers based on polylactide-block-poly(δ-valerolactone)-block-polylactide triblock copolymers

Biodegradable supramolecular polymers (SMPs) were synthesized by the end-functionalization of polylactide-block-poly(δ-valerolactone)-block-polylactide (PLA–PVL–PLA) triblock copolymers with 2-ureido-4[1H]-pyrimidinone (UPy) self-complementary quadruple hydrogen-bonding units. The end-functionalized PLA–PVL–PLA copolymers exhibit the typical characteristics of thermoplastic elastomers. Thermal properties, crystallization behavior, crystalline structure and other properties of SMPs can be adjusted by changing the length and stereostructure of PLA blocks. The UPy groups retard the crystallization of PLA and PVL blocks, and the crystallization of PVL blocks is also depressed with increasing PLA blocks. Tensile testing reveals that the prepared SMPs present excellent mechanical properties, and dynamic mechanical analysis indicates that the heat resistance of l-SMPs is better than that of d,l-SMPs. Shape memory property of SMPs was also studied, and the recovery ratio of SMPs with PDLLA blocks can reach 100%. The recovery ratio of l-SMPs is depressed as the crystallizable PLLA blocks increase. This study has systemically investigated the effect of the composition, stereostructure and crystallizability of PLA blocks on the properties of SMPs, which would provide potential approaches for the synthesis of biodegradable SMPs with tunable properties.