Enhancement of Crystallizability and Control of Mechanical and Shape-Memory Properties for Amorphous Enantiopure Supramolecular Copolymers via Stereocomplexation

Supramolecular stereo multiblock copolymers consisting of poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) hard blocks, poly(ethylene-co-butylene) (PEB) soft blocks, and 2-ureido-4[1H]-pyrimidinone (UPy) self-complementary quadruple hydrogen-bonding units were prepared upon blending of UPy-end-functionalized PLLA-PEB-PLLA and PDLA-PEB-PDLA triblock oligomers. Supramolecular copolymers (SMPs) based on UPy-terminated PLLA-PEB-PLLAs or PDLA-PEB-PDLA.s (denoted as L-SMPs and D-SMPs, respectively) are amorphous and non-crystallizable. However, the enantiomeric blends of L-SMPs and D-SMPs become crystalline and show relatively fast crystallization as a result of stereocomplexation of the PLLA and PDLA blocks. Stereocomplexes, rather than homocrystallites, are exclusively formed in the stereocomplexed SMPs (sc-SMPs) with various L-SMP/D-SMP mixing ratios. Because of the preferential crystallization of PLLA and PDLA blocks, sc-SMPs show less ordered microphase-separated morphologies and different domain spacings than the L-SMPs and D-SMPs. Compared with those of the amorphous L-SMPs and D-SMPs, the tensile strength, moduli, and heat resistance of sc-SMPs are increased with the stereocomplex crystallization or an increase in stereocomplex content. The sc-SMPs exhibit thermally induced shape-memory behavior, and their shape deformation and recovery temperatures (T-d and T-r respectively) can be modulated over a wide temperature range by varying the crystallinity or stereocomplex content. The T-d and T-r of sc-SMPs increase from 70 to 100 degrees C with increasing stereo complex content.