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

Abstract

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[1 H ]-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–PDLAs (denoted as l -SMPs and d -SMPs, respectively) are amorphous and noncrystallizable. 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 °C with increasing stereocomplex content.