Crystallization of Supramolecular Polymers Linked by Multiple Hydrogen Bonds

Pengju Pan, Jianna Bao, Xiaohua Chang, Ruoxing Chang, Guorong Shan, Yongzhong Bao

State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, 38 Zheda Road, Hangzhou 310027, P. R. China.

Supramolecular polymers (SMPs) have different crystallization behavior from conventional polymers. Crystallization of SMPs occurs in a “confined” and “dynamic” manner. Because of the reversible and stimuli-responsive natures of non-covalent bonds in SMPs, crystalline structure and crystallization kinetics of SMPs depend strongly on crystallization conditions (e.g., crystallization temperature, Tc). This offers a feasible way to tune the physical properties and functions of SMPs in processing. We first selected the 2-ureido-4[1H]-pyrimidione (UPy)-bonded poly(L-lactic acid) (PLLA) as a model SMP and investigated the crystallization kinetics, polymorphic crystalline structure, and phase transition of supramolecular PLLAs (SM-PLLAs). Crystallization rate and crystallinity of SM-PLLAs were strongly depressed as compared to the non-functionalized PLLA precursors. Crystalline structure of SM-PLLAs was sensitive to Tc. A low Tc (80~100 °C) facilitated the formation of metastable β crystals of PLLA in SM-PLLAs. The β crystals formed in SM-PLLAs transformed into the more stable α crystals in the following heating process. We further studied the stereocomplex crystallization between UPy-functionalized PLLA and poly(D-lactic acid) (PDLA). It was found that the stereocomplexation ability of PLLA and PDLA was highly improved after UPy end functionalization; this was ascribed to the enhanced interchain interaction.

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