State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, 38 Zheda Road, Hangzhou 310027, China.
Soft Matter. 2017 Nov 22;13(45):8502-8510. doi: 10.1039/c7sm01491k.
Physical hydrogels crosslinked by non-covalent interactions have attained increasing attention due to their good mechanical properties and processability. However, the use of feasible and controllable non-covalent interactions is highly essential for preparing such hydrogels. In this article, we report on stereocomplexed physical hydrogels prepared by simple casting and swelling of amphiphilic graft copolymers bearing a poly(acrylic acid) (PAA) backbone and poly(l-lactic acid) (PLLA) or poly(d-lactic acid) (PDLA) stereocomplexable side chains. The microstructure, swelling behavior, and mechanical and shape memory properties of the obtained hydrogels can be tuned by varying the copolymer composition and stereocomplex (SC) crystallization of PLLA/PDLA enantiomeric chains. The long PLLA or PDLA chains segregate to form hydrophobic, crystallized domains in water, serving as physical crosslinking junctions for hydrogels. SC crystallization between PLLA and PDLA further enhances the number density of physical crosslinkers of enantiomerically mixed hydrogels. The SC content increases as the PLLA/PDLA ratio approaches 1/1 in enantiomerically mixed hydrogels. The average distance between crosslinking junctions declines for the hydrogels with a high PLLA (or PDLA) mass fraction (M) and SC content, due to the increased number density of physical crosslinkers. Accordingly, the tensile strength and the Young's modulus increase but the swelling ratio and the elongation-at-break of the hydrogels decrease with an increase in M and SC content. The hydrogels exhibit shape memory behavior; the shape fixing ability is enhanced by the SC crystallization of PLLA/PDLA side chains in the hydrogels.
由于具有良好的机械性能和可加工性，通过非共价相互作用交联的物理水凝胶受到了越来越多的关注。然而，对于制备这种水凝胶，使用可行且可控的非共价相互作用是非常重要的。在本文中，我们报告了通过简单浇铸和溶胀带有聚（丙烯酸）（PAA）主链和聚（L-乳酸）（PLLA）或聚（D-乳酸）（PDLA）立体复合侧链的两亲性接枝共聚物来制备的立体复合物理水凝胶。通过改变共聚物组成和 PLLA/PDLA 对映体链的立体复合物（SC）结晶，可以调节所得水凝胶的微观结构、溶胀行为以及机械和形状记忆性能。长 PLLA 或 PDLA 链在水中分离形成疏水性结晶域，作为水凝胶的物理交联结。PLLA 和 PDLA 之间的 SC 结晶进一步增加了对映体混合水凝胶中物理交联剂的数密度。在对映体混合水凝胶中，随着 PLLA/PDLA 比接近 1/1，SC 含量增加。对于具有高 PLLA（或 PDLA）质量分数（M）和 SC 含量的水凝胶，由于物理交联剂的数密度增加，交联结之间的平均距离减小。因此，随着 M 和 SC 含量的增加，水凝胶的拉伸强度和杨氏模量增加，而溶胀比和断裂伸长率降低。水凝胶表现出形状记忆行为；水凝胶中 PLLA/PDLA 侧链的 SC 结晶增强了形状固定能力。
