Salt‐Induced Changes in Sol‐to‐Gel Transition and Structure of Stereocomplexable Poly(lactic acid)/Poly(ethylene glycol) Copolymers

Abstract

While stereocomplexable hydrogels composed of poly(l‐lactic acid) (PLLA)– poly(ethylene glycol) (PEG)–PLLA and poly(d‐lactic acid) (PDLA)–PEG–PDLA have been widely investigated, very few studies have reported the influence of salts on thermogelling behaviors in corresponding aqueous solutions. In this study, NaCl is selected as a model and stereocomplexable solutions with a wide range of salt concentrations (0–3 wt%) are prepared with the aim to tune Ts‐g. When polymer concentration is 8 wt%, the resulting hydrogels containing 1 wt% NaCl exhibits a notably lower Ts‐g of 34 °C, while salt‐free system shows a Ts‐g of 42 °C. The presence of NaCl leads to a higher content of stereocomplex crystallites, a larger size of micelle clusters, an amplified distance of interclusters and a smaller thickness of micelle shell, which is supposed to be ascribed to the salts effect on ion–water and water–PEG interactions and increased hydrophobicity of enantiomeric micelles by NaCl. For hydrogels governed by self‐assembly of micelles and stereocomplexation, this study provides a safe, practical, and feasible way to tune the thermogelling behaviors and physical properties by the addition of salts.