聚甲基丙烯酸羟乙酯/乙二醛交联体系的溶液-凝胶-溶液转变研究

聚合物凝胶的溶液-凝胶（sol-gel）/凝胶-溶液（gel-sol）转变通常依赖于外界条件（温度、pH等）的变化，但构建可在恒定条件下实现sol-gel-sol转变的凝胶体系依然是一个挑战。本文基于聚甲基丙烯酸羟乙酯（PHEMA）、乙二醛（GX）和N,N-二甲基甲酰胺（DMF）成功构建了一种恒温自发随时间进行sol-gel-sol转变的聚合物凝胶体系（HGX）。通过改变GX的含量、温度等条件，可对HGX的成胶时间、凝胶强度及降解时间进行调控。结果表明，不同条件下HGX可在10~1500 min内形成弹性模量可达847 Pa的凝胶，然后在1.5 h到＞15 d后降解为低粘液体（＜30 mPa·s）。并利用红外光谱和凝胶色谱揭示了sol-gel-sol转变的内在机理是缩醛反应和酯基断键的动态竞争所致。

Sequential sol-gel-sol transition of PHEMA/GX

Responsive polymer gels, which can undergo sol-gel/gel-sol transition by responding to external physical or chemical stimuli, have attracted significant attention over the past decades. However, implementing the sol-gel-sol transition under constant temperature remains a major challenge. Herein, a novel polymer gel (HGX), which can undergo a sequential sol-gel-sol transition upon simply heating at a fixed temperature, was developed based on poly (2-hydroxyethyl methacrylate) (PHEMA) and glyoxal (GX). The gelation and degradation times could be tuned over wide ranges (10-1500 min and 1.5 h ~ 15 days, respectively) by changing GX content and temperature. After gelation, the elastic modulus of HGX was as large as 847 Pa. Before gelation or after degradation, the apparent viscosity of HGX was below 30 mPa·s. This unique transition is mainly ascribed to the dynamic competition between aldolization and hydrolysis of ester.