Abstract:

Stimuli-responsive polymer gels have attracted significant attention owing to their controlled rheological properties resulted from sol-gel/gel-sol transition. Generally, the change of external conditions such as temperature and pH is usually essential to sol-gel/gel-sol transition. However, in some application scenarios, external conditions are not easy to change. Therefore, it is important to construct a gel system that can realize continuous sol-gel-sol phase transition under constant conditions. Herein, a novel polymer gel system （AGX） with the characteristic of continuous sol-gel-sol phase transition at constant temperature, was successfully constructed by using poly（hydroxyethyl acrylamide） （PHEAA） as the skeleton molecule, glyoxal （GX） as the crosslinking agent, and N, N-dimethylformamide （DMF） and water as the solvent. The effects of temperature, GX content, polymer content and water content on the gelation time, gel-breaking time and gel strength of AGX were investigated. The results showed that by changing the GX content and temperature, AGX could form a polymer gel with elastic modulus of 560 Pa within 7-2 000 min and could turn to a low-viscosity liquid （<30 mPa·s） in just 2 h. The greater the concentration of GX or PHEAA, the faster the gelation and the slower the gel-breaking. With the increase of temperature, both the gelation and gel-breaking became faster. The introduction of electrolytes had little effect on the gelation time but could greatly reduce the gel-breaking time. The sol-gel transition was mainly ascribed to the aldol condensation between GX and PHEAA, while the gel-sol transition might be resulted from the breaking of amide bonds.

Key words: poly（hydroxyethyl acrylamide）, glyoxal, acetalation, phase transition