Acrylamide-induced enhanced solubilization of poly(propylene glycol) in aqueous solution

Acrylamide (AM)-induced enhanced solubilization of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) has been phenomenologically reported in a previous study. However, little is known about its mechanism. In this study, poly(propylene glycol) (PPG) serves as a model system to clarify this enhanced solubilization phenomenon, driven by two specific reasons. First, it helps eliminate any interference from PEO segments. Second, the liquid state of low molecular weight PPG proves advantageous for characterizing molecular interactions. The phenomenon of AM-induced enhanced solubilization has been conclusively demonstrated in the PPG system for the first time. Addition of AM consistently raises the cloud point of PPG aqueous solution. Subsequently, the structure and molecular interactions within the PPG/AM aqueous solution were investigated. Notably, there is no robust association or hydrogen bond between PPG and AM molecules; instead, only van der Waals forces are found to be at play. A model has been constructed, grounded in the contacts between PPG and the solvent during the coil-to-globule transition, to better understand the observed impact of AM on the clouding behavior of PPG aqueous solutions. The mechanism behind the enhanced solubilization has been ascribed to AM's ability to contact with PPG during the temperature-induced dehydration process, thereby assisting in sustaining the PPG's dissolved state.