The synthesis and characteristics of a novel hydrogel based on linear polyethylenimine

Hydrogels have been employed in a variety of situations because of the vast possibilities of their structures. They have been made to respond to a variety of stimuli and as such behave as intelligent materials. Linear polyethylenimine is a hydrophilic polymer at high temperatures and as the temperature decreases it becomes hydrophobic. The aim of this study was to capture this response to temperature by synthesizing a hydrogel based on linear polyethylenimine. This was done by crosslinking linear polyethylenimine with 1,4-butanediol diglycidyl ether. The resulting chemically crosslinked polymer network retained a relationship with temperature similar to that of native linear polyethylenimine, becoming more hydrophilic at higher temperatures while becoming hydrophobic at low temperatures. The crosslinked linear polyethylenimine was then modified to contain 2-hydroxypropyl pendent chains. In response to solvent temperature the resulting hydrogel exhibited negative temperature-sensitive swelling behavior, meaning the hydrogel swells at low temperatures (hydrophilic) and contracts at high temperatures (hydrophobic). The hydrogel also responds to the presence of salts and changes in the solvent pH. These characteristics allow the hydrogel to respond to two different external stimuli making it an important area of research.