Temperature dependence of swelling of crosslinked poly(N,N′‐alkyl substituted acrylamides) in water

The swelling of crosslinked poiy(N,N′‐alkyl substituted acrylamides) in water was studied in relation to temperature changes. Conventional swelling theory and separation of the polymer solvent interaction parameter into enthalpic and entropic contributions were used to characterize the temperature dependence of swelling in water. The thermosensitivity of swelling can be attributed to the delicate hydrophilic/hydrophobic balance of polymer chains and is affected by the size, configuration, and mobility of alkyl side groups. A sharp swelling transition may occur at an optimum hydrophilic/hydrophobic balance but was found only in the N‐isopropylacrylamide network among the networks tested. This swelling transition pattern was also reflected by the endothermic peak of the DSC thermogram of the swollen sample.