ABSTRACT
Interpenetrating polymer networks of poly(methacrylic acid) (PMAA)/poly(N-isopropyl acrylamide) (PNIPAAm)were prepared. Differential scanning calorimetry (DSC) were conducted on PMAA/PNIPAAm IPN hydrogels swollen at different pH values. DSC experiments were conducted on preswollen hydrogel samples, with a total weight of approximately 15 mg. The IPN hydrogels were cut into 10-mm-diameter disks and dried under vacuum at 37°C. The ionic strength also plays an important role in the IPN swelling behavior. Hydrogels are hydrophilic three-dimensional networks formed by Hcrosslinked polymer chains, entanglements, or crystalline regions. From theophylline to FITC-Dextran, the permeability decreases, which is an indication of the size exclusion behavior in the IPN membrane: at the same gel swollen state, the IPNs show higher permeability for the smaller solutes. At temperatures lower than 32°C, the gel is swollen, whereas at temperatures higher than 32°C, the gel dehydrates to the collapsed state due to the breakdown of the delicate hydrophilic/hydrophobic balance in the network structure.
