Novel Poly(N-vinylcaprolactam-co-2-(diethylamino)ethyl methacrylate) Gels: Characterization and Detailed Investigation on Their Stimuli-Sensitive Behaviors and Network Structure

Poly(N-vinylcaprolactam-co-2-(diethylamino)ethyl methacrylate), P(VC-co-DEAEMA), gels were synthesized in ethanol by using free radical cross-linking polymerization method at 60 degrees C for 24 h in the presence of azobis(isobutyronitrile) (AIBN) as initiator. Homopolymer gels of N-vinylcaprolactam (PVC) and 2-(diethylamino)ethyl methacrylate (PDEAEMA) were also synthesized at the same conditions and used for comparison purposes. In the synthesis of homopolymer and copolymer gels, ethylene glycol dimethacrylate (EGDMA) and allyl methacrylate (AMA) cross-linking agents were employed in order to determine the effects of crosslinker type on the equilibrium swelling value (ESV) and percentage of gelation (PG). pH and temperature sensitivities of gels were investigated for both cross-linkers, and network parameters of gels were also found. In addition, detailed characterization studies were performed by Fourier transform infrared and scanning electron microscopy techniques. It was observed that PVC gel had the lowest PG and highest ESV. Compared to EGDMA, AMA increased thee percentage of gelation and decreased the equilibrium swelling value of gels. pH-sensitive profiles of gels were substantially different from each other and strongly dependent on DEAEMA content. Copolymer gels containing the highest mole percentage of N-vinylcaprolactam (95%) showed non-Fickian and Fickian swelling behavior at pH 7.4 for EGDMA and AMA cross-linkers, respectively. It was found that both monomer concentration and cross-linker type affected the polymer-solvent interaction parameters (chi), mesh size (zeta), and experimental average molecular mass between the cross-links (M-c(E)) of gels