Synthesis, characterization, and modeling of cationic amphiphilic model hydrogels: Effects of polymer composition and architecture

Group transfer polymerization (GTP) was used for the preparation of eight amphiphilic networks based on 2-(dimethylamino)ethyl methacrylate (DMAEMA) and methyl methacrylate (MMA). Seven of the networks had linear segments of well-defined molecular weight between cross-links; i.e., they were model networks. In the eighth network the lengths of the segments between cross-links had a wide molecular weight distribution (random network) since the cross-linker was copolymerized with the monomers. Five model networks were based on ABA triblocks with polyDMAEMA mid-blocks and polyMMA end-blocks. In these networks the degree of polymerization (DP) of the polyDMAEMA midblock was 20, while the overall DPs were 25, 30, 40, 60, and 120. The sixth model network was based on an equimolar BAB triblock with a polyMMA mid-block and an overall DP = 40. The seventh model network was based on an equimolar statistical copolymer with a total DP = 40. The degrees of swelling (DSs) of the networks increased below pH 7. The DSs at low pH increased with the percentage of the hydrophilic monomer. The statistical copolymer-based model network exhibited higher DSs than the isomeric triblock copolymers. Calculations based on a molecular thermodynamic model provided aqueous DSs of ionized networks with the same qualitative trends as the experimental ones, although 30 times higher, reflecting catenation. The model also predicted microphase separation in most ionized ABA triblock-based networks.