PH-responsive poly(N,N-dimethylaminoethyl methacrylate-co-2-acrylamido-2-methyl-propanosulfonic acid) cryogels: Swelling, elasticity and diffusive properties

A series of ionic poly(N,N-dimethylaminoethyl methacrylate-co-2-acrylamido-2-methyl-propanosulfonic acid) (P(DMAEMA-co-AMPS)) cryogels were prepared by free-radical crosslinking copolymerization of N,N-dimethylaminoethyl methacrylate (DMAEMA) and 2-acrylamido-2-methyl-propanosulfonic acid (AMPS) in aqueous solution. The swelling properties and the elastic behavior of P(DMAEMA-co-AMPS) cryogels drastically change at a gel preparation temperature, -18 °C, below the bulk freezing temperature of the polymerization solvent, water. The equilibrium and dynamic swelling/deswelling properties of the prepared cryogels responding to pH as well as in aqueous solutions of NaCl, KCl, MgC1₂, Na₂S0₄, K₂S0₄, and MgS0₄ were investigated. The influence of the relative content of ionic comonomer AMPS on the swelling properties was examined in water and the obtained results were compared with P(DMAEMA-co-AMPS) hydrogels synthesized at usual polymerization temperature. The ionic gels prepared with higher DMAEMA contents exhibited a highly pH-dependent equilibrium swelling behavior. The extent of transition from the swollen state to the shrunken state was strongly related to the DMAEMA content of the network. The results indicated that P(DMAEMA-co-AMPS) cryogels not only had considerable swelling ratio as well as rapid swelling/deswelling kinetics, but also exhibited improved mechanical properties.