Hydrogels from N,N′-dimethylacrylamide-co-2-acrylamido-2-methyl-1- propanesulfonic acid with salt-, temperature- and pH-responsiveness properties

Abstract

The synthesis of copolymer hydrogels of N, N′-dimethylacrylamide (NNDMAAm) with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) were prepared by solution free radical polymerization at different feed mole ratios (mole ratios of nNNDMAAm/nAMPS = 0.5/0.5; 0.33/0.66; 0.66/0.33; 0.25/0.75; 0.75/0.25). In this reaction ammonium persulfate (APS) and N,N′-methylene-bis-acrylamide (MBA) were used as initiator and cross-linking reagents respectively. These copolymers were insoluble in water and it were characterized by elemental analysis, FT-IR spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Aqueous solutions of the copolymers showed lower critical solution temperature behavior (LCST). The phase transition temperatures of aqueous solutions of these copolymers increased with increasing of hydrophilic AMPS comonomer content in the copolymers. The effects of reaction parameters, including the concentration of cross-linking reagent, the monomer concentration, pH, temperature, salt solutions, and solvent polarity on the water absorption have been also studied. Under the experimental conditions, the copolymer poly(NNDMAAm-co-AMPS) with a feed mol ratio 1:2 presents the best swelling properties. The monomer reactivity ratios for poly(NNDMAAm-co-AMPS) are the following: r1 = 0.217 and r2 = 2.20, (r1x r 2 = 0.48).