Amphoteric superabsorbent polymers (SAPs) based on the anionic monomer sodium acrylate (SA) and the cationic monomer [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC) were synthesized by solution polymerization using N,N′-methylenebisacrylamide as a cross-linking agent. The ratio of anionic to cationic repeat units was varied to obtain anionic, cationic, and amphoteric SAPs. The synthesized SAPs were characterized by Fourier transform infrared spectroscopy. The equilibrium swelling capacity of the SAPs was found to be dependent on the nature and extent of the net charge on the SAPs but independent of pH. The equilibrium swelling capacity was lowest for the SAP whose ratio of anionic to cationic repeat units was unity. The equilibrium swelling capacity increased as this ratio deviated from unity. The adsorption of an anionic dye (orange G) and a cationic dye (methylene blue) was carried out from the individual solution as well as from their mixture. The adsorption of the dyes was found to be dependent on the nature and amount of net charge on the SAPs but independent of pH. The amount of the dye adsorbed decreased as the net charge on the amphoteric SAPs decreased. The amphoteric SAPs with net negative or positive charge selectively adsorbed oppositely charged dyes from the mixture, but the amounts adsorbed were lower than those adsorbed from the individual dye solutions.

Poly(acrylic acid-co-sodium acrylate-co-acrylamide) superabsorbent polymers (SAPs) cross-linked with ethylene glycol dimethacrylate (EGDMA) were synthesized by inverse suspension polymerization. The SAPs were swollen in DI water, and it was found that the equilibrium swelling capacities varied with the acrylamide content. The SAPs were subjected to reversible swelling/deswelling cycles in DI water and aqueous NaCl solution, respectively. The effect of the addition of an electrolyte on the swelling of the SAP was explored. The equilibrium swelling capacity of the SAPs was found to decrease with increasing concentration of added electrolyte in the swelling medium. The effect of the particle size of the dry SAPs on the swelling properties was also investigated. A first order model was used to describe the kinetics of swelling/deswelling, and the equilibrium swelling capacity, limiting swelling capacity, and swelling/deswelling rate coefficients were determined.

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The ultrasonic degradation of poly(acrylic acid), a water-soluble polymer, was studied in the presence of persulfates at different temperatures in binary solvent mixtures of methanol and water. The degraded samples were analyzed by gel permeation chromatography for the time evolution of the molecular weight distributions. A continuous distribution kinetics model based on midpoint chain scission was developed, and the degradation rate coefficients were determined. The decline in the rate of degradation of poly(acrylic acid) with increasing temperature and with an increment in the methanol content in the binary solvent mixture of methanol and water was attributed to the increased vapor pressure of the solutions. The experimental data showed an augmentation of the degradation rate of the polymer with increasing oxidizing agent (persulfate) concentrations. Different concentrations of three persulfates-potassium persulfate, ammonium persulfate, and sodium persulfate-were used. It was found that the ratio of the polymer degradation rate coefficient to the dissociation rate constant of the persulfate was constant. This implies that the ultrasonic degradation rate of poly(acrylic acid) can be determined a priori in the presence of any initiator.

Superabsorbent polymers (SAPs) of acrylic acid, sodium acrylate, and acrylamide (AM), crosslinked with ethylene glycol dimethacrylate, were synthesized by inverse suspension polymerization. The equilibrium swelling capacities of the SAPs were determined and these decreased with increasing AM content. The adsorption of the two cationic dyes, methylene blue and rhodamine 6G, on the dry as well as equilibrium swollen SAPs was investigated. The amount of the dye adsorbed at equilibrium per unit weight of the SAPs and the rate constants of adsorption were determined. The amount of the dye adsorbed at equilibrium by the SAPs decreased with increasing mol % of AM in the SAPs. The amount of the dye adsorbed at equilibrium was almost equal for the dry and equilibrium swollen SAPs. However, the equilibrium swollen SAPs adsorbed dyes at a higher rate than the dry SAPs. The higher rate of adsorption was attributed to the availability of all the anionic groups present in the fully elongated conformation of the SAPs in the equilibrium swollen state. The effect of initial dye concentration on the adsorption was also investigated and the adsorption was described by Langmuir adsorption isotherms.