Modified acrylic-based superabsorbents with hydrophobic monomers: synthesis, characterization and swelling behaviors

A novel family of acrylic acid-based superabsorbent polymers (SAP-n) with controlled-absorption rate were synthesized via aqueous solution polymerization using K2S2O8/NaHSO3 as the redox initiators, N, N'-methylenebisacrylamide (NMBA) as the crosslinker, 2-methacryloyloxyethyl n-alkyl dimethyl ammonium bromide (CnDM, n = 4, 8, 12, 16) as the hydrophobic comonomers. The structures of the copolymers were elucidated by FT-IR and ionic chromatographic (IC) analysis respectively, and the swelling properties of the copolymers were examined. It was found that the water absorbency capacity either in distilled water or in 0.9% NaCl brine decreased with increasing hydrophobe length or content, and the water absorbency rate of SAP-n was as expected lower than that of SAP without hydrophobic monomer; in addition, water retention evaluation under different temperatures revealed that this kind of copolymers could absorb and retain large amount of water at room temperature and release it at high temperature.