Polyvinylphosphonic acid copolymer hydrogels prepared with amide and ester type crosslinkers

Crosslinked hydrogels made of poly(vinylphosphonic acid-co-N,N′-methylenebisacrylamide) (P(VPA-co-MBAA)) and poly(vinylphosphonic acid-co-ethyleneglycol diacrylate) (P(VPA-co-EGDA)) were prepared by using precipitation polymerization in water medium. A comparison research was made between the resultant hydrogels containing different loads of vinylphosphonic acid segments when N,N′-methylenebisacrylamide (MBAA) or ethyleneglycol diacrylate (EGDA) were used as comonomers. Morphological observations indicated that the resultant copolymer appeared as a fine powder at low VPA loadings and strongly aggregated at the high loadings; especially, a copolymer containing 63 mol % of VPA segments in P(VPA-co-MBAA) was observed to have a flake-shaped appearance in its aggregated morphology. The resultant copolymer powders were characterized using FTIR spectroscopy and titrimetric analysis. Also, monomer reactivity ratios, r1 and r2, of VPA and MBAA or EGDA were estimated as 0.06 and 0.98 for VPA and MBAA and 0.05 and 1.82 for VPA and EGDA, respectively. This suggested that a large distribution of MBAA and EGDA was present in the resultant copolymer powders. Their crosslinked PVPA structure presented hydrogel properties having high water uptakes and an absorption mechanism independent from pH of bulk solution. The evidence showed that high VPA loadings could strongly interacted through hydrogen bonds between neighbor VPA segments even in the presence of water. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010