Super alcohol-absorbent gels of sulfonic acid-contained poly(acrylic acid)

Abstract

Alcohol-specific superabsorbing gels (super-alcogels) based on non-neutralized acrylic acid (AA, 60–94 mol%) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) were prepared via solution polymerization in water. Polyethylene glycol dimethacrylate and potassium persulfate were used as crosslinker and initiator, respectively. Characterization of samples was performed using FTIR, ¹H-NMR and thermomechanical analyses. Glass transition temperature and modulus of dried samples were found to be directly changed with their AA content. The gels exhibited enormous ability for absorbing and retaining a variety of mono- and poly-hydric alcohols. For example, in lieu of one gram of a typical sample composing 25 mol% AMPS, its absorption capacity was measured to be 53.0 g methanol, 42.1 g ethanol, 12.1 g n-propanol, 3.4 g iso-propanol, 41.2 g ethylene glycol, 20.7 g propylene glycol, 37.8 g 1,3-propanediol and 32.9 g glycerol. The absorbencies were superior to those of a known commercial poly(AA) sample, Carbopol. The alcohol absorbency was improved with increase of AMPS incorporated. It was recognized to be dependant on the alcohol characteristics such as H-bonding ability, OH/C ratio, electronic features (e.g. dielectric constant), steric hindrance of the neighboring groups of the solvent OH group, as well as the solvent viscosity. Normal phase transitions were observed in the gel swelling behavior in the alcohol-water binary mixtures. Rheological measurements of the water-swollen gel showed that more AMPS content resulted in gels with inferior storage modulus. All the empirical observations were discussed based on the related physicochemical principles.