Stimuli-sensitive behaviour of novel betaine-type polyampholytes

Abstract

Novel linear and crosslinked polyampholytes of betaine structure based on acrylic acid and ethyl 3-aminocrotonate (ethyl ester of 3-amino-2-butenoic acid) have been synthesized by Michael addition reaction followed by radical copolymerization. The mechanism of formation of monomer and polymer betaines is discussed. The linear polyampholyte has been characterized by potentiometric titration, IR, NMR and GPC. Crosslinked polymeric betaines were synthesized in the presence of N,N'-methylenebisacrylamide. The stimuli-sensitive properties of amphoteric gels have been studied as a function of pH, ionic strength, water-organic mixture composition, electric, and combined electric and magnetic fields. The isoelectric points of linear and crosslinked polymeric betaines correspond to pH 2.0-2.1. The effect of ionic strength on the solution and gel properties of polybetaine has been interpreted on the basis of destruction of inter-chain, intra-chain and intra-group salt bonds. Water-acetone, water-ethanol or water-DMF mixtures cause the shrinking of amphoteric gel due to change of the dielectric constant of the medium and decrease of the osmotic pressure. Electrocollapse is observed under the action of DC electric field. Simultaneously cross action of electric and magnetic fields enhances the collapsing rate. Appearance of pH gradient within the volume of polyampholyte gel under the externally imposed DC electric field has been observed. © 2003 Society of Chemical Industry.