1 e-Polymers 2008, no. 163 http://www.e-polymers.org ISSN 1618-7229 Synthesis and swelling characteristics of zwitterionic hydrogel Meenakshi Singh, 1* Paresh Kumar Singh, 2 Vinay Kumar Singh 2 1 Department of Chemistry, Mahila MahaVidyalaya, Banaras Hindu University, Varanasi-221005, India; e-mail: meenakshi_s4@rediffmail.com 2 Department of Chemistry, U.P.A.College, Varanasi-221002, India. (Received: 13 June, 2008; published: 27 December, 2008) Abstract: Hydrogels comprising of zwitterionic repeat units were synthesized. The amine groups of the poly (ester amine) were quaternized with 1,3-propane sultone. The gelation was observed on treatment with sultone. The hydrophilic gel thus formed is sensitive to temperature, pH, ionic strength and nature of electrolytes in aqueous solution. In absence of any electrolyte, the extent of swelling decreased with temperature, but in the monovalent salt solution the equilibrium swelling diminished with temperature and the contrary behaviour was experiential in bivalent electrolytes. Introduction Hydrogels, by definition, are three-dimensional cross-linked polymeric networks that can imbibe large amounts of water [1-4]. Based on the nature of cross-linking chemistry [5], this class of materials is categorized into physical gels consisting of polymeric networks bound together via polymer chain entanglement and/or non- covalent interactions that exist between polymeric chains [1, 3, 6, 7]. The forces accountable for the strength of such networks are characteristically based on hydrogen bonding, electrostatic or hydrophobic interactions and thus, the gels can be reversibly dissolved under certain conditions that would weaken these forces. Whereas, chemically crosslinked gels are bound together by covalent linkages, making them irreversible in the sense that the network structure cannot be ruined until the covalent bonds are destroyed. The responsive properties make these materials promising in different fields including biotechnology, pharmaceutical, agriculture and industrial applications [8-11]. The possible applications include metal extraction, wastewater treatment [12], soft contact lenses, controlled release of drugs, enzyme supports, wound dressing, water managing materials, diapers, agrochemical release and others. Recently, a surge in the synthesis and characterization of synthetic polyampholytes has been reported [13-19]. Polyampholytic hydrogels are defined as crosslinked macromolecular networks containing positively and negatively charged repeating units and show very unusual properties from those of the parent polyelectrolyte polymers, which contain the same charge. Significant attention was given to synthetic polyampholytes due to their widespread applications as selective sorbents, membranes, flocculants, drug carriers etc. The synthetic polyampholytic gels bearing a resemblance to proteins incited them to use for the modeling of biological processes. In ampholyte hydrogels,