Hydrosoluble Copolymers of Acrylamide-(2-acrylamido-2- methylpropanesulfonic acid). Synthesis and Characterization by Spectroscopy and Viscometry Fa ´tima Rosa, Joa ˜o Bordado, Miguel Casquilho Instituto Superior Te ´cnico, Ave. Rovisco Pais, IST, 1049-001 Lisboa, Portugal Received 27 June 2001; accepted 4 March 2002 ABSTRACT: Hydrosoluble copolymers containing sul- fonic acid groups incorporated into a macromolecule were synthesized. The group of polymers studied was obtained by free radical solution polymerization, using potassium persulfate as an initiator. The copolymerization of the mono- mers 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and acrylamide (AA) was carried out at different pH values of the reaction medium of the monomer mix. The copoly- mers were characterized by proton nuclear magnetic reso- nance spectroscopy ( 1 H NMR) and Fourier transform infra- red spectroscopy (FTIR). The viscosity behavior of the co- polymers in NaCl solution showed a dependency on the pH of the reaction medium, with higher pH leading to lower viscosities. The acidic conditions of this medium affect the initiator decomposition rate, which is a probable cause of the viscosity variation, and the extent of decomposition in- creases with increasing pH. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 192–198, 2003 Key words: copolymerization; acrylamide; 2-acrylamido-2- methylpropanesulfonic acid; synthesis; NMR; FTIR; spec- troscopy; viscosity INTRODUCTION Several sulfonic acid copolymers have been studied by us to synthesize superabsorbent polymers because these substances have industrial application in phar- maceutical, agricultural, and other industries. Varia- tion of the reaction solution pH leads to both non- hydrosoluble and hydrosoluble polymers, making it important to characterize the latter, as we do in the present study. The monomers chosen for this study were 2-acryl- amido-2-methyl-propanosulfonic acid (AMPS) and acrylamide (AA). The molar ratio of the two mono- mers was optimized by the factorial design technique, and the best monomer molar ratio was 70:30, without corrections of the reaction solution pH. The influence of the pH on superabsorbency was subsequently ob- served; that is, at pH  5, the copolymers synthesized became hydrosoluble. The solution properties of the copolymers were studied by viscometry, which is an important tool to characterize these copolymers. The vinyl structure of the AMPS monomer (Figure 1) minimizes chain transfer reaction and permits high molecular weight generation compared with other sulfonic acid monomers. The AMPS monomer is known for its hydrolytic stability and a high tolerance towards divalent cations, 1 thereby maintaining its ca- pacity for propagation. The hydrolytic stability is due to the shielding effect produced by the unique geminal dimethyl structure of the monomer. Moreover, AMPS copolymers are widely utilized in several applications; such as, to precipitate solids in water clarification, as lubricants in personal care, in textile manufacture, and in oil fields. 2,3 The other monomer selected was acrylamide (AA). In short, the aforementioned features of the AMPS monomer and the availability and relative cheapness of the AA monomer led us to combine the advantages of these monomers, with which the polymerization of AA–AMPS was performed. The objective of the research underlying the present study was to prepare and characterize water-soluble copolymers at different pHs of the monomers solution and to assess the effects of the pH on the copolymer structure and on the properties of its dilute solution. The polyelectrolytes in the cited category of sulfonic acids can be produced by a variety of techniques; such as, solution polymerization, suspension polymeriza- tion, and inverse suspension polymerization. A prac- tical method for the polymerization reaction for this purpose is solution polymerization. The low solubility of the monomer AMPS in organic solvents (e.g., 10 g/100 g ethanol, at 78°C) and its good solubility in water (150 g/100 g water, at 25°C) indicate water as the preferred solvent for the preparation of the co- polymers. Correspondence to: M. Casquilho (mcasquilho@ist.utl.pt). Journal of Applied Polymer Science, Vol. 87, 192–198 (2003) © 2002 Wiley Periodicals, Inc.