Synthesis and solution properties of hydrophobically associating ionic polymers made from diallylammonium salts/sulfur dioxide cyclocopolymerization Yunusa Umar a , Hasan A. Al-Muallem a , B.F. Abu-Sharkh b , Sk. Asrof Ali a, * a Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia b Department of Chemical Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia Received 26 November 2003; received in revised form 15 March 2004; accepted 15 March 2004 Abstract Sulfur dioxide, N,N-diallyl-N-carboethoxymethylammonium chloride and the hydrophobic monomers N,N-diallyl-N-dodecylammonium chloride or N,N-diallyl-N-octadecylammonium chloride were cyclocopolymerized in dimethyl sulfoxide using azobisisobutyronitrile (AIBN) as the initiator to afford water-soluble cationic polyelectrolyte (CPE) having five-membered cyclic structure on the polymeric backbone. The CPE on acidic (HCl) hydrolysis of the pendent ester groups gave the corresponding cationic acid salt (CAS) which was converted to the anionic polyelectrolyte (APE) by treatment with sodium hydroxide. The solution properties of the CPE and APE containing varying amount of the hydrophobic monomers in the range 0 – 10 mol% were investigated by viscometric techniques. The polymers showed that concentration (C p HA ) of less than 1 wt% was required for the manifestation of hydrophobic association, and displayed significant hydrophobic association in salt (NaCl)-free as well as salt-added solutions. q 2004 Elsevier Ltd. All rights reserved. Keywords: Hydrophobic association; Associating ionic polymers; Diallylammonium monomers 1. Introduction In recent years, an increasing number of studies have focused on the hydrophobic association of water-soluble polymers [1,2]. The copolymerization of a water-soluble monomer with a few mol% of a hydrophobic comonomer in a homogeneous solution in mixed solvents gives polymers with random distribution of the hydrophobes as isolated units. Whereas, the miceller systems [2] involving hydro- philic monomer (, 3 wt%) in the continuous water phase and hydrophobic monomer inside the micelles ensure a random distribution of the hydrophobes as small blocks in the hydrophilic polymer chains [3–7]. The concentration- dependent intermolecular associations in the microblocky copolymers lead to superior viscosity behavior in compari- son to the random copolymers which exhibit largely intramolecular associative behavior [8–11]. Although acrylamide is mostly used as the main water- soluble monomer, the miceller polymerization process has also been used in the synthesis of hydrophobically modified polyelectrolytes and polyampholytes using suitable ionic comonomers [12–18]. Above a certain polymer concen- tration (called concentration required for hydrophobic associations, C p HA ) in aqueous solution, intermolecular associations of the hydrophobic groups lead to a reversible formation of three-dimensional physical cross-links of polymer chains. The shear thinning feature associated with the reversible nature of these physical cross-links led to their applications in water-borne coatings, paints, cosmetics, and enhanced oil recovery [19–23]. The shear thinning or thixotropy behavior of these polymers makes it possible to avoid the irreversible mechanical degradation, which occurs for high molecular weight polymers when subjected to high shear stresses [24,25]. In contrast to polymers containing neutral hydrophilic acrylamide and neutral hydrophobic derivative of acryl- amide, the presence of ionic sites of similar charges along the hydrophilic backbone of associating polyelectrolytes leads to a great variety of behaviors [18]. While the 0032-3861/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2004.03.057 Polymer 45 (2004) 3651–3661 www.elsevier.com/locate/polymer * Corresponding author. Tel.: þ 966-3-860-3830; fax: þ966-3-860-4277. E-mail address: shaikh@kfupm.edu.sa (S.A. Ali).