Rev Chem Eng 2014; 30(5): 501–519 Ahmad Rabiee*, Amir Ershad-Langroudi and Hajar Jamshidi Polyacrylamide-based polyampholytes and their applications Abstract: Polyampholytes are charged macromolecules bearing both anionic and cationic groups along the poly- mer backbone. Polyampholytes can be synthesized by classic and controlled free radical polymerization, anionic polymerization, and group transfer polymerization (GTP). The aqueous solution behavior of polyampholytes is dic- tated by columbic interactions between the basic and acidic residues. Polyampholytes show both polyelectro- lyte and anti-polyelectrolyte behavior in aqueous media. Factors such as charge density, charge asymmetry (i.e., degree of charge balance), charge spacing and distribu- tion, substrate surface charge, structural conformation, and solution ionic strength are critical parameters. Poly- ampholytes are interesting for numerous reasons and are used for many technology processes such as water treat- ment, enhanced oil recovery (EOR), sludge dewatering, papermaking, pigment retention, mineral processing, and flocculation. In the present study, the main structural fea- tures, behaviors, mechanisms of interaction, and recent field applications of polyacrylamide (PAM)-based polyam- pholytes are reviewed. Keywords: applications; charged polymers; polyacryla- mide; polyampholytes; polyelectrolytes. DOI 10.1515/revce-2014-0004 Received January 20, 2014; accepted June 27, 2014; previously pub- lished online August 5, 2014 1 Introduction One of the most important classes of macromolecules are the ionic polymers carrying the one type charge [i.e., positive (acidic) or negative (basic)] or both (Lowe and McCormick 2002, Dobrynin et al. 2004). This class of poly- mers includes a wide range of naturally occurring biopoly- mers such as proteins modified to synthetic copolymer and terpolymer such as viscosifiers and soaps (McCormick 1991). These polymers may be divided into two groups: polyelectrolytes and polyampholytes (Mortimer 1991, Kudaibergenov 2002, Kudaibergenov et al. 2006). Polyelectrolytes are macromolecules with either anionic or cationic charged functional groups (Salamone 1996, Koetz and Kosmella 2007, Rabiee 2010). Amphoteric polyelectrolytes or polyampholytes are ionic polymers that contain both acidic (cationic) and basic (anionic) functional groups (Bekturov et al. 1990, Kudaibergenov 1999, Ezell et al. 2006a,b). The solubility behavior of these polymers shows differences from that of polyelectrolytes in aqueous solutions and depends on the charge density, charge balance, asymmetry, and the chemical nature of the ionizable groups on a polyampholyte. Polyampholytes can be divided into four subdivisions comprising a combination of the strength (i.e., weak or strong) of acidic or basic charged groups. Polyampho- lyte hydrogels can be produced by three-dimensional crosslinked polymer networks. Polyampholytes categorize in the literature regard- ing the charge location. Polyzwitterion was referred to all polymers that possess both cationic and anionic groups, while polyampholyte was referred to those polymers that specifically possess the charged groups on differ- ent monomer units, and polybetaine was considered as a special case of polyampholytes with the anionic and cationic groups on the same monomer unit (Lowe and McCormick 2002, Ezell et al. 2006a,b). Figure 1 shows a schematic illustration of charge groups in polyampholyte macromolecular chain and hydrogel polymeric network. The charge distribution macromolecule chain based on the solution properties of polyampholytes can be consid- ered as random copolymers, block copolymers, or nonlin- ear star polymer networks. An intrinsic characteristic of polyampholytes is the presence of cationic and anionic groups, which is joined by covalent bonds, thus creating a permanent dipole. This is the major difference between polyampholytes and polyelectrolytes, whose behavior in aqueous solutions *Corresponding author: Ahmad Rabiee, Faculty of Polymer Science, Iran Polymer and Petrochemical Institute, Pazhoohesh Boulevard, Km. 17, P.O. Box 14965/115, 14185/458, Tehran-Karaj Hwy Tehran, Iran, e-mail: a.rabbii@ippi.ac.ir Amir Ershad-Langroudi: Faculty of Polymer Processing, Iran Polymer and Petrochemical Institute, Pazhoohesh Boulevard, Km. 17, P.O. Box 14965/115, 14185/458, Tehran-Karaj Hwy Tehran, Iran Hajar Jamshidi: Faculty of Polymer Science, Iran Polymer and Petrochemical Institute, Pazhoohesh Boulevard, Km. 17, P.O. Box 14965/115, 14185/458, Tehran-Karaj Hwy Tehran, Iran Brought to you by | University of Pittsburgh Authenticated Download Date | 1/5/15 7:28 AM