ABSTRACT Polystyrene or polyacrylate-based cationic copolymers contain both hydrophobic and hydrophilic components. The solubility and colloidal behavior of the copolymers in water strongly depends on the fraction of the cationic component in the copolymer backbone. By controlling the charge density, the copolymers can be water insoluble, colloidally dispersible, or fully water soluble. These unique properties have led to many potential applications in areas such as paper coating, paper sizing, and papermaking retention. Several methods, including emulsion polymerization, miniemulsion polymerization, and solution polymerization, have been studied for preparation of the cationic copolymers. It has been found that emulsion polymerization resulted in two different fractions, hydrophobic enriched and hydrophilic enriched fractions, in preparing high cationically charged copolymers. High cationically charged copolymer might be prepared by solution polymerization. Miniemulsion polymerization with a dual initiator system has also been used for preparing the copolymers. The copolymers were characterized and their colloidal properties in water are reported. The potential applications of these copolymers and colloidal dispersions in the papermaking, paper recycling, and pressure-sensitive adhesives industries are discussed. Because most applications of cationic water-dispersible polymers strongly depend on the particle size, charge density, and uniformity, different methods of synthesizing the copolymers and colloidal particles were first reviewed for this paper. The applications of these colloidal particles in the paper industry, which include retention, sizing, and adhesives, are followed. It will be seen that both retention and sizing efficiency can be significantly improved by reducing the size of cationic colloidal particles.
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