A molecular complex is formed by the association of two or more molecules or ions. More specifically, a polyelectrolyte complex (PEC) is made up of differing macromolecules bound together by noncovalent bonds, which include primarily coulombic interactions.1 PECs often are referred to in the patent and technical literature as polymer-polymer complexes, interpolyelectrolyte complexes, or complex coacervates; these terms all are based on the interaction of large macromolecules. Regarding the formation and application of PECs, the authors propose they instead be characterized by the term complex system, as defined by complexity theory.
In this paper, PECs will be described in some detail, including their basic chemistry and formation process. Also, a mechanism will be proposed to explain how a microgel cross-linking structure formed from a PEC consisting of the two polymers PVM/MA copolymer and polyquaternium-28 repairs damaged hair. The potential benefit of this PEC for hair treatments illustrates how this complex system can produce results beyond what could be predicted from the characteristics of its individual polymers. As defined by complexity theory, a complex system contains multiple parts that have local relationships to each other. From the interaction of these parts, a new property of behavior emerges that could not have been predicted from a study of its individual parts alone.2
Although some may view complexes as insoluble species that form when something goes awry during formulating or processing a formula, they do have a functionality that has been demonstrated in various industries. Some examples include microencapsulation, separation membranes, controlled and sustained release of drugs, flocculation of colloidal dispersions, bioadhesion and, less frequently, personal care.