Studies on the formation of electrostatic complexes between benzethonium chloride and anionic polymers

The chemistry of a mixture of benzethonium chloride and a copolymer of methoxyethylene-maleic anhydride was investigated. This mixture was of interest because it was effective in reducing dental plaque, calculus, and gingival inflammation in vivo. Evidence from dialysis, pH measurements, and stoichiometry demonstrated that the benzethonium cation and the anion of the hydrolyzed copolymer formed an electrostatic complex. An emulsion was produced when a stoichiometric excess of either component was present, but this mixture coacervated at stoichiometric quantities. The stability of the complex was pH dependent, and it did not form in 50% acetone. The complex was decomposed by simulated saliva, mainly due to calcium and magnesium ions, but was unaffected by salivary proteins. Other anionic polymers also formed this type of complex.