Development of phosphonium containing poly(arylene ether)s as potential interphase materials in polymer matrix carbon fiber composites is described. Phosphonium containing poly(arylene ether)s were found to be soluble in methanol and ethanol at roughly 50% phosphonium content. The same polymers were insoluble in water up to 95% phosphonium content. A solvent exchange phenomena was observed when water was added to the phosphonium samples dissolved in methanol and ethanol which dispersed the polymer in solution. Rendering a phosphonium poly(arylene ether) soluble in a polar medium will improve adhesion with a polar carbon fiber compound through ionic interactions. Improved adhesion between an interphase and carbon fiber results in enhanced mechanical properties and a toughened composite material.