The degree of conversion of a flexible 2,2’-diacylbiphenyl unit into a rigid phenanthrene ring in poly(arylene ether) can be controlled by varying the amount of thionating agent, e.g., Lawesson’s reagent, used in the polymer transformation. When less than 1.5 molar equiv of Lawesson’s reagent is used, partial polymer transformation can be achieved, which affords random copolymers containing a different amount of phenanthrene units. The increase in the phenanthrene content in the polymer results in significant increases in the glass transition temperature, the thermal stability, and the solvent resistance.