Aramid copolymer

The invention concerns polymer comprising residues of 2-(4-amino phenyl)-5 (6) amino benzimidazole (DAPBI), paraphenylene diamine (PPD), and terephthaloyl dichloride, made by a process comprising the steps of: (a) forming a slurry of b mole percent DAPBI and y mole percent PPD in a solvent system comprising organic solvent and c weight percent of an inorganic salt, wherein the inorganic salt is present in an amount of at least 5 weight percent of the organic solvent, DAPBI and PPD being present in an amount sufficient for providing a polymer solution having a weight percent solids of 12 percent or greater on a polymer basis; and (b) contacting the slurry of step a) with a stoichiometric amount of terephthaloyl dichloride to form a product comprising the polymer; wherein the sum of y+b is 100 and the product of b×c is 225 or greater.