Process for preparing aramid copolymer

1. A process for forming a polymer comprising residues of 2-(4-amino phenyl)-5 (6) amino benzimidazole (DAPBI), paraphenylene diamine, and terephthaloyl dichloride, comprising the steps of:

a) forming a slurry of DAPBI and paraphenylene diamine in a solvent system comprising an organic solvent and an inorganic salt;

b) adding a stoichiometric amount of terephthaloyl dichloride to the slurry in a single addition and allowing the formation of said polymer;

c) isolating the polymer from the solvent system;

d) comminuting the polymer; and

e) treating the polymer with one or more neutralizing steps.

2. The process of claim 1 , wherein the organic solvent is N-methyl-2-pyrrolidone (NMP) or dimethylacetamide (DMAC).

3. The process of claim 1 , wherein the inorganic salt is LiCl or CaCl2.

4. The process of claim 1 , wherein the solvent system is NMP/CaCl2.

5. The process of claim 1 , wherein step b) is performed under agitation.

6. The process of claim 1 , further comprising the step of dissolving the polymer in a solvent comprising sulfuric acid to form a solution suitable for spinning fibers.

7. The process of claim 1 , wherein the DAPBI and phenylene diamine are present in a molar ratio in the range of from 0.25 to 4.

8. The process of claim 4 , wherein NMP/CaCl2 has a CaCl2 weight percent in the range of from 0.3 to 10%.

9. The process of claim 1 , wherein the amount of DAPBI used in forming the slurry in step (a) is in the range of from 0.3 to 9 weight %.

10. The process of claim 1 , wherein the amount of paraphenylene diamine used in forming the slurry in step (a) is 0.15 to 6.0 weight %.