Process of forming an aramid copolymer

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

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

b) adding less than a stoichiometric amount, relative to the amount of DAPBI, of terephthaloyl dichloride to the slurry;

c) agitating the slurry to react the DAPBI and terephthaloyl dichloride to form an oligomeric solution;

d) adding PPD to the oligomeric solution and agitating until essentially all of the PPD is dissolved, followed by the addition of terephthaloyl dichloride to form a prepolymer solution; and

e) allowing the prepolymer solution to form a polymer,

wherein the amount of the slurry that is DAPBI in step (a) is in the range of from 0.5 to 10 weight %.

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

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

b) adding less than a stoichiometric amount, relative to the amount of DAPBI, of terephthaloyl dichloride to the slurry;

c) agitating the slurry to react the DAPBI and terephthaloyl dichloride to form an oliqomeric solution;

d) adding PPD to the oliqomeric solution and agitating until essentially all of the PPD is dissolved, followed by the addition of terephthaloyl dichloride to form a prepolymer solution; and

e) allowing the prepolymer solution to form a polymer,

wherein the amount of paraphenylene diamine dissolved in the oligomeric solution in step (d) is in the range of from 0.2 to 6.0 weight %.

3. The process of claim 1 or 2 , wherein the total amount of terephthaloyl dichloride added is a stoichiometric amount relative to the total diamines including DAPBI and PPD.

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

5. The process of claim 1 or 2 , wherein the inorganic salt is LiCI or CaCl 2 .

6. The process of claim 1 or 2 , wherein the solvent system is NMP/CaCl 2 .

7. The process of claim 1 or 2 , wherein step e) is performed under agitation.

8. The process of claim 1 or 2 , further comprising isolating said polymer.

9. The process of claim 8 , further comprising the step of comminuting the polymer.

10. The process of claim 8 , further comprising treating the polymer with one or more washing steps, neutralizing steps, or both.

11. The process of claim 9 , further comprising treating the comminuted polymer with one or more washing steps, neutralizing steps, or both.

12. The process of claim 10 , further comprising the step of dissolving the polymer in a solvent comprising sulfuric acid to form a solution suitable for spinning fibers.

13. The process of claim 11 , further comprising the step of dissolving the polymer in a solvent comprising sulfuric acid to form a solution suitable for spinning fibers.

14. The process of claim 10 , further comprising the step of dissolving the polymer in a solvent comprising N-methyl-2-pyrrolidone (NMP) or dimethylacetamide (DMAC) and an inorganic salt to form a solution suitable for spinning fibers.

15. The process of claim 11 , further comprising the step of dissolving the polymer in a solvent comprising N-methyl-2-pyrrolidone (NMP) or dimethylacetamide (DMAC) and an inorganic salt to form a solution suitable for spinning fibers.

16. The process of claim 1 or 2 claim 1 , wherein DAPBI and phenylene diamine are present in a molar ratio in the range of from 0.25 to 4.0.

17. The process of claim 6 , wherein NMP/CaCl 2 has a CaCl 2 weight percent in the range of from 1 to 10%.