Process for forming an aramid copolymer

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

i) forming a slurry of b mole percent DAPBI 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;

ii) contacting the slurry with a less than stoichiometric amount of terephthaloyl chloride, based on the amount of DAPBI in step i), to form an prepolymer solution; and

iii) contacting the prepolymer solution with y mole percent of PPD and additional TCL to form a polymer solution;

wherein the total amount of TCL added in steps ii) and iii) is a stoichiometric amount based on the total amount of DAPBI added in step i) and PPD added in step iii);

wherein the DAPBI and PPD are added in an amount sufficient for providing a polymer solution having a weight percent solids of 12 percent or greater on a polymer basis and a weight percent solids of 14-25% on a monomer basis; and

wherein the sum of y+b is 100 and the product of b×c is 225 or greater.

2. The process of claim 1 , wherein the product of (b×c) is equal to 300 or greater.

3. The process of claim 2 , wherein the product of (b×c) is equal to 350 or greater.

4. The process of claim 1 wherein there is more than one addition of terephthaloyl dichloride in step ii).

5. The process of claim 1 , wherein the slurry in step i) and/or the solution in step iii) is cooled to a temperature of 20 ° C. or below prior to contacting said slurry and/or solution with a stoichiometric amount of terephthaloyl dichloride.

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

7. The process of claim 1 wherein the inorganic salt is LiCl or CaCl 2 .

8. The process of claim 6 , wherein the organic solvent is NMP and the inorganic salt is CaCl 2 .

9. The process of claim 1 wherein the steps are performed under agitation.

10. The process of claim 1 , further comprising isolating a polymer from said polymer solution.

11. The process of claim 10 , further comprising the step of comminuting the polymer.

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

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

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

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

16. The process of claim 1 wherein the DAPBI and PPD are present in a molar ratio in the range of from 0.25 to 4.

17. The process of claim 1 wherein the solvent has an inorganic salt weight percent in the range of from 5.0 to 10%.

18. The process of claim 1 wherein the amount of DAPBI used in forming the slurry in step (i) is in the range of from 2 to 9 weight %.

19. The process of claim 1 comprising 0.8 to 6.0 weight % of paraphenylene diamine in step i).

20. The process of claim 1 wherein the weight percent solids in the polymer solution is 12-15% on a polymer basis.