Method for reducing yellowness index of a polyetherimide, polyetherimide having a reduced yellowness index, and compositions and articles comprising the polyetherimide

1. A method of reducing yellowness of a polyetherimide solution, the method comprising

acidifying a first solution comprising a solvent and a polyetherimide to provide a second solution having a pH less than 5 under conditions effective for the second solution to attain a yellowness index that is 1 to 30 units less than the yellowness index of the first solution, as determined according to ASTM D1925.

2. The method of claim 1 , wherein the acidifying comprises combining the first solution with one or both of

an inorganic acid;

an organic acid.

3. The method of claim 1 , further comprising exposing the second solution to light for a predetermined amount of time to provide a third solution, wherein the third solution has a yellowness index that is 1 to 100 units less than the yellowness index of the first solution, as determined according to ASTM D1925.

4. The method of claim 1 , further comprising adding a base to the second solution to increase the pH to 6 to 12 to provide a fourth solution, wherein the fourth solution has a yellowness index that is 110 to 170 as determined according to ASTM D1925.

5. The method of claim 3 , wherein the third solution has a yellowness index that is 1 to 30 units less than the yellowness index of the second solution, as determined according to ASTM D1925.

6. The method of claim 1 , wherein the conditions include

a temperature of 10 to 200° C.; and

a time of 1 minute to 72 hours.

7. The method of claim 1 , wherein the solvent comprises benzene, ortho-dichlorobenzene, or a combination comprising at least one of the foregoing.

8. The method of claim 1 , wherein the polyetherimide comprises units of the formula

wherein

R is a C 2-20 hydrocarbon group,

T is a group of the formula —O—Z—O— wherein the divalent bonds of the —O—Z—O— group are in the 3,3′, 3,4′, 4,3′, or the 4,4′ positions, and

is an aromatic C 6-24 monocyclic or polycyclic group optionally substituted with 1 to 6 C 1-8 alkyl groups, 1-8 halogen atoms, or a combination comprising at least one of the foregoing.

9. The method of claim 8 , wherein R is a divalent group of the formula

wherein Q 1 is —O—, —S—, —C(O)—, —SO 2 —, —SO—, —C y H 2y — and a halogenated derivative thereof wherein y is an integer from 1 to 5, or —(C 6 H 10 ) z — wherein z is an integer from 1 to 4; and

Z is a group derived from a dihydroxy compound of the formula

wherein

R a and R b are each independently a halogen atom or a monovalent C 1-6 alkyl group;

p and q are each independently integers of 0 to 4;

c is 0 to 4; and

X a is a single bond, —O—, —S—, —S(O)—, —SO 2 —, —C(O)—, or a C 1-18 organic bridging group.

10. The method of claim 8 , wherein each R is independently meta-phenylene, para-phenylene, bis(4,4′-phenylene)sulfone, or a combination comprising at least one of the foregoing, and the Z is 4-4′-diphenylene isopropylidene.

11. The method of claim 8 , wherein at least 10 mole percent of the R groups comprise a sulfone group and Z is 4,4′-diphenylene isopropylidene.

12. The method of claim 1 , wherein the polyetherimide is a copolymer further comprising units of the formula

wherein each R′ is independently a C 1-13 monovalent hydrocarbyl group, each R 4 is a C 2 -C 20 hydrocarbyl group, E of the siloxane is 2 to 50, the R and Z of the imide are as in claim 9 , and n is an integer from 5 to 100.

13. The method of claim 1 , further comprising isolating the polyetherimide from the solvent.

14. The method of claim 13 , wherein the isolating comprises precipitating the polyetherimide, evaporating the solvent, or a combination comprising at least one of the foregoing.

15. A polyetherimide having a reduced yellowness index made from the method of claim 1 .

16. The polyetherimide of claim 15 , wherein the polyetherimide has a yellowness index of less than 95, as determined according to ASTM D1925.

17. A composition comprising the polyetherimide of claim 15 .

18. An article comprising the polyetherimide of claim 15 .