Thermoplastic polyimides

1. A process for producing solid particles of semicrystalline and semiaromatic (co)polyimide, having a median diameter D50 of between 0.01 and 2 mm, said polyimide being thermoplastic and having a melting temperature of between 50 and 350° C., the process comprising:

(a) charging a reactor with a salt formed by reaction of at least one diamine, in which each of the amine functional groups is bound to a respective aliphatic carbon atom, with at least one aromatic tetracarboxylic acid;

(b) polymerizing the salt from step (a) in the solid state to give the (co)polyimide, at an absolute pressure of between 0.005 and 1 MPa and at a temperature T which obeys the following relation:

Tf of the salt from step (a)>T>Tg of the (co)polyimide to be obtained; and

(c) recovering the solid (co)polyimide particles.

2. The process as claimed in claim 1 , wherein the (co)polyimide has a glass transition temperature Tg of less than or equal to 200° C.

3. The process as claimed in claim 1 , wherein the at least one aromatic tetracarboxylic acid is selected from the group consisting of pyromellitic acid, 3,3′,4,4′-biphenyltetracarboxylic acid, 2,3,3′,4′biphenyltetracarboxylic acid, 2,2′,3,3′-biphenyltetracarboxylic acid, 3,3′,4,4′benzophenonetetracarboxylic acid, 2,2′,3,3′-benzophenonetetracarboxylic acid, 1,2,5,6-naphthalenetetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, 2,3,5,6-pyridinetetracarboxylic acid, 3,4,9,10-perylenetetracarboxylic acid, 3,3′,4,4′tetraphenylsilanetetracarboxylic acid, and 2,2′-bis(3,4-bicarboxyphenyl) hexafluoropropanetetracarboxylic acid.

4. The process as claimed in claim 1 , wherein the at least one diamine is selected from molecules of formula NH 2 —R—NH 2 with a divalent alkylaromatic or cycloaliphatic, or linear or branched, saturated and/or unsaturated aliphatic hydrocarbon radical R, optionally comprising one or more heteroatoms.

5. The process as claimed in claim 4 , wherein the radical R comprises from 2 to 50 carbon atoms, and optionally one or more heteroatoms.

6. The process as claimed in claim 1 , wherein the at least one diamine is selected from the group consisting of 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 2-methyl-1,5-diaminopentane, hexamethylenediamine, 3-methylhexamethylenediamine, 2,5-dimethylhexamethylenediamine, 2,2,4- and 2,4,4-trimethylhexamethylenediamine, 1,7-diaminoheptane, 1,8-diaminooctane, 2,2,7,7-tetramethyloctamethylenediamine, 1,9-diaminononane, 5-methyl-1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,13-diaminotridecane, and 1,14-diaminotetradecane.

7. The process as claimed in claim 1 , wherein the at least one diamine is selected from the group consisting of isophoronediamine, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, and diaminodicyclohexylmethane.

8. The process as claimed in claim 1 , wherein the at least one diamine is selected from molecules of formula NH 2 (CH 2 ) n′ -Ph-(CH 2 ) n —NH 2 where n and n′ are nonzero integers which are independent of one and Ph is a phenyl group.

9. The process as claimed in claim 1 , wherein the salt is admixed with an excess of one of the monomers so as to create a stoichiometric imbalance.

10. The process as claimed in claim 1 , wherein the absolute pressure during step (b) is between 0.005 MPa and 0.2 MPa.

11. The process as claimed in claim 1 , wherein the temperature during step (b) is between 50° C. and 250° C.

12. The process as claimed in claim 1 , wherein the number-average molar mass Mn of the (co)polyimide is between 500 g/mol and 50,000 g/mol.

13. Solid particles of (co)polyimide (I), obtained by the process as claimed in claim 1 .

14. Solid particles of semicrystalline and semiaromatic (co)polyimide, having a median diameter D50 of between 0.01 and 2 mm, said polyimide being thermoplastic and having a melting temperature of between 50 and 350° C., said (co)polyimide being obtained from the polymerization of a salt formed by reacting at least one diamine in which each of the amine functional groups is bound to a respective aliphatic carbon atom with at least one aromatic tetracarboxylic acid.

15. A process for producing a composition, the process comprising melt or nonmelt mixing of the solid particles of (co)polyimides (I) as claimed in claim 14 with reinforcing or bulking fillers and/or with impact modifiers and/or with additives.

16. A plastics article, wherein the article comprises the solid particles of (co)polyimide (I) as claimed in claim 14 .

17. The solid particles of claim 14 , wherein the solid particles exhibit less than or equal to a 10% change in relative viscosity after 10 minutes in the melt state, measured with a viscosimeter as a 10 g/L sample in 96% sulfuric acid at a temperature of 25° C.

18. The solid particles of claim 14 , wherein the solid particles exhibit less than or equal to a 10% change in number-average molar mass after 10 minutes in the melt state, determined by 1 H NMR in D 2 SO 4 at 300 K.

19. The process as claimed in claim 1 , wherein the salt formed by reaction of at least one diamine with at least one aromatic tetracarboxylic acid has the general structure shown below:

wherein Ar represents the aromatic group from the aromatic tetracarboxylic acid used in the salt forming reaction and R is dependent on the at least one diamine used in the salt forming reaction.

20. The process as claimed in claim 1 , wherein the salt is formed in a reaction medium comprising a water and alcohol mixture.

21. The process as claimed in claim 1 , wherein the salt is admixed with at least one chain transfer agent.

22. The process as claimed in claim 1 , further comprising:

reacting at least one diamine, in which each of the amine functional groups is bound to a respective aliphatic carbon atom, with at least one aromatic tetracarboxylic acid to produce the salt; and

collecting the produced salt.