Process for preparing a block copolymer from polyimides and use of the block copolymer for producing powders and mouldings
The invention describes a process for preparing pulverulent polyimide-polyimide block copolymers. The result polyimide-polyimide block copolymers and compounds produced using them can be compressed into moldings by the direct forming method or by the hot compression molding method. Polymeric moldings can be produced therefrom by customary mechanical and thermal machining and forming methods.
1. A process for preparation of particles of a pulverulent polyimide-polyimide block copolymer of the formula (I):
said process comprising the steps of:
(i) continuously passing into a boiling aprotic dipolar solvent a solution of a polyimide-polyamidecarboxylic acid block copolymer having the following structure:
or a solution of a polyamidecarboxylic acid-polyamidecarboxylic acid block copolymer, having the following structure:
(ii) converting the polyamidecarboxylic acid portion of the block copolymers represented by formulas (A) or (B) into an insoluble polyimide-polyimide block copolymer via thermal imidation and water elimination;
(iii) precipitating the insoluble polyimide-polyimide block copolymer; and
(iv) removing the resulting water from the reaction mixture,
wherein:
n and m=from 2 to 20;
x=from 1 to 300;
R 1 and R 3 are defined as follows:
R 2 and R 4 are defined as follows:
—C n′ H 2n′ —;
n′ is from 1 to 12;
with the proviso that R 1 and R 3 , and R 2 and R 4 , may not simultaneously take the same values, and
further wherein said particles have particle size d50 of from 0.4 to 70 μm.
2. The process of claim 1 , wherein the boiling aprotic dipolar solvent is N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or a mixture thereof.
3. The process claim 1 , wherein an anhydrous acid is used as catalyst for the imidation reaction.
4. The process of claim 1 , further including a step of mixing the block copolymers represented by formulas (A) or (B) with one or more auxiliaries in a ratio by weight of from 1:100 to 100:1, wherein the block copolymers represented by formulas (A) or (B) are mixed in dry form or in suspension.
5. The process of claims 4 , wherein the reaction is carried out in the presence of additional auxiliaries and the resultant block copolymer of formulas (A) or (B) is permitted to encapsulate the additional auxiliaries.
6. The process of claim 5 , wherein the thickness of the block copolymer encapsulating the auxiliary is from 0.1 μm to 10 μm.
7. The process of claim 1 , further including the steps of:
(e) pressing the pulverulent polyimide-polyimide block copolymers of formula (I) at high pressures of from 2000 to 10 000 bar at from 0° C. to 200° C. to a density of greater than 1.20 g/ml, thereby directly forming a moulding; and
(f) sintering the material obtained in step (e) above its glass transition temperature at atmospheric pressure.
8. The process of claim 7 , wherein step (e) takes place at the temperature from 10° C. to 100° C.
9. The process of claim 8 , wherein step (e) takes place at the temperature from 20° C. to 50° C.
10. The process of claim 1 , further including the steps of:
(e) pressing the pulverulent polyimide-polyimide block copolymers of formula (I) at pressures of from 100 to 1000 bar above the glass transition temperature until complete sintering occurs, thereby producing moulding by hot compression.
11. A method for production of moulded plastic products, comprising preparing particles according to the process of claim 1 , and molding said particles.