Process for producing polyamides via anionic polymerization
The present invention relates to a process for producing polyamides, preferably crosslinked polyamides, via anionic polymerization of lactams in the presence of an anionic catalyst and of a caprolactam-capped polyisocyanate, where said isocyanate comprises more than 3.5 capped isocyanate groups.
1. A process for producing polyamide, comprising:
performing anionic polymerization of at least one lactam in the presence of an anionic catalyst and an activator,
wherein:
the activator comprises a single activator having an average molecular weight Mw of less than 1500;
the activator comprises a caprolactam-capped polyisocyanate; and
the activator comprises on average more than 3.5 capped isocyanate groups.
2. The process of claim 1 , wherein the activator comprises on average more than 4 capped isocyanate groups.
3. The process of claim 1 , wherein the activator is a capped aliphatic polyisocyanate.
4. The process of claim 1 , wherein the at least one lactam is selected from the group consisting of caprolactam, lauryllactam, and a mixture thereof.
5. The process of claim 1 , wherein all lactams are selected from the group consisting of caprolactam, lauryllactam, and a mixture thereof.
6. The process of claim 1 , wherein the at least one lactam is a precisely one lactam.
7. The process of claim 1 , wherein the anionic catalyst is selected from the group consisting of sodium hydrides, sodium metal, sodium caprolactamate, and a mixture thereof.
8. The process of claim 1 , wherein a molar ratio of the lactam to the activator is from 1:1 to 10 000:1.
9. The process of claim 1 , wherein a temperature during the polymerization is from 70° C. to 300° C.
10. The process of claim 1 , wherein a modulus of elasticity of the polyamide is more than 2000 MPa.
11. A polyamide which can be produced by the process of claim 1 .
12. A method for using a polyamide produced by the process of claim 1 , as coating, structural element, packaging film, or laser-sintering powder, and/or during rotor molding.
13. The process of claim 8 , wherein the molar ratio of the lactam to the activator is from 20:1 to 500:1.
14. The process of claim 9 , wherein the temperature during the polymerization is from 100° C. to 170° C.
15. The process of claim 1 , wherein the activator is free of a polyol.
16. The process of claim 1 , further comprising:
oligomerizing a diisocyanate to obtain the activator prior to performing the anionic polymerization.