Reduction of monomer content and stabilization of polyaziridines
View Patent ↗The invention relates to a process for reducing the monomeric aziridine content in a polyaziridine forming reaction mixture by adding to the polyaziridine forming reaction mixture an excess of a carbodiimide scavenger wherein the excess is based on the equivalent ratio of scavenger to monomeric aziridine, and to a product obtained by this process and to a coating composition containing the product obtained by the process.
1. A process for reducing the monomeric aziridine content in a polyaziridine forming reaction mixture comprising adding to the polyaziridine forming reaction mixture an excess of a carbodiimide scavenger wherein the excess is based on the equivalent ratio of carbodiimide scavenger to monomeric aziridine;
wherein the polyaziridine forming reaction mixture comprises monomeric aziridine, acrylates, and polyaziridines; and
wherein the carbodiimide scavenger comprises symmetric and unsymmetric carbodiimides represented by the formula
R′—N═C═N—R″
wherein R′ and R″ independently represent alkyl and cycloalkyl with up to about 20 carbon atoms, aryl, alkaryl, or aralkyl.
2. The process of claim 1 wherein the equivalent ratio of carbodiimide scavenger to monomeric aziridine is between 15:1 to 1.01:1.
3. The process of claim 1 wherein the equivalent ratio of scavenger to monomeric aziridine is between 3:1 and 1.01:1.
4. The process of claim 1 wherein the polyaziridine forming reaction mixture has a content of monomeric aziridine between 100 ppm and 1000 ppm.
5. The process of claim 4 comprising adding between 0.05 and 1.5% by weight of the carbodiimide scavenger based on the polyaziridine forming reaction mixture.
6. The process of claim 4 comprising adding between 0.1 and 1.0% by weight of the scavenger.
7. The process of claim 4 comprising adding between 0.15 and 0.6% by weight of the scavenger.
8. The process of claim 1 comprising reacting an acrylate component and an aziridine component to form the polyaziridine forming reaction mixture.
9. The process of claim 8 comprising reacting an acrylate component and an aziridine component before adding the scavenger.
10. The process of claim 8 comprising adding a stabilizer to the reaction mixture before, during or after the reaction.
11. The process of claim 10 wherein the stabilizer comprises a tertiary amine.
12. The process of claim 10 wherein the stabilizer is tetramethylethylene diamine.
13. The process of claim 8 comprising reacting the components at a temperature above the melting point of the aziridine compound and below 100° C.
14. The process of claim 1 comprising adding between 0.05 and 1.5% by weight of the carbodiimide scavenger based on the polyaziridine forming reaction mixture.
15. The process of claim 1 wherein the scavenger comprises a symmetric carbodiimide.
16. The process of claim 1 wherein the scavenger comprises an unsymmetric carbodiimide.
17. The process of claim 1 wherein the scavenger is N,N-dicyclohexylcarbodiimide (DCC).