Method for preparing a photochromic polyurethane latex and application to ophthalmic optics

1. A method of preparing a photochromic polyurethane latex comprising:

forming a hydrophilic polyurethane prepolymer with isocyanate end groups, by polyaddition of at least one polyol and at least one polyisocyanate in the presence of at least one internal emulsifying agent, wherein the quantities of the polyol and polyisocyanate are such that the molar ratio of OH groups/NCO groups is about 1/2;

mixing the polyurethane prepolymer with a photochromic agent;

adding water or a mixture of water and solvent, under agitation, to the mixture of the polyurethane prepolymer and the photochromic agent, to form an emulsion; and

adding at least one chain extension agent to the emulsion and performing a chain extension reaction to give a final photochromic polyurethane latex.

2. The method of claim 1 , wherein the internal emulsifying agent is an ionic emulsifying agent.

3. The method of claim 2 , wherein the ionic internal emulsifying agent is an anionic internal emulsifying agent.

4. The method of claim 3 , wherein the internal emulsifying agent is a diamine sulfonate, a diol sulfonate, or a dihydroxycarboxylic acid.

5. The method of claim 4 , wherein the internal emulsifying agent is α,α-dimethylolpropionic acid.

6. The method of claim 2 , further comprising neutralizating the polyurethane prepolymer prior to mixing it with the photochromic agent.

7. The method of claim 6 , wherein neutralizing comprises the addition of a tertiary amine.

8. The method of claim 1 , wherein the polyisocyanate is a diisocyanate.

9. The method of claim 8 , wherein the diisocyanate is further defined as toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, diphenylmethane-4,4′-diisocyanate, diphenylmethane-2,4′-diisocyanate, paraphenylene diisocyanate, biphenyldiisocyanate, 3,3′-dimethyl-4,4′-diphenylene diisocyanate, tetramethylene-1,4-diisocyanate, hexamethylene-1,6-diisocyanate, 2,2,4-trimethyl hexane-1,6-diisocyanate, lysine methyl ester diisocyanate, bis(isocyanatoethyl)fumarate, isophorone diisocyanate, ethylene diisocyanate, dodecane-1,12-diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate, methylcyclohexyl diisocyanate, hexahydrotoluene-2,4-diisocyanate, hexahydrotoluene-2,6-diisocyanate, hexahydrophenylene-1,3-diisocyanate, hexahydrophenylene-1,4-diisocyanate, perhydrodiphenylmethane-2,4′-diisocyanate, perhydrophenylmethane-4,4′-diisocyanate, or a mixture of two or more such diisocyantates.

10. The method of claim 9 , wherein the diisocyanate is isophorone diisocyanate.

11. The method of claim 1 , wherein the polyol is further defined as a polyol of low molecular weight, a polyester polyol, a polyether polyol, a polyol containing an amide group, a polyacrylic polyol, an epoxy polyol, a polyvinyl polyol, a urethane polyol, or a mixture of two or more such polyols.

12. The method of claim 11 , wherein the polyol is a polycaprolactone diol.

13. The method of claim 1 , comprising adding a quantity of the photochromic agent representing from 0.1 to 15% by weight with respect to the total weight of polyol, polyisocyanate, internal emulsifying agent, and photochromic agent.

14. The method of claim 13 , further defined as comprising adding a quantity of the photochromic agent representing from 2 to 10% by weight with respect to the total weight of polyol, polyisocyanate, internal emulsifying agent, and photochromic agent.

15. The method of claim 1 , wherein the photochromic agent is added in the form of a solution in a solvent.

16. The method of claim 15 , wherein the solvent is N-methylpyrrolidone.

17. The method of claim 1 , further defined as comprising the addition of a solvent during the process of forming the hydrophilic polyurethane prepolymer.

18. The method of claim 17 , wherein the solvent is N-methylpyrrolidone.

19. The method of claim 1 , wherein the chain extension agent is an aliphatic diamine, a cycloaliphatic diamine, a triamine, a tetramine, or a mixture of two or more such extension agents.

20. The method of claim 19 , wherein the chain extension agent is ethylenediamine, diethylenetriamine, or tris(2-aminoethyl)amine.

21. The method of claim 1 , wherein the final polyurethane latex has a concentration of solids of at least 30% by weight.

22. The method of claim 21 , wherein the final polyurethane latex has a concentration of solids of 30 to 35% by weight.

23. The method of claim 1 , wherein the final polyurethane latex has a particle size of from 50 to 300 nm.

24. The method of claim 23 , wherein the final polyurethane latex has a particle size of from 150 to 250 nm.

25. The method of claim 1 , comprising using a quantity of internal emulsifying agent of from 3 to 5% by weight with respect to the total weight of polyol, polyisocyanate, and internal emulsifying agent.

26. The method of claim 1 , wherein the photochromic agent is chromene, a chromene compound, an oxazine compound, a fulgide, a fulgimide, or a metallic salt of dithizonate.

27. The method of claim 1 , further defined as comprising using a molar ratio prepolymer/chain extension agent of between 0.2 and 2.

28. A method of preparing a photochromic polyurethane latex comprising:

forming a hydrophilic polyurethane prepolymer with isocyanate end groups, by polyaddition of at least one polyol and at least one polyisocyanate in the presence of at least one internal emulsifying agent, wherein the amount of the internal emulsifying agent is from 3 to 5% by weight with respect to the total weight of polyol, polyisocyanate, and internal emulsifying agent;

mixing the polyurethane prepolymer with a photochromic agent;

adding water or a mixture of water and solvent, under agitation, to the mixture of the polyurethane prepolymer and the photochromic agent, to form an emulsion; and

adding at least one chain extension agent to the emulsion and performing a chain extension reaction to give a final photochromic polyurethane latex.