Electrochromic layer and devices comprising same

• US 5,679,283 A
• Filed: 07/22/1994
• Issued: 10/21/1997
• Est. Priority Date: 07/22/1994
• Status: Expired due to Term

• Current Assignee: Gentex Corporation
• Original Assignee: Gentex Corporation
• Inventors: Tonar, William L., Anderson, John S., Theiste, David A.
• Primary Examiner(s): TUCKER, PHILIP C
• Application Number:
  US08/278,913
• Time in Patent Office: 1,187 Days
• Field of Search: 252/583, 359/265, 359/272, 359/273, 359/275
• US Class Current: 252/583
• CPC Class Codes: C09K 2211/1029 containing one nitrogen atom as the heteroatom
• CPC Class Codes: C09K 9/02 Organic tenebrescent materials
• CPC Class Codes: G02F 1/1503 caused by oxidation-reduction reactions in organic liquid solutions, e.g. viologen solutions
• CPC Class Codes: G02F 2001/1502 complementary cell
• CPC Class Codes: G02F 2001/15145 the electrochromic layer comprises a mixture of anodic and cathodic compounds
• CPC Class Codes: G02F 2202/022 polymeric

Abstract

The present invention provides electrochromic layers, which comprise polymeric matrices with electrochromic solutions interspersed therein. Varying an electrical potential difference across a layer of the invention results in reversible variation in the transmittance of light across the layer because of electrochemical processes in the electrochromic solution of the layer. The invention further provides electrochromic devices, in which the electrochromic layers of the invention provide reversibly variable transmittance to light, and various apparatus in which the devices of the invention provide light-filtering or light-color modulation. Such apparatus include windows, including those for use inside and on the outside walls of buildings and in sunroofs for automobiles, and variable reflectance mirrors, especially rearview mirrors for automobiles.

Claims

1. An electrochromic layer of reversibly variable transmittance to light which comprises:

(a) a polymer matrix of a polyol polymer which has an hydroxyl functionality of at least 2 and wherein the polyol polymer chains are covalently cross-linked through hydroxyl groups; and

(b) an electrochromic solution which comprises an anodic and a cathodic electrochromic compound interspersed in the polymer matrix.

2. An electrochromic layer according to claim 1 wherein the polyol polymer is a polyester polyol.

3. An electrochromic layer according to claim 2 wherein the polyester polyol is selected from the group consisting of polyester polyols made from diethylene glycol and adipic acid, and polyester polyols made from diethylene glycol, adipic acid and trimethylol propane.

4. An electrochromic layer according to claim 1 wherein the polyol polymer is a polyacrylate polyol.

5. An electrochromic layer according to claim 4 wherein the polyacrylate polyol is a polymer formed from a mono hydroxy caprolactone-monoacrylate.

6. An electrochromic layer according to claim 1 wherein the polyol polymer is a polyether polyol.

7. An electrochromic layer according to claim 6 wherein the polyolether polyol is made from propylene oxide and ethylene oxide started on a trifunctional material.

8. An electrochromic layer according to claim 1 wherein the polyol polymer chains are cross-linked by reaction with a compound selected from the group consisting of a polyisocyanate with an isocyanate functionality of at least 2, a metal alkoxide with an alkoxide functionality of at least 2, and a bisketene, provided that, if the hydroxyl functionality of the polyol polymer is 2, the reaction is with a compound selected from the group consisting of a polyisocyanate with an isocyanate functionality of more than 2, a metal trialkoxide and a metal tetraalkoxide.

9. An electrochromic layer according to claim 8 wherein the polyol polymer chains are cross-linked by reaction with a polyisocyanate.

10. An electrochromic layer according to claim 9 wherein the polyisocyanate is selected from the group consisting of isophorone diisocyanate, a polyisocyanate containing biuret groups, and a polyisocyanate containing an isocyanurate ring.

11. An electrochromic layer according to claim 10 wherein the polyisocyanate is isophorone diisocyanate and the polyol is a polyacrylate polyol with an hydroxyl functionality greater than 2.

12. An electrochromic layer according to claim 11 wherein the polyacrylate polyol is a polymer formed from a mono hydroxy caprolactone acrylate.

13. An electrochromic layer according to claim 10 wherein the polyisocyanate is selected from the group consisting of the polyisocyanate containing biuret groups, and the polyisocyanate containing an isocyanurate ring and the polyol is selected from the group consisting of polyester polyols and polyether polyols.

14. An electrochromic layer according to claim 13 wherein the polyol is selected from the group consisting of a polyol made from diethylene glycol and adipic acid, and a polyol made from diethylene glycol, adipic acid and trimethylol propane.

15. An electrochromic layer according to claim 8 wherein the polyol polymer chains are cross-linked by reaction with a metal alkoxide.

16. An electrochromic layer according to claim 15 wherein the metal alkoxide is tetramethyl orthosilicate.

17. An electrochromic layer according to claim 16 wherein the polyol is a polymer formed from a mono hydroxy caprolactone-monoacrylate.

18. An electrochromic layer according to claim 8 wherein the polyol polymer has an hydroxyl functionality greater than 2 and the polyol polymer chains are cross-linked by reaction with a bisketene.

19. An electrochromic layer according to claim 18 wherein the bisketene is 9,10-hydroanthracene-9,10-bisketene.

20. An electrochromic layer according to claim 19 wherein the polyol is a polymer formed from a mono hydroxy caprolactone-monoacrylate.

21. An electrochromic layer according to any one of claims 1-20 wherein, in the electrochromic solution, the solvent is a liquid at room temperature and is selected from the group consisting of acetonitrile, propionitrile, dimethylformamide, dimethylsulfoxide, glutaronitrile, propylene carbonate, isobutylene carbonate, gamma-butyrolactone, gamma-valerolactone, any homogeneous mixture that is liquid at room temperature of any two or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone, and any homogenous mixture that is liquid at room temperature of any one or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone with ethylene carbonate.

22. An electrochromic layer according to any one of claims 1-20 wherein, in the electrochromic solution, the solvent is selected from the group consisting of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, gamma-valerolactone, any homogeneous mixture that is liquid at room temperature of any two or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone, and any homogenous mixture that is liquid at room temperature of any one or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone with ethylene carbonate.

23. An electrochromic layer according to any one of claims 1-20 wherein, in the electrochromic solution, the solvent is propylene carbonate.

24. An electrochromic layer of claim 1 which is formed in situ within an electrochromic device after a precursor composition, which comprises in combination the electrochromic solution and precursors of the polymers, is loaded into the device.

25. An electrochromic layer according to claim 1 wherein the solution comprises at least 50% by weight of the layer and less than the percentage by weight of the layer at which at room temperature formation of a free-standing gel does not occur.

26. An electrochromic layer according to claim 1 which is self-erasing.

27. An electrochromic layer according to claim 1 wherein the electrochromic solution comprises a tinting compound.

28. An electrochromic layer according to claim 9 wherein the reaction between the polyol and the polyisocyanate is catalyzed by a catalyst selected from the group consisting of tin-based polyurethane polymerization catalysts, platinum-based polyurethane polymerization catalysts, and amine-based polyurethane polymerization catalysts.

29. An electrochromic layer according to claim 28 wherein the catalyst employed in the polymerization is selected from the group consisting of dibutyltin dilaurate and dibutyltin diacetate.

30. An electrochromic layer according to claim 1 which is self-erasing and wherein the electrochromic solution comprises

(A) a solvent;

(B) at least one cathodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible reduction waves;

(C) at least one anodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible oxidation waves; and

(D) if all cathodic and anodic compounds in their zero-potential equilibrium states in solution in the solvent are not ionic, an inert current-carrying electrolyte.

31. An electrochromic layer according to claim 9 which is self-erasing and wherein the electrochromic solution comprises

(A) a solvent;

(B) at least one cathodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible reduction waves;

(C) at least one anodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible oxidation waves; and

(D) if all cathodic and anodic compounds in their zero-potential equilibrium states in solution in the solvent are not ionic, an inert current-carrying electrolyte.

32. An electrochromic layer according to claim 11 which is self-erasing and wherein the electrochromic solution comprises

(A) a solvent;

(B) at least one cathodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible reduction waves;

(C) at least one anodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible oxidation waves; and

(D) if all cathodic and anodic compounds in their zero-potential equilibrium states in solution in the solvent are not ionic, an inert current-carrying electrolyte.

33. An electrochromic layer according to claim 13 which is self-erasing and wherein the electrochromic solution comprises

(A) a solvent;

(B) at least one cathodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible reduction waves;

(C) at least one anodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible oxidation waves; and

(D) if all cathodic and anodic compounds in their zero-potential equilibrium states in solution in the solvent are not ionic, an inert current-carrying electrolyte.

34. An electrochromic layer according to claim 16 which is self-erasing and wherein the electrochromic solution comprises

(A) a solvent;

(B) at least one cathodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible reduction waves;

(C) at least one anodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible oxidation waves; and

(D) if all cathodic and anodic compounds in their zero-potential equilibrium states in solution in the solvent are not ionic, an inert current-carrying electrolyte.

35. An electrochromic layer according to claim 18 which is self-erasing and wherein the electrochromic solution comprises

(A) a solvent;

(B) at least one cathodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible reduction waves;

(C) at least one anodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible oxidation waves; and

(D) if all cathodic and anodic compounds in their zero-potential equilibrium states in solution in the solvent are not ionic, an inert current-carrying electrolyte.

36. An electrochromic layer according to any one of claims 30-35 wherein there is one anodic electrochromic compound, which is selected from the group consisting of 5,10-dihydro-5,10-dimethylphenazine, N,N,N'"'"'.N'"'"'-tetramethyl-p-phenylene-diamine, N,N,N'"'"', N'"'"'-tetraphenyl-p-phenylene-diamine, bis-3,3'"'"'-diethyl-2, 2'"'"'-benzothiazole azine, and tetrathiafulvalene.

37. An electrochromic layer according to claim 36 wherein there is one anodic electrochromic compound, which is 5,10-dihydro-5,10-dimethylphenazine.

38. An electrochromic layer according to any one of claims 30-35 wherein there is one cathodic electrochromic compound, which is a salt of a dication selected from the group consisting of N, N'"'"'-substituted dipyridyls with hydrogen at all of the 2, 2'"'"', 6, and 6'"'"' positions and with the N and N'"'"' substituents being the same or different and each being selected from the group consisting of alkyl groups of 1-10 carbons, phenyl, benzyl, 2-phenylethyl, 3-phenyl(n-propyl), and 4-phenyl(n-butyl) and N, N'"'"'-substituted dipyridyls with an alkyl group of 1-4 carbons at each of the 2, 2'"'"', 6, and 6'"'"' positions and with the N and N'"'"' substituents being the same or different and each being selected from the group consisting of alkyl groups of 1-10 carbons, benzyl, 2-phenylethyl, 3-phenyl(n-propyl), and 4-phenyl(n-butyl).

39. An electrochromic layer according to claim 36 wherein there is one cathodic electrochromic compound, which is a salt of a dication selected from the group consisting of N, N'"'"'-substituted dipyridyls with hydrogen at all of the 2, 2'"'"', 6, and 6'"'"' positions and with the N and N'"'"' substituents being the same or different and each being selected from the group consisting of alkyl groups of 1-10 carbons, phenyl, benzyl, 2-phenylethyl, 3-phenyl(n-propyl), and 4-phenyl(n-butyl) and N, N'"'"'-substituted dipyridyls with an alkyl group of 1-4 carbons at each of the 2, 2'"'"', 6, and 6'"'"' positions and with the N and N'"'"' substituents being the same or different and each being selected from the group consisting of alkyl groups of 1-10 carbons, benzyl, 2-phenylethyl, 3-phenyl(n-propyl), and 4-phenyl(n-butyl).

40. An electrochromic layer according to claim 37 wherein there is one cathodic electrochromic compound, which is a salt of a dication selected from the group consisting of N, N'"'"'-substituted dipyridyls with hydrogen at all of the 2, 2'"'"', 6, and 6'"'"' positions and with the N and N'"'"' substituents being the same or different and each being selected from the group consisting of alkyl groups of 1-10 carbons, phenyl, benzyl, 2-phenylethyl, 3-phenyl(n-propyl), and 4-phenyl(n-butyl) and N, N'"'"'-substituted dipyridyls with an alkyl group of 1-4 carbons at each of the 2, 2'"'"', 6, and 6'"'"' positions and with the N and N'"'"' substituents being the same or different and each being selected from the group consisting of alkyl groups of 1-10 carbons, benzyl, 2-phenylethyl, 3-phenyl(n-propyl), and 4-phenyl(n-butyl).

41. An electrochromic layer according to claim 40 wherein the cathodic electrochromic compound is a salt of 1,1'"'"'-di(3-phenyl(n-propyl))-4, 4'"'"'-dipyridinium.

42. An electrochromic layer according to claim 41 wherein the salt is the difluoroborate.

43. An electrochromic layer according to claim 39 wherein, in the electrochromic solution, the solvent is selected from the group consisting of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, gamma-valerolactone, any homogeneous mixture that is liquid at room temperature of any two or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone, and any homogenous mixture that is liquid at room temperature of any one or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone with ethylene carbonate.

44. An electrochromic layer according to claim 40 wherein, in the electrochromic solution, the solvent is selected from the group consisting of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, gamma-valerolactone, any homogeneous mixture that is liquid at room temperature of any two or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone, and any homogenous mixture that is liquid at room temperature of any one or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone with ethylene carbonate.

45. An electrochromic layer according to claim 41 wherein, in the electrochromic solution, the solvent is selected from the group consisting of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, gamma-valerolactone, any homogeneous mixture that is liquid at room temperature of any two or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone, and any homogenous mixture that is liquid at room temperature of any one or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone with ethylene carbonate.

46. An electrochromic layer according to claim 42 wherein, in the electrochromic solution, the solvent is selected from the group consisting of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, gamma-valerolactone, any homogeneous mixture that is liquid at room temperature of any two or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone, and any homogenous mixture that is liquid at room temperature of any one or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone with ethylene carbonate.

47. An electrochromic layer according to claim 43 wherein, in the electrochromic solution, the solvent is propylene carbonate.

48. An electrochromic layer according to claim 44 wherein, in the electrochromic solution, the solvent is propylene carbonate.

49. An electrochromic layer according to claim 45 wherein, in the electrochromic solution, the solvent is propylene carbonate.

50. An electrochromic layer according to claim 46 wherein, in the electrochromic solution, the solvent is propylene carbonate.

51. An electrochromic layer according to claim 1 wherein the electrochromic solution comprises a UV-stabilizing agent.

52. An electrochromic layer according to claim 51 wherein the UV-stabilizing agent is selected from the group consisting of ethyl 2-cyano-3,3-diphenyl acrylate, 2-ethylhexyl-2-cyano-3,3 diphenyl acrylate, 2-(2-hydroxy-4-methyl-phenyl)-benzo triazole, 2-hydroxy-4-methoxy-benzophenone, and 2-ethyl-2'"'"'-ethoxyoxalanilide.

53. An electrochromic layer according to claim 52 wherein the UV-stabilizing agent is ethyl 2-cyano-3, 3-diphenyl acrylate.

54. An electrochromic layer according to claim 1 wherein the electrochromic solution comprises a thickener, which is a non-cross-linked polymer.

55. An electrochromic layer according to claim 54 wherein the thickener is selected from the group consisting of polymethylmethacrylate, polyethylene oxide and polyvinylbutyral.

56. An electrochromic layer according to claim 55 wherein the thickener is polymethylmethacrylate.

62. An electrochromic device of any one of claims 57-60 wherein the electrochromic layer is an electrochromic layer according to claim 11.

63. An electrochromic device of any one of claims 57-60 wherein the electrochromic layer is an electrochromic layer according to claim 13.

64. An electrochromic device of any one of claims 57-60 wherein the electrochromic layer is an electrochromic layer according to claim 16.

65. An electrochromic device of any one of claims 57-60 wherein the electrochromic layer is an electrochromic layer according to claim 18.

67. An electrochromic device of claim 62 wherein the electrochromic layer is self-erasing and wherein the solution of the layer comprises

(A) at least one cathodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible reduction waves;

(B) at least one anodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible oxidation waves; and

(C) if all cathodic and anodic compounds in their zero-potential equilibrium states in solution in the solvent are not ionic, an inert current-carrying electrolyte.

68. An electrochromic device of claim 63 wherein the electrochromic layer is self-erasing and wherein the solution of the layer comprises

(A) at least one cathodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible reduction waves;

(B) at least one anodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible oxidation waves; and

(C) if all cathodic and anodic compounds in their zero-potential equilibrium states in solution in the solvent are not ionic, an inert current-carrying electrolyte.

69. An electrochromic device of claim 64 wherein the electrochromic layer is self-erasing and wherein the solution of the layer comprises

(A) at least one cathodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible reduction waves;

(B) at least one anodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible oxidation waves; and

(C) if all cathodic and anodic compounds in their zero-potential equilibrium states in solution in the solvent are not ionic, an inert current-carrying electrolyte.

70. An electrochromic device of claim 65 wherein the electrochromic layer is self-erasing and wherein the solution of the layer comprises

(A) at least one cathodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible reduction waves;

(B) at least one anodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible oxidation waves; and

(C) if all cathodic and anodic compounds in their zero-potential equilibrium states in solution in the solvent are not ionic, an inert current-carrying electrolyte.

57. An electrochromic device which comprises, as the medium of reversibly variable transmittance to light, an electrochromic layer of reversibly variable transmittance to light which comprises:

(a) a polymer matrix of a polyol polymer which has an hydroxyl functionality of at least 2 and wherein the polyol polymer chains are covalently cross-linked through hydroxyl groups; and

(b) an electrochromic solution which comprises an anodic and a cathodic electrochromic compound interspersed in the polymer matrix.

58. An electrochromic device of claim 57 wherein, in the electrochromic solution of the electrochromic layer, the solvent is a liquid at room temperature and is selected from the group consisting of acetonitrile, propionitrile, dimethylformamide, dimethylsulfoxide, glutaronitrile, propylene carbonate, isobutylene carbonate, gamma-butyrolactone, gamma-valerolactone, any homogeneous mixture that is liquid at room temperature of any two or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone, and any homogenous mixture that is liquid at room temperature of any one or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone with ethylene carbonate.

59. An electrochromic device of claim 58 wherein, in the electrochromic solution of the electrochromic layer, the solvent is selected from the group consisting of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, gamma-valerolactone, any homogeneous mixture that is liquid at room temperature of any two or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone, and any homogenous mixture that is liquid at room temperature of any one or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone with ethylene carbonate.

60. An electrochromic device of claim 59 wherein, in the electrochromic solution of the electrochromic layer, the solvent is propylene carbonate.

61. An electrochromic device of any one of claims 57-60 wherein the electrochromic layer is an electrochromic layer according to claim 9.

66. An electrochromic device of claim 61 wherein the electrochromic layer is self-erasing and wherein the solution of the layer comprises

(A) at least one cathodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible reduction waves;

(B) at least one anodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible oxidation waves; and

(C) if all cathodic and anodic compounds in their zero-potential equilibrium states in solution in the solvent are not ionic, an inert current-carrying electrolyte.

71. A window which comprises, as the variable transmittance element, an electrochromic device which comprises, as the medium of reversibly variable transmittance to light, an electrochromic layer of reversibly variable transmittance to light which comprises:

(a) a polymer matrix of a polyol polymer which has an hydroxyl functionality of at least 2 and wherein the polyol polymer chains are covalently cross-linked through hydroxyl groups; and

(b) an electrochromic solution which comprises an anodic and a cathodic electrochromic compound interspersed in the polymer matrix.

72. A variable reflectance mirror which comprises, as the variable transmittance element, an electrochromic device which comprises, as the medium of reversibly variable transmittance to light, an electrochromic layer of reversibly variable transmittance to light which comprises:

(a) a polymer matrix of a polyol polymer which has an hydroxyl functionality of at least 2 and wherein the polyol polymer chains are covalently cross-linked through hydroxyl groups; and

(b) an electrochromic solution which comprises an anodic and a cathodic electrochromic compound interspersed in the polymer matrix.

73. An electrochromic layer of reversibly variable transmittance to light which comprises:

(a) a polymer matrix of a polyol polymer which has an hydroxyl functionality of at least 2; and

(b) an electrochromic solution which comprises at least one electrochromic compound interspersed in the polymer matrix.

74. An electrochromic layer according to claim 73 wherein the polyol polymer chains are covalently cross-linked through hydroxyl groups.

75. An electrochromic layer according to claim 73 where the polyol polymer is the product of monomers going through a chain lengthening polymerization prior to insertion into an electrochromic device and where the polyol polymer is crosslinked in situ within an electrochromic device.

76. An electrochromic layer according to claim 75 where the monomer chain lengthening takes place in the presence of an azo thermal initiator.

77. An electrochromic layer according to claim 76 wherein the polyol is a polyacrylate polyol.

78. An electrochromic layer according to claim 77 wherein the polyol is a polymer formed from a mono hydroxy caprolactone acrylate.

79. An electrochromic layer according to claim 73 wherein the polyol polymer is selected from the group consisting of a polyester polyol, a polyacrylate polyol and a polyether polyol.

80. An electrochromic layer according to claim 79 wherein the polyol polymer chains are cross-linked by reaction with a compound selected from the group consisting of an isocyanate with an isocyanate functionality of at least 2, a metal alkoxide with an alkoxide functionality of at least 2, and a bisketene, provided that, if the hydroxyl functionality of the polyol polymer is 2, the reaction is with a compound selected from the group consisting of a polyisocyanate with an isocyanate functionality of more than 2, a metal alkoxide with an alkoxide functionality of more than two.

81. An electrochromic layer according to claim 80 wherein there is one cathodic electrochromic compound, which is a salt of a dication selected from the group consisting of N, N'"'"'-substituted 4, 4'"'"'-dipyridyls with hydrogen at all of the 2, 2'"'"', 6, and 6'"'"' positions and with the N and N'"'"' substituents being the same or different and each being selected from the group consisting of alkyl groups of 1-10 carbons, phenyl, benzyl, 2-phenylethyl, 3-phenyl(n-propyl), and 4-phenyl (n-butyl) and N, N'"'"'-substituted dipyridyls with an alkyl group of 1-4 carbons at each of the 2, 2'"'"', 6, and 6'"'"' positions and with the N and N'"'"' substituents being the same or different and each being selected from the group consisting of alkyl groups of 1-10 carbons, benzyl, 2-phenylethyl, 3-phenyl(n-propyl), and 4-phenyl(n-butyl).

82. An electrochromic layer according to claim 81 wherein there is one anodic electrochromic compound, which is selected from the group consisting of 5,10-dihydro-5,10-dimethylphenazine, N,N,N'"'"',N'"'"'-tetramethyl-p-phenylene-diamine, N,N,N'"'"', N'"'"'-tetraphenyl-p-phenylene-diamine, bis-3,3'"'"'-diethyl-2, 2'"'"'-benzothiazole azine, and tetrathiafulvalene.

83. An electrochromic layer according to claim 81 wherein there is one anodic electrochromic compound, which is 5,10-dihydro-5,10-dimethylphenazine.

84. An electrochromic layer according to claim 83 wherein the cathodic electrochromic compound is a salt of 1,1'"'"'-di(3-phenyl(n-propyl))-4,4'"'"'-dipyridinium.

85. An electrochromic layer according to claim 84 wherein the salt is the difluoroborate.

86. An electrochromic layer according to claim 84 wherein, in the electrochromic solution, the solvent is propylene carbonate.

87. An electrochromic device which comprises, as the medium of reversibly variable transmittance to light, the electrochromic layer of claim 84.

88. A variable transmittance electrochromic window which comprises, as the medium of reversibly variable transmittance to light, the electrochromic layer of claim 84.

89. An electrochromic layer according to claim 79 wherein the polyol polymer chains are cross-linked by reaction with a polyisocyanate.

90. An electrochromic layer according to claim 89 wherein the isocyanate is selected from the group consisting of isophorone diisocyanate, an isocyanate containing biuret groups, and an isocyanate containing an isocyanurate ring, and the polyol is selected from the group consisting of polyacrylate polyols, polyester polyols and polyether polyols.

91. An electrochromic layer according to claim 90 wherein the polyol is selected from the group consisting of the polyol made from diethylene glycol and adipic acid, and the polyol made from diethylene glycol, adipic acid and trimethylol propane.

92. An electrochromic layer according to claim 89 wherein the reaction between the polyol and the polyisocyanate is catalyzed by a catalyst selected from the group consisting of tin-based polyurethane polymerization catalysts, platinum-based polyurethane polymerization catalysts, and amine-based polyurethane polymerization catalysts.

93. An electrochromic layer according to claim 92 wherein the catalyst employed in the polymerization is selected from the group consisting of dibutyltin dilaurate and dibutyltin diacetate.

94. An electrochromic device which comprises, as the medium of reversibly variable transmittance to light, the electrochromic layer of claim 93.

95. A variable transmittance electrochromic window which comprises, as the medium of reversibly variable transmittance to light, the electrochromic layer of claim 93.

96. An electrochromic layer according to claim 79 wherein the polyol polymer chains are cross-linked by reaction with a metal alkoxide.

97. An electrochromic layer according to claim 96 wherein the metal alkoxide is tetramethyl orthosilicate.

98. An electrochromic layer according to claim 97 wherein the polyol is a polymer formed from a mono hydroxy caprolactone mono acrylate.

99. An electrochromic device which comprises, as the medium of reversibly variable transmittance to light, the electrochromic layer of claim 98.

100. A variable transmittance electrochromic window which comprises, as the medium of reversibly variable transmittance to light, the electrochromic layer of claim 98.

101. An electrochromic layer according to claim 79 where the monomer chain lengthening takes place in the presence of an azo thermal initiator.

102. An electrochromic layer according to claim 101 wherein the polyol is a polyacrylate polyol.

103. An electrochromic layer according to claim 102 wherein the polyol is a polymer formed from a mono hydroxy caprolactone mono acrylate.

104. An electrochromic layer according to claim 79 wherein the polyol polymer has an hydroxyl functionality greater than 2 and the polyol polymer chains are cross-linked by reaction with a ketene having a functionality of at least two.

105. An electrochromic layer according to claim 104 wherein the bisketene is 9, 10-hydroanthracene-9, 10-bisketene.

106. An electrochromic layer according to claim 104 where electrochromic layer is catalyst-free.

107. An electrochromic device which comprises, as the medium of reversibly variable transmittance to light, the electrochromic layer of claim 104.

108. A variable transmittance electrochromic window which comprises, as the medium of reversibly variable transmittance to light, the electrochromic layer of claim 104.

109. An electrochromic layer according to claim 79 wherein, in the electrochromic solution, the solvent is a liquid at room temperature and is selected from the group consisting of acetonitrile, propionitrile, dimethylformamide, dimethylsulfoxide, glutaronitrile, propylene carbonate, isobutylene carbonate, gamma-butyrolactone, gamma-valerolactone, any homogeneous mixture that is liquid at room temperature of any two or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, and gamma-valerolactone, and any homogenous mixture that is liquid at room temperature of any one or more of propylene carbonate, isobutylene carbonate, gamma-butyrolactone, gamma-valerolactone and ethylene carbonate.

110. An electrochromic layer according to claim 109 wherein the solution comprises at least 50% by weight of the layer and less than the percentage by weight of the layer at which at room temperature formation of a free-standing gel does not occur.

111. An electrochromic layer according to claim 79 which is self-erasing.

112. An electrochromic device which comprises, as the medium of reversibly variable transmittance to light, the electrochromic layer of claim 79.

113. An electrochromic device according to claim 112 where the polyol polymer is the product of monomers going through a chain lengthening polymerization prior to insertion into an electrochromic device and where the polyol polymer is crosslinked within the electrochromic device.

114. A variable transmittance electrochromic window which comprises, as the medium of reversibly variable transmittance to light, the electrochromic layer of claim 79.

115. An electrochromic window according to claim 114 where the polyol polymer is the product of monomers going through a chain lengthening polymerization prior to insertion into an electrochromic window and where the polyol polymer is crosslinked within the electrochromic window.

116. An electrochromic layer of reversibly variable transmittance to light which comprises:

(a) a solvent

(b) a polymer matrix, where the polymer matrix comprises a cross-linked polyol polymer having a hydroxyl functionality of at least 2 and where, prior to crosslinking, the polyol polymer is formed in the solvent by polymerization of a monomer; and

(c) at least one electrochromic compound interspersed in the polymer matrix and the solvent.

117. An electrochromic layer according to claim 116 where the monomer is polymerized prior to insertion into an electrochromic device and where the polyol polymer is crosslinked within the electrochromic device.

118. An electrochromic layer according to claim 117 where the monomer polymerization takes place in the presence of an azo thermal initiator.

119. An electrochromic layer according to claim 118 wherein the polyol is a polyacrylate polyol.

120. An electrochromic layer according to claim 119 wherein the polyol is a polymer formed from a mono hydroxy caprolactone acrylate.