Curable photochromic compositions

Abstract

A curable photochromic composition can include: (a) a first component having a first compound with at least two active hydrogen-functional groups and an active hydrogen-functional group equivalent weight of at least 1000; (b) a second component having at least one of a polyisocyanate and a blocked polyisocyanate; and (c) at least one photochromic compound. The ratio of total isocyanate and blocked isocyanate group equivalents of the second component to total active hydrogen-functional group equivalents is at least 4:1.

Claims

1. A curable photochromic composition comprising: (a) a first component comprising a first compound having at least two active hydrogen-functional groups and an active hydrogen-functional group equivalent weight of at least 1000, wherein said first compound comprises a polyol, and said polyol of said first compound is selected from polyether polyols, polyester polyols, polycarbonate polyols, and combinations thereof; (b) a second component comprising at least one of a polyisocyanate and a blocked polyisocyanate; and (c) at least one photochromic compound, wherein the ratio of total isocyanate and blocked isocyanate group equivalents of the second component to total active hydrogen-functional group equivalents is at least 4:1.

2. The curable photochromic composition of claim 1, further comprising: (d) a third component comprising a second compound having three or more active hydrogen-functional groups and an active hydrogen-functional group equivalent weight of less than or equal to 500.

3. The curable photochromic composition of claim 1, wherein the ratio of total isocyanate and blocked isocyanate group equivalents of the second component to total active hydrogen-functional group equivalents is at least 5:1.

4. The curable photochromic composition of claim 1, wherein the ratio of total isocyanate and blocked isocyanate group equivalents of the second component to total active hydrogen-functional group equivalents is up to 50:1.

5. The curable photochromic composition of claim 1, wherein the polyisocyanate of the second component (b) is selected from a polyureadiisocyanate, a blocked polyureadiisocyanate, a polyurethanediisocyanate, a blocked polyurethanediisocyanate, a polythiourethanediisocyanate, a blocked polythiourethanediisocyanate, and combinations thereof.

6. The curable photochromic composition of claim 1, wherein the curable photochromic composition further comprises a prepolymer comprising a reaction product of (a) and (b).

7. The curable photochromic composition of claim 2, wherein the first compound and the second compound each independently comprise active hydrogen-functional groups chosen from hydroxyls, primary amines, secondary amines, thiols, or combinations thereof.

8. The curable photochromic composition of claim 2, wherein the second compound independently comprises polyol.

9. The curable photochromic composition of claim 8, wherein the polyol of the second compound comprises an acrylic polyol.

10. The curable photochromic composition of claim 1, wherein the at least one photochromic compound (c) is an organic photochromic material selected from photochromic spirooxazines, benzopyrans, naphthopyrans, indenonaphthopyrans, fulgides, metal dithizonates, diarylethenes, or combinations thereof.

11. The curable photochromic composition of claim 1, wherein when applied to a substrate and cured to form a coating, the first component forms a plurality of soft segment domains and the second component forms a plurality of hard segment domains.

12. The curable photochromic composition of claim 2, wherein when applied to a substrate and cured to form a coating, the first component forms a plurality of soft segment domains and the second component and the third component together form a plurality of hard segment domains.

13. The curable photochromic composition of claim 11, wherein the plurality of soft segment domains have a Tg of −10° C. to −150° C., and the plurality of hard segment domains have a Tg of 0° C. to 150° C.

14. The curable photochromic composition of claim 11, wherein the plurality of soft segment domains each comprise a size of less than 300 nm.

15. The curable photochromic composition of claim 11, wherein the plurality of soft segment domains each comprise a size of less than 100 nm.

16. The curable photochromic composition of claim 11, wherein the at least one photochromic compound (c) at least partially resides in the plurality of soft segment domains formed from the first component.

17. The curable photochromic composition of claim 12, wherein the plurality of soft segment domains have a Tg of −10° C. to −150° C., and the plurality of hard segment domains have a Tg of 0° C. to 150° C.

18. The curable photochromic composition of claim 12, wherein the plurality of soft segment domains each comprise a size of less than 300 nm.

19. The curable photochromic composition of claim 12, wherein the plurality of soft segment domains each comprise a size of less than 100 nm.

20. The curable photochromic composition of claim 12, wherein the at least one photochromic compound (c) at least partially resides in the plurality of soft segment domains formed from the first component.

21. The curable photochromic composition of claim 1, wherein when applied to a substrate and cured to form a coating, the coating exhibits a Fischer microhardness of at least 10 N/mm.sup.2.

22. A photochromic article comprising: (a) a substrate; and (b) at least one coating layer formed from the curable photochromic composition of claim 1 residing over at least a portion of the substrate.

23. The photochromic article of claim 22, wherein the substrate is an optical substrate.

24. The photochromic article of claim 22, wherein the ratio of total isocyanate and blocked isocyanate group equivalents of the second component to total active hydrogen-functional groups equivalents of the first component is at least 5:1.

Description

EXAMPLE 1

Preparation of a Polyester Polycarbonate Diol

(1) A polyester polycarbonate diol was prepared from the components listed in Table 1.

(2) TABLE-US-00001 TABLE 1 Component Weight (grams) ETERNACOLL ® UH-50 .sup.1 250.1 Adipic acid 67.16 Triphenyl phosphite 0.3 Dibutyltinoxide 0.3 .sup.1 Polycarbonate diol available from UBE Industries.

(3) The components listed in Table 1 were added to a 500 ml 4-Neck round bottom flask equipped with a mechanical stirrer and Dean-Stark trap. The mixture was heated to 140° C. under nitrogen, and stirred for one hour. The reaction was raised to 180° C. and stirred for an additional hour. Temperature was then raised to 200° C. and stirred for 11 hours. The reaction was cooled to 120° C. under nitrogen and then to room temperature to yield a polyester polycarbonate diol with a number average molecular weight (Mn) of 7,850 and a polydispersity of 2.02. The acid value was less than 0.19 mg KOH/g (based on solids), and the hydroxyl equivalent weight was 2,318 based on solids.

EXAMPLE 2

Preparation of a Polycarbonate Diol

(4) A polycarbonate diol was prepared according to the Polycarbonate Polyol B (PP-B) preparation in Part 1 of the Examples section of U.S. Pat. No. 8,608,988 at column 19, lines 47-59, which is incorporated by reference herein. The hydroxyl equivalent weight of the polycarbonate diol was 1810 (based on solids). The final resin was reduced to 60% solids with dipropylene glycol methyl ether acetate (DPMA).

EXAMPLE 3

Preparation of an Active Hydrogen-Functional Prepolymer

(5) An active hydrogen-functional prepolymer was prepared from the components listed in Table 2.

(6) TABLE-US-00002 TABLE 2 Component Weight (grams) DURANOL ® T5652A .sup.2 181.9 N-methyl-2-pyrrolidone 131.9 VESTANAT ® TMDI .sup.3 15.6 K-KAT ® 348 .sup.4 0.34 .sup.2 Polycarbonate diol available from Asahi Kasei Chemicals Corporation. .sup.3 Isocyanate available from Evonik Industries. .sup.4 Bismuth catalyst available from King Industries Inc.

(7) In accordance with Table 1, DURANOL® T5652A was mixed under nitrogen with N-methyl-2-pyrrolidone and VESTANAT® TMDI for 15 minutes followed by addition of K-KAT® 348. The reaction mixture was stirred at room temperature for one hour and then heated to 80° C. for three hours until all free isocyanates were consumed, as determined by FTIR spectroscopy. The reaction mixture was cooled to room temperature and the resulting clear, viscous polymer solution was collected. The final product had a number average molecular weight (Mn) of 16,600, a weight average molecular weight (Mw) of 32,200, and 59.7% total solids. The theoretical active hydrogen equivalent weight of the material was 5,011 based on solids.

EXAMPLE 4

Preparation of an Isocyanate Functional Prepolymer

(8) An active isocyanate functional prepolymer was prepared from the components listed in Table 3.

(9) TABLE-US-00003 TABLE 3 Component Weight (grams) Polycarbonate diol of Example 2 30 VESTANAT ® TMDI .sup.3 14.6 Dibutyltin dilaurate 0.05 Di(propylene glycol) methyl ether acetate 4 3,5-Dimethylpyrazole 10.9

(10) In accordance with Table 3, the polycarbonate diol of Example B was added dropwise into a 40° C. solution of VESTANAT® TMDI and dibutyltin dilaurate, followed by a rinse with di(propylene glycol) methyl ether acetate. The solution was heated to 60° C. for 1.5 hours. 3,5-dimethylpyrazole was then added in portions until isocyanate was not observed by FTIR spectroscopy. The reaction mixture was cooled to provide a viscous oil with a solids content of 73% (one hour, 120° C.). The number average molecular weight (Mn) of the polymer portion was 7,390 and the weight average molecular weight (Mw) was 9,850. The isocyanate equivalent weight of the sample was 400 based on solids.

EXAMPLE 5

Preparation of a Polyureapolyurethane Diisocyanate

(11) A polyureapolyurethane diisocyanate was prepared from the components listed in Table 4.

(12) TABLE-US-00004 TABLE 4 Component Weight (grams) Hexafluoropentanediol 3 Hexamethylenediamine 1.6 VESTANAT ® TMDI .sup.3 11.9 Dibutyltin dilaurate 0.05 N-methyl-2-pyrrolidone 11.5 3,5-Dimethylpyrazole 5.35

(13) In accordance with Table 4, a solution of hexafluoropentanediol, hexamethylenediamine, and 3,5-dimethylpyrazole in N-methyl-2-pyrrolidone was added dropwise to a solution of VESTANAT® TMDI and dibutyltin dilaurate at 40° C. After rinsing with N-methyl-2-pyrrolidone, the reaction mixture was stirred at 65° C. for two hours. Additional 3,5-dimethylpyrazole was then added in portions until isocyanate was not observed by FTIR spectroscopy. The reaction mixture was cooled to provide a viscous oil with a solids content of 68%. The isocyanate equivalent weight of the sample was 410 based on solids.

EXAMPLES 6-16

Preparation of Curable Photochromic Compositions

(14) Curable photochromic compositions were prepared from the components listed in Tables 5 and 6. All components are listed in parts per weight and quantities in Charge 2 are listed by solid component only.

(15) TABLE-US-00005 TABLE 5 Comparative Comparative Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Charge 1 Photochromic dyes .sup.5 4.00 3.99 4.11 3.99 4.01 3.96 TINUVIN ® 144 .sup.6 2.00 2.00 2.00 2.02 1.82 Stabilizer .sup.7 1.97 IRGANOX ® 245 .sup.8 2.00 2.00 1.95 2.00 2.02 1.82 N-methyl-2-pyrrolidone 55.33 34.08 67.93 37.17 32.72 35.65 Charge 2 ETERNACOLL ® 33.18 PH200D .sup.9 Compound of Example 1 35.83 Compound of Example 2 33.18 33.16 31.36 Compound of Example 3 Poly(ethylene glycol- ran-propylene glycol) .sup.10 K-KAT ® 348 .sup.4 0.74 0.77 1.10 0.72 0.79 0.90 SILQUEST ® A-187 .sup.11 3.98 3.85 6.20 3.88 4.05 5.31 Acrylic polyol .sup.12 22.69 17.84 3.48 5.05 TRIXENE ® BI-7960 .sup.13 44.13 48.97 64.17 63.36 29.32 49.87 Compound of Example 4 65.63 Compound of Example 5 18.76 BYK ® 333 .sup.14 0.07 0.07 0.09 0.07 0.09 0.11 Solvent from resins .sup.15 34.02 55.20 28.70 52.28 40.26 51.42 % Solids (theory) 55.8 55.8 54.4 55.7 60.8 56.7

(16) TABLE-US-00006 TABLE 6 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Charge 1 Photochromic dyes .sup.5 4.01 4.01 4.01 4.04 3.99 TINUVIN ® 144 .sup.6 2.01 2.01 2.01 2.01 1.99 Stabilizer .sup.7 IRGANOX ® 245 .sup.8 2.00 2.00 2.00 2.01 1.99 N-methyl-2-pyrrolidone 33.87 33.87 33.87 24.84 25.81 Charge 2 ETERNACOLL ® PH200D .sup.9 Compound of Example 1 Compound of Example 2 28.39 31.30 34.16 Compound of Example 3 31.82 Poly(ethylene glycol-ran- 31.48 propylene glycol) .sup.10 K-KAT ® 348 .sup.4 0.91 0.91 0.91 0.87 0.79 SILQUEST ® A-187 .sup.11 4.53 4.53 4.53 4.19 3.92 Acrylic polyol .sup.12 9.16 6.26 3.41 4.25 3.38 TRIXENE ® BI-7960 .sup.13 62.45 62.44 62.43 63.93 65.13 Compound of Example 4 Compound of Example 5 BYK ® 333 .sup.14 0.11 0.11 0.11 0.11 0.14 Solvent from Resins .sup.15 51.74 51.86 51.97 70.24 35.07 % Solids (theory) 57.0 57.0 57.0 54.4 65.0 .sup.5 Blend of photochromic indenofused naphthopyran dyes designed to give a green-gray color. .sup.6 Hindered amine light stabilizer, commercially available from BASF. .sup.7 Stabilizer corresponding to Compound 23 in U.S. Pat. No. 4,198,334. .sup.8 Antioxidant commercially available from BASF. .sup.9 Polycarbonate diol with an average equivalent weight of 983, commercially available from Ube Chemicals. .sup.10 Available from Sigma-Aldrich Inc. with a Mn of 12,000, and a hydroxyl equivalent weight of 6,000. .sup.11 Gamma-glycidoxypropyl trimethoxysilane, available from OSi Specialties. .sup.12 Made from free radical polymerization of Hydroxypropyl methacrylate (40.4%), Butyl methacrylate (57.6%) and Acrylic acid (2.0%) with a number average molecular weight (Mn) of 5500 as determined by GPC with polystyrene standard and tetrahydrofuran diluent. Hydroxyl Equivalent weight (on solids) of 360. Material reduced to 61% solids using dipropylene glycol methyl ether acetate. .sup.13 Blocked hexamethylene diisocyanate available from Baxenden Chemical Co. .sup.14 A polyether modified dimethylpolysiloxane copolymer available from BYK-Chemie. .sup.15 Total solvent from raw materials.

(17) For each coating composition shown in Tables 5 and 6, the components of Charge 1 were added to a suitable vessel with stirring and heated to 40-60° C. for a minimum of 30 minutes until the solids dissolved. The ingredients of Charge 2 were combined, mixed thoroughly, and then added to the solution of Charge 1. The resulting mixture was placed on a WHEATON® 348923-A Benchtop Roller, available from Wheaton Industries, Inc., for a minimum of six hours prior to use. The centi-equivalents (cEq) and resulting NCO to active hydrogen ratios for each Example are shown in Table 7.

(18) TABLE-US-00007 TABLE 7 cEq cEq cEq 1.sup.st 2.sup.nd 3.sup.rd NCO:Active Example Component Component Component Hydrogens 6 3.38 15.38 6.30 .sup. 1.6:1.0.sup.16 7 1.77 17.06 4.96 2.5:1.0 8 1.55 22.36 — 14.4:1.0  9 1.77 22.08 0.97 8.1:1.0 10 1.47 31.43 1.40 10.9:1.0  11 1.73 21.92 — 12.6:1.0  12 1.57 21.76 2.54 5.3:1.0 13 1.73 21.76 1.74 6.3:1.0 14 1.89 21.75 0.95 7.7:1.0 15 3.03 24.67 1.18 5.9:1.0 16 0.52 22.70 0.94 15.5:1.0  .sup.16The first component of Comparative Example 6 comprises a polyol having an equivalent weight of 983.

EXAMPLE 17

Application of Photochromic Coatings

(19) The compositions of Examples 6-9 and 11-16 were each applied to a PDQ® coated Gentex® polycarbonate plano lens having a diameter of 76 millimeters. The composition of Example 10 was applied to 2″×2″ (5.08 cm×5.08 cm) CR-39 chips from Homalite of Wilmington, Delaware. All substrates were treated with oxygen plasma at a flow rate of 100 milliliters (mL) per minute of oxygen at 100 watts of power for three minutes prior to being coated with the compositions of Examples 6-16 via a spin coating process. About 1-2 mL of each composition was dispensed onto the substrate and then rotated for eight seconds at a spin speed sufficient to deposit 0.25-0.35 g of wet coating onto the lens or about 0.15-0.19 g of wet coating onto the CR39 chip. The spin coating parameters are shown in Table 8 below.

(20) TABLE-US-00008 TABLE 8 Spin Spin Photochromic Time speed coating weight Example Substrate (sec) (rpm) (g) 6 Polycarbonate Lens 8 916 0.27 7 Polycarbonate Lens 8 976 0.26 8 Polycarbonate Lens 8 916 0.27 9 Polycarbonate Lens 8 916 0.26 10 CR39 Chip 8 1308 0.16 11 Polycarbonate Lens 8 1112 0.25 12 Polycarbonate Lens 8 916 0.30 13 Polycarbonate Lens 8 916 0.31 14 Polycarbonate Lens 8 916 0.31 15 Polycarbonate Lens 12 1157 0.35 16 Polycarbonate Lens 8 1399 0.30

(21) The coated substrates were made in duplicate and designated as Set “A” and Set “B”. The coated substrates were then placed in a 40° C. oven until all lenses or chips were accumulated. The chips or lenses were then cured in a forced air oven at 125° C. for one hour and subsequently cooled to room temperature. The lenses and chip of Set “A” were then subjected to an additional thermal cure for three hours at 105° C. and set aside for evaluation. The lenses and chip of Set “B” were further treated with oxygen plasma as previously described and coated with a protective coating according to the formulation reported in Table 1 of Example 1 in U.S. Pat. No. 7,410,691, which is incorporated herein by reference, using an additional 0.5% polybutyl acrylate. The protective coating was applied by spin coating and UV cured in an EyeUV oven equipped with D bulbs. Following this, each lens or chip was further cured at 105° C. for three hours. The lenses and chip of Set “B” were then evaluated for photochromic properties.

EXAMPLE 18

Microhardness and Photochromic Performance Evaluation

(22) The coated substrates of Set “A” of Example 17 were subjected to microhardness testing using a Fischerscope HCV, Model H100SMC available from Fischer Technology, Inc. Each lens was measured from 2 to 5 times and the resulting data was averaged. The hardness measurements were taken as the hardness at a penetration depth of 2 microns after a 100 Newton load for 15 seconds.

(23) In addition, the photochromic performance of the coated substrates of Set “B” of Example 17 were tested on the Bench for Measuring Photochromics (“BMP”) made by Essilor, Ltd. France. The optical bench was maintained at a constant temperature of 73.4° F. (23° C.) during testing. Prior to testing on the optical bench, each of the coated lenses were exposed to 365-nanometer ultraviolet light for about 10 minutes at a distance of about 14 centimeters to activate the photochromic materials. The UVA (315 to 380 nm) irradiance at the lens was measured with a LICOR® Model Li-1800 spectroradiometer and found to be 22.2 watts per square meter. Each lens was then placed under a 500 watt, high intensity halogen lamp for about 10 minutes at a distance of about 36 centimeters to bleach (inactivate) the photochromic materials. The illuminance at the lens was measured with the LICOR® spectroradiometer and found to be 21.9 Klux. Each lens was then kept in a dark environment at room temperature (from 70 to 75° F., or 21 to 24° C.) for at least one hour prior to testing on an optical bench. Prior to measurement, each lens was measured for ultraviolet absorbance at 390 nanometers.

(24) The BMP optical bench was fitted with two 150-watt Newport Model #6255 Xenon arc lamps set at right angles to each other. The light path from Lamp 1 was directed through a 3 mm SCHOTT® KG-2 band-pass filter and appropriate neutral density filters that contributed to the required UV and partial visible light irradiance level. The light path from Lamp 2 was directed through a 3 mm SCHOTT® KG-2 band-pass filter, a SCHOTT® short band 400 nm cutoff filter and appropriate neutral density filters in order to provide supplemental visible light illuminance. A 2 inch×2 inch (5.08 cm×5.08 cm) 50% polka dot beam splitter set at 45° to each lamp is used to mix the two beams. The combination of neutral density filters and voltage control of the Xenon arc lamp were used to adjust the intensity of the irradiance. Software i.e., BMPSoft version 2.1e was used on the BMP to control timing, irradiance, air cell and sample temperature, shuttering, filter selection, and response measurement. A ZEISS® spectrophotometer, Model MCS 601, with fiber optic cables for light delivery through the lens was used for response and color measurement. Photopic response measurements were collected on each lens.

(25) The power output of the optical bench, i.e., the dosage of light that the lens was exposed to, was adjusted to 6.7 watts per square meter (W/m.sup.2) UVA, integrated from 315-380 nm, and 50 Klux illuminance, integrated from 380-780 nm. Measurement of this power setpoint was made using an irradiance probe and the calibrated Zeiss spectrophotometer. The lens sample cell was fitted with a quartz window and self-centering sample holder. The temperature in the sample cell was controlled at 23° C. through the software with a modified Facis, Model FX-10, environment simulator. Measurement of the sample's dynamic photochromic response and color measurements were made using the same Zeiss spectrophotometer with fiber optic cables for light delivery from a tungsten halogen lamp through the sample. The collimated monitoring light beam from the fiber optic cable was maintained perpendicular to the test sample while passing through the sample and directed into a receiving fiber optic cable assembly attached to the spectrophotometer. The exact point of placement of the sample in the sample cell was where the activating xenon arc beam and the monitoring light beam intersected to form two concentric circles of light. The angle of incidence of the xenon arc beam at the sample placement point was ≈30° from perpendicular.

(26) Response measurements, in terms of a change in optical density (*OD) from the unactivated or bleached state to the activated or colored state were determined by establishing the initial unactivated transmittance, opening the shutter from the Xenon lamp(s) and measuring the transmittance through activation at selected intervals of time. Change in optical density was determined according to the formula: *OD=log.sub.10(% T.sub.b/% T.sub.a), where % T.sub.b is the percent transmittance in the bleached state and % T.sub.a is the percent transmittance in the activated state. Optical density measurements were based on photopic optical density.

(27) The results of the microhardness and photochromic performance are shown in Table 9. The ΔOD at saturation is after 15 minutes of activation and the Fade Half Life (“T½”) value is the time interval in seconds for the ΔOD of the activated form of the photochromic material in the coating to reach one half the fifteen-minute ΔOD at 73.4° F. (23° C.), after removal of the activating light source.

(28) TABLE-US-00009 TABLE 9 NCO:OH Fischer microhardness T½ @ Photopic Example (OH = 1.0) (N/mm.sup.2) (seconds) 6 1.6 28 131 7 2.5 35 109 8 14.4 11 97 9 8.1 28 101 10 18.9 17 93 11 12.6 19 103 12 5.3 43 104 13 6.3 28 100 14 7.7 18 99 15 9.2 30 101 16 15.5 24 77

(29) As shown in Table 9, the photochromic coatings of Examples 8-16, which had a NCO:OH ratio of at least 4:1, exhibited superior photochromic performance with good hardness as compared to Comparative Examples 6 and 7, which had a NCO:OH ratio of less than 4:1.

EXAMPLE 19

Dynamic Mechanical Analysis

(30) Examples 6, 7, 9, and 16 were evaluated for dynamic mechanical analysis (DMA) using TA Instruments 2980 DMA unit in tension film mode. Amplitude was set at 20 μm, preload force of 0.01N, force track of 150% and frequency of 1 Hz. The temperature cycle chosen was −100 to 175° C. with a heating rate of 3° C./minute. Clamping force of 20 cNm was also used. Sample dimensions were 15 mm×6.4 mm with a thickness of 20-30 μm. The DMA results are shown in Table 10.

(31) TABLE-US-00010 TABLE 10 Peak 1 Peak 2 Fade Tan Delta Peak 1 Tan Delta Peak 2 Phase T½ Example (Tg, ° C.) Description (Tg, ° C.) Description Separation (sec.) 6 55 Major Peak −14 Very Minor Shoulder Very Slight 131 7 71 Major Peak −20 Minor Shoulder Slight 109 9 70 Major Peak −19 Separate Peak Moderate 101 16 93 Major Peak −68 Major Peak Substantial 77

(32) Dynamic mechanical analysis (DMA) can relate to the miscibility of the polymer blend. Two separate Tg peaks means a heterogeneous system in which the two polymers exist as separate phases. One single peak indicates that the polymer blend is completely miscible. There is a continuum between these two states. As shown in Table 10, Comparative Examples 6 and 7 show a shoulder as the low Tg material. Example 9 shows a much more pronounced peak at a low Tg indicating increased separation between the hard and soft polymer domains. Example 16 shows an even greater degree of phase separation as evidenced by the increased separation of its two peaks.

(33) The present invention is also directed to the following clauses.

(34) Clause 1: A curable photochromic composition comprising: (a) a first component comprising a first compound having at least two active hydrogen-functional groups and an active hydrogen-functional group equivalent weight of at least 1000; (b) a second component comprising at least one of a polyisocyanate and a blocked polyisocyanate; and (c) at least one photochromic compound, wherein the ratio of total isocyanate and blocked isocyanate equivalents of the second component to total active hydrogen-functional group equivalents of the first component is at least 4:1.

(35) Clause 2: The curable photochromic composition of clause 1, further comprising: (d) a third component comprising a second compound having three or more active hydrogen-functional groups and an active hydrogen-functional group equivalent weight of less than or equal to 500, wherein the ratio of total isocyanate and blocked isocyanate equivalents of the second component to total active hydrogen-functional group equivalents of the first and third components is at least 4:1.

(36) Clause 3: The curable photochromic composition of clause 1, wherein the ratio of total isocyanate and blocked isocyanate equivalents of the second component to total active hydrogen-functional group equivalents of the first component is at least 5:1.

(37) Clause 4: The curable photochromic composition of clause 1, wherein the ratio of total isocyanate and blocked isocyanate equivalents of the second component to total active hydrogen-functional group equivalents of the first component is up to 50:1.

(38) Clause 5: The curable photochromic composition of any of clauses 1-4, wherein the second component (b) comprises a polyureadiisocyanate, a blocked polyureadiisocyanate, a polyurethanediisocyanate, a blocked polyurethanediisocyanate, a polythiourethanediisocyanate, a blocked polythiourethanediisocyanate, or combinations thereof.

(39) Clause 6: The curable photochromic composition of any of clauses 1-5, wherein the curable photochromic composition comprises a prepolymer comprising a reaction product of (a) and (b).

(40) Clause 7: The curable photochromic composition of any of clauses 1-6, wherein the first compound and second compound each independently comprise active hydrogen-functional groups chosen from hydroxyls, primary amines, secondary amines, thiols, or combinations thereof.

(41) Clause 8: The curable photochromic composition of any of clauses 1-7, wherein the first compound and/or the second compound each independently comprise a polyol.

(42) Clause 9: The curable photochromic composition of any of clauses 1-8, wherein the polyol of the first compound is independently selected from polyether polyols, polyester polyols, polycarbonate polyols, or combinations thereof.

(43) Clause 10: The curable photochromic composition of any of clauses 2-9, wherein the polyol of the second compound comprises an acrylic polyol.

(44) Clause 11: The curable photochromic composition of any of clauses 1-10, wherein the at least one photochromic compound is an organic photochromic material selected from photochromic spirooxazines, benzopyrans, naphthopyrans, indenonaphthopyrans, fulgides, metal dithizonates, diarylethenes, or combinations thereof.

(45) Clause 12: The curable photochromic composition of any of clauses 1-11, wherein when applied to a substrate and cured to form a coating, the first component forms a plurality of soft segment domains and the second component forms a plurality of hard segment domains.

(46) Clause 13: The curable photochromic composition of any of clauses 2-12, wherein when applied to a substrate and cured to form a coating, the first component forms a plurality of soft segment domains and the second and third components together form a plurality of hard segment domains.

(47) Clause 14: The curable photochromic composition of any of clauses 12-13, wherein the plurality of soft segment domains have a Tg of −10° C. to −150° C., and the plurality of hard segment domains have a Tg of 0° C. to 150° C.

(48) Clause 15: The curable photochromic composition of claim of any of clauses 12-14, wherein the plurality of soft segment domains each comprise a size of less than 300 nm.

(49) Clause 16: The curable photochromic composition of any of clauses 12-14, wherein the plurality of soft segment domains each comprise a size of less than 100 nm.

(50) Clause 17: The curable photochromic composition of claim of any of clauses 12-16, wherein the at least one photochromic compound at least partially resides in the plurality of soft segment domains formed from the first component.

(51) Clause 18: The curable photochromic composition of any of clauses 1-17, wherein when applied to a substrate and cured to form a coating, the coating exhibits a Fischer microhardness of at least 10 N/mm.sup.2.

(52) Clause 19: A photochromic article comprising: (a) a substrate; and (b) at least one coating layer formed from the composition of any of clauses 1-18 residing over at least a portion of the substrate.

(53) Clause 20: The photochromic article of clause 19, wherein the substrate is an optical substrate.

(54) Clause 21: The photochromic article of any of clauses 19-20, wherein the ratio of total isocyanate and blocked isocyanate equivalents of the second component to total active hydrogen-functional group equivalents of the first component is at least 5:1.

(55) Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.