Composition comprising epoxy resin with constrained aromatic rings and photobase

Abstract

A composition is described comprising an epoxy resin that is a liquid at 25°C; an epoxy resin comprising constrained aromatic rings; an epoxy curative comprising at least two thiol groups; and a photobase. The composition is suitable for use as a coating, structural adhesive, or molded part. Also described are methods and articles.

Description

[0001] COMPOSITION COMPRISING EPOXY RESIN WITH CONSTRAINED AROMATIC RINGS AND PHOTOBASE

[0002] Summary

[0003] In one embodiment, a composition is described comprising an epoxy resin that is a liquid at 25°C; an epoxy resin comprising constrained aromatic rings; an epoxy curative comprising at least two thiol groups; and a photobase. Illustrative epoxy resins comprising constrained aromatic include those having a naphthyl or fluorene moiety. The epoxy resin comprising constrained aromatic rings can advantageously dissolve photobase salts. The composition is suitable for use as a coating, structural adhesive, or molded part.

[0004] In another embodiment, a method of use is described comprising providing a curable epoxy composition as described herein; applying the composition to a substrate; and allowing the composition to cure. Preferably the curing comprises exposing the composition to light with a wavelength within the range of 350 nm to 500 nm.

[0005] In another embodiment, an article is described comprising a substrate and a cured epoxy coating or structural epoxy adhesive, as described herein.

[0006] In another embodiment, a composition is described comprising an epoxy resin comprising constrained aromatic rings as a carrier material for a photobase.

[0007] Brief Description of the Drawings

[0008] FIG. 1 is a plot of a DMA temperature ramp depicting storage modulus and tan delta for a cured (e.g. adhesive) composition.

[0009] Detailed Description

[0010] Photobase and Other Catalysts

[0011] The composition described herein comprises a photobase, optionally in combination with other catalysts. A photobase refers to a chemical compound that decomposes when irradiated with light, so that it generates a free base, such as a tertiary amine. One illustrative reaction scheme is depicted as follows: Photobase

[0012]

[0013] The generation of free base will proceed without sensitizer when the wavelength of light used is light that is absorbed by the photobase molecule. For example, PLB-SCD-090 photobase generates free base with ultraviolet light (e.g. D-BULB example).

[0014] The generated base can act as a catalyst for acuring reaction of an epoxy resin. The catalyst can directly react with the oxirane ring of the epoxy resin, can catalyze or accelerate the reaction of the polythiol compound with the epoxy resin, or can catalyze or accelerate the self-polymerization of the epoxy resin.

[0015] Various photobases are known and described in the literature. See for example US 9933701; US2011 / 00285585; and US9150723; incorporated herein by reference.

[0016] The photobase has the general formula:

[0017] (I) Ar-L-B; or (II) [Ar-L-B]+[A]’

[0018] wherein Ar is an aromatic group;

[0019] L is a covalent bond or (e.g. divalent) organic linking group;

[0020] B is a nitrogen-containing group;

[0021] and A’ is an anion of a salt.

[0022] Examples of Ar include phenyl, naphthyl, anthryl, phenanthryl, anthraquinonyl, xanthenyl, thianthrenyl, phenoxathiinyl, chromanyl, isochromanyl, coumarinyl, xanthonyl, and thioxanthonyl.

[0023] In some embodiments, the aromatic group may further comprise substituents such as an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, an alkynyl group having 2 to 18 carbon atoms, an aryl group having 6 to 14 carbon atoms, a nitro group, a hydroxyl group, a cyano group, an alkoxy, an aryl oxy, an acyl group, an acyloxy group, an alkylthio group or arylthio group, an arnino, or halogen.

[0024] When the photobase is of the general formula I, the nitrogen-containing group typically has a general formula as follows:

[0025]

[0026] I-A I-B I-C I-D I-E When a photobase is of the general formula II, the nitrogen-containing group typically has a general formula as follows:

[0027] N

[0028] ArL

[0029]

[0030] I-F I-G I-H I-I

[0031]

[0032] L is typically alkylene having 1 to 18 carbon atoms or an arylene with 6 to 14 carbon atoms; that optionally comprise substituents.

[0033] In some embodiments. A’ is an anion of a borate salt having the formula:

[0034] R2

[0035] Q+RI — B“— R3

[0036] I

[0037]

[0038] R4

[0039] wherein R!to R4are independently an alkyl group having 1 to 18 carbon atoms or an aromatic group, such as phenyl; and Q+is a monovalent onium cation .

[0040] In some embodiments, the photobase is capable of generating amines upon exposure to light with a wavelength within the range of 350 nm to 500 nm. In some embodiments, the photobase is capable of generating amines upon exposure to light with a wavelength within the range of 440 nm to 500 nm, or in other words blue light.

[0041] In some embodiments, the photobase(s) are the sole (e.g. nitrogen-containing) catalyst of the total epoxy composition. The epoxy compositions described here can be cured in short durations of time at room temperature. In other embodiments, the epoxy composition may comprise additional catalysts, such as heat activated (e.g. nitrogen-containing) catalysts for composition that is at least partially cured by exposure to light, followed by thermal curing. In other embodiments, the curable epoxy composition may comprise other (e.g. nitrogencontaining) catalysts in combination with or in the absence of photobase(s).

[0042] Suitable catalyst include for example an amine having the formula NR1R2R3, R1and

[0043] R2independently represent H or a monovalent organic group having from 1 to 18 carbon atoms and may contain hetero atoms such as O and N (e.g., methyl, ethyl, propyl, butyl, isobutyl, ethoxyethyl, pentyl, hexyl, cyclohexyl, phenyl, 2,4-dimethylphenyl, octyl, decyl, hexadecyl, or octadecyl); R3represents a monovalent organic group having from 2 to 18 carbon atoms and may contain hetero atoms such as O and N (e.g., ethyl, propyl, butyl, isobutyl, ethoxyethyl, pentyl, hexyl, cyclohexyl, phenyl, 2,4-dimethylphenyl, octyl, decyl, hexadecyl, or octadecyl); or R2and R3taken together represent a divalent organic group having from 2 to 18 carbon atoms (e.g., ethylene, propane-1, 3-diyl, butane- 1,4-diyl, pentane-l,5-diyl, hexane- 1 ,6-diyl, heptane- 1 ,7-diyl, — CH2CH2OCH2CH2 — , or 2, 2-diphenylpropane-l, 3-diyl); or R1, R2, and R3taken together represent a trivalent organic group having from 2 to 18 carbon atoms (e.g., nonane-1 ,5,9-triyl and 3-(ethyl-2'-yl)pentan-l,5-diyl).

[0044] Specific examples include triethylamine; l,4-diaza[2.2.2]bicyclooctane (DABCO); aniline; N,N-dimethylaniline; 2,6-dimethylaniline; 1 -methylimidazole; pyridine; N,N-dimethyl-4-aminopyridine; benzylamine; dicyclohexylamine; N,N-dicyclohexylmethylamine; 4-methylmorpholine; cyclohexylamine; piperidine; morpholine; l-[bis[3-(dimethylamino)propyl]amino]-2-propanol; 1-methylpiperidine; quinuclidine; 2,2,6,6-tetramethylpiperidine; 1-methylpyrrolidine; N-benzyhnethylamine; 1,2,2,6,6-pentamethylpiperidine; 2-{[2-(dimethylamino)ethyl]methylamino}ethanol; 3-dimethylamino-l-propanol; and 2-[2-(dimethylamino)ethoxy]ethanol.

[0045] Commercially available catalysts include a trifunctional amine-terminated polyether available as JEFF AMINE T-403 Polyetheramine and difunctional amine-terminated polyether available as

[0046] JEFF AMINE THF-100 Polyetheramine, both from Huntsman Corp.; 1,3-benzenedimethanamine, reaction products with epichlorohydrin, available as GASKAMINE 328; and aspartic acid, secondary diamine available as Desmophen NH1220 from Covestro LLC.

[0047] Other catalysts include substituted pyridines having 5 to 23 carbon atoms. Substituted pyridines include chloropyridine, bromopyridine, fluoropyridine, iodopyridine, methylpyridine, ethylpyridine, propylpyridine, tert-butylpyridine, phenylpyridine, methoxypyridine, ethoxypyridine, phenoxypyridine, nitropyridine, dichloropyridine, dibromopyridine, dimethylpyridine, diethylpyridine, di-tert-butylpyridine, methyl nicotinate, ethyl nicotinate, methyl picolinate, ethyl picolinate, methyl isonicotinate, cyanopyridine, and trimethylpyridine.

[0048] In some embodiments, the curable epoxy composition comprises at least 0.25, 0.50, 0.75, 1.0, 1.25, 1.50, 1.75 or 2 wt.% of photobase catalyst based on the total weight of the (adhesive, coating, or molding) composition. In some embodiments, the curable epoxy composition comprises no greater than 8, 7, 6, 5, 4, 3, 2, or 1 wt.% of photobase catalyst. A single photobase catalyst or combinations of two or more catalysts wherein at least one is a photobases can be utilized.

[0049] 25 °C for 1 day, 7 days, or greater than 14 days. In some cases when soluble, the photobase is not a separated (e.g. crystal) solid after storage at -20 °C for 10 day, 14 days, or greater than 21 days. Epoxy Resin Comprising Constrained Aromatic Rings

[0050] The composition comprises an epoxy resin comprising constrained aromatic rings.

[0051] In some embodiments, the epoxy resin comprises at least two aromatic rings fused to each other. A fused aromatic ring is one which shares one side of the ring. The fused aromatic ring typically comprises a moiety selected from naphthalene, anthracene or phenanthrene, optionally comprising nitrogen substitutions.

[0052]

[0053] Naphthalene Anthracene Phenanthrene Fluorene

[0054] Representative epoxy resins include for example:

[0055]

[0056] HP-4770 HP-4700

[0057] Such epoxy resins are commercially available from Mitsubishi jER (e.g., YX-8800), DIC (e.g., EPICLON HP-4032, HP-4700 and HP-4770).

[0058] In other embodiments, the epoxy resin comprises at least two aromatic rings and at least two carbon atoms of each ring are bonded to each other with a linking atom or linking group.

[0059] Representative epoxy resins includes epoxy resins that comprises a fluorene moiety.

[0060] A representative epoxy resin has the formula:

[0061]

[0062] wherein L is a Cl to C12 alkylene group optionally substituted with an alkoxy group. In some embodiments, L is a Cl to C4 alkylene group optionally substituted with an alkoxy group.

[0063] Such epoxy resins are commercially available from Osaka Gas Chemicals as the trade designations OGSOL PG-100, CG-500, EG-200, EG-280. In some embodiments, compositions comprising an epoxy resin with a fluorene moiety have a greater depth of cure than epoxy resins having a naphthyl moiety (e.g. HP4032D).

[0064] In typical embodiments, the epoxy resin comprising constrained rings is a solid at 25°C. In the case of epoxy resin (e.g. adhesives or coatings) that are liquids at 25°C, the composition typically further comprises one or more second epoxy resin(s) that are liquid at 25°C. The epoxy resin comprising constrained rings is soluble in the second liquid epoxy resin(s)

[0065] For ease of adding the photobase catalyst(s) to an epoxy resin composition, the manufacturer of the photobase catalyst(s) may prepare and sell a premix of the photobase catalyst(s) dissolved in a liquid epoxy resin, wherein the liquid comprises a dissolved (e.g., solid) epoxy resin with constrained aromatic rings. Thus, the (e.g., solid) epoxy resin with constrained rings may be characterized as a carrier material for the photobase catalyst(s).

[0066] In another embodiment, the liquid comprising the dissolved (e.g., solids) epoxy resin with constrained aromatic rings comprising the dissolved photobase catalyst(s) may be a (e.g. second) part of a two-part epoxy composition.

[0067] In yet another embodiment, the liquid comprising the (e.g., solid) epoxy resin with constrained aromatic rings comprising the dissolved photobase catalyst(s) may be a one-part epoxy composition further comprising a thiol curative.

[0068] When the composition is a two-part epoxy composition, the first and second part of the curable epoxy composition each have a viscosity and the viscosity of the first part differs from the viscosity of the second part by no greater than 10X, 5X or 3X of the viscosity of the lower viscosity part.

[0069] The viscosity’ at room temperature (23°C) of the first, second part, and initial viscosity of the combination thereof of the curable epoxy composition is typically at least 500, 1000, 1500, 2000, 2500, or 30,000 mPas. The viscosity is typically no greater than 75,000; 50,000; 25,000; or 10,000 mPas. However, highly filled curable epoxy compositions that are typically not dispensed with a hand-held apparatus may have a considerably higher viscosity, e.g. ranging up to 100,000 or 150,000 mPas or greater.

[0070] The weight ratio of epoxy resin(s) comprising constrained aromatic rings to photobase(s) is typically approximately at least 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1. In some embodiments, it is no greater than 10:1, 9:1, 8:1, 7:1, 6: 1, 5:1, 4:1, or 3:1.

[0071] In some embodiments, the curable or cured epoxy composition comprises at least 5, 10, 15, 20, 25 wt.% of epoxy resin(s) comprising constrained aromatic rings, based on a total weight of the organic components of the composition. In some embodiments, the curable or cured epoxy composition comprises no greater than 25, 20, 15, or 10 wt.% of epoxy resin(s) comprising constrained aromatic rings.

[0072] Other Epoxy Resins

[0073] In some embodiments, the epoxy composition described herein further comprises other epoxy resins (i.e., that lack constrained aromatic rings). For example, when the other epoxy resin comprising lack constrained aromatic rings is a solid, at least one second liquid epoxy resin is included in the epoxy resin composition (e.g. in the second part with the photobase and optionally in the first part). In some embodiments, additional epoxy resins are selected to reduce the hardness contributed by the aromatic epoxy resins.

[0074] The other epoxy resin component comprises an epoxy resin that has at least two epoxy functional groups (i.e., oxirane groups) per molecule. As used herein, the term oxirane group refers to the following divalent group.

[0075] H H

[0076]

[0077] 0

[0078] The asterisks denote a site of attachment of the oxirane group to another group. If an oxirane group is at the terminal position of the epoxy resin, the oxirane group is typically bonded to a hydrogen atom.

[0079] H H

[0080]

[0081] 0

[0082] This terminal oxirane group is often part of a glycidyl group.

[0083] H H

[0084] *— OCI l2J H

[0085]

[0086] 0

[0087] The epoxy resin component can include a single epoxy resin or mixture of epoxy resins (e.g., monomeric, oligomeric, or polymeric compounds). The epoxy resins are selected to provide the desired viscosity characteristics before curing and to provide the desired (e.g. mechanical) properties after curing. When the epoxy resin includes a mixture of materials, at least one of the epoxy resins of the mixture comprises at least two oxirane groups per molecule. For example, an epoxy resin can have 2 to 10, 2 to 6, or 2 to 4 oxirane groups per molecule.

[0088] The portion of the epoxy resin that is not an oxirane group (i.e., an epoxy resin compound minus the oxirane groups) can be aromatic, aliphatic, or a combination thereof and can be linear, branched, cyclic, or a combination thereof. The aromatic and aliphatic portions of the epoxy resin can include heteroatoms or other groups that are not reactive with the oxirane groups. That is, the epoxy resin can include halo groups, oxy groups such as in an ether linkage group, thio groups such as in a thio ether linkage group, carbonyl groups, carbonyloxy groups, carbonylimino groups, phosphono groups, sulfono groups, nitro groups, nitrile groups, and the like. The epoxy resin can also be a silicone-based material such as a polydiorganosiloxane-based material.

[0089] Although the epoxy resin can have any suitable molecular weight, the weight average molecular weight is usually at least 100 grams / mole, at least 150 grams / mole, at least 175 grams / mole, at least 200 grams / mole, at least 250 grams / mole, or at least 300 grams / mole. The weight average molecular weight can be up to 50,000 grams / mole or even higher for polymeric epoxy resins. The weight average molecular weight is often up to 40,000 grams / mole, up to 20,000 grams / mole, up to 10,000 grams / mole, up to 5,000 grams / mole, up to 3,000 grams / mole, or up to 1,000 grams / mole. For example, the weight average molecular weight can be in the range of 100 to 50,000 grams / mole, in the range of 100 to 20,000 grams / mole, in the range of 10 to 10,000 grams / mole, in the range of 100 to 5,000 grams / mole, in the range of 200 to 5,000 grams / mole, in the range of 100 to 2,000 grams / mole, in the range of 200 to 2,000 grams / mole, in the range of 100 to 1,000 grams / mole, or in the range of 200 to 1,000 grams / mole.

[0090] In some embodiments, the epoxy resin component comprises an epoxy resin that is a liquid at room temperature. In some embodiments, the epoxy resin component comprises an epoxy resin that is solid at room temperature that can be dissolved in one of the other components of the composition, such as a liquid epoxy resin.

[0091] The epoxy resin is typically a glycidyl ether. Exemplary glycidyl ethers can be of Formula (I).

[0092]

[0093] (I)

[0094] In Formula (I), group R1is a polyvalent group that is aromatic, aliphatic, or a combination thereof. Group R1can be linear, branched, cyclic, or a combination thereof. Group R1can optionally include halo groups, oxy groups, thio groups, carbonyl groups, carbonyloxy groups, carbonylimino groups, phosphono groups, sulfono groups, nitro groups, nitrile groups, and the like. Although the variable p can be any suitable integer greater than or equal to 2, p is often an integer in the range of 2 to 10, in the range of 2 to 6, or in the range of 2 to 4.

[0095] In some embodiments, the epoxy resin is a polyglycidyl ether of a polyhydric phenol, such as polyglycidyl ethers of bisphenol A, bisphenol F, bisphenol AD, catechol, and resorcinol. In this embodiment, the epoxy resin may be characterized as having aromatic moieties, such as a bisphenol moiety. In some embodiments, the epoxy resin is a reaction product of a polyhydric alcohol with epichlorohydrin. Exemplary polyhydric alcohols include butanediol, polyethylene glycol, and glycerin. In some embodiments, the epoxy resin is an epoxidized (poly)olefinic resin, epoxidized phenolic novolac resin, epoxidized cresol novolac resin, and cycloaliphatic epoxy resin. In some embodiments, the epoxy resin is a glycidyl ether ester, such as that which can be obtained by reacting a hydroxycarboxylic acid with epichlorohydrin, or a polyglycidyl ester, such as that which can be obtained by reacting a polycarboxylic acid with epichlorohydrin. In some embodiments, the epoxy resin is a urethane-modified epoxy resin. In other embodiments, the epoxy resin may lack polymeric material comprising the reaction product of a uretdione -containing material comprising a reaction product of a diisocyanate with itself and a hydroxyl-containing compound having more than one OH group, such as described in W02020 / 065438.

[0096] Various combinations of two or more epoxy resins can be used if desired.

[0097] In some exemplary epoxy resins of Formula (I), the variable p is equal to 2 (i.e., the epoxy resin is a diglycidyl ether) and R1includes an alkylene (i.e., an alkylene is a divalent radical of an alkane and can be referred to as an alkane-diyl), heteroalkylene (i.e., a heteroalkylene is a divalent radical of a heteroalkane and can be referred to as a heteroalkane-diyl), arylene (i.e., a divalent radical of an arene compound), or combination thereof. Suitable alkylene groups often have 1 to 20 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Suitable heteroalkylene groups often have 2 to 50 carbon atoms, 2 to 40 carbon atoms, 2 to 30 carbon atoms, 2 to 20 carbon atoms, 2 to 10 carbon atoms, or 2 to 6 carbon atoms with 1 to 10 heteroatoms, 1 to 6 heteroatoms, or 1 to 4 heteroatoms. The heteroatoms in the heteroalkylene can be selected from oxy, thio, or -NH- groups but are often oxy groups. Suitable arylene groups often have 6 to 18 carbon atoms or 6 to 12 carbon atoms. For example, the arylene can be phenylene, fluorenylene, or biphenylene. Group R1can further optionally include halo groups, oxy groups, thio groups, carbonyl groups, carbonyloxy groups, carbonylimino groups, phosphono groups, sulfono groups, nitro groups, nitrile groups, and the like. The variable p is usually an integer in the range of 2 to 4.

[0098] Some epoxy resins of Formula (I) are diglycidyl ethers where R1includes (a) an arylene group or (b) an arylene group in combination with an alkylene, heteroalkylene, or both. Group R1can further include optional groups such as halo groups, oxy groups, thio groups, carbonyl groups, carbonyloxy groups, carbonylimino groups, phosphono groups, sulfono groups, nitro groups, nitrile groups, and the like. These epoxy resins can be prepared, for example, by reacting an aromatic compound having at least two hydroxyl groups with an excess of epichlorohydrin. Examples of useful aromatic compounds having at least two hydroxyl groups include, but are not limited to, resorcinol, catechol, hydroquinone, p,p’-dihydroxydibenzyl, p,p’-dihydroxyphenylsulfone, p,p’ -dihydroxybenzophenone, 2,2 ’-dihydroxyphenyl sulfone, and p,p’ -dihydroxybenzophenone. Still other examples include the 2,2’, 2,3’, 2,4’, 3,3’, 3,4’, and 4,4’ isomers of dihydroxydiphenylmethane, dihydroxydiphenyldimethylmethane, dihydroxydiphenylethylmethylmethane, dihydroxydiphenylmethylpropylmethane, dihydroxydiphenylethylphenylmethane, dihydroxydiphenylpropylenphenylmethane, dihydroxydiphenylbutylphenylmethane, dihydroxydiphenyltolylethane, dihydroxydiphenyltolylmethylmethane, dihydroxydiphenyldicyclohexylmethane, and dihydroxydiphenylcyclohexane .

[0099] Some commercially available diglycidyl ether epoxy resins of Formula (I) are derived from bisphenol (e.g. bisphenol A is 4,4 ’-dihydroxydiphenylmethane). Examples include, but are not limited to, those available under the trade designation EPON (e.g., EPON 1510, EPON 1310, EPON 828, EPON 872, EPON 1001, EPON 1004, and EPON 2004) from Momentive Specialty Chemicals, Inc. (Columbus, OH), those available under the trade designation DER (e.g., DER 331, DER 332, DER 336, and DER 439) from Olin Epoxy Co. (St. Louis, MO), and those available under the trade designation EPICLON (e.g., EPICLON 850) from Dainippon Ink and Chemicals, Inc. (Parsippany, NJ). Other commercially available diglycidyl ether epoxy resins are derived from bisphenol F (i.e., bisphenol F is 2,2’-dihydroxydiphenylmethane). Examples include, but are not limited to, those available under the trade designation DER (e.g., DER 334) from Olin Epoxy Co. (St. Louis, MO), those available under the trade designation EPICLON (e.g., EPICLON 830) from Dainippon Ink and Chemicals, Inc. (Parsippany, NJ), and those available under the trade designation ARALDITE (e.g., ARALDITE 281) from Huntsman Corporation (The Woodlands, TX).

[0100] Other epoxy resins of Formula (I) are diglycidyl ethers of a poly(alkylene oxide) diol. These epoxy resins also can be referred to as diglycidyl ethers of a poly(alkylene glycol) diol. The variable p is equal to 2 and R1is a heteroalkylene having oxygen heteroatoms. The poly(alkylene glycol) portion can be a copolymer or homopolymer and often includes alkylene units having 1 to 4 carbon atoms. Examples include, but are not limited to, diglycidyl ethers of polyethylene oxide) diol, diglycidyl ethers of polypropylene oxide) diol, and diglycidyl ethers of poly(tetramethylene oxide) diol. Epoxy resins of this type are commercially available from Polysciences, Inc. (Warrington, PA) such as those derived from a polyethylene oxide) diol or from a polypropylene oxide) diol having a weight average molecular weight of 400 grams / mole, about 600 grams / mole, or about 1000 grams / mole.

[0101] Still other epoxy resins of Formula (I) are diglycidyl ethers of an alkane diol (R1is an alkylene and the variable p is equal to 2). Examples include a diglycidyl ether of 1,4-dimethanol cyclohexyl, diglycidyl ether of 1,4-butanediol, and a diglycidyl ether of the cycloaliphatic diol formed from a hydrogenated bisphenol A such as those commercially available under the trade designation EPONEX (e.g., EPONEX 1510) from Hexion Specialty Chemicals, Inc. (Columbus, OH) and under the trade designation EP ALLOY (e.g., EP ALLOY 5001) from CVC Thermoset Specialties (Moorestown, NJ).

[0102] For some applications, the epoxy resins chosen for use in the curable coating compositions are novolac epoxy resins, which are glycidyl ethers of phenolic novolac resins. These resins can be prepared, for example, by reaction of phenols with an excess of formaldehyde in the presence of an acidic catalyst to produce the phenolic novolac resin. Novolac epoxy resins are then prepared by reacting the phenolic novolac resin with epichlorohydrin in the presence of sodium hydroxide. The resulting novolac epoxy resins typically have more than two oxirane groups and can be used to produce cured coating compositions with a high crosslinking density. The use of novolac epoxy resins can be particularly desirable in applications where corrosion resistance, water resistance, chemical resistance, or a combination thereof is desired. One such novolac epoxy resin is poly[(phenyl glycidyl ether)-co-formaldehyde] . Other suitable novolac resins are commercially available under the trade designation ARALDITE (e.g., ARALDITE GY289, ARALDITE EPN 1183, ARALDITE EP 1179, ARALDITE EPN 1139, and ARALDITE EPN 1138) from Huntsman Corporation (The Woodlands, TX), under the trade designation EP ALLOY (e.g., EP ALLOY 8230) from CVC Thermoset Specialties (Moorestown, NJ), and under the trade designation DEN (e.g., DEN 424 and DEN 431) from Olin Epoxy Co. (St. Louis, MO).

[0103] Yet other epoxy resins include silicone resins with at least two glycidyl groups and flame retardant epoxy resins with at least two glycidyl groups (e.g., a brominated bisphenol-type epoxy resin having at least two glycidyl groups such as that commercially available from Dow Chemical Co.

[0104] (Midland, MI) under the trade designation DER 580).

[0105] In some embodiments, the other epoxy resins can be selected to be a mixture that provides the desired viscosity or flow characteristics prior to curing. For example, the epoxy resin component comprises reactive diluents that include monofunctional or certain multifunctional epoxy resins. The reactive diluent typically has a viscosity which is lower than that of the epoxy resin having at least two epoxy groups. In some embodiments, the reactive diluent should have a viscosity less than 250 mPa s (cPs). Typical reactive diluents have only one functional group (i.e., oxirane group) such as various monoglycidyl ethers. Some exemplary monofunctional epoxy resins include, but are not limited to, those with an alkyl group having 6 to 28 carbon atoms, such as (C6-C28)alkyl glycidyl ethers, (C6-C28)fatty acid glycidyl esters, (C6-C28)alkylphenol glycidyl ethers, and combinations thereof. In some embodiments, a monofunctional epoxy resin is present in an amount up to 50 parts based on the total of the epoxy resin component.

[0106] In some embodiments, the curable or cured epoxy composition comprises at least 20, 25, 30, 35, 40, 45, or 60 wt.% of other epoxy resin(s), based on a total weight of the composition. In some embodiments, the curable or cured epoxy composition comprises no greater than 80, 75, 70, 65 or 60 wt.% of other epoxy resin(s), based on a total weight of the composition. In some embodiments, the first part and second part each comprise a portion of the total amount of other epoxy resins.

[0107] Thiol Epoxy Curative

[0108] In some embodiments, the epoxy composition comprises an epoxy curative comprising at least two thiol group or in other words a polythiol epoxy curative. When the composition is a two-part composition, the first part comprises the polythiol curative (i.e. separated from the photobase). A thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl or mercapto (-C-SH) group. Useful thiol-containing compounds are organic compounds having at least 2, 3, 4, 5, or 6 thiol groups. In some embodiments, a polythiol may be utilized in combination with a monothiol such as ethanethiol, 1-propanethiol, 1 -butanethiol, 6-mercapto-l -hexanol, 3 -mercapto- 1 -hexanol, 4-mercapto-4-methylpentan-2-ol, 3 -mercaptobutyl acetate, 8-mercapto-l -octanol, 9-mercapto-l -nonanol, 1 -nonanethiol, 1-decanethiol, and 3 -mercaptohexyl hexanoate. In some embodiments, the polythiol may be an alkylene, arylene, alkylarylene, arylalkylene, or alkylenearylalkylene having at least two mercaptan groups, wherein any of the alkylene, alkylarylene, arylalkylene, or alkylenearylalkylene are optionally interrupted by one or more oxa (i.e., -O-), thia (i.e., -S-), or imino groups (i.e., -NR3- wherein R3is a hydrocarbyl group or H), and optionally substituted by alkoxy or hydroxyl.

[0109] Examples of useful dithiols include C1-C12 alkyl polythiols such as 1,2-ethanedithiol, 1,2-propanedithiol, 1,3 -propanedithiol, 1,3-butanedithiol, 1,4-butanedithiol, 2,3-butanedithiol, 1,3-pentanedithiol, 1,5 -pentanedithiol, 1,6-hexanedithiol, 1, 3 -dimercapto-3 -methylbutane, dipentenedimercaptan, ethylcyclohexyldithiol (ECHDT), dimercaptodiethyl sulfide, methyl-substituted dimercaptodiethyl sulfide, dimethyl-substituted dimercaptodiethyl sulfide; dimercaptodioxaoctane, 1,5-dimercapto-3-oxapentane; (C6-C12) aromatic polythiols such as benzene- 1,2-dithiol, benzene- 1,3 -dithiol, benzene- 1,4-dithiol; tolylene-2,4-dithiol; p-xylenedithiol and 1,3,5-tris (mercaptomethyl)benzene.

[0110] Examples of polythiols having more than two mercaptan groups include propane-1, 2, 3-trithiol; 1,2-bis[(2-mercaptoethyl)thio]-3-mercaptopropane; tetrakis(7-mercapto-2,5-dithiaheptyl)methane; and trithiocyanuric acid.

[0111] Also useful are polythiols formed from the esterification of polyols with thiol-containing carboxylic acids or their derivatives. Examples of polythiols formed from the esterification of polyols with thiol-containing carboxylic acids or their derivatives include those made from the esterification reaction between thiogly colic acid or 3 -mercaptopropionic acid and several polyols to form the mercaptoacetates or mercaptopropionates, respectively.

[0112] Examples of polythiol compounds preferred because of relatively low odor level include, but are not limited to, esters of thioglycolic acid, a-mercaptopropionic acid, and P-mercaptopropionic acid with polyhydroxy compounds (polyols) such as diols (e.g., glycols), triols, tetraols, pentaols, and hexaols. Specific examples of such polythiols include, but are not limited to, ethylene glycol bis(thioglycolate), ethylene glycol bis( -mercaptopropionate), trimethylolpropane tris(thioglycolate), trimethylolpropane tris( -mercaptopropionate) and ethoxylated versions, pentaerythritol tetrakis(thioglycolate), pentaerythritol tetrakis( -mercaptopropionate), and tris(hydroxyethyl)isocyanurate tris(P-mercaptopropionate). However, in those applications where concerns about possible hydrolysis of the ester exists, these polyols are typically less desirable.

[0113] Examples of thiol epoxy curatives include trimethylolpropane tris(beta-mercaptopropionate) (TMPMP), trimethylolpropane tris(thioglycolate) (TMPMA), pentaerythritol tetrakis(thioglycolate), pentaerythritol tetrakis(beta-mercaptopropionate) (THIOCURE PETMP), dipentaerythritol poly(beta-mercaptopropionate), ethylene glycol bis(beta-mercaptopropionate), , (ethoxylated trimethylolpropane tri(3 -mercaptopropionate) such as ETTMP 1300 and ETTMP 700); glycol di(3 -mercaptopropionate) (GDMP); tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate) (TEMPIC), propylene glycol 3-mercaptopropionate (PPGMP) from Bruno Bock Chemische Fabrik GmbH & Co. KG, and polymeric polythiols such as polypropylene-ether glycol bis(P-mercaptopropionate), which is prepared from polypropylene-ether glycol (e.g., PLURACOL P201, Wyandotte Chemical Corp.) and P- mercaptopropionic acid by esterification. Other useful thiol epoxy curatives include “Multhiol Y-2”, “Multhiol Y-4”, and “Multhiol Y-3”, composed primarily pentaerythritol tripropanethiol, 2,2-bis(hydroxmethyl)- 1,3 -propanediol 3 -mercaptopropyl ether.

[0114] Suitable polythiols also include those prepared from esterification of polyols with thiol-containing carboxylic acids or their derivatives, those prepared from a ring-opening reaction of epoxides with H2S (or its equivalent), those prepared from the addition of H2S (or its equivalent) across carboncarbon double bonds, polysulfides, polythioethers, and polydiorganosiloxanes. Specifically, these include the 3 -mercaptopropionates (also referred to as P-mercaptopropionates) of ethylene glycol and trimethylolpropane (the former from Chemische Fabrik GmbH & Co. KG, the latter from Sigma-Aldrich); POLYMERCAPTAN 805C (mercaptanized castor oil); POLYMERCAPTAN 407 (mercaptohydroxy soybean oil) from Chevron Phillips Chemical Co. LLP, and CAPCURE, specifically CAPCURE 3-800 (a polyoxyalkylenetriol with mercapto end groups of the structure R3[O(C3H6O)nCH2CH(OH)CH2SH]3wherein R3represents an aliphatic hydrocarbon group having 1-12 carbon atoms and n is an integer from 1 to 25), from Gabriel Performance Products, Ashtabula, Ohio, and GPM-800, which is equivalent to CAPCURE 3-800, also from Gabriel Performance Products.

[0115] Examples of oligomeric or polymeric polythioethers useful for practicing the present disclosure are described, for example, in U.S. Pat. Nos. 4,366,307 (Singh et al.), 4,609,762 (Morris et al.), 5,225,472 (Cameron et al.), 5,912,319 (Zook et al.), 5,959,071 (DeMoss et al.), 6,172,179 (Zook et al.), and 6,509,418 (Zook et al.).

[0116] In some embodiments, the polythiol is oligomeric or polymeric. Examples of useful oligomeric or polymeric polythiols include polythioethers and polysulfides. Polythioethers include thioether linkages (i.e., — S — ) in their backbone structures. Polysulfides include disulfide linkages (i.e., — S — S — ) in their backbone structures.

[0117] Polythioethers can be prepared, for example, by reacting dithiols with dienes, diynes, divinyl ethers, diallyl ethers, ene-ynes, alkynes, or combinations of these under free-radical conditions. Useful dithiols include any of the dithiols listed above. Examples of suitable divinyl ethers include divinyl ether, ethylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, cyclohexanedimethanol divinyl ether, polytetrahydrofuryl divinyl ether, and combinations of any of these. Useful divinyl ethers of formula CH2=CHO(R8O)mCH=CH2, in which m is a number from 0 to 10, and R8is C2to Cg branched alkylene. Such compounds can be prepared by reacting a polyhydroxy compound with acetylene.

[0118] Examples of compounds of this type include compounds in which R8is an alkyl-substituted methylene group such as — CH(CH3) — (e.g., those obtained from BASF, Florham Park, N.J., as “PLURIOL”, for which R8is ethylene and m is 3.8) or an alkyl-substituted ethylene (e.g., — CH2CH(CH3) — such as those obtained from International Specialty Products ofWayne, N.J., as “DPE” (e.g., DPE-2 and DPE-3). Examples of other suitable dienes, diynes, and diallyl ethers include 4-vinyl-l -cyclohexene, 1,5-cyclooctadiene, 1,6-heptadiyne, 1,7-octadiyne, and diallyl phthalate. Small amounts of trifunctional compounds (e.g., triallyl-1, 3, 5-triazine-2, 4, 6-trione, 2,4,6-triallyloxy-l,3,5-triazine) may also be useful in the preparation of oligomers.

[0119] Examples of oligomeric or polymeric polythioethers useful for practicing the present disclosure are described, for example, in U.S. Pat. No. 4,366,307 (Singh et al.), U.S. Pat. No. 4,609,762 (Morris et al.), U.S. Pat. No. 5,225,472 (Cameron et al.), U.S. Pat. No. 5,912,319 (Zook et al.), U.S. Pat. No.

[0120] 5,959,071 (DeMoss et al.), U.S. Pat. No. 6,172,179 (Zook et al.), and U.S. Pat. No. 6,509,418 (Zook et al.). In some embodiments, the polythioether is represented by formula HSR9[S(CH2)2O[R10O]m(CH2)2SR9]nSH, wherein each R9and R10is independently a C2-6 alkylene, wherein alkylene may be straight-chain or branched, Cg-8 cycloalkylene, Cg-io alkylcycloalkylene, — [(CH2)pX]q(CH2)rin which at least one — CH2 — is optionally substituted with a methyl group, X is one selected from the group consisting of O, S and — NR11— , where R11denotes hydrogen or methyl, m is a number from 0 to 10, n is a number from 1 to 60, p is an integer from 2 to 6, q is an integer from 1 to 5, and r is an integer from 2 to 10. Polythioethers with more than two mercaptan groups may also be useful.

[0121] Polythioethers can also be prepared, for example, by reacting dithiols with diepoxides, which may be carried out by stirring at room temperature, optionally in the presence of a tertiary amine catalyst (e.g., l,4-diazabicyclo[2.2.2]octane (DABCO)). Useful dithiols include any of those described above. Useful epoxides can be any of those having two epoxide groups. In some embodiments, the diepoxide is a bisphenol diglycidyl ether, wherein the bisphenol (i.e., — OCgHsCFECgHsO — ) may be unsubstituted (e.g., bisphenol F), or either of the phenyl rings or the methylene group may be substituted by halogen (e.g., fluoro, chloro, bromo, iodo), methyl, trifluoromethyl, or hydroxymethyl. Polythioethers prepared from dithiols and diepoxides have pendent hydroxyl groups and can have structural repeating units represented by formula — SR9SCH2CH(OH)CH2OCgH5CH2CgH5OCH2CH(OH)CH2SR9S — , wherein R9is as defined above, and the bisphenol (i.e., — OCgHsCFECgHsO — ) may be unsubstituted (e.g., bisphenol F), or either of the phenyl rings or the methylene group may be substituted by halogen (e.g., fluoro, chloro, bromo, iodo), methyl, trifluoromethyl, or hydroxymethyl. Mercaptan terminated polythioethers of this type can also be reacted with any of the dienes, diynes, divinyl ethers, diallyl ethers, and ene-ynes listed above under free-radical polymerization conditions.

[0122] Other useful polythiols can be formed from the addition of hydrogen sulfide (H2S) (or its equivalent) across carbon-carbon double bonds. For example, dipentene and triglycerides which have been reacted with H2S (or its equivalent). Specific examples include dipentene dimercaptan and those polythiols available as POEYMERCAPTAN 358 (mercaptanized soybean oil) and POLYMERCAPTAN 805C (mercaptanized castor oil) from Chevron Phillips Chemical Co. LLP. At least for some applications, the preferred polythiols are POLYMERCAPTAN 358 and 805C since they are produced from largely renewable materials, i.e., the triglycerides, soybean oil and castor oil, and have relatively low odor in comparison to many thiols. Useful triglycerides have at least 2 sites of unsaturation, i.e., carbon-carbon double bonds, per molecule on average, and sufficient sites are converted to result in at least 2 thiols per molecule on average. In the case of soybean oil, this requires a conversion of approximately 42 percent or greater of the carbon-carbon double bonds, and in the case of castor oil this requires a conversion of approximately 66 percent or greater of the carbon-carbon double bonds.

[0123] Typically, higher conversion is preferred, and POLYMERCAPTAN 358 and 805C can be obtained with conversions greater than approximately 60 percent and 95 percent, respectively. Useful polythiols of this type also include those derived from the reaction of ELS (or its equivalent) with the glycidyl ethers of bisphenol A epoxy resins, bisphenol F epoxy resins, and novolak epoxy resins. A preferred polythiol of this type is QX11, derived from bisphenol A epoxy resin, from Japan Epoxy Resins (JER) as EPOMATE. Other polythiols suitable include those available as EPOMATE QX10 and EPOMATE QX20 from JER.

[0124] Other useful polythiols are polysulfides that contain thiol groups such as those available as THIOKOL LP-2, LP-3, LP-12, LP-31, LP-32, LP-33, LP-977, and LP-980 from Toray Fine Chemicals Co., Ltd., and polythioether oligomers and polymers such as those described in PCT Publ. No. WO 2016130673 Al (DeMoss et al.).

[0125] In some embodiments, the curable epoxy composition comprises other (i.e. non-thiol) curatives or other curatives in combination with a thiol curative. In some embodiments, the addition curative is a quaternary phosphonium salt. Examples of the quaternary phosphonium salt include tetraethylphosphonium bromide, tributylmethylphosphonium iodide, tetraethylphosphonium hexafluorophosphate, tetraethylphosphonium tetrafluoroborate, tributyl(cyanomethyl)phosphonium chloride, tetrakis(hydroxymethyl)phosphonium chloride, tetrabutylphosphonium hydroxide, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tetrakis(hydroxymethyl)phosphonium sulfate, tributyl-n-octylphosphonium bromide, tetra-n-octylphosphonium bromide, tetrabutylphosphonium tetrafluoroborate, tetrabutylphosphonium hexafluorophosphate, tributyldodecylphosphonium bromide, tributylhexadecylphosphonium bromide, trihexyl(tetradecyl)phosphonium dicyanamide, methyltriphenylphosphonium iodide, methyltriphenylphosphonium bromide, methyltriphenylphosphonium chloride, tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide, tetraphenylphosphonium bromide, tetraphenylphosphonium chloride, tetraphenylphosphonium iodide, (bromomethyl)triphenylphosphonium bromide, (chloromethyl)triphenylphosphonium chloride, (cyanomethyl)triphenylphosphonium chloride, ethyltriphenylphosphonium bromide, ethyltriphenylphosphonium iodide, isopropyltriphenylphosphonium iodide, triphenylvinylphosphonium bromide, allyltriphenylphosphonium bromide, allyltriphenylphosphonium chloride, butyltriphenylphosphonium bromide, (formylmethyl)triphenyl chloride, (methoxymethyl)triphenylphosphonium chloride, triphenylpropylphosphonium bromide, triphenylpropargylphosphonium bromide, amyltriphenylphosphonium bromide, acetonyltriphenylphosphonium chloride, benzyltriphenylphosphonium chloride, 3-bromopropyltriphenylphosphonium bromide, benzyltriphenylphosphonium bromide, cyclopropyltriphenylphosphonium bromide, 2-dimethylaminoethyltriphenylphosphonium bromide, hexyltriphenylphosphonium bromide, heptyltriphenylphosphonium bromide, tetraphenylphosphonium tetraphenylborate, (3-trimethylsilyl-2-propyl)triphenylphosphonium bromide, triphenyl(tetradecyl)phosphonium bromide, (2 -trimethylsilylethyl) triphenylphosphoniu m iodide, tetrabutylphosphonium tetraphenylborate, tributyl(l,3-dioxan-2-ylmethyl)phosphonium bromide, trans-2- butane- l,4-bis(triphenylphosphonium chloride), (tert-butoxy carbonyl methyl)triphenylphosphonium bromide, (4-bromobenzyl)triphenylphosphonium bromide, cinnamyltriphenylphosphonium bromide, (4-chlorobenzyl)triphenylphosphonium chloride, (3-carboxypropyl)triphenylphosphonium bromide, (2-chlorobenzyl)triphenylphosphonium chloride, ethoxycarbonyl methyl(triphenyl)phosphonium triphenyl)phosphonium bromide, methoxycarbonyl methyl(triphenyl)phosphonium triphenyl)phosphonium bromide, (l-naphthylmethyl)triphenylphosphonium chloride, phenacyltriphenylphosphonium bromide, 2-(trimethylsilyl)ethoxy methyltriphenylphosphonium chloride, tetraphenylphosphonium tetra-p-tolyl borate, 4-(carboxybutyl)triphenylphosphonium bromide, (1,3-dioxan-2-yl)methyltriphenylphosphonium bromide, (2,4-dichlorobenzyl)triphenylphosphonium chloride, (3,4-dimethoxybenzyl)triphenylphosphonium bromide, 4-ethoxybenzyltriphenylphosphonium bromide, (2 -hydroxybenzyl) triphenylphosphonium bromide, (3-methoxybenzyl)triphenylphosphonium chloride, (4-nitrobenzyl)triphenylphosphonium bromide, 2-( 1 ,3-dioxan-2-yl)ethyltriphenylphosphonium bromide, 2-(l,3-dioxan-2-yl)ethyltriphenylphosphonium bromide, triphenyl(2-thienyhnethyl)phosphonium bromide, dodecyltributylphosphonium chloride, ethyltrioctylphosphonium bromide, hexadec yltributylphosphonium chloride, methyltributylphosphonium dimethylphosphate, methyltributylphosphonium iodide, tetraethylphosphonium bromide, tetraethylphosphonium hydroxide, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tetrabutylphosphonium o,o-diethylphosphorodithioate, tetrabutylphosphonium benzotriazolate, tetrabutylphosphonium tetraphenyl borate, triethylpentylphosphonium bromide, triethyloctylphosphonium bromide, triethylpentylphosphonium bis(trifluoromethylsulfonyl)imide, triethyloctylphosphonium bis(trifluoromethylsulfonyl)imide, and tri-n-butylmethylphosphonium bis (trifluoromethylsulfonyl) imide.

[0126] Preferred quaternary phosphonium salt can include methyltributylphosphonium dimethylphosphate and tetrabutylphosphonium o,o-diethylphosphorodithioate (e.g. HISHICOLIN™ and PX-4ET manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD.; and ethyltriphenylphosphonium bromide manufactured by Tokyo Chemical Industry Co., Ltd.

[0127] In some embodiments, the curable epoxy composition comprises at least 25, 30, or 35 wt. %, (e.g. thiol) epoxy curative, based on a total weight of the curable epoxy composition. In some embodiments, the curable epoxy composition typically comprises no greater than 70, 65, 60, 55, 50, 45, or 40 wt.%, (e.g. thiol) epoxy curative, based on a total weight of the curable epoxy composition. Combinations of two or more (e,g, polythiol) curatives can be used if desired.

[0128] The weight ratio of the epoxy component to the (e,g. thiol) epoxy curative typically ranges from 0.5:1 to 1.5:1. In some embodiments, the amount of epoxy component is greater than the amount of (e.g. thiol) epoxy curative. In this embodiment, the weight ratio of the epoxy component to the (e.g. thiol) epoxy curative is at least 1.1:1, 1.2:1, 1.3:1, 1;4:1, or 1.5:1. Sensitizer

[0129] The epoxy composition typically further comprises a sensitizer having a chromophore. The chromophore is typically a group such as benzophenone, fluorenone, xanthone, thioxanthone, coumarin, and anthraquinone.

[0130] In some embodiments, the sensitizer is a fluorenone compound, such as depicted as follows:

[0131]

[0132] In some embodiments, the sensitizer is a thioxanthone compound, such as depicted as follows:

[0133]

[0134] In some embodiments, the sensitizer is an anthraquinone compound, such as depicted as follows:

[0135]

[0136] The aromatic ring(s) of these chromophore may further comprise various substituents such as a halogen atom, a hydroxy group, a linear or branched alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, amino group, or combinations of such substituents. Various substituted fluorenone compounds, for use as a sensitizer, are described in US 9,150,723; incorporated here by reference.

[0137] In some embodiments, a single aromatic ring of the chromophore comprises a linear or branched alkyl group having 1 to 20 carbon atoms. In some embodiments, the alkyl group is a linear or branched methyl, ethyl, propyl, or butyl group. In some embodiments, the chromophore comprises -OR instead of the double bonded oxygen group. The R group is typically hydrogen or an alkyl group having 1 to 20 carbon atoms. In some embodiments, the R group has at least 2, 3, or 4 carbon atoms. In some embodiments, the R group has no greater than 16, 14, 12, 10, or 8 carbon atoms.

[0138] Some illustrative sensitizer compounds are depicted in the forthcoming examples. The curable epoxy composition may comprise a single sensitizer or a combination of sensitizers e.g., with different chromophores.

[0139] In some embodiments, the curable epoxy composition comprises at least 0.1, 0.2, or 0.25% sensitizer, based on a total weight of the curable epoxy composition. In some embodiments, the curable epoxy composition typically comprises no greater than 6, 5, 4, 3, 2, or 1 wt.% sensitizer, based on a total weight of the curable epoxy resin composition. In typical embodiments, the first part comprises the sensitizer together with the thiol epoxy curative and epoxy component.

[0140] Optional Component in the Curable Composition

[0141] The curable composition can include various optional components. In some embodiments, the composition further comprises a (meth)acrylate oligomer. The (meth)acrylate oligomer typically has a molecular weight of at least 1000, 2000, 3000, 4000, or 5000 g / mole. In some embodiments, the (meth)acrylate oligomer has a molecular weight no greater than 10,000, 9000, 8000, 7000, 6000, or 5000 g / mole. The molecular weight can be determined by Gel Permeation Chromatograpy, ASTM D6579-11 using polystyrene molecular weight standards and differential refractive index (dRI) detection. A suitable solvent, such as tetrahydrofuran (stabilized with 250 ppm BHT), can be used as the solvent and eluent.

[0142] The (meth)acrylate oligomer typically comprises at least two (meth)acrylate groups. In some embodiments, the (meth)acrylate oligomer is selected such that a homopolymer of the oligomer has a low glass transition temperature (Tg), i.e. no greater than 0, -10, -20, -30, -40, or -50°C. Hie Tg of a homopolymer of the (meth)acrylate oligomer may be at least -80°C, -70°C, or -60°C. The Tg of various (meth)acrylate oligomers is Apically reported by the supplier. Tire viscosity (e.g. at 60°C) can be indicative of the molecular weight.

[0143] The (meth)acrylate oligomer may be aromatic or aliphatic. Combinations of aromatic and aliphatic oligomers may be utilized.

[0144] In some embodiments, the (meth)acrylate oligomer is a urethane (meth)acrylate oligomer(s) Suitable examples of urethane (meth)acrylate oligomer(s) may be obtained from Arkema, King of Prussia, Pennsylvania, and marketed as CN1964 (aliphatic urethane dimethacrylate), CN1968 (low viscosity urethane methacrylate oligomer), CN310 (urethane acrylate oligomer), CN996 (aromatic polyester-based urethane diacrylate oligomer), CN8881, CN8888; SOLTECH LTD., Yangsan, South Korea, and marketed as SUA5371 (difimctional aliphatic urethane acrylate oligomer); Nippon Soda Co. Ltd., Chiyoda, Japan, and marketed as TE-2000 (polybutadiene urethane methacrylate), TEAI-1000 (polybutadiene urethane acrylate); Dymax, Torrington, Connecticut, and marketed as BR-3747AE (aliphatic polyether urethane acrylate), BRC-843S (hydrophobic urethane acrylate), BR640D (polybutadiene urethane acrylate); Allnex and marked as Ebecryl 4827 (urethane acrylate), Ebecryl 8402, Ebecryl 210 and combinations thereof.

[0145] The curable composition can include various optional additives. One such optional additive is a toughening agent. Toughening agents can be added to provide the desired overlap shear, peel resistance, and impact strength. Useful toughening agents are polymeric materials that may react with the epoxy resin and that may be cross-linked. Suitable toughening agents include polymeric compounds having both a rubbery phase and a thermoplastic phase or compounds which are capable of forming, with the epoxide resin, both a rubbery phase and a thermoplastic phase on curing. Polymers useful as toughening agents are preferably selected to inhibit cracking of the cured epoxy composition.

[0146] Some polymeric toughening agents that have both a rubbery phase and a thermoplastic phase are acrylic core-shell polymers wherein the core is an acrylic copolymer having a glass transition temperature below 0 °C. Such core polymers may include polybutyl acrylate, polyisooctyl acrylate, polybutadienepolystyrene in a shell comprised of an acrylic polymer having a glass transition temperature above 25 °C, such as polymethylmethacrylate. Commercially available core-shell polymers include those available as a dry powder under the trade designations ACRYLOID KM 323, ACRYLOID KM 330, and PARALOID BTA 731, from Dow Chemical Co., and KANE ACE B-564 from Kaneka Corporation (Osaka, Japan). These core-shell polymers may also be available as a predispersed blend with a diglycidyl ether of bisphenol A at, for example, a ratio of 12 to 37 parts by weight of the core-shell polymer and are available under the trade designations KANE ACE (e.g., KANE ACE MX 157, KANE ACE MX 257, and KANE ACE MX 125) from Kaneka Corporation (Japan).

[0147] Another class of polymeric toughening agents are carboxyl-terminated butadiene acrylonitrile compounds. Commercially available carboxyl-terminated butadiene acrylonitrile compounds include those available under the trade designations HYCAR (e.g., HYCAR 1300X8, HYCAR 1300X13, and HYCAR 1300X17) from Lubrizol Advanced Materials, Inc. (Cleveland, Ohio) and under the trade designation PARALOID (e.g., PARALOID EXL-2650) from Dow Chemical (Midland, MI).

[0148] Other polymeric toughening agents are graft polymers, which have both a rubbery phase and a thermoplastic phase, such as those disclosed in U.S. Pat. No. 3,496,250 (Czerwinski). These graft polymers have a rubbery backbone having grafted thereto thermoplastic polymer segments. Examples of such graft polymers include, for example, (meth)acrylate-butadiene-styrene, and acrylonitrile / butadiene-styrene polymers. The rubbery backbone is preferably prepared so as to constitute from 95 wt-% to 40 wt-% of the total graft polymer, so that the polymerized thermoplastic portion constitutes from 5 wt.% to 60 wt.% of the graft polymer.

[0149] Still other polymeric toughening agents are polyether sulfones such as those commercially available from BASF (Florham Park, NJ) under the trade designation ULTRASON (e.g., ULTRASON E 2020 P SR MICRO).

[0150] The curable composition can additionally contain a non-reactive plasticizer to modify rheological properties. Commercially available plasticizers include those available under the trade designation BENZOFLEX 131 from Eastman Chemical (Kingsport, TN), JAYFLEX DINA available from ExxonMobil Chemical (Houston, TX), and PLASTOMOLL (e.g., diisononyl adipate) from BASF (Florham Park, NJ). Other plasticizers include various phthalate esters such as diethyl phthalate, diisobutyl phthalate, dibutyl phthalate, diisoheptyl phthalate, dioctyl phthalate, diisooctyl phthalate, dinonyl phthalate, diisononyl phthalate, diisodecyl phthalate, and benzylbutyl phthalate; various adipate esters such as di-2-ethylhexyl adipate, dioctyl adipate, diisononyl adipate, and diisodecyl adipate; various phosphate esters such as tri-2-ethylhexyl phosphate, 2-ethylhexyl diphenyl phosphate, trioctylphosphate, and tricresyl phosphate; various trimellitate esters such as tris-2 -ethylhexyl trimellitate and trioctyl trimellitate; various sebacate and azelate esters; and various sulfonate esters. Other example plasticizers include polyester plasticizers that can be formed by a condensation reaction of propanediols or butanediols with adipic acid. Liquid plasticizers can also be utilized as the liquid carrier for the catalyst.

[0151] The curable composition optionally contains a flow control agent or thickener, to provide the desired rheological characteristics to the composition. Suitable flow control agents include fumed silica, such as treated fumed silica, available under the trade designation CAB-O-SIL TS 720, and untreated fumed silica available under the trade designation CAB-O-SIL M5, from Cabot Corp. (Alpharetta, GA).

[0152] In some embodiments, the curable composition optimally contains adhesion promoters to enhance the bond to the substrate. The specific type of adhesion promoter may vary depending upon the composition of the surface to which it will be adhered.

[0153] In some embodiments, the curable composition may comprise cure inhibitors such as acids or compounds hydrolysable to acids, including a) organic carboxylic acids, such as acetic acid, benzoic acid, salicylic acid, 2 -nitrobenzoic acid and lactic acid; b) organic sulfonic acids, such as methanesulfonic acid, p-toluenesulfonic acid and 4-dodecylbenzenesulfonic acid; c) sulfonic acid esters; d) inorganic acids, such as phosphoric acid; e) Lewis acid compounds, such as BE? amine complexes, SbFc, sulfonium compounds, bis-arene iron complexes; f) Bronsted acid compounds, such as pentafluoroantimonic acid complexes; and, e) mixtures ofthe aforementioned acids and acid esters.

[0154] Other examples of suitable cure inhibitors include barbituric acid derivatives, such as described in W02018109617; incorporated herein by reference. Herein, the barbituric acid "derivatives" include those barbituric acid compounds substituted at one or more ofthe 1, 3, and / or 5 positions, or at the 1 and / or 3 N positions and optionally at the 5 N position, with an aliphatic, cycloaliphatic, or aromatic group. Examples of suitable substituted barbituric acid derivatives include l-benzyl-5- phenylbarbituric acid, l-cycloheyl-5-ethylbarbituric acid (available from Chemische Fabrik Berg, Bitterfeld-Wolfen, Germany), 1,3-dimethylbarbituric acid (available from Alfa Aesar, Tewksbury, MA), and combinations thereof.

[0155] The curable composition optionally may also contain one or more conventional additives such as fdlers (e.g., aluminum powder, carbon black, glass bubbles, talc, clay, calcium carbonate, barium sulfate, titanium dioxide, silica such as fused silica, silicates, glass beads, wollastonite, and mica), colorants pigments and dyes, stabilizers including antioxidants, thermal stabilizers, hydrolysis stabilizers, and light stabilizers including UV stabililizers flexibilizers, reactive diluents, non-reactive diluents, (meth)acrylate monomers, fire retardants, antistatic materials, thermally and / or electrically conductive particles, and expanding agents including, for example, chemical blowing agents such as azodicarbonamide or expandable polymeric microspheres containing a hydrocarbon liquid, such as those sold under the trade designation EXPANCEL by Expancel Inc. (Duluth, GA). Particulate fillers can be in the form of flakes, rods, spheres, and the like. Additives are typically added in amounts to produce the desired effect in the resulting adhesive.

[0156] Conductive fillers include for example silver; copper; gold; palladium; platinum; nickel; gold or silver-coated nickel; carbon black; carbon fibre; graphite; aluminium; indium tin oxide; silver coated copper; silver coated aluminium; metallic coated glass spheres; metallic coated filler; metallic coated polymers; silver coated fibre; silver coated spheres; antimony doped tin oxide; conductive nanospheres; nano silver; nano aluminium; nano copper; nano nickel; carbon nanotubes; and mixtures thereof.

[0157] In some embodiments, the first part may comprise an electrolyte such as an ionic liquid such as described in WO2024 / 079548 and US patent application serial no. 18 / 631645; incorporated herein by reference. Compositions with electrolyte can be suitable for electrically debonding. In other embodiments, the composition comprises little or no electrolyte (e.g. less than 2, 1, 0.5 or 0.1 wt.%).

[0158] As the concentration of unreactive additive(s) increases, the percentage of reactive (e.g. epoxy) component decreases. At high concentrations of unreactive additives(s), the advantage of the volume ratio of the first part to second part ranging from 5: 1 to 20: 1 is less significant. In some embodiments, the total amount of unreactive additive(s) is no greater than 40, 35, 30, 25, 10, 5, or 1 wt.% of the first part, second part, or total composition.

[0159] The components of the first and second part are typically chosen such that each part and the mixture thereof is 100% solids, comprising little or no volatile organic solvent e.g. less than 5, 4, 3, 2, or 1 wt.% volatile organic solvent. Alternatively, one or both parts may comprise an organic solvent.

[0160] The amount and type of such additives may be selected by one skilled in the art, depending on the intended end use of the composition.

[0161] Methods of Making and Use

[0162] The two-part epoxy composition is typically manufactured and provided to an end-user such that the components of each part are separately mixed and the first part is provided in a separate container as the second part.

[0163] The two-part (e.g. adhesive) compositions described herein can be utilized with cartridges as well as dispensing and mixing apparatus that are currently used for two-part epoxy compositions. An illustrative apparatus for mixing and dispensing a two-part composition commercially available as the trade designation “3M™EPX Plus II Epoxy Applicator”.

[0164] The chambers of the cartridge are typically pre-filled with the two-component (e.g. adhesive) composition. Prior to use the chambers are sealed from exposure to air with a cap. In typical embodiments, the (e.g. photobase) catalyst is sufficiently dispersed or dissolved in the liquid material (e.g of the second part) for a sufficient period of time (e.g. up to 1 year or greater at 23 °C) such that the cartridge is ready to use as received.

[0165] The first chamber and second chamber typically have a volume ranging from 1 : 1 to 20: 1. In some embodiments, the first chamber and second chamber have a volume ratio of at least 2:1, 3:1, or 4:1. In some embodiments, the first chamber and second chamber have a volume ratio less than 20: 1 such as 15:1 or 10:1.

[0166] The composition may be utilized as a coating, an adhesive, or may be utilized to make molded parts.

[0167] In one embodiment, a method of use is described comprising providing the epoxy resin composition as described herein; applying the composition to a substrate; and allowing the composition to cure. When the composition is a two-part epoxy composition, the method further comprises mixing the first part with the second part (e.g. with a static mixer element) prior to applying the composition to a substrate.

[0168] In typical embodiments, wherein a fast rate of cure is desired, the method comprises exposing the mixed parts to actinic radiation (i.e., electromagnetic actinic radiation). By definition, actinic radiation is electromagnetic radiation that is absorbed by one or more components of the photopolymerizable composition that ultimately leads to at least partial free-radical polymerization of the composition.

[0169] Exemplary actinic radiation has a wavelength of from 250 nanometers to 700 nanometers or 350 nm to 500 nm or a wavelength within the range of 440 nm to 500 nm. The actinic radiation is absorbed by both the photobase and the sensitizer, either simultaneously or sequentially. For example, the same or different wavelengths of actinic radiation may be used for the photobase and the sensitizer. It is appreciated that the exposure to light initiates the curing and the curing continues after exposure to light. In typical embodiments, curing occurs after applying the (e.g. adhesive) composition to a substrate.

[0170] The source(s) of actinic radiation are selected such that the actinic radiation is of an appropriate wavelength to be absorbed by the photobase and sensitizer. Exemplary sources of actinic radiation may include lasers (ultraviolet or visible), broad spectrum flashlamps (e.g., xenon flashlamps), and low, medium, and high-pressure mercury arc lamps, microwave-driven mercury lamps (e.g., using H-type, V-type, or D-type bulbs), and light emitting diode (LEDs). Further details associated with radiation curing are with the capabilities of those skilled in the art.

[0171] The exposure time can vary depending on the intensity of the light source. Low light intensity sources generally provide intensities ranging from 0.1 or 0.5 mW / cm2(milliwatts per square centimeter) to 10 mW / cm2(as measured in accordance with procedures approved by the United States National Institute of Standards and Technology as, for example, with a UVIMAP UM 365 L-S radiometer manufactured by Electronic Instrumentation & Technology, Inc., in Sterling, VA). High light intensity sources generally provide intensities greater than 10, 15, or 20 mW / cm2ranging up to 450 mW / cm2or greater. In some embodiments, high intensity light sources provide intensities up to 500, 600, 700, 800, 900 or 1000 mW / cm2. In some embodiments, complete curing with a low intensity light source can be accomplished with an exposure time ranging from about 30 to 300 seconds; whereas complete curing with a high intensity light source can be accomplished with shorter exposure time ranging from about 5 to 20 seconds. Partial curing with a high intensity light source can typically be accomplished with exposure times ranging from about 2 seconds to about 5 or 10 seconds.

[0172] In some embodiments, the method comprises exposing the composition to an elevated temperature (e.g. at least 45, 50, 60, 70, 80, 90, 100, 110, 120 or 130 ° C. Higher temperatures can increase the curing rate. In some embodiments, the composition is exposed to an elevated temperature after exposure to light. In other embodiments, the composition is exposed to an elevated temperature in the absence of exposure to light.

[0173] The composition can be coated on a substrate using conventional coating techniques, such as a knife coater, wire wound rod, or doctor blade. For example, these compositions can be applied to a variety of substrates by methods such as by manual or automated extrusion, roller coating, flow coating, dip coating, spin coating, spray coating, knife coating, and die coating. Coating (dry) thickness typically ranges from 25 (e.g. about 1 mil) to 1500 microns (60 mils). In some embodiments, the coating thickness ranges from about 50 to 350 microns.

[0174] The composition may be coated upon a variety of flexible and inflexible substrates. In some embodiments, the substrate is a film, sheet, or (e.g. non-planar) molded plastic article.

[0175] The substrate may comprise various thermoplastic materials such as polyolefins (e.g. polypropylene, polyethylene), polyvinyl chloride, polyester (polyethylene terephthalate), polycarbonate, polymethyl(meth)acrylate (PMMA), cellulose acetate, cellulose triacetate, and ethyl cellulose. In some embodiments, the substrate is comprised of a bio-based material such as polylactic acid (PLA). In other embodiments, the substrate is an engineered plastics such as polyamide (e.g. nylon 6, nylon 6,6), polyether sulfone (PES), polystyrene (PS), polyphenylene sulfide (PPS), polyether ether ketone (PEEK) poly ether imide (PEI).

[0176] Substrates may also be prepared of fabric such as woven fabric formed of synthetic or natural fibrous materials such as cotton, nylon, rayon, glass, ceramic materials, and the like or nonwoven fabric such as air laid webs of natural or synthetic fibers or blends of these.

[0177] The substrate may also be formed of metal (e.g. steel, aluminum, copper), metalized polymer films, ceramic sheet materials, or foam (e.g., polyacrylic, polyethylene, polyurethane, neoprene), and the like.

[0178] The epoxy composition is typically not a pressure sensitive adhesive after curing. In this embodiment, the storage modulus (G’) of the adhesive after curing is at least (e.g. 25°C) 3 x 105Pa (0.3 Mpa) at a frequency of 1 Hz. In some embodiments, the adhesive composition has a storage modulus of a least 0.5 MPa, 1 MPa, 10 MPa, 100 MPa, 500 MPa, 1000 MPa, 1500 MPA or 2000 MPa at 25°C and 1 Hz after curing, as illustrated by FIG. 1. In some embodiments, the cured epoxy composition has a peak tan delta at a temperature of at least 30 °C and typically no greater than 120 °C. These properties are characteristic a structural adhesive composition.

[0179] The adhesive composition is typically a semi-structural or structural adhesive after curing. As used herein, the term “semi-structural adhesive" refers to those cured compositions that have an overlap shear strength of at least 1.5 megaPascals (MPa). More preferably, the overlap shear strength is at least 2.0 or at least 3.0 MPa. Those cured compositions having a particularly high overlap shear strength, however, are referred to herein as “structural adhesives”. Structural adhesives are those cured compositions that have an overlap shear strength of at least 4, 5, 6, or 7 MPa.

[0180] Objects and advantages of this invention are further illustrated by the following examples. The particular materials a On-7d amounts, as well as other conditions and details, recited in these examples should not be used to unduly limit this invention.

[0181] o

[0182] Table 1 - Materials:

[0183] Tradename / Description - Supplier

[0184] Abbreviation

[0185] DIC HP-4032D

[0186] o

[0187] o

[0188] cr IA O

[0189] 0^°

[0190] Epoxy equivalent weight 136-148 g / equivalent.

[0191] 500-600 dPa.s at 50°C

[0192] Osaka Gas

[0193] Chemical FEP

[0194] Fluorene

[0195] Epoxy- OGSOL PG- 100

[0196] Westlake Epon Bisphenol A Epoxy Resin

[0197] 828

[0198] I W I

[0199] |:

[0200] L J n

[0201] Westlake Epon Bisphenol F Epoxy Resin

[0202] 862

[0203] L °HJ n

[0204] PMGE Phenyl methyl glycidyl ether

[0205]

[0206] Shin A T&C

[0207] TPDGE SE650

[0208] Tactix 742 O

[0209] 0-7

[0210] s

[0211] o

[0212] EBECRYL™ Aromatic Urethane Diacylate ol oigomer - Viscosity 238,000 at 25°C, 4241 at 60°C 4827 Allnex Tg = -6°C, Tesnile Strength 900 psi, Tensile Elongation 78%

[0213] San Apro PB- D02 / UCAT

[0214] 5002 Photobase

[0215] + TJ- QJ’B- O h

[0216] 9-Fluorenone Sensitizer - Sigma Aldrich

[0217] O

[0218] 0^0

[0219] Bruno Bock Pentaerythritol tetrakis(3 -mercaptopropionate) (PETMP) - Bruno Bock THIOCURE

[0220] 0 O

[0221] 440 (PETMP)

[0222] XX JI A / x

[0223] HS '0— ■, 0 SH

[0224] X

[0225] ' Y I "

[0226] 0 0

[0227] Bruno Bock Hs~~\ 20A5 H

[0228] THIOCURE o

[0229] 430 (TMPMP)

[0230] O Z\

[0231] H S _ /

[0232] DMDO Thiol Curative - 2,2'-(Ethylenedioxy)diethanethiol - Sigma Aldrich

[0233] H Ss H

[0234]

[0235]

[0236] Test Methods

[0237] Peak Tan Delta and Room Temperature Modulus determined with Dynamic Mechanical Analysis (DMA) The (e.g. adhesive) composition was cured for 5 min at 500 mW / cm2at 450 nm with Clearstone CT2000 (Clearstone Technologies, Hopkins MN USA) LED curing equipment. A DMA850 (TA Instruments, Waters Corp.) was used to evaluate the Tg through peak tan delta as well as the room temperature modulus of the cured (e.g. adhesive) composition. A temperature ramp was run from 10 °C to 100 °C at 3 °C / min rate with the adhesive in a tensile mode. The cured adhesive strip used was roughly 0.5 mm thick, 6 mm wide, and 15 mm long. A preload force of 0.2N was used with an oscillation amplitude of 4 um and a frequency of 1 Hz. The storage modulus at 25 °C and the temperature that the peak tan delta occurred at in the temp ramp were recorded.

[0238] Composition Preparation Solid epoxy resins were homogenized into epoxy resins without constrained aromatic rings with temperature and stirring until homogenous in a 60 MAX polypropylene mixing cup (from FlackTek, Inc., Landrum, SC). To this was the photobase PBD-02 was added and homogenized into the liquid resin with heating and stirring until a clear mixture resulted. Subsequently sensitizer and thiol components were charged to the mixture and mixed on a SPEEDMIXER DAC 150 FVZ (Hauschild SpeedMixer Inc., Farmington Hills, MI) for at least 60 s at 2500-3000 revolutions per minute (rpm). If utilized other additives such as acrylate oligomers or fumed silica were added last and homogenized into the formulation by mixing in a SPEEDMIXER DAC 600.2 VAC-P (Hauschild SpeedMixer Inc., Farmington Hills, MI) for 30 s at 1200 revolutions per minute (rpm), 5 min at 2350 rpm, 30 s at 1200 rpm under reduced pressure 20 mBar for vacuum assisted degassing of the formulation. Once homogenized the formulation was allowed to cool to RT before separating a portion to age at room temperature another portion going into the fridge (4 °C) where they were checked under an optical microscope after 1 d and 14 d respectively for presence of crystallinity.

[0239] Stability Rating of Compositions

[0240] 1 = no crystals observed

[0241] 2 = some crystals

[0242] 3 = substantial crystals observed The storage time and temperature are reported in the following tables.

[0243] Table 2 - Compositions

[0244] Comp. Comp. Comp. Comp

[0245] Epoxy Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6

[0246] Epon 828 39% 49% 59% 39% 39% 39% FEP 20%

[0247] TPDGE 20%

[0248] Tactix 742 20%

[0249] HP-4032D 20% PMGE 10%

[0250] DMDO 3.5% 3.5% 3.5% 3.5% 3.5% 3.5%

[0251] PETMP 33% 33% 33% 33% 33% 33%

[0252] PB-D02 2.9% 2.9% 2.9% 2.9% 2.9% 2.9% Weight

[0253] Ratio of

[0254] Constrained

[0255] Aromatic

[0256] Epoxy to

[0257] Photobase 6.8:1 6.8:1 Fluorenone

[0258]

[0259] Sensitizer 1.4% 1.4% 1.4% 1.4% 1.4% 1.4%

[0260] Table 3 - Stability of Compositions

[0261] 14 d (4° C) 1 dRT Ex. 1 1 1 Comp. Ex. 2 3 3 Comp. Ex. 3 1 3 Comp. Ex. 4 2 3 Comp Ex. 5 2 3

[0262]

[0263] Ex. 6 1 1

[0264] Table 4 - Compositions 7 and 8 and Stability

[0265] Ex. 7 Ex. 8

[0266] EPON 828 36% 30%

[0267] HP4032 0% 0%

[0268] FEP Epoxy 11% 18%

[0269] Ebercryl 4827 14% 13%

[0270] TMPMP 18% 18%

[0271] PETMP 16% 15%

[0272] Fluorenone 1.4% 1.4%

[0273] PB-D02 2.8% 2.8%

[0274] H18 0.9% 0.8%

[0275] Crystal rating 1 (still 1

[0276]

[0277] (IdRT) 2 after lldRT)

Claims

1. What Is Claimed:

1. A composition comprising:3.an epoxy resin that is a liquid at 25°C;4.an epoxy resin comprising constrained aromatic rings;5.an epoxy curative comprising at least two thiol groups; and6.a photobase.

2. The composition of claim 1 wherein the epoxy resin comprises at least two aromatic rings fused to each other.

3. The composition of claims 1-2 wherein the fused aromatic ring comprises a moiety selected from naphthalene or anthracene, optionally comprising nitrogen substitutions.

4. The composition of claims 1-3 wherein the epoxy resin comprises at least two aromatic rings and at least two carbon atoms of each ring are bonded to each other with a covalent bond, linking atom, or organic linking group.

5. The composition of claim 4 wherein the epoxy resin comprises a fluorene moiety.

6. The composition of claims 1-5 wherein the epoxy resin comprising the constrained aromatic rings is a solid at 25 °C.

7. The composition of claims 1-6 wherein the photobase has the general formula13.(I) Ar-L-B; or (II) [Ar-L-B]+[A]’14.wherein Ar is an aromatic group;15.L is a covalent bond or (e.g. divalent) organic linking group;16.B is a nitrogen-containing group;17.and A’ is an anion of a salt.

8. The composition of claim 7 wherein the composition comprises a photobase having the general formula (II) [Ar-L-B]+[A]“ .

9. The composition of claims 1-8 wherein the composition is a two-part composition comprising the photobase and epoxy resin comprising constrained aromatic rings in a separate container or chamber than the thiol curative.

10. The composition of claims 1-9 wherein the composition comprises 10 to 30 wt.% of the-epoxy resin(s) comprising constrained aromatic rings.

11. The composition of claims 1-10 wherein the photobase is soluble at 23 °C at a concentration up to 5 wt.% of the total composition.

12. The composition of claim 1-11 wherein the composition further comprises a sensitizer.

13. The composition of claims 1-12 wherein the photobase generates an amine when exposed to light with a wavelength within the range of 350 nm to 500 nm.

14. The composition of claim 1-13 further comprising a (meth)acrylate oligomer.

15. The composition of claim 1-14 further comprising a urethane (meth)acrylate.

16. The composition of claims 1-15 wherein the composition is a coating, structural adhesive, or molded part.

17. A method of use comprising:27.providing the composition of claims 1-16;28.applying the composition to a substrate; and29.allowing the composition to cure.

18. The method of claim 17 wherein curing further comprises exposing the composition to light with a wavelength within the range of 350 nm to 500 nm.

19. The method of claims 17-18 wherein curing further comprises exposing the composition to a temperature in the range of 50 to 130°C.

20. The method of claims 17-19 wherein the method comprises applying the composition between a first substrate and second substrate to bond the substrates after curing.

21. An article comprising a substrate and a cured coating or structural adhesive of claims 1-20.

22. A composition comprising an epoxy resin comprising constrained aromatic rings as a carrier material for a photobase.

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