METHOD OF MAKING AN ADHESIVE COMPOSITION

FIELD

The present disclosure broadly relates to acrylic adhesives and compositions and methods useful for their preparation.

BACKGROUND

Acrylic adhesives have been commercially used for more than 50 years. These adhesives, typically based on acrylates and/or methacrylates, are supplied as two separate components (often termed part A and part B) that can be mixed prior to application to two adherends to form an adhesive bond, or each component can be applied to separate adherend surfaces which are then joined. Typically, both parts A and B contain free-radically polymerizable monomers,

One type of acrylic adhesive, described in WIPO International Publ. No. WO 2013/126377 Al

(Kropp et al.), uses a cure system including a barbituric acid and/or a malonyl sulfamide and organic peroxide, optionally combined with a quaternary ammonium chloride salt and/or certain metal salt(s).

SUMMARY

To avoid premature curing, acrylic adhesives of the general type reported in WO 2013/126377

Al (Kropp et al.) can be formulated as a two-part (i.e., part A and part B) kit. Part A contains organic peroxide and a beta-dicarbonyl compound, while part B contains a quaternary ammonium chloride salt and/or certain metal salt(s). Ordinarily, part B further includes a free-radically polymerizable monomer. To facilitate handling and mixing, part A desirably also contains a free-radically polymerizable diluent. However, premature curing of the part A component (e.g., resulting in unacceptably shortened shelf- life) may result in this circumstance. It would be desirable to improve the shelf-life of the part A component, preferably without adversely affecting cure of the adhesive when parts A and B are combined.

Advantageously, the present inventors have discovered that inclusion of aromatic nitro compounds can effectively increase the shelf-life of part A compositions containing beta-dicarbonyl compounds according to the present disclosure.

Accordingly, in one aspect, the present disclosure provides an adhesive precursor composition comprising:

at least one free-radically polymerizable compound;

a beta-dicarbonyl compound represented by the formula

or a salt thereof, wherein:

R1 and R^ independently represent hydrocarbyl or substituted-hydrocarbyl group having from 1 to 18 carbon atoms;

R^ represents hydrogen, or a hydrocarbyl or substituted-hydrocarbyl group having from 1 to 18 carbon atoms; and

R ⁴ R ⁴

I I

each X independently represents O, S,— N— , or— C— ,

R ⁴

wherein each R^ independently represents H or hydrocarbyl having from 1 to 18 carbon atoms, or taken together any two of R^ , R^, R3 _; or R^ form a ring; and

at least one nitro compound represente formula

wherein

represents an n-valent substituted or unsubstituted aromatic group having from 1 to 20 carbon atoms and free of nitroxyl groups, and

n represents a positive integer.

In another aspect, the present disclosure provides a two-part adhesive kit comprising:

a part A composition comprising:

i) at least one free-radically polymerizable compound;

ii) a beta-dicarbonyl compound represented by the formula

a salt thereof, wherein:

R1 and R^ independently represent hydrocarbyl or substituted- hydrocarbyl group having from 1 to 18 carbon atoms;

R^ represents hydrogen, or a hydrocarbyl or substituted-hydrocarbyl group having from 1 to 18 carbon atoms; and I I

each X independently represents O, S,— N— , or— C— ,

R ⁴ wherein each independently represents H or hydrocarbyl having from

1 to 18 carbon atoms, or taken together any two of R^, R^, R3 _; or R^ form a ring; and

iii) at least one nitro compound represented by the formula

R ⁵ - NO ₂ wherein

represents an n-valent substituted or unsubstituted aromatic group having from 1 to 20 carbon atoms and free of nitroxyl groups, and

n represents a positive integer; and

ii) a part B composition comprising:

at least one free-radically polymerizable compound,

a salt or oxide of a polyvalent metal, and

a non-metallic halide salt.

In yet another aspect, the present disclosure provides a method of making an adhesive composition, the method comprising combining the part A and part B compositions of a two-part adhesive kit according to the present disclosure.

As used herein, the prefix "(meth)acryl" refers to acryl and/or methacryl. For example,

(meth)acrylate refers to acrylate and/or methacrylate.

As used herein, the term "hydrocarbyl" refers to a monovalent group derived from a hydrocarbon. Examples include methyl, phenyl, and methylcyclohexyl.

As used herein, the term "hydrocarbylene" refers to a divalent group derived from a hydrocarbon. Examples include methylene, phenylene, and 1,3-propane-diyl.

Features and advantages of the present disclosure will be further understood upon consideration of the detailed description as well as the appended claims.

DETAILED DESCRIPTION

Adhesive precursor compositions according to the present disclosure (corresponding to part A in two-part adhesive kits according to the present disclosure) include at least one free-radically

polymerizable compound and a beta-dicarbonyl compound as described above. Suitable free-radically polymerizable compounds include, for example, at least one of

(meth)acrylates, (meth)acrylamides, other vinyl compounds, and combinations thereof. Useful free- radically polymerizable compounds may comprise an ethylenically -unsaturated compound having one or more (e.g., one, two, three, four, or more) free-radically polymerizable groups.

Examples of suitable (meth)acrylates include mono-, di-, and poly-(meth)acrylates and

(meth)acrylamides such as, for example, 1,2,4-butanetriol tri(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,3-propanediol di(meth)acrylate, 1 ,4-butanediol di(meth)acrylate, 1 ,4-cyclohexanediol di(meth)acrylate, 1 ,6-hexanediol di(meth)acrylate, 1 ,6-hexanediol monomethacrylate monoacrylate, 2- phonexyethyl (meth)acrylate, alkoxylated cyclohexanedimethanol di(meth)acrylates, alkoxylated hexanediol di(meth)acrylate, alkoxylated neopentyl glycol di(meth)acrylate, allyl (meth)acrylate, bis [ 1 -(2-(meth)acryloxy)] -p-ethoxyphenyldimethylmethane,

bis[l-(3-(meth)acryloxy-2-hydroxy)]-p-propoxyphenyldimeth ylmethane, caprolactone modified dipentaerythritol hexa(meth)acrylate, caprolactone modified neopentyl glycol hydroxypivalate di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, diethylene glycol di(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipropylene glycol di(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ethoxylated (10) bisphenol A di(meth)acrylate, ethoxylated (20) trimethylolpropane tri(meth)acrylate, ethoxylated (3) bisphenol A di(meth)acrylate, ethoxylated (3) trimethylolpropane tri(meth)acrylate, ethoxylated (30) bisphenol A di(meth)acrylate, ethoxylated (4) bisphenol A

di(meth)acrylate, ethoxylated (4) pentaerythritol tetra(meth)acrylate, ethoxylated (6) trimethylolpropane tri(meth)acrylate, ethoxylated (9) trimethylolpropane tri(meth) aery late, ethoxylated bisphenol A di(meth) aery late, ethyl (meth)acrylate, ethylene glycol di(meth)acrylate, 2-ethylhexyl (meth)acrylate, glycerol tri(meth)acrylate, hydroxypivalaldehyde modified trimethylolpropane di(meth)acrylate, isobornyl (meth)acrylate, isopropyl (meth)acrylate, methyl (meth)acrylate, neopentyl glycol

di(meth)acrylate, n-hexyl (meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol

tri(meth)acrylate, polyethylene glycol (200) di(meth)acrylate, polyethylene glycol (400) di(meth)acrylate, polyethylene glycol (600) di(meth)acrylate, propoxylated (3) glyceryl tri(meth)acrylate, propoxylated (3) trimethylolpropane tri(meth)acrylate, propoxylated (5.5) glyceryl tri(meth)acrylate, propoxylated (6) trimethylolpropane tri(meth)acrylate), propoxylated neopentyl glycol di(meth)acrylate, sorbitol hexa(meth)acrylate, stearyl (meth)acrylate, tetraethylene glycol di(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tripropylene glycol di(meth)acrylate, tris(2- hydroxyethyl)isocyanurate tri(meth)acrylate, (meth)acrylamide, Ν,Ν-dimethylacrylamide, N- vinylpyrrolidone, N-vinylcaprolactam, methylene bis(meth)acrylamide, diacetone (meth)acrylamide, urethane (meth)acrylates, polyester (meth)acrylates, epoxy (meth)acrylates, copolymerizable mixtures of (meth)acrylated monomers such as those in U.S. Pat. No. 4,652,274 (Boettcher et al.), (meth)acrylated oligomers such as those of U.S. Pat. No. 4,642,126 (Zador et al.), and poly(ethylenically-unsaturated) carbamoyl isocyanurates such as those disclosed in U.S. Pat. No. 4,648,843 (Mitra).

Examples of suitable free-radically polymerizable vinyl compounds include styrene, diallyl phthalate, divinyl succinate, divinyl adipate, and divinyl phthalate. Other suitable free-radically polymerizable compounds include siloxane- functional (meth)acrylates as disclosed, for example, in

WIPO International Publication Nos. WO 00/38619 (Guggenberger et al.), WO 01/92271 (Weinmann et al.), WO 01/07444 (Guggenberger et al.), WO 00/42092 (Guggenberger et al.), and fluoropolymer- functional (meth)acrylates as disclosed, for example, in U.S. Pat. Nos. 5,076,844 (Fock et al.), 4,356,296 (Griffith et al.), EP 0 373 384 (Wagenknecht et al.), EP 0 201 031 (Reiners et al.), and EP 0 201 778 (Reiners et al.).

Suitable free-radically polymerizable compounds may contain hydroxyl groups and free-radically active functional groups in a single molecule. Examples of such materials include hydroxyalkyl

(meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate, glycerol mono- or di-(meth)acrylate, trimethylolpropane mono- or di-(meth)acrylate, pentaerythritol mono-, di-, and tri-(meth)acrylate, sorbitol mono-, di-, tri-, terra-, or penta-(meth)acrylate, and 2,2-bis[4-(2-hydroxy- 3 -methacryloxypropoxy)phenyl] -propane (bisGMA).

Suitable free-radically polymerizable compounds are available from a wide variety of commercial sources such as, for example, Sartomer Co., Exton, Pennsylvania, or can be made by known methods.

Typically, a sufficient quantity of free-radically polymerizable compound(s) is used to provide the desired setting or hardening rate and desired overall properties following curing/hardening. Mixtures of free-radically polymerizable compounds can be used if desired. In some embodiments, free-radically polymerizable compounds are present in the adhesive precursor composition, part A composition, and/or part B composition at a level of at least 50, 60, 70, 80, or even at least 90 percent by weight.

The curable composition comprises a beta-dicarbonyl compound represented by the formula

or a salt thereof. Exemplary salts thereof include alkali metal (e.g., Li, Na, K) salts and quaternary ammonium (e.g., tetrabutylammonium, ethyltrimethylammonium, and tetraethylammonium) salts.

In some embodiments, ^ and ^ independently represent a hydrocarbyl group having from 1 to

18 carbon atoms. Exemplary groups ^ and ^ include methyl, ethyl, isopropyl, n-propyl, butyl, pentyl, hexyl, octyl, decyl, dodecyl, hexadecyl, and octadecyl.

In some embodiments, ^ and ^ taken together form a ring. In those embodiments, ^ and ^ taken together may represent, for example, a divalent group selected from hydrocarbylene groups having O R ⁴

I I I

from 1 to 4, 6, or 8 carbon atoms; a carbonyl group; -O- or -S- (e.g., in the case that ;— S— ;— N—

I I O

R ⁴

I

; or— C— . Each R ⁴ may independently represent H or an alkyl group having from 1 to 18 carbon R ⁴

atoms. Exemplary groups R^ include methyl, ethyl, isopropyl, n-propyl, butyl, pentyl, hexyl, octyl, decyl, dodecyl, hexadecyl, and octadecyl.

R^ represents hydrogen or a hydrocarbyl group having from 1 to 18 carbon atoms. Exemplary groups R^ include methyl, ethyl, isopropyl, n-propyl, butyl, pentyl, hexyl, cyclohexyl, methylcyclohexyl, octyl, decyl, dodecyl, hexadecyl, and octadecyl.

R ⁴ R ⁴

I I

Each X independently represents O, S,— N— , or— C— wherein each R ⁴ independently

R ⁴

represents H or a hydrocarbyl (e.g., alkyl) group having from 1 to 18 carbon atoms. Exemplary groups R^ include methyl, ethyl, isopropyl, n-propyl, butyl, pentyl, hexyl, octyl, decyl, dodecyl, hexadecyl, and octadecyl.

In some embodiments, the beta-dicarbonyl compound comprises barbituric acid (i.e., R^ = H, both X =— N— , R^ =H, and taken together R1 and R^ = carbonyl) or a derivative thereof (e.g., a 1,3- dialkylbarbituric acid). Examples of suitable barbituric acid derivatives include 1,3,5-trimethylbarbituric acid, 1,3,5-triethylbarbituric acid, l,3-dimethyl-5-ethylbarbituric acid, 1,5-dimethylbarbituric acid, 1- methyl-5-ethylbarbituric acid, l-methyl-5-propylbarbituric acid, 5-ethylbarbituric acid, 5-propylbarbituric acid, 5-butylbarbituric acid, l-benzyl-5-phenylbarbituric acid, and l-cyclohexyl-5-ethylbarbituric acid.

The adhesive precursor composition further comprises at least one nitro compound represented by the formula

wherein represents an n-valent substituted or unsubstituted aromatic group having from 1 to 20 carbon

O

I

atoms and free of nitroxyl (i.e.,— N— ) groups, and n represents a positive integer (e.g., 1, 2, or 3).

Exemplary nitro compounds include nitrobenzene; 1 ,2-dinitrobenzene; 1,3-dinitrobenzene; 1,4- dinitrobenzene; 2-nitrophenol; 4-nitrophenol; 4-nitrochlorobenzene; 3-nitrobromobenzene; 1- nitronaphthalene; 4-nitrostilbene; 2-nitrotoluene; 3-nitrotoluene; 4-nitrotoluene; 2,4-dinitrotoluene; 2- nitrobenzoic acid; 3-nitrobenzoic acid; and 4-nitrobenzoic acid. Preferably, the nitro compound comprises 2-nitrobenzoic acid.

Typically, the nitro compound is present in an amount that is effective to extend the shelf life of the adhesive precursor (or part A) composition. Exemplary amounts may range from about 0.1 percent by weight up to about 1, 5, or even 10 percent by weight, based on the total weight of the adhesive precursor (or part A) composition.

Optionally, but preferably, the adhesive precursor (or part A) composition may further comprise one or more organic peroxides (e.g., mono- or multi-functional carboxylic acid peroxyesters), which typically act to decrease the cure time of the composition. Commercially available organic peroxides include, for example, t-alkyl esters of peroxycarboxylic acids, t-alkyl esters of monoperoxydicarboxylic acids, di(t-alkyl) esters of diperoxydicarboxylic acids, alkylene diesters of peroxycarboxylic acids, dialkyl peroxydicarbonates, and OO-t-alkyl O-alkyl diesters of monoperoxycarbonic acid. Exemplary organic peroxides include diisopropyl peroxydicarbonate, t-butyl peroxyneodecanoate, t-amyl

peroxyneodecanoate, maleic acid t-butyl monoperoxyester, t-butyl peroxybenzoate, t-butyl peroxy-2- ethylhexanoate, t-amyl peroxy-2-ethylhexanoate, O-isopropyl 0,0-t-butyl monoperoxycarbonate, dicyclohexyl peroxycarbonate, dimyristyl peroxycarbonate, dicetyl peroxycarbonate, di(2-ethylhexyl) peroxycarbonate, 0,0-t-butyl O-2-ethylhexyl peroxycarbonate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-amyl peroxybenzoate, t-butyl peroxyacetate, di(4-t-butylcyclohexyl) peroxycarbonate, cumyl peroxyneodecanoate, t-amyl peroxypivalate, and t-butyl peroxypivalate.

Typically, the organic peroxide (if present) is present in an effective amount to participate in initiating free-radical polymerization. Exemplary amounts may range from about 0.1 percent by weight up to about 1 , 5 percent by weight, based on the total weight of the adhesive precursor (or part A) composition.

In some embodiments, the adhesive precursor (or part A) composition may contain little or no organic peroxide. For example, it may be essentially free of (e.g., contain less than 1 percent by weight of, less than 0.1 percent by weight of, or even contain less than 0.01 percent by weight of) organic peroxide.

The part B composition comprises at least one free-radically polymerizable compound, a salt or oxide of a polyvalent metal, and at least one free-radically polymerizable compound (e.g., as described hereinabove), a salt or oxide of a polyvalent metal, and a non-metallic halide salt.

Suitable salts and oxides of polyvalent metals include soluble ionic salts of the type generally used in oil drying technology. The metals should have several valency states and suitable metal salts are those of multivalent metals, especially transition metals. The metal ions are suitably present in their low valency state. The metal salt should be at least partially soluble in the composition, and may be present in the composition in an effective amount which is generally in a range of between about 1 and about 5000 parts per million (ppm), particularly about 1 to 3000 ppm, and more particularly about 500 to 30000 ppm. The choice of metal may have a rate-determining effect on initiation of polymerization because of a temperature dependence of the metal component in the process. Iron, cobalt, copper, manganese and vanadium are typically highly active at room temperature. In addition, compounds of these metals can be also be used and/or combined with the foregoing metals mixed with one or more other metallic components such as lead, cerium, calcium, barium, zinc and/or zirconium.

Metal naphthenates or metal acetylacetonates are generally soluble in the composition, but other salts or organometallics may be used if they are sufficiently soluble.

Suitable non-metallic halide salts include, for example, quaternary ammonium halides that are at least partially soluble in that composition. The quaternary ammonium halide may accelerate the free- radical polymerization rate. Suitable quaternary ammonium halides include those having four hydrocarbyl (e.g., alkyl, alkenyl, cycloalkyl, aralkyl, alkaryl, and/or aryl) groups. Preferably, the hydrocarbyl groups are independently selected from hydrocarbyl groups having from 1 to 18 carbon atoms, more preferably 1 to 12 carbon atoms, and more preferably 1 to 4 carbon atoms. Examples of suitable hydrocarbyl groups include methyl, ethyl, propyl, butyl, hexyl, octyl, dodecyl, hexadecyl, and octadecyl, benzyl, phenyl, tolyl, cyclohexyl, and methylcyclohexyl. Exemplary suitable quaternary ammonium compounds include tetramethylammonium halides, tetraethylammonium halides, tetrapropylammonium halides, tetrabutylammonium halides, ethyltrimethylammonium halides, diethyldimethylammonium halides, trimethylbutylammonium halides, and benzyltributylammonium halides. Any halide (e.g., F, CI, Br, I) ion may be used in the quaternary ammonium halide, but preferably the halide ion is chloride or bromide.

Exemplary total amounts of the non-metallic halide salt(s) may range from about 1 to 5000 parts per million (ppm), preferably from about 1 to 3000 ppm, and more preferably about 500 to 3000 ppm, based on the total weight of the part B composition, although other amounts may also be used.

Adhesive precursor compositions and part A and part B compositions according to the present disclosure may optionally include additives such, as for example, one or more fillers, thickeners, fragrances, hindered amine light stabilizers (HALS), UV stabilizers, inhibitors (e.g., which may accompany free-radically polymerizable compounds), colorants, coating aids, thixatropes, coupling agents, toughening agents, or a combination thereof. Examples of fillers include silica, clays, and surface modified clays. Exemplary toughening agents include elastomeric materials such as various synthetic rubbers (e.g., methyl methacrylate-butadiene-styrene (MBS) copolymers, acrylonitrile-butadiene-styrene (ABS) copolymers, linear polyurethanes, acrylonitrile -butadiene rubbers, styrene -butadiene rubbers, chloroprene rubbers, butadiene rubbers, and natural rubbers. Among them, acrylonitrile-butadiene rubbers are particularly useful because of their typically good solubility in the curable composition. Tougheners may be used alone or in combination.

The part A and part B components are preferably prepared so that they can be mixed at a ratio of

10: 1 to 1 : 10, preferably 7:3 to 3:7, more preferably, 4: 1 to 1 :4, and more preferable 2: 1 to 1 :2, and more preferably about 1 : 1. The components can be mixed together, for example, by conventional techniques such as paddle mixing, propeller mixers, and mixing/dispensing nozzles.

Generally, the two-part adhesive kit will include respective separate containers of part A and part B, although this is not a requirement. In one preferred embodiment, part A and part B are supplied in a single dual-barrel syringe-type dispenser adapted to engage a disposable mixing nozzle.

SELECT EMBODIMENTS OF THE PRESENT DISCLOSURE

In a first embodiment, the present disclosure provides an adhesive precursor composition comprising:

at least one free-radically polymerizable compound;

a beta-dicarbonyl compound represented by the formula

or a salt thereof, wherein:

R1 and R^ independently represent hydrocarbyl or substituted- hydrocarbyl group having from 1 to 18 carbon atoms;

R^ represents hydrogen, or a hydrocarbyl or substituted-hydrocarbyl group having from 1 to 18 carbon atoms; and

R ⁴ R ⁴

I I

each X independently represents O, S,— N— , or— C— ,

R ⁴

wherein each R^ independently represents H or hydrocarbyl having from 1 to 18 carbon atoms, or taken together any two of R^ , R^, R3 _; or R^ form a ring; and

at least one nitro compound represented by the formula

R ⁵ - NO ₂ wherein

R^ represents an n-valent substituted or unsubstituted aromatic group having from 1 to 20 carbon atoms and free of nitroxyl groups, and

n represents a positive integer.

In a second embodiment, the present disclosure provides an adhesive precursor composition according to the first embodiment, further comprising at least one organic peroxide. In a third embodiment, the present disclosure provides an adhesive precursor composition according to the first or second embodiment, wherein the nitro compound is present in an amount of less than 10 percent by weight based on the total weight of the composition.

In a fourth embodiment, the present disclosure provides an adhesive precursor composition according to any one of the first to third embodiments, wherein said at least one nitro compound comprises 2-nitrobenzoic acid.

In a fifth embodiment, the present disclosure provides an adhesive precursor composition according to any one of the first to fourth embodiments, wherein at least one of said at least one beta- dicarbonyl compound is represented by the formula

wherein R and R are independently selected from the group consisting of H, an alkyl group having 1 to 18 carbon atoms, an aryl group having from 6 to 14 carbon atoms, an alkaryl group having from 7 to 15 carbon atoms, and an aralkyl groups having from 7 to 15 carbon atoms.

In a sixth embodiment, the present disclosure provides an adhesive precursor composition according to any one of the first to fifth embodiments, wherein the at least one free-radically

polymerizable compound comprises a methacrylate monomer or acrylate monomer.

In a seventh embodiment, the present disclosure provides a two-part adhesive kit comprising: a part A composition comprising:

i) at least one free-radically polymerizable compound;

at least one beta-dicarbonyl compound represented by the formula

or a salt thereof, wherein:

R1 and ^ independently represent hydrocarbyl or substituted- hydrocarbyl group having from 1 to 18 carbon atoms;

^ represents hydrogen, or a hydrocarbyl or substituted-hydrocarbyl group having from 1 to 18 carbon atoms; and

R ⁴

each X independently represents O, S,

wherein each R^ independently represents H or hydrocarbyl having from

1 to 18 carbon atoms, or taken together any two of R^, R^, R^, or R^ form a ring; and

iii) at least one nitro compound represented by the formula

wherein

R^ represents an n-valent substituted or unsubstituted aromatic group having from 1 to 20 carbon atoms and free of nitroxyl groups, and

n represents a positive integer; and

ii) a part B composition comprising:

at least one free-radically polymerizable compound,

at least one salt or oxide of a polyvalent metal, and

at least one non-metallic halide salt.

In an eighth embodiment, the present disclosure provides a two-part adhesive kit composition according to the seventh embodiment, wherein the part A composition further comprises at least one organic peroxide.

In a ninth embodiment, the present disclosure provides a two-part adhesive kit composition according to the seventh or eighth embodiment, wherein at least one of the part A composition or the part B composition further comprises a toughening agent.

In a tenth embodiment, the present disclosure provides a two-part adhesive kit composition according to any one of the seventh to ninth embodiments, wherein said at least one nitro compound is present in an amount of less than 10 percent by weight based on the total weight of the part A

composition.

In an eleventh embodiment, the present disclosure provides a two-part adhesive kit composition according to any one of the seventh to tenth embodiments, wherein said at least one nitro compound comprises 2-nitrobenzoic acid.

In a twelfth embodiment, the present disclosure provides a two-part adhesive kit composition according to any one of the seventh to eleventh embodiments, wherein at least one of said at least one beta-dicarbonyl compound is represented by the formula

wherein R and R are independently selected from the group consisting of H, an alkyl group having 1 to 18 carbon atoms, an aryl group having from 6 to 14 carbon atoms, an alkaryl group having from 7 to 15 carbon atoms, and an aralkyl group having from 7 to 15 carbon atoms.

In a thirteenth embodiment, the present disclosure provides a two-part adhesive kit composition according to any one of the seventh to twelfth embodiments, wherein said at least one free-radically polymerizable compound comprises a methacrylate monomer or acrylate monomer.

In a fourteenth embodiment, the present disclosure provides a method of making an adhesive composition, the method comprising combining the part A and part B compositions of a two-part adhesive kit according to any one of the seventh to thirteenth embodiments.

Objects and advantages of this disclosure are further illustrated by the following non- limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure.

EXAMPLES

Unless otherwise noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. Unless otherwise noted, all chemicals used in the examples can be obtained from Sigma-Aldrich Corp., Saint Louis, Missouri. In the Examples, examples with the prefix EX- are working examples and those with the prefix CE- are comparative examples.

TABLE OF ABBREVIATIONS

THFMA tetrahydrofurfuryl methacrylate

Preparation of Compositions A-F

Each of compositions A-F was composed of THFMA and an initiator molecule in the amounts indicated in Table 1 (below).

TABLE 1

Effect of nitro compound additive on storage stability of a Part A adhesive precursor

For each of Examples EX- 1 to EX- 1 1, Composition A (see Table 1) and a nitro compound additive in the parts by weight indicated in Table 2 were mixed in a vial to provide a part A adhesive precursor. For example, EX- 1 includes THFMA (9.5 pbw) as an acrylic monomer, l-benzyl-5- phenylbarbituric acid (0.2 pbw) as an initiator, and 2-nitrobenzoic acid (0.3 pbw) as a nitro compound additive. Similarly, for each of Comparative Examples CE- 1 to CE- 17, Composition A (i.e., 9.5 pbw THFMA and 0.2 pbw l-benzyl-5-phenylbarbituric acid) was combined with the indicated additive in the parts by weight shown in Table 2. Each vial and its contents were then stored at either room temperature (~23°C) or at 50°C until the contents were cured (i.e., unable to flow when the vial was inverted), with the resulting storage stability values summarized in Table 2 (below). TABLE 2

Effect of nitro compound additive on cure time in a two-part adhesive

A part B composition designated as Composition Δ- 1 was prepared using the components and parts by weight listed in Table 3 (below).

TABLE 3

The part B composition Δ-l of Table 3 was combined in a vial in a 1 : 1 weight ratio with part B and part A as listed in Table 4. Each vial and its contents were then stored at room temperature (~23°C) until the contents were cured (i.e., unable to flow when the vial was inverted), with the resulting cure times summarized in Table 4 (below).

TABLE 4

Effect of initiator compounds on cure time in a two-part adhesive, with and without nitro compound additive

Components of each of the part A compositions listed in Table 5 were mixed in a vial to provide an adhesive precursor. Each vial and its contents were then stored at either room temperature (~23°C) or at 50°C until the contents were cured (i.e., solid and unable to flow when the vial was inverted).

A fresh sample of part A composition listed in Table 5 was combined in a vial in a 1 : 1 weight ratio with a sample of the part B composition Δ-l of Table 3. Each vial and its contents was then stored at room temperature (-23 °C) until the contents were cured (i.e., unable to flow when the vial was inverted), and the resulting cure times were summarized in Table 5 (below).

TABLE 5

All cited references, patents, and patent applications in the above application for letters patent are herein incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control. The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.