Curable (meth)acrylate composition

Abstract

A two-part curable composition comprising Part A and Part B, Part A comprising (i) a curable (meth)acrylate component, (ii) a free radical initiator, and (iii) a cyclic β-ketoester, the cyclic portion of the cyclic β-ketoester comprising a ring composed of at least six atoms, and Part B comprising (i) a curable (meth)acrylate component, and (ii) a transition metal component. The composition of the present invention exhibits tack-free cure in the presence of oxygen.

Description

[Technical field]

[0001] The present invention relates to compositions, particularly curable (meth)acrylate compositions. Of interest are those that cure to provide a non-tacky (tack-free) form. Compositions are described that can be cured despite the effects of oxygen inhibition. Such compositions are useful in applications with relatively high effects of oxygen inhibition. Two-part (also called "2K" for short) compositions are of interest. [Background technology]

[0002] Air, and in particular oxygen, has an inhibitory effect on the cure of curable (meth)acrylate compositions, a well-known property, and in fact anaerobically curable compositions based on (meth)acrylate compositions have been provided.

[0003] Incomplete curing of curable (meth)acrylate compositions, such as adhesives, due to oxygen inhibition can be problematic. For example, such technical problems can arise when the relative surface area of ​​the composition exposed to air is large compared to the amount of curable composition. For example, if a bead of composition is applied, its exposed ends may be subject to oxygen inhibition. This means that the composition may not fully cure at those exposed ends and may remain sticky or gummy. It will be understood that such exposure of a large surface area can occur when the applied bead of composition is thin (bead width) or thin (bead height), or both. In the present invention, the width of the applied bead is considered to be the dimension of the bead in the direction along the surface of the substrate to which it is joined. The thickness / height / depth of the bead is considered to be the dimension of the bead that represents the distance the bead extends above the surface of the substrate to which it is joined.

[0004] Incomplete curing can be a problem, for example, when there is a relatively thin bead of curable composition applied between substrates: the composition may bond the substrates together, but the composition exposed at the edge of the substrate may not cure completely due to oxygen inhibition.

[0005] Such problems may occur, for example, when there are thin beads, such as those less than 1.0 mm thick.

[0006] US Patent Publication 2010 / 297457 (Sika) "(Meth)acrylate Compositions Characterized by Reduced Oxygen Inhibition" describes 2K methacrylate compositions containing a metal salt and a dicarbonyl compound on the one hand and a peroxide on the other hand. These compositions improve the drying time to reach a tack-free cure, but have limited stability due to the reaction of the peroxide with the dicarbonyl compound.

[0007] U.S. Patent 4,442,138 (Westinghouse Electric Corp.) entitled "Pretreatment of Substrates with Metal-β-Ketoester Complexes in a Method for Curing Anaerobic Resins" discloses that pretreatment of substrates with metal-ketoesters can be used to cure anaerobic resins, but this requires an oxygen-free environment to initiate a tack-free cure.

[0008] European Patent EP 53740 (Bayer) for "Air-curable polyacrylate coatings" discloses the use of β-mono-olefinically unsaturated C3-C5-carboxylic acids, but the stability of these dicarbonyl compounds in the presence of peroxides is limited.

[0009] European Patent EP3161084 (3M) entitled "Adhesive precursor composition, two-part adhesive kit, and method for producing adhesive composition" discloses stable compositions of methacrylates containing dicarbonyl and 2-nitrobenzoic acid.

[0010] Garra et al., Macromolecules 2018, 51, pp. 6395-6404, describe the use of metal acetylacetonates and acetylbutyrolactone for the free radical cure of methacrylates. They also show that this improves the surface and depth of cure compared to tertiary amine / benzoyl peroxide-based free radical cures. However, the most effective combination, manganese tris acetylacetonate and acetylbutyrolactone, has very limited shelf stability.

[0011] International (PCT) Publication WO2019 / 038040 describes the use of cobalt salts and allyl-functionalized polyester diols as a means of overcoming oxygen inhibition of cure in two-component acrylic systems.

[0012] Notwithstanding the above, alternative solutions to the above problems are desirable. Summary of the Invention

[0013] For the above reasons, it would be desirable to provide a curable (adhesive) composition that addresses the market needs for non-tacky surfaces, cure at exposed edges, and desirable adhesive strength on active and passive substrates. As noted above, it would be desirable to provide a composition that cures to provide a non-tacky form. It would be desirable to provide a composition that can cure despite oxygen inhibition. It would be desirable to achieve adhesion on both active and inactive surfaces. It would further be desirable to achieve good adhesive strength. Additionally, it would be desirable to provide a composition that is non-volatile. It will be appreciated that compositions that achieve all, or any sub-combination of such desirable properties would be useful.

[0014] (Meth)acrylate end uses, such as structural (meth)acrylate compositions such as adhesives, may utilize beads of the composition having a bead width of less than 1 mm.

[0015] In such applications, the surface area of ​​the bead is large compared to the inner core of the bead. As a result, the thickness / height / depth of the bead is more susceptible to oxygen ingress at narrower bead widths. Therefore, the use of (meth)acrylate compositions with reduced oxygen cure inhibition improves performance at such narrow bead widths.

[0016] In one embodiment, the present invention provides a two-part curable composition comprising part A and part B: Part A is (i) a curable (meth)acrylate component; (ii) a free radical initiator; and (iii) A cyclic β-ketoester, wherein the cyclic portion of the cyclic β-ketoester contains a ring consisting of at least 6 atoms (at least 6-membered ring). and Part B is (i) a curable (meth)acrylate component; and (ii) Transition metal component The present invention provides a two-part curable composition comprising:

[0017] The compositions of the present invention exhibit good curing properties and are not substantially inhibited by oxygen (air). In particular, a tack-free cure is achieved even when the compositions are exposed to air. The compositions exhibit improved cure in exposed bond areas along with excellent metal and composite adhesion and high impact resistance. In the context of the present invention, tack-free means dry / non-sticky to the touch.

[0018] The compositions of the present invention have reduced oxygen cure inhibition, which is particularly useful as these compositions cure in end uses where the amount of the composition exposed to air is relatively high and oxygen inhibition occurs.

[0019] The compositions of the present invention exhibit good adhesion as measured by adhesive strength, which can be achieved with low bead thicknesses, for example bead thicknesses of less than 1 mm.

[0020] The compositions of the present invention exhibit good stability and may be stored prior to use without impairing final performance when cured.

[0021] The compositions of the present invention exhibit good structural performance.

[0022] The cyclic β-ketoester component in the compositions of the present invention may include cyclic β-ketoesters in which the ring structure is interrupted by one or more heteroatoms, such as oxygen.

[0023] Additionally, or alternatively, the ester oxygen atom of the β-keto ester group may be part of a ring in a cyclic structure.

[0024] Additionally or alternatively, the carbon atom to which the carbonyl oxygen of the ester group is bonded, or the carbon atom to which the carbonyl oxygen of the keto group is bonded, or both, can be part of a ring in a cyclic structure.

[0025] A ring consisting of at least six atoms may be a carbocyclic ring (not including heteroatoms).

[0026] The cyclic portion of the cyclic β-ketoester may be formed by a ring composed of at least seven atoms.

[0027] For example, cyclic β-keto esters are (i) Ethyl 2-oxocyclohexanecarboxylate; (ii) methyl 2-oxocyclohexanecarboxylate; (iii) ethyl 2-oxocycloheptanecarboxylate; (iv) methyl 2-oxocycloheptanecarboxylate; (v) ethyl 2-oxocyclooctanecarboxylate; (vi) methyl 2-oxocyclooctanecarboxylate; and Any combination thereof may be selected.

[0028] Additionally or alternatively, the β-keto ester component can be a cyclohexyl, cyclohexenyl, cycloheptyl, cycloheptenyl, cyclooctyl, or cyclooctenyl β-keto ester, a β-keto ester having a fused ring structure, e.g.

[0029] [ka] Or any combination thereof.

[0030] Desirably, the cyclic β-ketoester is present in an amount of about 0.5% to about 5% by weight based on the total weight of the composition, for example, the cyclic β-ketoester is present in an amount of about 1% to about 3% by weight based on the total weight of the composition.

[0031] In the two-part curable composition according to the present invention, the curable (meth)acrylate component is suitably present in an amount of from about 10% to about 90% by weight based on the total weight of the composition, for example, the curable (meth)acrylate component is present in an amount of from about 30% to about 70% by weight based on the total weight of the composition.

[0032] The two-part curable composition according to the present invention may further comprise an acidic (meth)acrylate monomer. The acidic (meth)acrylate monomer is desirably present in an amount of about 1% by weight to about 30% by weight based on the total weight of the composition, for example, the acidic (meth)acrylate monomer is present in an amount of about 5% by weight to about 20% by weight based on the total weight of the composition.

[0033] Desirably, the two-part curable composition of the present invention includes a toughening agent. The toughening agent may be a rubber component. The toughening agent may be a block copolymer component. The toughening agent is suitably present in an amount of from about 10% to about 60% by weight based on the total weight of the composition, for example from about 20% to about 40% by weight based on the total weight of the composition.

[0034] The two-part curable compositions of the present invention may include a core-shell rubber. Desirably, the core-shell rubber is present in an amount up to about 25% by weight based on the total weight of the composition. For example, when present, the core-shell rubber is present in an amount of about 5% to about 20% by weight based on the total weight of the composition.

[0035] The two-part curable composition of the present invention may include a liquid rubber, which is desirably present, and when present, is present in an amount of up to about 20% by weight based on the total weight of the composition. For example, when the liquid rubber is present, it is desirably present in an amount of about 2.5% to about 15% by weight based on the total weight of the composition.

[0036] In the two-part curable compositions of the present invention, the free radical initiator component may be present in an amount of about 0.5% to about 5% by weight based on the total weight of the composition, for example, the free radical initiator component may be present in an amount of about 1% to about 3% by weight based on the total weight of the composition.

[0037] Desirably, the free radical initiator component comprises a peroxide and / or a hydroperoxide. Combinations of two or more peroxides and / or two or more hydroperoxides may be used.

[0038] In the two-part curable compositions of the present invention, the transition metal component is desirably a vanadium(III) salt or a vanadyl(IV) salt, or any combination thereof. The transition metal component is desirably present in an amount of about 0.1% to about 1% by weight based on the total weight of the composition, for example, the transition metal component may be present in an amount of about 0.25% to about 0.75% by weight based on the total weight of the composition.

[0039] Desirably, the two-part curable composition according to the present invention includes a free radical stabilizer component. Suitably, the free radical stabilizer is present in an amount of up to about 1 wt %, based on the total weight of the composition, and optionally, the free radical stabilizer is present in an amount of about 0.1 wt % to about 0.5 wt %, based on the total weight of the composition.

[0040] The two-part curable compositions of the present invention may also include a chelating agent, such as the tetrasodium salt of ethylenediaminetetraacetic acid ("EDTA"). Desirably, the chelating agent is present in an amount of up to about 1 wt. % based on the total weight of the composition, for example, the chelating agent is present in an amount of about 0.01 wt. % to about 0.1 wt. % based on the total weight of the composition.

[0041] The two-part curable composition according to any of the preceding claims may be formulated such that Part A and Part B are present in a weight ratio of about 1:1.

[0042] The present invention also relates to the cured product of the two-part curable composition of the present invention.

[0043] The present invention also relates to an assembly comprising a first substrate bonded to a second substrate, the first substrate being bonded to the second substrate by a two-part curable composition according to the present invention.

[0044] Desirably, at least one of the substrates is a glass substrate, for example glass that forms part of an electronic device, such as a display screen (eg, a touch-sensitive display screen).

[0045] The present invention can be described as comprising a two-part system, with both parts containing methacrylate monomers and oligomers, rubber toughening agents, fillers, free radical stabilizers, and other additives commonly used in structural methacrylate adhesives.

[0046] Part A contains a suitable β-ketoester and a free radical initiator such as a peroxide oxidizer. Part B contains a redox active metal catalyst, preferably a vanadium(III) or vanadyl(IV) salt.

[0047] The present invention provides a two-component methacrylate composition comprising in one part a redox active metal catalyst, preferably vanadyl(IV) or vanadium(III) acetylacetonate, and in the other part a free radical initiator such as a peroxide and a β-ketoester (the ketone contains a cyclic hydrocarbon ring). The ring may contain 4 to 8 carbons, most preferably 6 to 7 carbons. When the free radical initiator is a peroxide, it is preferably a hydroperoxide.

[0048] The (meth)acrylate component is H2C=CGCO2R 1 where G may be hydrogen or an alkyl group having 1 to about 4 carbon atoms, and R 1 may be selected from alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkaryl, aralkyl, or aryl groups having 1 to about 16 carbon atoms, any of which may optionally be substituted or interrupted by silane, silicon, oxygen, halogen, carbonyl, hydroxyl, ester, carboxylic acid, urea, urethane, carbonate, amine, amide, sulfur, sulfonate, sulfone, and the like.) For example, phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, butyl (meth)acrylate, hydroxyethyl (meth)acrylate, and hydroxypropyl (meth)acrylate.

[0049] Additional (meth)acrylates suitable for use herein include multifunctional (meth)acrylates, such as di- or trifunctional (meth)acrylates, such as polyethylene glycol di(meth)acrylate, tetrahydrofuran (meth)acrylate, and di(meth)acrylate, hydroxypropyl (meth)acrylate ("HPMA"), hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate ("TMPTMA"), diethylene glycol dimethacrylate, triethylene glycol dimethacrylate ("TRIEGMA"), tetraethylene glycol dimethacrylate, dipropylene glycol dimethacrylate ("PDEMA"). These include, but are not limited to, glycol dimethacrylate, di(pentamethylene glycol) dimethacrylate, tetraethylene diglycol diacrylate, diglycerol tetramethacrylate, tetramethylene dimethacrylate, ethylene dimethacrylate, neopentyl glycol diacrylate, trimethylolpropane triacrylate, and bisphenol A mono- and di(meth)acrylates, such as ethoxylated bisphenol A (meth)acrylate ("EBIPMA"), and bisphenol F mono- and di(meth)acrylates, such as ethoxylated bisphenol F (meth)acrylate.

[0050] Further (meth)acrylates that may be used herein include silicone (meth)acrylates ("SiMA"), such as those taught and claimed in U.S. Pat. No. 5,605,999 (Chu), the disclosure of which is expressly incorporated herein by reference.

[0051] Of course, combinations of these (meth)acrylates may also be used, but desirably the (meth)acrylate component is selected from one or more of N,N-dimethylacrylamide, phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, butyl (meth)acrylate, hydroxyethyl (meth)acrylate, and hydroxypropyl (meth)acrylate.

[0052] The curable compositions of the present invention may incorporate free radical polymerization initiators, including hydroperoxides such as cumene hydroperoxide ("CHP"), p-menthane hydroperoxide, t-butyl hydroperoxide ("TBH"), and t-butyl perbenzoate. Other free radical polymerization initiators include peroxides such as benzoyl peroxide, dibenzoyl peroxide, 1,3-bis(t-butylperoxyisopropyl)benzene, 1,1,3,3-tetramethylbutyl hydroperoxide; diacetyl peroxide, butyl 4,4-bis(t-butylperoxy)valerate, p-chlorobenzoyl peroxide, cumene hydroperoxide, t-butylcumyl peroxide, t-butyl perbenzoate, di-t-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, 2,5-dimethyl-2,5-di-t-butyl-peroxyhex-3-yne, 4-methyl-2,2-di-t-butylperoxypentane, and combinations thereof.

[0053] The component of the composition of the present invention that is a cyclic β-keto ester (wherein the cyclic portion of the cyclic β-keto ester includes a ring made up of at least six atoms) is different from the free radical initiator component of the composition of the present invention. The two components are separate, and each of the two distinct components is independent of the other. Both are present. Thus, there are two separate components, both of which are present in Part A of the composition.

[0054] Reinforcing agents include vinyl terminated polybutadiene, rubbers such as ABS rubber, SBS rubber, NBR rubber, and SIS rubber, and particulate rubber powders such as core-shell rubbers, such as MBS core-shell rubber, and non-core-shell rubbers. For example, BLENDEX 338 is an ABS powder from GE Plastics.

[0055] The vinyl terminated polybutadiene is desirably liquid at room temperature. The glass transition temperature of the vinyl terminated polybutadiene is desirably less than 0° C. The vinyl termination may be in the form of (meth)acrylate termination, such as (meth)acrylate terminated polybutadiene-acrylonitrile copolymers, such as HYCAR VTBN, or (meth)acrylate terminated polybutadienes, such as HYCAR VTB, Emerald Performance Polymers.

[0056] The compositions of the present invention may further include conventional additives such as thickeners, fillers, pigments, stabilizers, etc., provided that such additives do not interfere with effective curing of the adhesive compositions of the present invention.

[0057] Fillers can provide bulk without significantly sacrificing strength of the adhesive and can be selected from high or low density fillers, and certain fillers, such as silica, can provide rheology modification or small particle reinforcement. Commercially available examples include CAB-O-SIL 610 and AEROSIL R8200.

[0058] Low density fillers are of interest because the resulting final product has a lower density than the product without the filler, yet has strength properties in essentially the same range as when the filler is not present. For example, glass spacer beads, which may or may not be hollow.

[0059] It will be understood that the compositions of the present invention may contain non-reactive species, such as resins. Such components do not participate in the (anaerobic) curing reaction. They are non-reactive. However, such components may be incorporated into other components during their curing and become part of the cured product. Examples of such non-reactive species include fumed silica, polyethylene, PTFE, mica, polyamide wax, titanium dioxide, barium sulfate, etc. [Brief description of the drawings]

[0060] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0061] [Figure 1] Testing showing improved oxygen resistance of cured adhesive samples (top: glass slide coated with Loctite HHD8540, bottom: glass slide coated with the cured composition of Example 3).

[0062] Detailed Description The invention will now be illustrated with reference to the following examples.

[0063] Comparative Examples and Examples of the Invention Comparative Example 1 is the commercially available product Loctite® HHD8540, a two-part methyl methacrylate (MMA) adhesive, available from Henkel Ireland, Dublin, Ireland.

[0064] Comparative Example 2 - Formulation using dicarbonylacetylbutyrolactone as in the example of US20100297457A1 (Sika) mentioned above.

[0065] Comparative Example 3 - Formulation using dicarbonylethyl acetoacetate as in the example of US20100297457A1 (Sika).

[0066] Comparative Example 4 - Formulation using manganese(III) trisacetylacetonate as described above in Garra et al., Macromolecules 2018, 51, 6395-6404.

[0067] Comparative Example 5-Formulation with Ethyl 2-oxocyclopentanecarboxylate.

[0068] Examples 1-4 are illustrative of the present invention and comprise in Part A a suitable β-ketoester according to the present invention and a free radical initiator in the form of a peroxide oxidant, and in Part B a redox active metal catalyst, preferably a vanadium(III) or vanadyl(IV) salt.

[0069] Sample preparation method: The components of the stock solution were added to a mixing vessel with a lid and mixed in a speed mixer DAC 150.1 FVZ-K at 2500 rpm for 10 minutes. To prepare part A and part B, the components were added to the stock solution and mixed at 2500 rpm for 2 minutes. The formulation was then filled in a 2-component cartridge with a 1:1 mix ratio of 50 ml, up to the height of the piston. The cartridge was centrifuged at 1500 rpm for 2 minutes to remove air bubbles. The piston was then placed on top of the cartridge.

[0070] [Table 1-1]

[0071] [Table 1-2]

[0072] [Table 2]

[0073] MMA is methyl methacrylate. Bis-HEMA phosphate is an adhesion promoter and is bis[2-(methacryloyloxy)ethyl]phosphate.

[0074] In this test, the dispense of the sample loaded into the cartridge was tested. Y means that the part could be dispensed. N means that the part could not be dispensed. NT means that it was not tested.

[0075] This test shows that Comparative Example 3, Part B, has very limited stability when manganese(III) trisacetylacetonate is combined with the methacrylate adhesive components necessary for good adhesive performance, demonstrating the limitations of the curing system shown in the above-mentioned Garra et al., Macromolecules 2018, 51, 6395-6404 literature.

[0076] [Table 3]

[0077] In this test, the dispense of the sample loaded into the cartridge was tested. Y means that the part could be dispensed. N means that the part could not be dispensed. NT means that it was not tested. This test shows that the cyclic β-keto ester compound must contain a ring of at least six atoms, such as a ring of at least six atoms including the ketone of the keto ester, to allow sufficient stability of the composition.

[0078] Adhesive performance

[0079] Adhesion testing was performed according to ASTM D3163-01. Testing was performed on lap shears of 50% glass filled polyarylamide primed with Loctite SF7952. Primer volatiles were allowed to evaporate for 5 minutes in a fume hood after brush application onto the substrate. The adhesive was dispensed in a 50 ml cartridge through a static mixer nozzle type. Bonds were made with a 0.25 inch (0.635 cm) overlap and cured initially at 45°C for 20 minutes and then at room temperature for 24 hours.

[0080] [Table 4]

[0081] This demonstrates that the example compositions exhibit adhesive performance on composite substrates, as would be expected for a structural methacrylate adhesive.

[0082] Impact resistance test.

[0083] Testing was performed according to ISO 11343 "Adhesive - Determination of the dynamic resistance to cleavage under impact conditions of high strength adhesive bonds - Wedge impact method". Test substrates were symmetrical hot-dip galvanized steel DC-04 wedge coupons. The adhesive was applied with an induced adhesive gap of 125 μm as in the previous tests. The bonded specimens were cured at 45°C for 20 minutes and then at room temperature for 24 hours.

[0084] Testing was performed on a CEAST 9350 drop impact tower with an impact velocity of 2 m / s.

[0085] [Table 5]

[0086] This demonstrates that examples made with this new technology can provide the excellent impact resistance expected of a structural methacrylate adhesive.

[0087] Testing of cured adhesive samples showing improved oxygen resistance.

[0088] The test was carried out as follows: the adhesive was dispensed onto the glass slides through a Sulzer MBH-04-16S mixing nozzle from a 50ml 1:1 ratio two-component cartridge. The coating thickness was controlled at 75μm thickness / depth. The coated glass slides were then placed in a 45°C oven for 20 minutes, removed and cured at room temperature for an additional 24 hours.

[0089] The coated slides were then subjected to a grit retention test. Silicon carbide F80 grit was applied to the adhesive surface, covering it completely. The grit was then brushed off with a 1-inch (2.54 cm) wide soft, fine-bristled paint brush.

[0090] FIG. 1 shows the grit retention on the coated surface after the grit has been removed with a brush. The grit retention is due to the tackiness of the adhesive surface. The coated slide shown on the top is coated with the two-component MMA Loctite HHD8540. The coated slide on the bottom is coated with the composition of Example 1. From FIG. 1 it is clear that the cured composition of Example 1 has much less grit retention and therefore a less tacky surface. This indicates greater resistance to oxygen inhibition of cure.

[0091] As used herein in connection with the present invention, the terms "comprises / comprising" and "having / including" are used to specify the presence of stated features, integers, steps, or ingredients, but do not exclude the presence or addition of one or more other features, integers, steps, ingredients, or groups thereof.

[0092] It is appreciated that certain features of the invention that are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.

Claims

1. A two-part curable composition comprising Part A and Part B, Part A is (i) a curable (meth)acrylate component; (ii) a free radical initiator; and (iii) a cyclic β-ketoester, wherein the cyclic portion of the cyclic β-ketoester contains a ring consisting of at least six atoms; and Part B is (i) a curable (meth)acrylate component; and (ii) Transition metal component 1. A two-part curable composition comprising:

2. 10. The two-part curable composition of claim 1, wherein the ring of at least six atoms is carbocyclic (and does not contain heteroatoms).

3. The two-part curable composition of claim 1 or 2, wherein the cyclic portion of the cyclic β-ketoester is formed by a ring consisting of at least seven atoms.

4. The cyclic β-ketoester is Ethyl 2-oxocyclohexanecarboxylate; Methyl 2-oxocyclohexanecarboxylate; Ethyl 2-oxocycloheptanecarboxylate; Methyl 2-oxocycloheptanecarboxylate; Ethyl 2-oxocyclooctanecarboxylate; methyl 2-oxocyclooctanecarboxylate; and The two-part curable composition of claim 1 or 2 selected from any combination thereof.

5. 3. The two-part curable composition of claim 1, wherein the cyclic β-ketoester is present at about 0.5% to about 5% by weight, based on the total weight of the composition.

6. 3. The two-part curable composition of claim 1, wherein the cyclic β-ketoester is present in an amount of from about 1% to about 3% by weight, based on the total weight of the composition.

7. 3. The two-part curable composition of claim 1, wherein the curable (meth)acrylate component is present in an amount of from about 10% to about 90% by weight, based on the total weight of the composition.

8. 3. The two-part curable composition of claim 1, wherein the curable (meth)acrylate component is present at about 30% to about 70% by weight, based on the total weight of the composition.

9. The two-part curable composition of claim 1 or 2, wherein the composition comprises an acidic (meth)acrylate monomer.

10. 10. The two-part curable composition of claim 9, wherein the acidic (meth)acrylate monomer is present in an amount of from about 1% to about 30% by weight, based on the total weight of the composition.

11. 10. The two-part curable composition of claim 9, wherein the acidic (meth)acrylate monomer is present in an amount of from about 5% to about 20% by weight, based on the total weight of the composition.

12. The two-part curable composition of claim 1 or 2, wherein the composition includes a toughening agent.

13. 13. The two-part curable composition of claim 12, wherein the toughening agent is a rubber component.

14. 13. The two-part curable composition of claim 12, wherein the toughening agent is a block copolymer component.

15. 13. The two-part curable composition of claim 12, wherein the toughening agent is present in an amount of about 10% to about 60% by weight, based on the total weight of the composition.

16. 13. The two-part curable composition of claim 12, wherein the toughening agent is present in an amount of about 20% to about 40% by weight, based on the total weight of the composition.

17. 3. The two-part curable composition of claim 1 or 2, wherein the composition comprises a core-shell rubber.

18. 20. The two-part curable composition of claim 17, wherein said core-shell rubber is present in an amount up to about 25% by weight, based on the total weight of the composition.

19. 18. The two-part curable composition of claim 17, wherein the core-shell rubber is present in an amount of from about 5% to about 20% by weight, based on the total weight of the composition.

20. 3. The two-part curable composition of claim 1 or 2, wherein the composition comprises a liquid rubber.

21. 21. The two-part curable composition of claim 20, wherein the liquid rubber is present in an amount up to about 20% by weight based on the total weight of the composition.

22. 21. The two-part curable composition of claim 20, wherein the liquid rubber is present in an amount of from about 2.5% to about 15% by weight, based on the total weight of the composition.

23. 3. The two-part curable composition of claim 1, wherein the free radical initiator component is present in an amount of from about 0.5% to about 5% by weight, based on the total weight of the composition.

24. 3. The two-part curable composition of claim 1, wherein the free radical initiator component is present in an amount of about 1% to about 3% by weight, based on the total weight of the composition.

25. 3. The two-part curable composition of claim 1 or 2, wherein the transition metal component comprises a vanadium (III) salt or a vanadyl (IV) salt or any combination thereof.

26. 3. The two-part curable composition of claim 1 or 2, wherein the transition metal component is present in an amount of about 0.1 wt % to about 1 wt %, based on the total weight of the composition.

27. 3. The two-part curable composition of claim 1 or 2, wherein the transition metal component is present in an amount of about 0.25 wt % to about 0.75 wt %, based on the total weight of the composition.

28. 3. The two-part curable composition of claim 1 or 2, wherein the composition includes a free radical stabilizer component.

29. 30. The two-part curable composition of claim 28, wherein a free radical stabilizer is present and is present in an amount up to about 1 wt. %, based on the total weight of the composition.

30. 30. The two-part curable composition of claim 28, wherein the free radical stabilizer is present and is present in an amount of about 0.1 wt % to about 0.5 wt %, based on the total weight of the composition.

31. 3. The two-part curable composition of claim 1 or 2, wherein the composition includes a chelating agent such as the tetrasodium salt of ethylenediaminetetraacetic acid ("EDTA").

32. 32. The two-part curable composition of claim 31, wherein the chelating agent is present and is present in an amount of up to about 1 wt. %, based on the total weight of the composition.

33. 32. The two-part curable composition of claim 31, wherein the chelating agent is present and is present in an amount of about 0.01 wt % to about 0.1 wt %, based on the total weight of the composition.

34. 3. The two-part curable composition of claim 1 or 2, wherein Part A and Part B are present in a weight ratio of about 1:

1.

35. A cured product of the two-part curable composition described in claim 1 or 2.

36. 10. An assembly comprising a first substrate bonded to a second substrate, the first substrate being bonded to the second substrate by the two-part curable composition of claim 1 or 2.

37. 37. The assembly of claim 36, wherein at least one substrate is a glass substrate, such as a display screen.

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