CATALYTIC COMPOSITIONS AND THIOLENE-BASED COMPOSITIONS WITH EXTENDED LIFE

Abstract

The present invention relates to catalytic compositions and curable compositions containing them; the catalytic compositions of the present invention consist essentially of: (i) a metal compound; and (ii) a compound other than (i) that catalyzes an addition reaction between an ethylenically unsaturated compound and a thiol, wherein said catalytic composition is essentially free of vanadium compounds; the curable compositions according to the present invention comprise: (a) a polyene, (b) a polythiol, and (c) a catalytic component, which consists of the above-mentioned catalytic composition.

Description

The present invention relates to catalytic compositions and curable compositions with a prolonged shelf life, wherein the curable compositions comprise a polyene, a polythiol and the catalytic composition. BACKGROUND OF THE INVENTION Catalysis is the initiation or acceleration of a chemical reaction due to the participation of a material called a catalyst. Catalysts that speed up a reaction are known as positive catalysts. Catalysts that slow down a reaction are known as negative catalysts, or inhibitors. Unlike reactants, the reaction itself does not consume a catalyst. A catalyst works by providing an alternative pathway in the reaction mechanism from reactants to product. The reaction rate increases when this alternative pathway has a lower activation energy than the reaction pathway without the catalyst. Catalysts can also enable reactions that would otherwise be blocked or slowed by a thermodynamic or kinetic barrier. The catalyst can increase the reaction rate or the selectivity of the reactants, or allow the reaction to proceed at lower temperatures than would otherwise be possible. As such, catalysts can be very valuable tools in industrial chemical processes. However, there can be drawbacks to using catalysts. For example, tin compounds are widely used in industrial products such as coatings as catalysts for isocyanate / hydroxyl reactions. Amine compounds are used as catalysts for polyene / thiol reactions. Unfortunately, the levels of these catalysts required to provide acceptably fast curing rates and desired final product properties often result in a short application time after the reactants are mixed. Therefore, there is a need to work in a timely manner so that the mixed components maintain a viscosity low enough for application to a substrate, such as by spraying. The period of time during which the coating is ready to be applied to a substrate and still has a viscosity low enough for application is commonly referred to as pot life. It is defined more quantitatively later. Generally, the pot life must be balanced with the curing speed of the applied coating. For example, in a multi-component coating system using a catalyst, both the pot life and the curing speed are primarily controlled by the amount of catalyst present. Consequently, if a fast curing speed is required, more catalyst can be used, but this will also result in a shorter pot life. Conversely, if a longer pot life is needed, less catalyst can be used, but the curing speed will also be slowed. It is also important that the applied coating composition dries and hardens quickly so that dirt collection is minimized and valuable workshop space, such as a car, is not occupied while it dries. The time between when a coating is applied to a substrate and when the coating has dried or cured sufficiently that dust or other debris falling onto the coated substrate does not adhere to it is called dust-free time or tack-free time and is an indicator of the curing rate.One way to accelerate the drying and curing of the composition is to add additional catalyst, but this shortens the time available for processing, for example, by spraying, since higher catalyst levels also cause the viscosity of the composition to increase more rapidly as reaction rates increase. Polyenes containing unsaturated groups, such as acryloyl groups, react with compounds containing active hydrogen. This reaction is thought to involve the addition of an anion derived from the nucleophilic active hydrogen-containing compound, which acts as a donor, to an activated unsaturated group, which serves as an acceptor. When these active hydrogen-containing compounds are CH compounds such as malonic ester or acetoacetate, the reaction is known as a Michael addition reaction. Compounds containing SH are also known to function as active hydrogen-containing compounds in a reaction mechanism similar to the Michael addition reaction. This reaction mechanism with SH-containing compounds is known as a thiolene reaction. Catalysts for the reaction of thiolene include amine compounds, for example, tetramethylguanidine, diaza-bicyclo-undecene, and diaza-bicyclo-nonene. Thiolene reactions catalyzed by these strong bases can be difficult to control, and such reaction mixtures generally have a short lifespan. It would be desirable to catalyze the chemical reactions between polyenes and thiols by using catalysts that overcome these drawbacks of the state of the art by extending the service life of the composition and / or accelerating the reaction rate of thiolene after application, in order to achieve a short tack-free time, without adversely affecting the service life of the composition and / or the chemical resistance of the coatings derived from it. BRIEF DESCRIPTION OF THE INVENTION It has now been discovered that these objectives can be achieved through the use of certain catalytic compositions. The catalytic compositions of the present invention consist essentially of: (i) a metal compound; and (ii) a compound that catalyzes an addition reaction between an ethylenically unsaturated compound and a thiol. The catalytic compositions of the present invention are essentially free, as well as completely free, of vanadium compounds. Compound (ii) is different from the metal compound (i). Therefore, the catalytic composition according to the present invention includes two distinct types of compounds. It is generally essentially free, as well as completely free, of reactive compounds comprising groups with acid functionality, anhydride groups, or reaction products of an active hydrogen compound with an anhydride or polyacid. The transition phrase "essentially" means that the composition is limited to the specified steps or materials and those that do not substantially affect the basic and novel features of the claimed invention. In re Herz, 537 F.2d 549, 551-52, 190 USPQ 461, 463 (CCPA 1976) (emphasis in the original). The present invention also relates to curable compositions comprising: (a) a polyene; (b) a polythiol, present in an amount greater than 10 percent by weight based on the total weight of resin solids in the curable composition; and (c) a catalytic component, consisting of the catalytic composition according to the present invention, described above and in more detail below. DETAILED DESCRIPTION OF THE INVENTION For the purposes of the following detailed description, it should be understood that the invention may assume various variations and alternative sequences of steps, except where expressly stated otherwise. Furthermore, apart from any operational example, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and the claims shall be understood as being modified in all cases by the expression "around." Consequently, unless otherwise stated, the numerical parameters set forth in the following specification and the appended claims are approximations that may vary depending on the properties desired to be obtained with the present invention.At a minimum, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be interpreted at least in light of the number of significant digits reported and by applying common rounding techniques. Although the numerical parameters and ranges that establish the broad scope of the invention are approximations, the numerical values ​​stated in the specific examples are reported as accurately as possible. However, any numerical value inherently contains certain errors that necessarily result from the standard variation found in their respective test measurements. Furthermore, it should be understood that any numerical range mentioned herein is intended to include all subranges within it. For example, a range from 1 to 10 is intended to include all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, it has a minimum value equal to or greater than 1 and a maximum value equal to or less than 10. In this application, the use of the singular includes the plural and the plural includes the singular, unless specifically stated otherwise. Furthermore, in this application, the use of "or" means "and / or" unless specifically stated otherwise, although "and / or" may be used explicitly in certain cases. It should be noted that the phrase "and / or," when used in a list, is intended to encompass alternative forms of realization that include each individual component of the list, as well as any combination of components. For example, the list A, B, and / or C is intended to encompass seven separate forms of realization, including A, or B, or C, or A + B, or A + C, or B + C, or A + B + C. Unless otherwise stated, molecular weights are reported as number-average molecular weights determined by gel permeation chromatography with respect to polystyrene standards with the unit g / mol. As previously stated, the catalytic compositions of the present invention contain (i) a metal compound. Suitable metal compounds include at least one metal oxide, a metal salt (including organic and inorganic salts), and an organometallic compound. Metals that may be present in the metal compound (i) include, for example, iron, tin, cobalt, magnesium, manganese, and mixtures thereof. The metal compound (i) present in the catalytic composition according to the present invention may often comprise an iron compound. Example metal compounds include, for example, iron(II) and iron(III) compounds such as iron oxides, ferrous or ferric acetate, and metal halides such as ferric chloride and ferrous chloride. The catalytic compositions of the present invention also contain (i) a IVIA / a / ¿U41 / UU l ¿ó (compound that catalyzes an addition reaction between an ethylenically unsaturated compound and a thiol. The catalytic compound (i) may comprise, for example, a base. The catalytic compound (i) may comprise, for example, an organic compound having one or more nitrogen and / or phosphorus atoms. Suitable catalytically active compounds (i) include, for example, primary, secondary, and tertiary amines and phosphines. Specific, non-limiting examples of such compounds include, for example, oxazolidines, triethylamine, dimethylhexylamine, dimethylcyclohexylamine, dimethyloctylamine, dimethyldodecylamine, dimethylamino alcohols such as dimethylaminoethanol, tetramethylguanidine, diaza-bicyclooctane, diaza-bicycloundecene, diaza-bicyclononene, n-methyl-triazabicyclodecene, trioctylphosphine, and triphenylphosphine. Compound (ii) may comprise a substituted carbonate salt. For example, quaternary ammonium and phosphonium carbonates are suitable. Particular examples include tetrahexylammonium methylcarbonate, tetrahexylammonium bicarbonate, tetradecyltrihexylammonium methylcarbonate, and tetradecylammonium methylcarbonate. Such substituted carbonate salts are disclosed in U.S. Patent Application Publication No. 2013 / 0210986 in paragraphs

[0032] to

[0039] . Combinations of any of the aforementioned compounds may also be used when appropriate. Typically, the molar ratio of nitrogen (as in an amine or ammonium group) or phosphorus (as in a phosphine or phosphonium group) in compound (i) to the metal in metal compound (i) is from 0.4 to 500:1, such as from 1 to 100:1 or from 25 to 75:1. For example, when metal compound (i) comprises an iron compound and compound (ii) comprises a compound containing a secondary or tertiary amine group, the molar ratio of the amine group (and therefore N) to iron is normally from 0.4 to 500:1, such as from 0.9 to 30:1, or from 1 to 10:1 or from 25 to 75:1. The catalytic compositions of the present invention are essentially free, and may be completely free, of vanadium compounds. Furthermore, they may be essentially free, or completely free, of reactive compounds comprising groups with acid functionality or groups that can be converted into groups with acid functionality through a suitable chemical reaction. Examples of such reactive compounds include an anhydride, an acid (including, for example, carboxylic, phosphonic, or sulfonic acids), or a reaction product of an active hydrogen compound with an anhydride or polyacid. Essentially free of a material means that a composition has only minimal or incidental amounts of a given material, and that the material is not present in a sufficient quantity to affect any property of the composition.These materials are not essential to the composition, and therefore the composition does not contain these materials in perceptible or essential quantities. Furthermore, they may substantially affect the basic and novel features of the invention because they may exhibit catalytic activity. If present, they are only in incidental quantities, generally less than 0.1 percent by weight, such as less than 0.05 percent by weight or less than 0.01 percent by weight, depending on the total weight of solids in the composition. "Completely free," as used herein, means that the composition does not contain the aforementioned materials at all or at least not in measurable quantities. The catalytic compositions of the present invention are useful for extending shelf life, as defined below, while simultaneously providing a rapid cure time for various curable compositions, particularly compositions that undergo thiolene-type reactions. The catalytic compositions of the present invention are more effective at extending the shelf life of compositions that undergo thiolene-type reactions than conventional catalysts. These curable compositions are often useful as automotive topcoats because they can be reactive and cure at ambient temperatures. "Ambient" means the condition of the environment without adjustment of temperature, humidity, or pressure. Typically, ambient temperature ranges from 40 to 95°F (about 4 to 35°C), often from 60 to 95°F (about 15 to 35°C), such as a typical ambient temperature of 72°F (22.2°C). The catalytic compositions of the present invention can also be used to extend shelf life and provide a rapid cure time for thiolene reactions in aerospace coating and sealant systems based on thiolene curing chemistry. Coatings and sealants useful in aerospace applications must meet a number of demanding performance requirements, including resistance to aviation fluids. Prepolymers having sulfur groups in the main chain, such as polythioethers, polysulfides, and sulfur-containing polyformals, can be advantageously used in aerospace coatings and sealants. These sulfur-containing prepolymers can be reacted with a polyene in the presence of an amine catalyst to provide a cured coating or sealant suitable for aerospace applications.Compositions comprising thiol-terminated sulfur-containing prepolymers and polyenes such as acrylates are disclosed in U.S. Application Publication No. 2006 / 0270796 and are suitable for use in the curable compositions of the present invention described below. Compositions comprising thiol-terminated sulfur-containing prepolymers are disclosed in U.S. Application Publications Nos. 2013 / 0343371, 2014 / 0378649, 2015 / 0119549, 2015 / 0252233, 2013 / 0345389, 2015 / 0099858, and 2015 / 0252232 and are suitable for use in the curable compositions of the present invention. Compositions comprising thiol-terminated sulfur-containing prepolymers suitable for use in aerospace senator applications and thiolene curing chemicals are disclosed, for example, in U.S. application publications N.° 2012 / 00401303 and 2014 / 0186543 and are suitable for use in the curable compositions of the present invention. The term polymer iviA / a / zuzi ιυν is also intended to include copolymer, oligomer, and prepolymer; i.e., a material that can be chain-extended to increase its molecular weight. The present invention also relates to curable compositions comprising: (a) a polyene, (b) a polythiol, and (c) a catalytic component, consisting of the catalytic composition of the present invention as described above. The term catalytic component or catalytic composition, as used herein, refers collectively to all the materials disclosed above, each of which, either individually or in some combination with one or more of the other materials, has a catalytic effect on the reaction of the polyene (a) and the polythiol (b), i.e., affects the reaction kinetics without being permanently consumed by the reaction.While not intended to be purely theoretical, it is believed that the metal compound (i) provides surface curing to the composition. For example, when the curable composition is applied to a substrate as a coating, the metal compound (i) catalyzes the curing of the coating composition in the outermost region of the coating layer opposite the substrate surface and exposed to air. Similarly, when the curable composition is molded or otherwise shaped into a manufactured article, the metal compound (i) catalyzes the curing of the composition on its surface. It is further believed that the compound (i) provides complete curing to the composition, meaning curing throughout most of the composition. The polyenes (a) suitable for use in the curable compositions of the present invention are numerous and can vary widely. Such polyenes may include those known in the art. Non-limiting examples of suitable polyenes may include those represented by the formula: A - (X)men where A is an organic portion, X is an olefinic unsaturated portion, an alkyl group and / or a Michael acceptor group, and m is at least 2, usually from 2 to 6. The organic portion A may comprise C, H, and heteroatoms. The organic portion A may comprise, for example, contain one or more groups selected from ester and urethane groups. The organic portion A may be derived, for example, from a polyisocyanate as indicated below for polyurethane (meth)acrylates and polyurethanes containing (meth)allyl groups. Non-limiting examples of X are groups of the following structures: -CC(R)=CH2 and -CH2-C(R)=CH2 II O (meth)acrylate (meth)allyl, where each R is selected from H and a methyl group. Note that acrylic and methacrylic are hereby designated in summary form as (meth)acrylic. Note that allyl and methylyl are hereby designated in summary form as (meth)allyl. The phrase "derivative of a polyisocyanate" refers hereto to a portion resulting from the reaction of an isocyanate group (-N=C=O) of a polyisocyanate with a reactive group containing an isocyanate group, such as a hydroxyl group. Similarly, "derivative of a polyol," as in the expression "derivative of a polyol," refers to a portion resulting from the reaction of an alcoholic hydroxyl group (-OH) of a polyol with a reactive group containing a hydroxyl group, such as a carboxyl group. Suitable polyenes include compounds or polymers that have polymerizable olefinic double bonds in the molecule, such as those formed by exposure to radiation. Examples of such materials are (meth)acrylic copolymers with (meth)acrylic functionality, epoxy resin (meth)acrylates, polyester (meth)acrylates, polyether (meth)acrylates, polyurethane (meth)acrylates, amino (meth)acrylates, silicone (meth)acrylates, and melamine (meth)acrylates, of which polyester (meth)acrylates and polyurethane (meth)acrylates are particularly useful. The number-average molecular weight (Mn) of these compounds is often around 200 to 10,000. Suitable polyenes typically contain, on average, 2 to 20 polymerizable olefinic double bonds per molecule, for example, those formed by exposure to radiation. Aliphatic and / or cycloaliphatic (meth)acrylates are generally used.Aliphatic and cycloaliphatic are herein referred to collectively as (cyclo)aliphatic. (Cyclo)aliphatic polyurethane (meth)acrylates and (cyclo)aliphatic polyester (meth)acrylates are particularly suitable. Combinations of a plurality of polyenes, such as any of those mentioned herein, may also be used as polyene (a) in the curable compositions according to the present invention. As mentioned above, polyurethane (meth)acrylates are suitable for use as polyene (a). Examples of polyurethane (meth)acrylates include reaction products of polyisocyanates such as 1,6-hexamethylene diisocyanate and / or isophorone diisocyanate, including isocyanurate and biuret derivatives thereof, with hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate and / or hydroxypropyl (meth)acrylate. The polyisocyanate can be reacted with hydroxyalkyl (meth)acrylate in an NCO / OH equivalent ratio of 1:1 or it can be reacted with an NCO / OH equivalent ratio greater than 1:1 to form a reaction product with NCO functionality that can then be chain extended with a polyol such as a diol or triol, for example, 1,4-butanediol, 1,6-hexanediol and / or trimethylolpropane. Polyester (meth)acrylates are also suitable for use as polyene (a), and include, for example, reaction products of (meth)acrylic acid or (meth)acrylic acid anhydride with polyols, such as diols, triols, tetraols, and higher polyols, including alkylated polyols, such as propoxylated diols and triols. Examples of suitable polyols include glycerol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, trimethylolpropane, pentaerythritol, and propoxylated 1,6-hexanediol. Specific examples of suitable polyester (meth)acrylates are, for example, glycerol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol penta(meth)acrylate. (Met)allyl compounds or polymers can also be used alone or in combination with (meth)acrylate compounds such as those described above as polyene (a) in the curable compositions according to the present invention. Examples of (met)allyl materials are polyallyl ethers such as the diallyl ether of 1,4-butanediol and the trialyl ether of trimethylolpropane. Examples of other (met)allyl compounds are polyurethanes containing (met)allyl groups, including reaction products of polyisocyanates such as 1,6-hexamethylene diisocyanate and / or isophorone diisocyanate (including isocyanurate and biuret derivatives thereof) with allyl ethers having hydroxyl functionality, such as the monoallyl ether of 1,4-butanediol and the diallyl ether of trimethylolpropane.The polyisocyanate can be reacted with the diallyl ether with hydroxyl functionality in an equivalent NCO / OH ratio of 1:1 or it can be reacted with an equivalent NCO / OH ratio greater than 1:1 to form a reaction product containing NCO that can then be chain extended with a polyol such as a diol or triol, for example, 1,4-butanediol, 1,6-hexanediol and / or trimethylolpropane. As mentioned previously, polyene (a) may also comprise one or more Michael acceptor groups. A Michael acceptor group refers to an alkenyl / alkynyl portion in which one or more electron-withdrawing groups, such as carbonyl (C=O), nitro (-NO2), nitrile (-CN), alkoxycarbonyl (-COOR), phosphonate (-PO(OR)2), trifluoromethyl (-CF3), sulfonyl (-SO2-), p-toluenesulfonyl (-SO2-C6H4-CH3), etc., are directly attached to a carbon atom of the carbon-carbon double or triple bond, respectively. Examples of compounds containing a Michael acceptor group include vinyl ketones, quinones, nitroalkenes, acrylonitriles, acrylates, methacrylates, cyanoacrylates, acrylamides, maleimides, dialkyl vinylphosphonate, and vinylsulfones. Other examples of Michael acceptors are disclosed in Mather et al., Proq. Polym. ScL 2006, 31, 487-531. Michael acceptor compounds having more than one Michael acceptor group are also known.Examples include diacrylates such as ethylene glycol diacrylate and diethylene glycol diacrylate, dimethacrylates such as ethylene glycol methacrylate and diethylene glycol methacrylate, bismaleimides such as N,N'-(1,3-phenylenedi)dimaleimide and 1,1'-(methylene-4,1-phenylenedi)bismaleimide, vinylsulfones such as divinylsulfone and 1,3-bis(vinylsulfonyl)2-propanol, etc. A Michael acceptor group, which may be present in the polyene (a) according to the present invention, may have, for example, the structure of Formula (a) or Formula (b):. -CH2-CH2-S(O)2-Ra <H(-OH)-Ra-S(O)2-CH=CH2 (la) -CH2-CH2-S(O)2-CH2-CH(-OH)-CH2-S(O)2-CH=CH2 (Ib) where each Rase independently selects C1-3 alkandiyl and C1-3 to be substituted, wherein the one or more substituent groups is -OH. A maleimide herein refers to a compound that has a maleimide group: A bismaleimide refers to a compound that has two maleimide groups, where the two maleimide groups are linked by the nitrogen atoms through a bonding atom or group. Accordingly, a Michael acceptor compound can be used as a polyene (a) in the curable composition according to the present invention. A Michael acceptor compound refers to a compound comprising at least one terminal Michael acceptor group. In certain examples, a Michael acceptor compound is a divinylsulfone and a Michael acceptor group is vinylsulfonyl, i.e. -S(O)2-CH=CH2. For example, a Michael acceptor compound can be a bis(vinylsulfonyl)alkanol, and a Michael acceptor group can be, for example, l-(ethylenesulfonyl)-n-(vinylsulfonyl)alkanol or 1(ethylenesulfonyl)-3-(vinylsulfonyl)propan-2-ol. A Michael acceptor group that may be present in suitable compounds such as polyene (a) in curable compositions according to the present invention may also be a maleimide and, in certain examples, an l-(4-(4-(3-yl-2,5-dioxopyrrolidinl-l)benzyl)phenyl)lH-pyrrole-2,5-dione group. Michael addition chemistries can be employed in various ways to provide suitable curable compositions particularly for use in aerospace sealant applications. For example, a curable composition provided by this disclosure may comprise (i) a thiol-terminated sulfur-containing prepolymer as polythiol (b) and a Michael acceptor-terminated sulfur-containing prepolymer as polyene (a); (ii) a mixture of a thiol-terminated sulfur-containing prepolymer and a low-molecular-weight polythiol as polythiol (b), and a Michael acceptor-terminated sulfur-containing prepolymer as polyene (a); (iii) a thiol-terminated sulfur-containing prepolymer as polythiol (b), and a mixture of a Michael acceptor-terminated sulfur-containing prepolymer and a low-molecular-weight compound having at least two Michael acceptor groups as polyene (a);or (iv) a mixture of a thiol-terminated sulfur-containing prepolymer and a low molecular weight polythiol as polythiol (b), and a mixture of a Michael acceptor-terminated sulfur-containing prepolymer and a low molecular weight compound having at least two Michael acceptor groups as polyene (a).; Sulfur-containing Michael acceptor-terminated prepolymers and sulfur-containing thiol-terminated polymers can be derived from polythioethers, polysulfides, sulfur-containing polyformals, or combinations of any of the above. Low molecular weight polythiols and low molecular weight Michael acceptor compounds can have an average molecular weight of less than around 400 daltons or less than around 1,000 daltons. Sulfur-containing Michael-acceptor terminated prepolymers may have at least two terminal unsaturated groups that are activated for Michael addition, such as activated unsaturated groups that serve as a Michael addition acceptor. The Michael acceptor-terminated sulfur-containing prepolymers that can be used as polyene (a) in the curable compositions according to the present invention generally comprise at least two terminal Michael acceptor groups. Therefore, suitable Michael acceptor-terminated sulfur-containing prepolymers may be, for example, difunctional, or may have a functionality greater than 2, such as 3, 4, 5, or 6. The Michael acceptor-terminated sulfur-containing prepolymer may also comprise a mixture of Michael acceptor-terminated sulfur-containing prepolymers, which may have different functionalities, characterized by an average functionality of 2.05 to 6, 2.1 to 4, 2.1 to 3, 2.2 to 2.8, or 2.4 to 2.6.Accordingly, suitable Michael acceptor-terminated sulfur-containing prepolymers may have at least two terminal Michael acceptor groups, or they may have two, three, four, five, or six terminal Michael acceptor groups. A Michael acceptor-terminated sulfur-containing prepolymer may also comprise a combination of adducts, each of which may have different numbers of terminal Michael acceptor groups, characterized, for example, by an average Michael acceptor functionality of 2.05 to 6, 2.1 to 4, 2.1 to 3, 2.2 to 2.8, or 2.4 to 2.6. Suitable Michael acceptor-terminated sulfur-containing prepolymers include Michael acceptor-terminated polythioethers, iviA / a / ¿u4i / uu i ¿ó i polysulfides Michael, sulfur-containing polyformals terminated in Michael accept, and combinations thereof. For example, any of the sulfur-containing polythioethers, polysulfides, and polyformals suitable for use as sulfur-containing prepolymers terminated in thiol can also be used as the main chain for a sulfur-containing prepolymer terminated in Michael accept. Sulfur-containing prepolymers terminated in Michael's accept suitable for use in aerospace senator applications are disclosed, for example, in U.S. Application Publications No. 2014 / 0378649, 2014 / 0378649 and 2015 / 0119549. As mentioned above, a sulfur-containing prepolymer terminated in Michael accept useful as a polyene (a) in curable compositions according to the present invention may comprise a Michael accept-terminated polythioether. A Michael-accepted sulfur-containing prepolymer may comprise, for example, a Michael-accepted polythioether comprising: (a) a main chain comprising the structure of Formula (2): -R1-[-S-(CH2)2-O-[-R2-O-]m-(CH2)2-S-R1]n- (2) wherein (i) each R1 is independently selected from a C2-10 n-alkandiyl group, a branched C3-6 alkandiyl group, a Ce-s cycloalkandiyl group, a Ce-io alkancycloalkandiyl group, a divalent heterocyclic group, a -[(-CHR3-)pX-]q-(CHR3)r~ group, wherein each R3 is independently selected from hydrogen and methyl; (i) each R2 is independently selected from a C2-10 n-alkandiyl group, a C3-6 branched alkandiyl group, a Ce-8 cycloalkandiyl group, a C6-14 alkancycloalkandiyl group, a divalent heterocyclic group, and a -[(-CH2-)PX-]q-(CH2)i~ group; (iii) each X is independently selected from O, S, and an -NR4- group, wherein R4 is selected from H and a methyl group; (iv) m is an integer ranging from 0 to 50; (v) n is an integer ranging from 1 to 60; (vi) p is an integer ranging from 2 to 6; (vii) q is an integer ranging from 1 to 5; and (viii) r is an integer ranging from 2 to 10;and (b) at least two terminal Michael acceptor groups, each of which may be individually selected from any of the Michael acceptor groups described herein.; In a compound of Formula (2), R1 can be in particular -[-(CHR3)pX-]q(CHR3)r- where each X can be selected independently of -O- and -S-, where generally each X is -O- or each X is -S-. More specifically, in a compound of Formula (2), R1 can be in particular —[—(CH2)p—X—]q—(CH2)r- where each X can be independently selected from -O- and -S-. Generally, each X is either -O- or each X is -S- in the present. Even more specifically, in a compound of Formula (2), R1 can be -[( iviA / a / zuzi / uu (¿ói CH2-)pX-]q-(CH2)r-, where p can be 2, X can be O, q is 2, r can be 2, R2 can be ethanendiyl, m can be 2 and n can be 9. A sulfur-containing Michael acceptor-terminated prepolymer useful as a polyene (a) according to the present invention may comprise, for example, a Michael acceptor-terminated polythioether of Formula (3a), a Michael acceptor-terminated polythioether of Formula (3b), or a combination thereof: R6-S-R5-[-S-(CH2)PO-(R7-O)m-(CH2)2-S-R5-]nS-R6(3a) {R6-S-R5-[-S-(CH2)PO-(R7-O)m-(CH2)2-S-R5-]nS—V'-}zB (3b) wherein: each R5 is independently selected from C2-10 alkandiyl, Ce-s cycloalkandiyl, Ce-io alkancycloalkandiyl, C5-8 heterocycloalkandiyl and -[(-CHR8-)sX-]q-(-CHR8-)i-, wherein: s is an integer from 2 to 6; q is an integer from 1 to 5; r is an integer from 2 to 10; each R8 is independently selected from hydrogen and methyl; and each X is selected independently from -O-, -S-, -NH- and -N(-CH3)-; each R7 is selected independently from C1-10 alkandiyl, Ce-s cycloalkandiyl, Ce-14 alkancycloalkandiyl and -[(-CHR8-)sX-]q-(-CHR8-),~, where s, q, r, R8 and X are as defined for R5; m is an integer from 0 to 50; n is an integer from 1 to 60; p is an integer from 2 to 6; B represents a core of a z-valent polyfunctional agent B(-V)zen where: z is an integer from 3 to 6;and each V is a group comprising a terminal group reactive with thiol groups; and each -V- is derived from the reaction of -V with a thiol; and each R6 is independently a portion comprising a terminal Michael acceptor group. In the prepolymers of Formula (3a) and Formula (3b), R5 can be in particular -[(-CH2-)sX-]q-(CH2)i~, where s can be 2, X can be -O-, q can be 2, r can be 2, R7 can be etandiyl, m can be 2 and n can be 9. In the prepolymers of Formula (3a) and Formula (3b), R5 can be selected, for example, from C2-6 alkandiyl and -[-(CHR8)sX-]q-(CHR8)^. In the prepolymers of Formula (3a) and Formula (3b), R5 can be in particular -[-(CHR8)sX-]q-(CHR8)i—, where X is -O- or X is -S-. More specifically, in the prepolymers of Formula (3a) and Formula (3b), R5 can be -[-(CHR8)sX-]q-(CHR8),~, where s can be 2, r can be 2, q can be 1 and X can be -S-; or where s can be 2, q can be 2, r can be 2 and X can be -O-; or where s can be 2, r can be 2, q can be 1 and X can be -O-, Furthermore, in the prepolymers of Formula (3a) and Formula (3b), where R5 can be-[-(CHR8)sX-]q-(CHR8)i~, each R8 or at least one R8 can be methyl. In the prepolymers of Formula (3a) and Formula (3b), each R5 can be the same or at least one R5 can be different. In the prepolymers of Formula (3b), each -V may comprise a terminal alkenyl group. In the adductions of Formula (3a) and Formula (3b), each R6 can be selected independently, for example, from a vinyl ketone, a vinyl sulfone, and a quinone. Each of the Michael acceptor groups can be the same, or at least some of the Michael acceptor groups can be different from each other. In the adducts of Formula (3a) and Formula (3b), each R6 can equally independently be a bis(sulfonyl)alkanol group. In the adducts of Formula (3a) and Formula (3b), each R6 can also be independently derived from a bis(sulfonyl)alkanol and have the structure of Formula (4a) or Formula (4b): -CH2- CH2-S(O)2-R9-CH(-OH) -R9-S(O)2-CH=CH2 (4a) -CH2- CH2-S(O)2-CH2-CH(-OH) -CH2-S(O)2-CH=CH2(4b) where each R9 is selected independently of C1-3 alkandiyl. However, a Michael acceptor group that terminates a sulfur-containing prepolymer useful as a polyene in curable compositions according to the present invention is not particularly limited and can generally be any suitable Michael acceptor group. En los prepolímeros de la Fórmula (3a) y la Fórmula (3b), cada R6puede derivarse, por ejemplo, de una bismaleimida tal como l,l'-(metilenb¡s(4,l-fen¡len)b¡s(l / 7Lp¡rrol-2,5-diona), ethylenbismaleimida, 1,6-bismaleimidohexano, 2,4-dimaleimidotolueno, A / / Vl,3-fenilendimaleimida; trimetilenbismaleimida de l,4-bis(maleim¡do)butano; ρ,ρ'-dimaleimidodifenilmethane; pentametilenbismaleimida lH-pirrol-2,5-diona; l,l'-(l,8-octandül)bis-, 1 / 7-pyrrol-2,5-diona, 1,1'-(1,7heptandiyl)bis-, 4,4'-dit¡ob¡s(phenylmale¡mida); methylenbis( / V-carbamylmaleim¡da), 1,9bis(maleim¡da)nonane; l,l'-decane-l,10-diylbis(l / 7-pyrrol-2,5-diona); O-phenylene dimaleimida, bis( / Vmaleim¡domet¡l)éter; 1,5-bis(maleimida)-2-methylpentane; A / / Vl,4-phenylenedimaleimida; 1,1'-(2-methyl,3-phenylene)b¡s(1 / y-pyrrol-2,5-diona); Kerimid 601 resin; tetrakis( / V-2-aminoet¡lmaleam¡da); 1-(2,5dimethylphenol)prrol-2,5-diona; SureCN331305; SureCN349749; ol,l'-bifen¡l-4,4'-d¡ilb¡s(l / / -p¡rrol-2,5diona). Michael's sulfur-containing prepolymer terminated in accept can comprise at least two terminal maleimide groups. As previously stated, the Michael acceptor group may also comprise a bis(sulfonyl)alkanol group such as an l-(ethylenesulfonyl)-n-(vinylsulfonyl)alkanol group or an l-(ethylenesulfonyl)-3-(vinylsulfonyl)propan-2-ol group. Each of the Michael acceptor groups of the sulfur-containing prepolymer terminated in Michael acceptor may be the same, or at least some of the Michael acceptor groups may be different from each other. A bis(sulfonyl)alkanol group refers to a group comprising a portion of iviA / a / ¿u¿i / uu / ¿ j / the general formula: -S(O)2-R10-CH(-OH)-R10-S(O)2 where each R10 is independently selected from C1-3 alkandiyl and substituted C1-3 alkandiyl, where one or more substituent groups are -OH. In certain examples, a bis(sulfonyl)alkanol group has the structure: -CH2-CH2-S(O)2-R10-CH(-OH)-R10-S(O)2-CH2-CH2 and in certain cases, the structure: R11-S(O)2-R10-CH(-OH)-R10-S(O)2-R11 where each R11 is a portion having a terminal reactive group. Each R11 may comprise a terminal reactive group with a thiol group such as, for example, an alkenyl group, an epoxy group, or a Michael acceptor group. In certain cases, a bis(sulfonyl)alkanol may be a bis(vinylsulfonyl)alkanol comprising terminal alkenyl groups. For example, a bis(sulfonyl)alkanol may be a bis(vinylsulfonyl)alkanol in which R11 comprises a terminal alkenyl group, such as a compound having the formula: CH2=CH-S(O)2-R10-CH(-OH)-R10-S(O)2-CH=CH2. A bis(vinylsulfonyl)alkanol may comprise, for example, 1,3-bis(vinylsulfonyl)-2-propanol. A bis(sulfonyl)alkanol may be prepared by reacting a bis(vinylsulfonyl)alkanol with a compound having a terminal group reactive with the terminal alkenyl groups of the bis(vinylsulfonyl)alkanol, such as a thiol group or an epoxy group. In such situations, the bis(sulfonyl)alkanol may have the structure: R12-CH2-CH2-S(O)2-R10-CH(-OH)-R10-S(O)2-CH2-CH2-R12 where each R12 is a portion derived from the reaction of the compound with the terminal alkenyl groups of the bis(vinylsulfonyl)alkanol. A bis(sulfonyl)alkanol group can be either a monovalent bis(sulfonyl)alkanol group or a divalent bis(sulfonyl)alkanol group. A monovalent bis(sulfonyl)alkanol group can be a terminal bis(sulfonyl)alkanol group, such as an l-(ethylenesulfonyl)-n-(vinylsulfonyl)alkanol group. A terminal bis(sulfonyl)alkanol group can be derived from the reaction of a bis(sulfonyl)alkanol and can have a terminal portion with the general structure -R13-S(O)2-R15-CH(OH)-R15-S(O)2-R14, where R13 is a portion derived from the reaction of a bis(sulfonyl)alkanol with a compound that has a group reactive with the bis(sulfonyl)alkanol. Each R15 is independently selected from C1-3 alkandiyl and substituted C1-3 alkandiyl, wherein one or more substituent groups are -OH. R14 can be an alkylene group such as -CH=CH2.In certain examples, a terminal bis(sulfonyl)alkanol group is a 1-(ethylenesulfonyl)-n-(vinylsulfonyl)alkanol group such as 1-(ethylenesulfonyl)-3-(vinylsulfonyl)propan-2-ol, that is, -CH2-CH2-S(O)2-CH2-CH(-OH)-CH2-S(O)2CH=CH2. A monovalent terminal bis(sulfonyl)alkanol group can have, for example, the structure. -CH2<H2-S(O)2-R15-CH(-OH)-R15-S(O)2<H=CH2. In certain examples, a bis(sulfonyl)alkanol group can also be divalent, such as when the group is incorporated into the main chain of a prepolymer such as the polythioethers disclosed herein. A divalent bis(sulfonyl)alkanol group can have the general structure R13-S(O)2-R15-CH(-OH)-R15-S(O)2-R13-; or -CH2-CH2-S(O)2-R,5-CH(-OH)-R15-S(O)2-CH2-CH2-, or -R13-S(O)2-CH2<H(-OH)<H2-S(O)2-R13-, or -CH2-CH2-S(O)2-CH2-CH(-OH)-CH2-S(O)2-CH2-CH2-, where R13 and R15 are as defined above. Each R13 can be, for example, an ethanediyl group and / or each R15 can be a methanediyl group. A polymer, prepolymer, or adduct containing bis(sulfonyl)alkanol refers to a polymer, prepolymer, or adduct in which one or more divalent bis(sulfonyl)alkanol groups are incorporated into the main chain of the polymer, prepolymer, or adduct. A divalent bis(sulfonyl)alkanol group can be incorporated into a prepolymer by reacting, for example, in a suitable ratio, a polythiol monomer or prepolymer of Formula I with a bis(sulfonyl)alkanol of Formula II: R(-SH)W(I) R16-S(O)2-R17-CH(-OH)-R17-S(O)2-R16(II) where R is an organic portion, each R17 is independently selected from C1-3 alkandiyl and substituted C1-3 alkandiyl, wherein one or more substituent groups are -OH; w is an integer of at least 2, and each R16 comprises a terminal group that is reactive with a thiol group such as, for example, an alkylene group and an epoxy group, or a group comprising a saturated carbon having a leaving group suitable for nucleophilic substitution such as, for example, -Cl, -Br, -I, -OSO2CH3 (mesylate), -OSO2-C6H4-CH3 (tosylate), etc. In certain situations, a bis(sulfonyl)alkanol of Formula II may be a bis(vinylsulfonyl)alkanol having the formula CH2=CH-S(O)2-R17-CH(-OH)-R17-S(O)2-CH=CH2 where each R17 is as defined above. A suitable bis(sulfonyl)alkanol can be exemplified, for instance, by 1,3-bis(vinylsulfonyl)-2-propanol. Alternatively, a bis(sulfonyl)alkanol group can be incorporated into a prepolymer backbone by reacting, in a suitable ratio, a thiol-terminated bis(sulfonyl)alkanol of Formula III with a reagent of Formula IV: HS-RS(O)2-R17-CH(-OH)-R17-S(O)2-R-SH (III) RRR (IV) wherein each R is a divalent portion, each R17 is as defined herein, and each R comprises a terminal group that is reactive with a thiol group such as, for example, an aIq uen i lo group, an epoxy group, or a group consisting of a saturated carbon having a known leaving group for nucleophilic substitution such as, for example, —Cl, -Br, -I, -OSO2CH3 (mesylate), OSO2-C6H4-CH3 (tosylate), etc. By choosing the appropriate ratio of reagents from Formula I and Formula II, or Formula III and Formula IV, one or more bis(sulfonyl)alkanol groups can be incorporated into a prepolymer as a chain segment, as part of a terminal group bearing a reactive group, or both. For example, bis(vinylsulfonyl)alkanol can be used to introduce one or more 1,n-bis(ethylenesulfonyl)alkanol groups into the main chain of a prepolymer chain, one or more terminal 1(ethylenesulfonyl)-n-(vinylsulfonyl)alkanol groups, or both. It may be desirable to react bis(vinylsulfonyl)-2-propanol with thiol-terminated monomers / polymers to incorporate 1,3-bis(ethylenesulfonyl)-2-propanol groups into the polymer chain. Bis(vinylsulfonyl)-2-propanol can also be reacted with thiol-terminated monomers / polymers to provide terminal l-(ethylenesulfonyl)-3-(vinylsulfonyl)2-propanol groups, where the terminal alkenyl group is a recognized Michael acceptor group. A portion derived from the reaction of a bis(sulfonyl)alkanol with a thiol group refers to the reaction product of a thiol group and a portion containing a terminal group reactive with the thiol group. Examples of terminal groups reactive with thiol groups include epoxy groups, ethylene groups, and Michael acceptors. In certain examples, a portion derived from the reaction of a bis(sulfonyl)alkanol with a thiol group has the structure: -CH₂-CH₂-R-, -CH(-OH)-CH₂-R-, -CH₂-CH(-OH)-R-, or -CH₂-CH₂-SO₂-R-, where R refers to a covalent bond or an organic portion attached to a sulfonyl group. Sulfur-containing Michael acceptor-terminated prepolymers useful as polyene (a) in curable compositions according to the present invention may comprise, for example, at least two terminal l-(ethylenesulfonyl)-n-(vinylsulfonyl)alkanol groups, such as two terminal l-(ethylenesulfonyl)-n-(vinylsulfonyl)alkanol groups, 3, 4, 5 or 6 terminal l-(ethylenesulfonyl)-n-(vinylsulfonyl)alkanol groups. A Michael acceptor-terminated sulfur-containing prepolymer may comprise a combination of adducts having different amounts of terminal 1-(ethylenesulfonyl)-n-(vinylsulfonyl)alkanol groups characterized, for example, by an average 1-(ethylenesulfonyl)-n-(vinylsulfonyl)alkanol functionality of 2.05 to 6, 2.1 to 4, 2.1 to 3, 2.2 to 2.8, or 2.4 to 2.6. A Michael acceptor group, which may be present in the polyenes that can be used in the curable composition according to the present invention, may also be derived from a vinylsulfone and may have the structure of Formula (5): -CH2-C(R18)2-S(O)2-CR18=CH2(5) wherein each R18 is independently selected from hydrogen and C1-3 alkyl. In the Michael acceptor groups of Formula (5), each R18 can be, for example, hydrogen. Michael acceptor-terminating bis(sulfonyl)alkanol polythioethers can be prepared, for example, by reacting a thiol-terminated bis(sulfonyl)alkanol-containing polythioether with a compound having a terminal Michael acceptor group and a thiol-reactive group such as divinylsulfone, in the presence of a phosphine catalyst. The chemistries and compounds of Michael acceptors / polythioethers are disclosed, for example, in U.S. Application Publication No. 2013 / 0345371. The sulfur-containing prepolymers terminated in Michael's accept used as polyene in curable compositions according to the present invention may comprise at least two terminal vinylsulfonyl groups. In certain examples, Michael-terminated sulfur-containing prepolymers may be terminated in at least two vinylsulfonyl groups or at least two terminal 1-(ethylenesulfonyl)n-(vinylsulfonyl)alkanol groups. A compound having a Michael acceptor group and a group that is reactive with the terminal groups of the sulfur-containing polymer can be a bis(sulfonyl)alkanol having the formula R-CH2-CH2-S(O)2-R19-CH(-OH)-R19-S(O)2-CH=CH2, where R can be a portion having a terminal group that is reactive with the terminal groups of the sulfur-containing polymer; and each R19 is independently selected from C1-3 alkandiyl. A bis(vinyl)alkanol can be a bis(vinylsulfonyl)alkanol. The sulfur-containing maleimide adducts provided by this disclosure may comprise at least two terminal maleimide groups. A sulfur-containing maleimide adduct may comprise a mixture of sulfur-containing maleimide adducts having different functionalities characterized by an average functionality of 2.05 to 6, 2.1 to 4, 2.1 to 3, 2.2 to 2.8, or 2.4 to 2.6. Sulfur-containing maleimide adducts may have at least two terminal maleimide groups, or they may have two 1-(4-(4-(341-2,5-dioxopyrrolidin-14l)benzyl)phenyl)-177-pyrrole-2,5-dione groups, or they may have more than two terminal groups such as 3, 4, 5 or 6 l-(4-(4-(3-yl-2,5-dioxopyrrolidin-l-yl)benzyl)phenyl)-l / 7-pyrrole-2,5-dione terminal groups.A sulfur-containing maleimide adduct may comprise a combination of adducts having different amounts of terminal 1-(4-(4-(341-2,5-dioxopyrrolidin-14l)benzyl)phenyl)l / 7-pyrrole-2,5-dione groups characterized, for example, by an average 1-(4-(4-(341-2,5-dioxopyrrolidin-1-l)benzyl)phenyl)-l / 7-pyrrole-2,5-dione functionality of 2.05 to 6, 2.1 to 4, 2.1 to 3, 2.2 to 2.8, or 2.4 to 2.6. The double bond of maleimides can react with thiol groups at a pH of 6.5 to 7.5 and is more reactive than (meth)acrylates. At neutral pH, the reaction of maleimides with thiols is approximately 1,000 times faster than the reaction of maleimides with amines. Compositions prepared from maleimide resins exhibit excellent thermomechanical stability and flame retardancy. A sulfur-containing prepolymer terminated in maleimide may comprise a polythioether maleimide prepolymer characterized by a polythioether having at least two terminal maleimide groups such as, for example, at least two terminal l-(4-(4-(3-yl-2,5-dioxopyrrolidinl-yl)benzyl)phenyl)-l / 7-pyrrole-2,5-dione groups. Terminal Michael acceptor groups can be selected from 1,3-bis(vinylsulfonyl)-2-propanol, 1,1'-(methylene-4,1-phenylene)bismaleimide, or a combination of these. A maleimide adduct containing useful sulfur as a polyene (a) in curable compositions according to the present invention may comprise a polythioether maleimide adduct comprising: (a) a main chain comprising the structure of Formula (6): -R20-[-S-(CH2)2-O-[-R21-O-]m-(CH2)2-S-R20]n- (6) wherein (i) each R20 is independently selected from a C2-10 n-alkandiyl group, a branched C3-6 alkandiyl group, a Ce-s cycloalkandiyl group, a Ce-io alkancycloalkandiyl group, a heterocyclic group, a -[(-CHR22-)pX-]q-(CHR22)i~ group, wherein each R22 is independently selected from hydrogen and methyl; (i) each R21 is independently selected from a C2-10 n-alkandiyl group, a branched C3-6 alkandiyl group, a Ce-s cycloalkandiyl group, a Ce14 alkancycloalkandiyl group, a heterocyclic group, and a —[(—CH2—)P—X—]q—(CH2)i— group; (iii) each X is independently selected from O, S, and an -NR23- group, wherein R23 is selected from H and a methyl group; (iv) m is an integer ranging from 0 to 50; (v) n is an integer ranging from 1 to 60; (vi) p is an integer ranging from 2 to 6; (vii) q is an integer ranging from 1 to 5; and (viii) r is an integer ranging from 2 to 10;and (b) at least two terminal maleimide groups, which may be selected individually, for example, from any of the terminal maleimide groups described herein. In an adduct of Formula (6), R20 can be, for example, -[-(CHR22)PX-]q(CHR22),- where each X is selected independently of -O- and -S-. More specifically, in an adduct of Formula (6), R20 can be —[—(CH2)p—X—]q— (CHzjr- where each X is selected independently of -O- and -S-, where each X is -O- or each X is -S-. Even more specifically, in the adducts of Formula (6), R20 can be -[(CH2-)PX-]q-(CH2)r-, where p can be 2, X can be O, q can be 2, r can be 2, R21 can be ethanendiyl, m can be 2 and n can be 9. A terminal maleimide group can have the structure of Formula (7): (7) iviA / a / zuzi / uu i ¿ó i A terminal bismaleimide portion refers to a portion that has a terminal maleimide group. A terminal maleimide group can be derived from a bismaleimide, such as a compound having the structure of Formula (8a): (8a) where R10 is a divalent organic portion and the terminal group may have the structure of Formula (8b): (8b) and is referred to herein as the group l-(4-(4-(3-yl-2,5-dioxopyrrol¡nl-¡l)benzyl)phen¡l)-lH-pyrrol-2,5dione. A terminal maleimide group can be derived from l,r-(met¡lend¡-4,l-phenylene)b¡smaleimide of Formula (9a), also called l,r-(met¡lenb¡s(4,l-phenylene)b¡s(lH-pyrrole-2,5-d¡one) and the terminal group can have the structure of Formula (9b): A maleimide group may comprise an l-(4-(4-(3-yl-2,5-dioxopyrrolidine-lyl)benzyl)phenyl)-l / 7-pyrrole-2,5-dione group. Each of the terminal maleimide groups may be the same, or at least some of the terminal maleimide groups may be different from each other. Other examples of compounds having two or more maleimide groups include ethylenebismaleimide; 1,6-bismaleimidohexane; 2,4-dimaleimidotoluene, A / . / Vyl,3-phen¡lendimale¡m¡da; trimethylenebismaleimide of l,4-bis(maleim¡do)butane; ρ,ρ'-dimaleimidodiphenylmethane; pentamethylenebismaleimide lH-pyrrole-2,5-dione; l,l'-(l,8-octanedyl)bis-, l / -Apyrrol-2,5-dione, 1,Γ-(1,7heptandyl)bis-, 4,4'-dit¡ob¡s(phen¡lmale¡imide); methylenbis( / V-carbamylmaleim¡da), 1.9bis(maleim¡da)nonane; l,l'-decane-l,10-diylbis(l / 7-pyrrole-2,5-dione); (9-phenylene dimaleimide, bis( / Vmaleimidomethyl ether; l,5-bis(maleimide)-2-methyl-pentanone; A / / l / -l,4-phenylenedimaleimide; l,l'-(2-methyl,3-phenylene)bis(l Mpyrrol-2,5-d) 60¡; tetrakis( / V-2-am¡noet¡lmaleam¡da); To prepare a sulfur-containing prepolymer terminated in a Michael acceptor, one can react a sulfur-containing prepolymer as disclosed herein with a compound having a Michael acceptor group and a group that is reactive with the terminal groups of the sulfur-containing prepolymer. A Michael acceptor group can be selected, for example, from a vinyl ketone, a vinyl sulfone, a maleimide, and a quinone. In compounds in which a Michael acceptor group is derived from divinyl sulfone, the sulfur-containing prepolymer can be thiol-terminated, such as a thiol-terminated polythioether, a thiol-terminated polysulfide, or a combination thereof. The polyene (a) is generally present in the curable composition of the present invention in an amount of at least 10 but less than 90 percent by weight, depending on the total weight of components (a) and (b) in the curable composition. For example, the polyene (a) may be present in the curable composition in an amount of at least 10 percent by weight, often at least 30 percent by weight, or at least 50 percent by weight, or even at least 60 percent by weight, depending on the total weight of components (a) and (b) in the curable composition, as demonstrated in the examples below. Furthermore, the polyene (a) may be present in the curable composition in an amount of up to 75 percent by weight, often up to 60 percent by weight, depending on the total weight of components (a) and (b) in the curable composition. The curable compositions of the present invention further include (b) a polythiol. As used herein, the term polythiol refers to compounds containing two or more groups with thiol functionality (-SH). Polythiols (b) suitable for use in the curable composition according to the present invention are numerous and can vary widely. Such polythiols may include those known in the art. Examples of suitable polythiols may include, among others, polythiols having at least two thiol groups, including monomeric compounds, oligomers, prepolymers, and polymers. The polythiol may have ether linkages (-O-), thioether linkages (-S-), including polysulfide linkages (-Sx-), where x is at least 2, such as from 2 to 4, and combinations of such linkages. The polythiols (b) for use in the present invention include materials of the formula: R24-(SH)n where R24 is an organic portion and n is an integer of at least 2, usually from 2 to 6. Such a polythiol may comprise, for example, a reaction product of an organic acid with thiol functionality and a polyol. Accordingly, the organic portion R24 may contain ester groups and / or be derived from a polyol. Examples of suitable polythiols that can be used in curable compositions according to the present invention may therefore include, for example, esters of thiol-containing acids of the formula HS-R25-COOH, wherein R25 is an organic portion, with polyhydroxy compounds of the structure R26-(OH)n, wherein R26 is an organic portion and n is at least 2, typically from 2 to 6. The thiol-containing acid component and the polyhydroxy component can be reacted under suitable conditions to obtain polythiols having the general structure: R26-(OC(=O)-R25-SH)n Examples of such thiol-containing acid esters include esters of thioglycolic acid (HS-CH2COOH), α-mercaptopropionic acid (HS-CH(CH3)-COOH), or β-mercaptopropionic acid (HS-CH2CH2COOH) with polyhydroxy compounds such as glycols, triols, tetraols, pentaols, hexols, and mixtures thereof. Specific examples of suitable polythiols include, for instance, ethylene glycol bis(thioglycolate), ethylene glycol bis(O-mercaptopropionate), trimethylolpropane tris(thioglycolate), trimethylolpropane tris(β-mercaptopropionate), pentaerythritol tetrakis(thioglycolate), and pentaerythritol tetrakis(β-mercaptopropionate), and mixtures thereof. A polythiol (b) suitable for use in the curable compositions according to the present invention, particularly useful for the aerospace industry, may include a thiol-terminated sulfur-containing prepolymer, such as a thiol-terminated polythioether prepolymer, a thiol-terminated polysulfide prepolymer, a thiol-terminated sulfur-containing polyformal prepolymer, or combinations thereof. The thiol-terminated sulfur-containing prepolymer may also comprise a mixture of different polythioethers and / or polysulfides, and the polythioethers and / or polysulfides may have the same or different thiol functionality. A thiol-terminated sulfur-containing prepolymer may have an average thiol functionality of 2 to 6, 2 to 4, 2 to 3, or 2.05 to 2.8.For example, a thiol-terminated sulfur-containing prepolymer may comprise a difunctional thiol-terminated sulfur-containing polymer, a trifunctional thiol-terminated sulfur-containing polymer, or a combination thereof. Examples of thiol-terminated polythioether prepolymers suitable for use in the curable compositions provided herein are disclosed, for example, in U.S. Patent No. 6,172,179. A sulfur-containing prepolymer terminated in a suitable thiol, such as a polythiol (b), in curable compositions according to the present invention may comprise, for example, a main chain comprising the structure of Formula (10): -R27-[-S-(CH2)2-O-[-R28-O-]m-(CH2)2-S-R27]n- (10) where: (i) each R27 is independently selected from a C2-10 n-alkandiyl group, a branched C3-6 alkandiyl group, a Ce-s cycloalkandiyl group, a Ce-io alkancycloalkandiyl group, a divalent heterocyclic group and a -[(-CHR^-jp-X-jq-ÍCHR29),-] group, wherein each R29 is selected from hydrogen and methyl; (i) each R2S is independently selected from a C2-10 n-alkandiyl group, a C3-6 branched alkandiyl group, a Cs-s cycloalkandiyl group, a Ce-w alkancycloalkandiyl group, a divalent heterocyclic group, and a —[(—CHz—)p—X—]q—(CH2)i— group; (i¡¡) each X is selected independently of O, S, -NH- and -N(-CH3)-; (iv) m is an integer that ranges from 0 to 50; (v) n is an integer that ranges from 1 to 60; (vi) p is an integer that varies from 2 to 6; (vii) q is an integer ranging from 1 to 5; and (viii) r is an integer ranging from 2 to 10. A sulfur-containing prepolymer terminated in a suitable thiol, such as a polythiol (b), in the curable compositions according to the present invention may comprise, for example, a thiol-terminated polythioether prepolymer of Formula (11a), a thiol-terminated polythioether prepolymer of Formula (11b), or a combination thereof: HS-R30-[-S-(CH2)PO-(R31-O)m-(CH2)2-S-R30-]n-SH (lia) {HS-R30-[-S-(CH2)PO-(R31^)m-(CH2)2-S-R30-]nS-V'-}zB (11b) wherein: each R30 is independently selected from C2-10 alkandiyl, Ce-s cycloalkandiyl, Ce-n alkancycloalkandiyl, C5-8 heterocycloalkandiyl and -[(-CHR32-)sX-]q-(-CHR32-)i-, wherein: s is an integer from 2 to 6; q is an integer from 1 to 5; r is an integer from 2 to 10; each R32 is independently selected from hydrogen and methyl; and each X is selected independently from -O-, -S-, -NH- and -N(-CH3)-; each R31 is selected independently from Ci-10 alkandiyl, Ce-s cycloalkandiyl, Oβ-κ alkancycloalkandiyl and -[(-CHR32-)sX-]q-(-CHR32-),~, where s, q, r, R32 and X are as defined for R30; m is an integer from 0 to 50; n is an integer from 1 to 60; p is an integer from 2 to 6; B represents a core of a z-valent vinyl-terminated polyfunctional agent B(-V)zen where: z is an integer from 3 to 6;and each V is a group comprising a terminal vinyl group; and each -V'- is derived from the reaction of -V with a thiol. In the prepolymers of Formula (11a) and Formula (11b), R30 can be, for example, -[(-CH2-)^X-]q-(CH2)i-, where s can be 2, X can be -O-, q can be 2, r can be 2, R2 can be ethanendiyl, m can be 2 and n can be 9. In the prepolymers of Formula (11a) and Formula (11b), R30 can be selected from C2-6 alkandiyl and -[-(CHR32)sX-]q-(CHR32)^. In the prepolymers of Formula (11a) and Formula (11b), R30 can be in particular -[-(CHR32)sX-]q-(CHR32),-, where X is -O- or X is -S-. In the specific prepolymers of Formula (11a) and Formula (11b), R30 can be -[-(CHR32)sX-]q-(CHR32)i-, where s is 2, r is 2, q is 1 and X is -S-; os is 2, q is 2, r is 2 and X is -O-; os is 2, r is 2, q is 1 and X is -O-. Furthermore, in the prepolymers of Formula (11a) and Formula (11b), R30 can be [-(CHR32)sX-]q-(CHR32)i-, wherein each R32 is hydrogen or at least one R32 is methyl. In the prepolymers of Formula (11a) and Formula (11b), R30 in general may be the same or at least one R30 may be different. Various methods may be used to prepare thiol-terminated polythioether prepolymers useful as polythiols in curable compositions according to the present invention. Examples of suitable thiol-terminated polythioether prepolymers and methods for their production are described, for example, in U.S. Patent No. 6,172,179. Thiol-terminated polythioether prepolymers may be difunctional, such as linear prepolymers having two terminal thiol groups, or polyfunctional, such as branched prepolymers having three or more terminal thiol groups. Thiol-terminated polythioether prepolymers may also comprise a combination of difunctional and polyfunctional thiol-terminated polythioether prepolymers. Suitable thiol-terminated polythioether prepolymers are commercially available, for example, as Permapol® P3.1E, through PRC-DeSoto International Inc., Sylmar, CA. Suitable difunctional thiol-terminated polythioether prepolymers can be produced by reacting a divinyl ether or mixtures of divinyl ethers with an excess of dithiol or a mixture of dithiols. For example, dithiols suitable for use in the preparation of thiol-terminated polythioether prepolymers include those having the structure of Formula (12), other dithiols disclosed herein, or combinations of any of the dithiols disclosed herein. A dithiol useful for preparing a thiol-terminated polythioether provided by the present disclosure may have, for example, the structure of Formula (12): HS-R33-SH (12) wherein: R33 is selected from C2-6 alkandiyl, Cs-s cycloalkandiyl, Ce-io alkancycloalkandiyl, C5-8 heterocycloalkandiyl and -[-(CHR34)pX-]q-(CHR34),~; wherein: each R34 is selected independently from hydrogen and methyl; each X is selected independently from -O-, -S and -NR- wherein R is selected from hydrogen and methyl; 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. In the dithiols of Formula (12), R33 can be in particular -[-(CHR34)PX-]q(CHR34)^. In the dithiols of Formula (12), X can be in particular -O- or -S-, and therefore -[-(CHR34)PX-]q-(CHR34)i- in Formula (12) can be -[(-CHR34-)P^-]q-(CHR3Vo-[(-CHR34)P—S-]q-(CHR34)r—. In the portions having the structure -[(-CHR34)pX-]q-(CHR34)i-, p and r can be equal, so that both p and r can be two. In the dithiols of Formula (12), R33 can be, for example, C2-6 alkandiyl or -[(CHR34)pX-]q-(CHR34)^. In the dithiols of Formula (12), where R33 is -[(-CHR34)pX-]q-(CHR34)i-, in particular X can be -O- or X can be -S-. In the dithiols of Formula (12), R33 can be, for example, —[—(CHR34)P—X—]q— (CHR34)i—, where p can be 2, r can be 2, q can be 1 and X can be -S-; op can be 2, q can be 2, r can be 2 and X can be -O-; op can be 2, r can be 2, q can be 1 and X can be -O-. In the dithiols of Formula (12), R33 can be, for example, -[(-CHR34)pX-]q(CHR34)i—, where each R34 is hydrogen or at least one R34 is methyl. Specific, non-limiting examples of suitable dithiols useful in the preparation of thiol-terminated polythioether prepolymer include 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, l,3-dimercapto-3-methylbutane, dipentendimercaptane, ethylcyclohexyldithiol (ECHDT), dimercaptodiethyl sulfide, methyl-substituted dimercaptodiethyl sulfide, dimethyl-substituted dimercaptodiethyl sulfide, dimercaptodioxaoctane, l,5-dimercapto-3-oxapentane, and a combination of any of the above. A polythiol may have one or more pendant groups selected from a lower alkyl group (e.g., C3-β), a lower alkoxy group (e.g., C3-β), and a hydroxyl group. Suitable pendant alkyl groups include, for example, linear C3-6 alkyl, branched C3-6 alkyl, cyclopentyl, and cyclohexyl. Therefore, it is also possible to use dithiols that include both heteroatoms in the main carbon chain and dangling alkyl groups, such as methyl groups. Such compounds include, for example, methyl-substituted DMDS, such as HS-CH2CH(CH3)-S-CH2CH2SH, HS-CH(CH3)CH2-S-CH2CH2-SH, and dimethyl-substituted DMDS, such as HS-CH2CH(CH3)-SCH(CH3)CH2-SH and HS-CH(CH3)CH2-S-CH2CH(CH3)-SH. Divinyl ethers suitable for use in the preparation of polythioether prepolymers include, for example, divinyl ethers of Formula (13): CH2=CH-O-(-R35-O-)m-CH=CH2 (13) where R35 in Formula (13) can be C2-6 n-alkandiyl, C3-6 branched alkandiyl, Ce-8 cycloalkandiyl, Ce-10 alkancycloalkandiyl or -[(-CH2-)PO-]q-(-CH2-)i~, where p is an integer ranging from 2 to 6, q is an integer from 1 to 5 and r is an integer from 2 to 10. Suitable divinyl ethers include, for example, divinyl ethers having at least one oxyalkandiyl group, such as from 1 to 4 oxyalkandiyl groups, i.e., compounds in which m in Formula (13) is an integer ranging from 1 to 4. In divinyl ethers of Formula (13), m may be, for example, an integer ranging from 2 to 4. It is also possible to use commercially available mixtures of divinyl ethers characterized by a non-integer average value for the number of oxyalkandiyl units per molecule. Therefore, m in Formula (13) may also take rational number values ​​ranging from 0 to 10.0, such as from 1.0 to 10.0, from 1.0 to 4.0, or from 2.0 to 4.0. Specific, non-limiting examples of suitable divinyl ethers include divinyl ether, ethylene glycol divinyl ether (EG-DVE), butanediol divinyl ether (BD-DVE), hexanediol divinyl ether (HD-DVE), diethylene glycol divinyl ether (DEG-DVE), triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, cyclohexanedimethanol divinyl ether, polytetrahydrofuryl divinyl ether, and combinations of two or more of such divinyl ether monomers. The divinyl ether may optionally have one or more pendant groups selected from alkyl groups, hydroxyl groups, alkoxy groups, and amine groups. In divinyl ethers of Formula (13), R35 may be, for example, a C3-6 branched alkandiyl group, which can be prepared by reacting a polyhydroxy compound with acetylene. Examples of divinyl ethers of this type include compounds in which R35 in Formula (13) is an alkyl-substituted methandyl group such as -CH(CH3)- (e.g., Pluriol® blends such as Pluriol® Divinyl Ether E-200 (BASF Corp., Parsippany, NJ), for which R35 in Formula (13) is ethanendiyl and m is 3.8) or an alkyl-substituted ethanendiyl group (e.g., -CH2CH(CH3)- such as DPE polymer blends including DPE-2 and DPE-3; International Specialty Products, Wayne, NJ). Other useful divinyl ethers include divinyl ethers in which R35 in Formula (13) is polytetrahydrofuryl (poly-THF) or polyoxyalkandiyl, such as those having an average of about 3 monomer units. Two or more types of dithiols and / or divinyl ether monomers of Formula (13) may be used in the preparation of thiol-terminated polythioether prepolymers. Thus, for example, two dithiols of Formula (12) and one divinyl ether monomer of Formula (13), one dithiol of Formula (12) and two divinyl ether monomers of Formula (13), two dithiols of Formula (12) and two divinyl ether monomers of Formula (13), and more than two dithiols of Formula (12) and two divinyl ethers of Formula (13) may be used to produce a variety of thiol-terminated polythioether prepolymers. The divinyl ether monomer may comprise from 20 mol% to less than 50 mol% of the reagents used to prepare the thiol-terminated polythioether prepolymer, or from 30 mol% to less than 50 mol%. The relative amounts of dithiols and divinyl ethers can be selected to obtain polythioether prepolymers having terminal thiol groups. Therefore, a dithiol of Formula (12) or a mixture of at least two different dithiols of Formula (12) can be reacted with a divinyl ether of Formula (13) or a mixture of at least two different divinyl ethers of Formula (13) in relative amounts such that the molar ratio of thiol groups to vinyl groups is greater than 1:1, such as from 1.1 to 2.0:1.0. The thiol-terminated polythioether prepolymers provided by this disclosure can be prepared by combining at least one dithiol of Formula (12) and at least one divinyl ether of Formula (13) followed by the addition of a suitable catalyst and by carrying out the reaction at a temperature of 30°C to 120°C, such as 70°C to 90°C, for a time of 2 hours to 24 hours, such as 2 hours to 6 hours. Thiol-terminated polythioether prepolymers may also comprise a higher-functionality polythioether, i.e., they may have an average thiol functionality greater than 2.0. Higher-functionality thiol-terminated polythioether prepolymers include, for example, those having the structure of Formula (14): B(-A-SH)z (14) where (i) A comprises a divalent binding group, (ii) B denotes a z-valent residue of a polyfunctional agent; and (ii) z may have an average value greater than 2.0, such as an average value between 2 and 3, an average value between 2 and 4, an average value between 3 and 6, or may be an integer from 3 to 6. Suitable polyfunctional agents for use in the preparation of such higher-functionality thiol-terminated prepolymers include trifunctional agents where z is 3. Suitable trifunctional agents include, for example, trialyl cyanurate (TAC), 1,2,3-propanetriol, isocyanurate-containing trithiols, and combinations thereof, as disclosed in U.S. Application Publication No. 2010 / 0010133. Other useful polyfunctional agents include trivinyl ether monomers, such as trimethylolpropane trivinyl ether; tetrafunctional ether monomers, such as pentaerythritol tetravinyl ether; and the polythiols described in U.S. Patent Nos. 4,366,307; 4,609,762; and 5,225,472. Mixtures of polyfunctional agents may also be used. As a result, the thiol-terminated polythioether prepolymers provided by this disclosure can be characterized by a wide range of average thiol functionality. For example, a combination of difunctional and trifunctional prepolymers can have average thiol functionality values ​​of 2.05 to 3.0, such as 2.1 to 2.6. Wider ranges of average thiol functionality can be achieved by using tetrafunctional or higher-functionality agents. Functionality can also be influenced by factors such as stoichiometry. Thiol-terminated polythioether prepolymers having a functionality greater than 2.0 can be prepared similarly to the difunctional thiol-terminated polythioether prepolymers described in U.S. Application Publication No. 2010 / 0010133. For example, thiol-terminated polythioether prepolymers can be prepared by combining (i) one or more dithiols described herein, with (ii) one or more divinyl ethers described herein, and (iii) one or more polyfunctional agents such as any of those mentioned above. The mixture can then be reacted, optionally in the presence of a suitable catalyst, to obtain a thiol-terminated polythioether prepolymer having a functionality greater than 2.0. The thiol-terminated polythioether prepolymers provided in this disclosure represent thiol-terminated polythioether prepolymers with a molecular weight distribution. For example, useful thiol-terminated polythioether prepolymers may be characterized by a number-average molecular weight ranging from 500 to 20,000 daltons, from 2,000 to 5,000 daltons, or from 3,000 to 4,000 daltons. Useful thiol-terminated polythioether prepolymers may exhibit a polydispersity (Mw / Mn; weight-average molecular weight / number-average molecular weight) ranging, for example, from 1 to 20 or from 1 to 5. The molecular weight distribution of the thiol-terminated polythioether prepolymers may be characterized by gel permeation chromatography. As mentioned above, thiol-terminated polysulfides such as polythiol (b) can also be used in the curable compositions according to the present invention. Herein, polysulfides may refer to prepolymers containing one or more sulfide bonds, i.e., -Sx- bonds, where x is from 2 to 4, in the polymer backbone and / or in pendant positions in the prepolymer chain. A polysulfide prepolymer may have two or more sulfur-sulfur bonds. Suitable thiol-terminated polysulfides are commercially available, for example, from Akzo Nobel and Toray Fine Chemicals under the names Thiokol-LP and Thioplast®. Thioplast® products are available in a wide range of molecular weights, for example, from less than 1,100 to more than 8,000, where molecular weight is the average molecular weight in grams per mole. In some cases, polysulfide has an average number molecular weight of 1,000 to 4,000 daltons.Examples of thiol-terminated polysulfides are disclosed in U.S. Patent No. 4,623,711. Thiol-terminated sulfur-containing polyformal prepolymers, which can be used as polythiol (b) in curable compositions according to the present invention for aerospace senator applications, are disclosed, for example, in U.S. Application Publication No. 2012 / 0234205 and U.S. Application Publication No. 2012 / 0238707. Thiol-terminated sulfur-containing prepolymers useful as polythiols in curable compositions according to the present invention may comprise a thiol-terminated sulfur-containing prepolymer containing a metal ligand, wherein a metal ligand is incorporated into the main chain of the prepolymer. Sulfur-containing metal-liganded prepolymers are disclosed, for example, in U.S. Application Nos. 2014 / 0275474, 2014 / 0378650, and 2014 / 0378649. The polythiol (b) is generally present in the curable composition of the present invention in an amount greater than 10 percent by weight to 90 percent by weight, depending on the total weight of components (a) and (b) in the curable composition. For example, the polythiol (b) may be present in the curable composition in an amount of at least 10 percent by weight, often at least 30 percent by weight, or at least 50 percent by weight, or even at least 60 percent by weight, depending on the total weight of components (a) and (b) in the curable composition, as demonstrated in the examples below. Furthermore, the polythiol (b) may be present in the curable composition in an amount of up to 75 percent by weight, often up to 60 percent by weight, depending on the total weight of components (a) and (b) in the curable composition.Generally, the equivalent ratio of groups with thiol functionality in the polythiol (b) with respect to ethylenically unsaturated groups in the polyene (a) is from 0.1 to 10:1, such as from 0.4 to 1.6:1. The curable compositions of the present invention further comprise (c) any of the catalytic compositions described herein. The metal compound (i) of the catalytic composition is generally present in the curable composition according to the present invention in amounts of 1 to 1000 ppm metal, such as 5 to 175 ppm metal, or 15 to 75 ppm metal, often 25 ppm metal, depending on the total weight of components (a) and (b) in the curable composition. The compound (i) is generally present in the curable composition according to the present invention in amounts of 0.001 to 10 percent by weight, such as 0.01 to 5 percent by weight, depending on the total weight of components (a) and (b) in the curable composition. When preparing the curable composition according to the present invention, both components of the catalytic composition (c) can be added as a single packet to one or more of the remaining components of the curable composition (i.e., added to (a) and / or (B)). Alternatively, one or more of each component of the catalytic composition (c) can be added in separate packets to one or more components of the curable composition. Optional ingredients, such as plasticizers, antioxidants, thixotropic agents, reactive diluents, hindered amine light stabilizers, UV light absorbers, and stabilizers, may be formulated into the curable compositions of the present invention. These ingredients may be present (individually) in amounts up to 30 percent by weight, often from 0.1 to 5 percent by weight, depending on the total weight of components (a) and (b) in the curable composition. Other optional ingredients such as colorants are often included in the curable compositions of the present invention. Examples of suitable pigments and / or pigment compositions include crude dioxazine carbazole pigment, azo, monoazo, disazo, naphthol AS, salt type (lagos), benzimidazolone, condensation, isoindolinone, isoindoline, and polycyclic phthalocyanine, quinacridone, perylene, perinone, diketopyrrolepyrrole, thioindigo, anthraquinone, indanthrone, anthrapyrimidine, flavantrone, pyrantrone, antantrone, dioxazine, triarylcarbonium, quinophthalone pigments, diketopyrrolepyrrole red (DPPBO red), carbon black, and mixtures thereof. The term pigment and the expression colored filler agent may be used interchangeably. Example dyes include those that are solvent-based and / or aqueous, such as acid dyes, azo dyes, basic dyes, direct dyes, disperse dyes, reactive dyes, solvent dyes, sulfur dyes, mordant dyes, for example, bismuth vanadate, anthraquinone, perylene, aluminum, quinacridone, thiazole, thiazine, azo, indigoid, nitro, nitroso, oxazine, phthalocyanine, quinoline, stilbene, and triphenylmethane. When present, the pigments are generally used in the curable composition according to the present invention in quantities up to 80, such as from 1 to 80 percent by weight, depending on the total weight of solids in the composition. The curable compositions of the present invention generally contain a diluent to dissolve and / or disperse the various ingredients in the composition. Examples of suitable diluents include, but are not limited to, organic materials such as aromatics like toluene and xylene, esters such as butyl acetate and amyl acetate, ethers such as ethylene dialkyl ethers and propylene glycol, and ketones such as methyl ethyl ketone and methyl amyl ketone. Other suitable diluents include water and water-miscible solvents such as solvents and alcoholic ethers. In certain instances of the present invention, the curable compositions of the present invention are essentially free of vanadium compounds, free-radical polymerization initiators such as peroxides and others known in the addition polymerization technique, and reactive compounds comprising groups with acid functionality, anhydride groups, or reaction products of an active hydrogen compound with an anhydride or polyacid. The curable compositions according to the present invention can be formulated with a solids content of 1 to 100 percent by weight, such as 20 to 90 percent by weight or 20 to 80 percent by weight, depending on the total weight of the composition. The composition ingredients are generally blended together using a low-shear mixing process to form the curable composition. When pigments are present, they are typically ground using a high-shear mixing process into one of the composition's resinous ingredients, such as polyene (a) or polythiol (b), to form a pigment paste, which is then incorporated into the composition using a low-shear mixing process. Curable compositions are useful as primers or as protective or decorative coating compositions and can be used as primer or topcoats, including color and clear coats. The compositions are curable at low temperatures, such as ambient temperatures, as low as -10 to 80°C, or can be subjected to higher temperatures to achieve curing, although higher temperatures are generally not required. The compositions are particularly useful in the manufacture or original refinishing of automobiles and trucks. Other uses of the compositions may include, but are not limited to, various protective and transport coatings. The curable compositions of the present invention can be applied to a variety of substrates, such as metal, glass, wood, and / or polymer substrates, and can be applied by conventional methods including, but not limited to, brushing, dipping, flow coating, spraying, and the like. The substrates can be bare, pre-treated, or coated with a primer and / or sealer. The curable compositions are most often applied to the substrate by spraying. Conventional air spraying, airless spraying, and electrostatic spraying techniques and equipment, employing manual and / or automated methods, can be used.Suitable substrates include metal substrates such as ferrous metals, zinc, copper, magnesium, aluminum, aluminum alloys, and other metal and alloy substrates, such as those commonly used in the manufacture of automobile and other vehicle bodies. Ferrous metal substrates may include iron, steel, and their alloys. Non-limiting examples of useful steel materials include cold-rolled steel, galvanized (zinc-coated) steel, electrogalvanized steel, stainless steel, pickled steel, zinc-iron alloys such as Galvanneal, and combinations thereof. Combinations or compounds of ferrous and non-ferrous metals may also be used. The curable compositions of the present invention can also be applied to elastomeric, plastic, or composite substrates such as those found in motor vehicles. "Plastic" means any synthetic, non-conductive thermoplastic or thermosetting material, including thermoplastic olefins such as polyethylene and polypropylene, thermoplastic urethane, polycarbonate, thermoset sheet molding compound, reaction-injection molding compound, acrylonitrile-based materials, nylon, and the like. "Composite" means any substrate consisting of fibers, generally glass or carbon, or other filler material incorporated with polymeric or plastic materials, commonly epoxy-type polymers. Each of the features and examples described above, and combinations thereof, may be considered to be encompassed by the present invention. In view of the foregoing, the present invention relates, among others, to the following non-limiting aspects: 1. A catalytic composition consisting essentially of: (i) a metal compound; and (ii) a compound other than (i) that catalyzes an addition reaction between an ethylenically unsaturated compound and a thiol, wherein said catalytic composition is essentially free of vanadium compounds. 2. The catalytic composition according to aspect 1, wherein the catalytic composition is essentially free of reactive compounds comprising groups with acid functionality, anhydride groups, or reaction products of an active hydrogen compound with an anhydride or polyacid. 3. The catalytic composition according to either aspect 1 or 2, wherein the metal compound (i) comprises at least one of a metal oxide, a metal salt, and an organometallic compound. 4. The catalytic composition according to either aspect 1 or 3, wherein the metal compound (i) comprises an iron compound. 5. The catalytic composition according to any of the above aspects 1-4, wherein the compound (i) comprises an organic compound containing N and / or P, such as a primary, secondary or tertiary amine or phosphine. 6. The catalytic composition according to aspect 5 above, wherein compound (ii) is selected from one or more of oxazolidines, triethylamine, dimethylcyclohexylamine, dimethyloctylamine, dimethyldodecylamine, dimethylaminoethanol, tetramethylguanidine, diaza-bicyclooctane, diaza-bicycloundecene, diaza-bicido-nonene, n-methyl-triaza-bicyclodecene, trioctylphosphine, and triphenylphosphine. 7. The catalytic composition according to aspect 5 or 6, wherein the molar ratio of nitrogen (as in an amine or ammonium group) or phosphorus (as in a phosphine or phosphonium group) in compound (i) with respect to the metal in metal compound (i) is from 0.4 to 500:1. 8. The catalytic composition according to any of the above aspects 1-7, wherein the metal compound (i) comprises an iron compound, the compound (ii) comprises a compound containing a secondary or tertiary amine group and the molar ratio of the amine group to iron is from 0.4 to 500:1. 9. A curable composition comprising: (a) a polyene; (b) a polythiol, present in an amount greater than 10 percent by weight based on the total weight of resin solids in the curable composition; and (c) a catalytic component, consisting of the catalytic composition according to any of aspects 1-8 above; wherein said curable composition is essentially free from vanadium compounds, free-radical polymerization initiators, and reactive compounds comprising groups with acid functionality, anhydride groups, or reaction products of an active hydrogen compound with an anhydride or polyacid. 10. The curable composition according to aspect 9, wherein the polyene has the structural formula A - (X)m where A is an organic portion; X is an olefinically unsaturated portion and m is at least 2, wherein the polyene A-(X)m generally comprises a polyurethane (meth)acrylate or a polyester (meth)acrylate. 11. The curable composition according to aspect 10, wherein X is selected from -C(O)CR=CH2, -CH2-CHR=CH2 and mixtures thereof, wherein R is hydrogen or methyl. 12. The curable composition according to any of aspects 10 or 11, wherein A contains selected groups of ester and urethane groups and / or is derived from a polyisocyanate. 13. The curable composition according to any of the above aspects 9-12, wherein the polythiol has 2 to 6 thiol groups. 14. The curable composition according to any of aspects 9 to 13, wherein the polythiol contains ester groups and / or is derived from a polyol. 15. The curable composition according to any of the above aspects 9-14, wherein the polythiol comprises a reaction product of an organic acid with thiol functionality and a polyol. 16. The curable composition according to any of the above aspects 9-15, wherein the metal compound (i) of the catalytic composition comprises an iron compound, present in the curable composition in an amount of 1 to 1000 ppm of metal, depending on the total weight of components (a) and (b) in the curable composition. 17. The curable composition in accordance with any of the above aspects 9-16, wherein the compound (i) of the catalytic composition is present in the curable composition in amounts of 0.001 to 10 percent by weight, based on the total weight of components (a) and (b) in the curable composition. 18. The curable composition according to any of the above aspects 9-17, wherein the equivalent ratio of groups with thiol functionality in the polythiol (b) with respect to ethylenically unsaturated groups in the polyene (a) is from 0.1 to 10:1. The present invention will be further described with reference to the following examples. The examples are merely illustrative of the invention and are not intended to be limiting. Unless otherwise stated, all parts are by weight. EXAMPLE A A pigment grind was prepared in a stainless steel beaker according to the following procedure: iviA / a / zuzi iuv Charge 1 Mass (g) Thiocure PETMP1 668.6 DISPERBYK-1632 7.5 BYK-3252 7.5 n-Butyl acetate 71.6 Charge 2 Mapico Black 8453 12.1 n-Butyl acetate 10.8 Charge 3 Talcron MP 15-384 417.5 Thioxide TR923 33.4 n-Butyl acetate 71.6 iviA / a / zuzi / uu i ¿ó i1Pentaerythritol Tetrakis(3-mercaptopropionate) from BRUNO BOCK Chemische Fabrik GmbH & Co. KG. 2Dispersing agent and flow additive from BYK USA Inc. Huntsman 3 Pigments. 4Talc from Barretts Minerals Inc. After the addition of each of Loads 1 and 2 to the beaker, the mixture was stirred with a Cowles knife for five minutes. After the addition of Load 3 to the beaker, the mixture was stirred with a Cowles knife for 20 minutes. The mixture from Example A was then placed in a Hockmeyer Micromill fitted with 1.2–1.7 mm Zirconox grinding medium for 3 hours, while ground dry ice was placed around the container to control the temperature. The mixture was reduced with 137 g of n-butyl acetate. The example formulations listed in Table 1 were combined and mixed by hand with a wooden spatula. The compositions in Examples 1A and 1D are comparable because they do not contain a metal compound (i) as in the catalytic compositions of the present invention. The compositions in Examples 1B and 1E are comparable because they do not contain a compound (ii) as in the catalytic compositions of the present invention. Examples 1C and 1F represent the curable compositions of the present invention. A 15 g aliquot of each sample was placed in a scintillation vial to measure the liquid's curing properties, such as pot life and gel time. Pot life was determined by measuring the change in viscosity over time using a Brookfield CAP 2000 viscometer with spindle #1 set at 900 RPM at 25°C. The time it took for the initial viscosity to double is reported as the sample's pot life and is a good indicator of the amount of time available to apply the sample to a substrate. TABLE 1 Formula by weight (g) 1A IB 1C ID 1E 1F Thiocure PETMP1 37.5 37.5 37.5 0 0 0 Ebecryl 8952 32.2 32.2 32.2 25.8 25.8 25.8 n-Butyl acetate 28.4 26.2 25.8 17.6 15.8 15.4 BYK-3003 0.28 0.28 0.28 0 0 0 Example A 0 0 0 64.4 64.4 64.4 Iron(III) chloride hexahydrate4 0 2.72 2.72 0 2.17 2.17 Catalyst5 0.56 0 0.56 0.42 0 0.42 Properties of the Film Thickness (mil) 2.0 2.1 2.0 3.0 3.3 3.2 Pot Life (min) 15-30 >300 >300 45-60 >300 >300 Tack-Free Time (min) >300 0-15 0-15 30-45 0-15 0-15 Double Rubs with MEK 1 hour 0 2 50 28 16 30 2 hours 0 10 66 100 36 100 3 hours 0 40 90 100 60 100 1Pentaerythritol tetrakis (3-mercaptopropionate) from BRUNO BOCK Chemische Fabrik GmdH & Co. KG. 2Pentafunctional acrylate available through Allnex. 3Flow additive from BYK USA Inc. 4. 1% by weight solution of iron(III) chloride hexahydrate in n-butyl acetate Compositions 1A, IB, and 1C were applied by spraying using a Devilbiss® GTI HVLP spray gun with a 1.4 mm nozzle. Compositions ID, 1E, and 1F were applied by spraying using a 3M Accu-Spray HG18 spray gun with a 1.8 mm nozzle. All compositions in Table 1 were applied in two coats with a 5-minute room-temperature flash-off time between coats to 4-inch by 12-inch ACT cold-rolled steel panels with an ED6060 electrocoat available from ACT Laboratories, Inc. A dry film thickness of 2.0–3.0 mils was the target for the non-pigmented compositions 1A, IB, and 1C, and a higher dry film thickness of 3.0–4.0 mils was the target for the pigmented compositions ID, 1E, and 1F. After the coating was applied, the panels were evaluated to determine the curing and drying properties of the film at room temperature.Tack-free time is the amount of time required for a coating to reach a level of dryness such that, after application and removal of a cotton ball, no cotton fibers are transferred to the coating surface. MEK double rubs are reported as the number of double rubs, with a cloth soaked in methyl ethyl ketone, required to dissolve the coating so that the substrate is visible. MEK double rubs are performed at 1-hour intervals after the film is tack-free, and the maximum number of double rubs recorded is 100. Table 1 shows that a longer shelf life is achieved with the addition of iron(III) chloride. However, the combination of iron(III) chloride and a catalyst is necessary to achieve a prolonged shelf life, a rapid tack-free time, and rapid development of solvent resistance. Although particular examples of this invention have been described above for illustrative purposes, it will be evident to persons of a middling skill that numerous variations of the details of the present invention can be made without departing from the invention as defined in the appended claims.

Claims

1. A catalytic composition consisting essentially of: (i) a metal compound; and (ii) a compound other than (i) that catalyzes an addition reaction between an ethylenically unsaturated compound and a thiol, wherein said catalytic composition is essentially free of vanadium compounds.

2. The catalytic composition according to claim 1, wherein said catalytic composition is essentially free of reactive compounds comprising groups with acid functionality, anhydride groups, and reaction products of an active hydrogen compound with an anhydride or polyacid.

3. The catalytic composition according to claim 1, wherein the metal compound (i) comprises at least one of a metal oxide, a metal salt, and an organometallic compound.

4. The catalytic composition according to claim 1, wherein the metal compound (i) comprises an iron compound.

5. The catalytic composition according to claim 1, wherein said compound (i) is selected from oxazolidines, triethylamine, dimethylcyclohexylamine, dimethyloctylamine, dimethyldodecylamine, dimethylaminoethanol, tetramethylguanidine, diaza-bicyclooctane, diaza-bicycloundecene, diaza-bicyclononene, n-methyl-triaza-bicyclodecene, trioctiphosphine, triphenylphosphine and mixtures thereof.

6. The catalytic composition according to claim 1, wherein the metal compound (i) comprises an iron compound, the compound (ii) comprises a compound containing a secondary or tertiary amine group and the molar ratio of the amine group to iron is from 0.4 to 500:

1.

7. A curable composition comprising: (a) a polyene; (b) a polythiol, present in an amount greater than 10 percent by weight based on the total weight of resin solids in the curable composition; and (c) a catalytic component, consisting of the catalytic composition according to claim 1.

8. The curable composition according to claim 7, wherein the polyene has the structural formula A - (X)m where A is an organic portion; X is an olefinicly unsaturated portion and m is at least 2.

9. The curable composition according to claim 8, wherein X is selected from -C(O)CR=CH2,-CH2-CHR=CH2 and mixtures thereof, wherein R is hydrogen or methyl.

10. The curable composition according to claim 8, wherein A contains selected groups of ester and urethane groups.

11. The curable composition according to claim 8, wherein A is derived from a polyisocyanate.

12. The curable composition according to claim 8, wherein A-(X)m comprises a polyurethane (meth)acrylate and / or a polyester (meth)acrylate.

13. The curable composition according to claim 7, wherein the polythiol comprises a reaction product of an organic acid with thiol functionality and a polyol.

14. The curable composition according to claim 7, wherein the polythiol contains from 2 to 6 thiol groups.

15. The curable composition according to claim 7, wherein the metal compound (i) of the catalytic composition comprises at least one of a metal oxide, a metal salt, and an organometallic compound.

16. The curable composition according to claim 15, wherein the metal compound (i) comprises an iron compound, present in the curable composition in an amount of 1 to 1000 ppm of metal, depending on the total weight of components (a) and (b) in the curable composition.

17. The curable composition according to claim 7, wherein compound (ii) of the catalytic composition is present in the curable composition in amounts of 0.001 to 10 percent by weight, depending on the total weight of components (a) and (b) in the curable composition.

18. The curable composition according to claim 7, wherein the metal compound (i) of the catalytic composition comprises an iron compound, the compound (i) of the catalytic composition comprises a compound containing a secondary or tertiary amine group, and the molar ratio of the amine group to iron is from 0.4 to 500:

1.

19. The curable composition according to claim 7, wherein the equivalent ratio of groups with thiol functionality in the polythiol (b) with respect to ethylenically unsaturated groups in the polyene (a) is from 0.1 to 10:

1.

20. The curable composition according to claim 7, wherein said curable composition is essentially free of vanadium compounds, free radical polymerization initiators, and reactive compounds comprising groups with acid functionality, anhydride groups, or reaction products of an active hydrogen compound with an anhydride or polyacid.