Patent Publication Number: US-7220811-B2

Title: Acrylic composition and a curable coating composition including the same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. Nos. 10/793,528 and 10/861,061, which were filed on Mar. 4, 2004 and Jun. 4, 2004, respectively. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an acrylic composition. More particularly, the present invention relates to an acrylic composition that can be incorporated into a curable coating composition and then used in coating applications, such as an automotive coating application, to produce films that have suitable scratch, mar, and chip performance. 
     2. Description of the Related Art 
     Acrylic compositions and their use in a wide variety of coating applications are known in the art. In a curable coating composition, acrylic compositions, along with a suitable cross-linking agent, generally produce a film having good film properties, such as resistance to scratch, mar, and chip. Curable coating compositions that utilize acrylic compositions typically require solvents to dissolve or otherwise reduce the acrylic composition for processing and application purposes. Solvents are required primarily due to a high molecular weight and a correspondingly high viscosity for the acrylic composition. 
     Although the conventional acrylic compositions are generally inexpensive to prepare, these particular compositions with large proportions of non-functional alkyl acrylic monomers provide poor recoat adhesion due to the formation of pendant and non-functional acrylic chains during cure. These acrylic chains migrate toward an upper surface of a cured film of a coating composition having the conventional acrylic composition and inhibit the adhesion of coating compositions that are subsequently applied to the cured film. It is also known in the art that other properties of the cured film, including scratch and mar resistance, may be compromised when the coating composition includes the conventional acrylic composition due to the formation of the acrylic chains described above. Furthermore, cured films formed from cross-linking the conventional acrylic compositions with aminoplasts typically exhibit poor resistance to acid etch. As a result, cured film formed from the conventional acrylic compositions is susceptible to damage due to acid rain. 
     It is known that there is a movement toward utilizing acrylic compositions that have lower molecular weights so as to reduce the overall amount of solvents, i.e., volatile organic compounds (VOCs), required in the coating composition. However, it is also known that coating compositions that utilize conventional acrylic compositions with lower molecular weights produce films that have poorer film properties as evidenced by decreased scratch, mar, and chip performance. 
     Highly branched, e.g. star, compositions are being utilized more frequently because they offer higher molecular weights yet they exhibit low viscosity, as compared to the viscosity of conventional acrylic compositions, i.e., acrylic compositions that are not highly branched. These highly branched compositions have, to date, primarily been polyester-based. However, some highly branched acrylic compositions have been developed by complex methods such as Atom Transfer Radical Polymerization (ATRP) and Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization. These methods are complex, and are therefore generally undesirable for a variety of reasons including, but not limited to, slow reaction times, poor manufacturability, use of metal or sulfur-containing compounds, and a requirement for post purification of the acrylic composition. 
     Due to the inadequacies associated with the acrylic polymers of the prior art, especially the highly branched acrylic compositions developed by ATRP and RAFT, it is desirable to provide a novel acrylic composition that is economical and highly-branched. It is also advantageous to provide an acrylic composition, and a curable coating composition including the acrylic composition, that promotes acid etch resistance, enhances recoat adhesion, and is optimized for cross-linking when used in coating compositions. 
     SUMMARY OF THE INVENTION AND ADVANTAGES 
     The subject invention provides an acrylic composition and a curable coating composition including the acrylic composition. The acrylic composition includes an acrylic polymer. The acrylic polymer includes the reaction product of a functionalized monomer, a first compound reactive with the functionalized monomer to form a functionalized intermediate, and a highly branched, polyfunctional core molecule reactive with the functionalized intermediate to form the acrylic polymer. The first compound includes vinyl functionality reactive with the functionalized monomer and epoxy functionality. The acrylic polymer is highly-branched and cost-effective, as compared to conventional acrylic polymers that are highly-branched. 
     The acrylic composition is further the reaction product of carbon dioxide. The carbon dioxide is reactive with the epoxy functionality of the acrylic polymer to form a carbonate-functional acrylic polymer. 
     The curable coating composition includes the acrylic composition and a cross-linking agent. When used in the curable coating composition, in combination with the cross-linking agent, the acrylic composition produces films, especially clearcoat films, that have optimum scratch, mar, and chip performance, and acid etch resistance. Furthermore, the acrylic compositions enhance recoat adhesion. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The acrylic composition of the present invention is preferably used in curable coating compositions and cured film to improve certain properties of the cured film including, but not limited to, acid etch resistance and recoat adhesion. More specifically, the acrylic composition has carbonate functionality, i.e., a carbonate group, that may be cross-linked with a cross-linking agent in the curable coating compositions. Alternatively, the carbonate functionality may first be modified with an amine, as will be described in further detail below, to form carbamate functionality, and this carbamate functionality may then be reacted with the cross-linking agent. As referred to herein, the acrylic composition may include the reaction product of the acrylic polymer and carbon dioxide, after reaction of those components. The final acrylic composition formed after the reaction of the aforementioned components includes carbonate functionality that may be cross-linked with the cross-linking agent, or may be modified with an amine to form carbamate functionality, which may be cross-linked with the cross-linking agent. Alternatively, the acrylic composition may include the acrylic polymer and the carbon dioxide unreacted. That is, the acrylic composition may include the acrylic polymer and the carbon dioxide prior to reaction between those components. 
     The acrylic polymer is also referred to in the art as a star acrylic polymer or a star polymer having a core and a plurality of functionalized acrylate branches (also referred to as chains, arms, appendages, and the like). Preferably, the acrylic polymer is formed via a free-radical, acrylic polymerization method that is described additionally below. More specifically, the acrylic polymer is the reaction product of a functionalized monomer, a first compound that is reactive with the functionalized monomer to form a functionalized intermediate, and a highly-branched, polyfunctional core molecule reactive with the functionalized intermediate to form the acrylic polymer. The first compound includes vinyl functionality that is reactive with the monomer. The first compound also includes epoxy functionality that remains unreacted in the acrylic polymer. The highly-branched, polyfunctional core molecule, hereinafter simply referred to as the core molecule, functions as the core of the acrylic polymer. The first compound and the core molecule are described additionally below. 
     In one embodiment, the functionalized monomer, hereinafter simply referred to as the monomer, includes hydroxyl-reactive functionality and vinyl functionality. The descriptive terminology ‘functionalized’ that precedes the monomers refers to any functionality that can react with the functionality from the core molecule. 
     The vinyl functionality of the monomer is suitable for stopping chain growth during the free-radical, acrylic polymerization of the monomer and the first compound. Preferably, the hydroxyl-reactive functionality remains unreacted in the functionalized intermediate, after the polymerization between the monomer and the first compound, and is reactive with the hydroxyl functionality present on the core molecule. For example, the monomer may include an aliphatic isocyanato functionality, which is reactive with hydroxyl functionality and may also be referred to as isocyanate functionality, if the core molecule includes a polyol, which has hydroxyl functionality. One such most preferred monomer is α,α-dimethyl isopropenyl benzyl isocyanate, which has both vinyl functionality and aliphatic isocyanato functionality as the hydroxyl-reactive functionality. α,α-dimethyl isopropenyl benzyl isocyanate is also known in the art as TMI® (Meta) Unsaturated Aliphatic Isocyanate and is commercially available from Cytec Industries. α,α-dimethyl isopropenyl benzyl isocyanate is also referred to in the art as 3-isopropenyl-α,α-dimethylbenzyl isocyanate, and α,α-dimethyl meta-isopropenyl benzyl isocyanate. Furthermore, although less preferred, the ortho and para forms of α,α-dimethyl isopropenyl benzyl isocyanate are also feasible. The α,α-dimethyl isopropenyl benzyl isocyanate has the chain-stopping effect of limiting the number of —NCO functionalities under normal acrylic polymerization conditions. For descriptive purposes, a chemical representation of α,α-dimethyl isopropenyl benzyl isocyanate is disclosed below. 
     
       
         
         
             
             
         
       
     
     Other suitable examples of hydroxyl-reactive functionality of the monomer may include cyano functionality, carboxylic acid halide functionality, melamine functionality, and combinations thereof. In other embodiments, the hydroxyl-reactive functionality may be replaced with hydroxyl functionality. It is to be appreciated that when the hydroxyl functionality replaces the hydroxyl-reactive functionality, the core molecule has hydroxyl-reactive functionality that will react with the hydroxyl functionality of the monomer. One such preferred monomer is modified TMI that has had the isocyanato functionality replaced by methylol functionality. 
     Other monomers are suitable for the acrylic composition so long as the monomers are functionalized for subsequent reaction with the core molecule and either have the ability to stop chain growth during the free-radical, acrylic polymerization or have the ability to dissociate for initiating the free-radical, acrylic polymerization with the first compound. Examples of other suitable monomers that have the ability to stop chain growth include, but are not limited to, functionalized styrene (preferably with substituents on the 2 and 6 positions), functionalized vinyltoluene, functionalized α-methylstyrene, functionalized diphenylethylene, functionalized dinapthalenethylene, and combinations thereof. In any event, the monomer is preferably present in the acrylic polymer in an amount of from 1 to 20, more preferably from 3 to 10, parts by weight based on the total weight of the acrylic polymer. 
     When the monomer including the vinyl functionality is used, an initiator is used to initiate the free-radical, acrylic polymerization between the monomer and the first compound. As understood by those skilled in the art, a wide variety of initiators may be used. However, it is preferred that the initiator is selected from the group of inorganic persulfates such as ammonium persulfate, (NH 4 ) 2 S 2 O 8 , potassium persulfate, K 2 S 2 O 8 , and sodium persulfate, Na 2 S 2 O 8 , dialkyl peroxides such as di-tert-butyl peroxide and dicumyl peroxide, hydroperoxides such as cumene hydroperoxide and tert-butyl hydroperoxide, peresters such as tert-butyl peroctoate (TBPO), which is also known as tert-butyl peroxy-2-ethylhexanoate, tert-butyl perbenzoate, tert-butyl perpivalate, tert-butyl per-3,4,5,-trimethylhexanoate and tert-butyl per-2-ethylhexanoate, azo compounds, and combinations thereof. Suitable azo compounds include, but are not limited to, Vazo® 52, 64, 67 and the like. Vazo® 52, 64, 67 are, respectively, 2,2′-azobis(2,4-dimethylpentanenitrile), 2,2′-azobis(2-methylpropanenitrile), and 2,2′-azobis(2-methylbutanenitrile). Inorganic peroxodisulfates and ammonium or alkali metal peroxydiphosphates can also be utilized to initiate the free-radical, acrylic polymerization method. Most preferably, the initiator is tert-butyl peroctoate. 
     In another embodiment, the monomer includes a radical-forming portion instead of the vinyl functionality. The term “radical-forming portion” is defined as any portion of the monomer that is dissociated in the presence of a catalyst, upon the application of heat, or through any other known method for dissociating the monomer. In addition, the monomer includes a functionality that may be hydroxyl functional or hydroxyl-reactive functionality, depending on the functionality of the core molecule that is used. After dissociation of the monomer, the radical-forming portion of the monomer has a free radical. 
     Preferably, the monomer includes the radical-forming portion, which preferably includes a peroxide, and hydroxyl functionality. The hydroxyl functionality can react with the core molecule that includes hydroxyl-reactive functionality. One such preferred monomer is Cyclonox® E, which is commercially available from Akzo-Nobel. Cyclonox® E is di-(1-hydroxycyclohexyl) peroxide, which is of the formula: 
     
       
         
         
             
             
         
       
     
     Dissociation of the di-(1-hydroxycyclohexyl) peroxide results in the oxygen-oxygen bond breaking, leaving two radicalized compounds that each have the free radical on the oxygen atom that was part of the oxygen-oxygen bond prior to dissociation, as shown by the following formula: 
                         
where “*” indicates the free radical.
 
     Other monomers that include the radical-forming portion and the hydroxy functionality are also suitable. Examples of such other monomers include, but are not limited to, VA-085 and VA-086, which may be characterized as azo compounds having hydroxyl functionality. VA-085 is of the formula: 
                         
and VA-086 is of the formula:
 
     
       
         
         
             
             
         
       
     
     In other embodiments, instead of the hydroxyl functionality, the monomer may include hydroxyl-reactive functionality and the radical forming portion. The hydroxyl-reactive functionality may react with the core molecule that includes hydroxyl functionality. One such suitable monomer may be formed from Vazo 67 by converting the cyano functionality to amino or amido functionality. The amino or amido functionality can then be reacted with an isocyanato or aminoplast, respectively. 
     As previously stated, the first compound is reactive with the monomer to form the functionalized intermediate. When the monomer including the vinyl functionality is used, the first compound is reactive with the vinyl functionality after the initiator initiates the free-radical, acrylic polymerization. When the monomer including the radical forming portion is used, the first compound is reactive with the radical-forming portion of the monomer. More specifically, it is the vinyl functionality of the first compound that is reactive with either the vinyl functionality of the monomer after initiation or the free radical portion of the monomer after dissociation, depending on the monomer used. 
     The first compound having the vinyl functionality and the epoxy functionality may be any epoxy functional acrylate or methacrylate. Preferably, the first compound is selected from the group of glycidyl acrylate, glycidyl alkacrylates, and combinations thereof. For descriptive purposes, a chemical representation of glycidyl methacrylate is disclosed below. 
     
       
         
         
             
             
         
       
     
     As stated above, the vinyl functionality is reactive with the monomer. The epoxy functionality is unreactive with the hydroxyl or hydroxyl-reactive functionality of either the monomer or the core molecule under target reaction conditions. In other words, the epoxy functionality remains unreacted in the acrylic polymer and is present to participate in further reactions, which will be described in further detail below. 
     The acrylic polymer may further include the reaction product of a second compound that is reactive with the monomer and the first compound to form the functionalized intermediate. The second compound may be included to modify a glass transition temperature T g  of the cured film formed from the curable coating composition, which curable coating composition will be described in further detail below. In addition, the second compound may also function to modify the equivalent weight and, therefore, cross-linking density in the cured film. Preferably, the second compound is selected from the group of, but not limited to, acrylates, methacrylates, acrylonitriles, styrenes, alkenes, alkene anhydrides (cyclic or acyclic), and combinations thereof, each of which has vinyl functionality. The second compound may be functionalized or non-functionalized with an additional functionality other than the vinyl functionality. More specifically, the second compound may include additional functionality so long as the additional functionality of the second compound is unreactive with the functionalities of the monomer, the first compound, or the core molecule. Preferably, the second compound is free of functionality other than the vinyl functionality. 
     In the preferred embodiment, the first compound, and optionally the second compound, is present in a total amount of from 10 to 99, more preferably from 15 to 90, parts by weight based on the total weight of the acrylic polymer. 
     Preferably, the acrylic polymer has a molecular weight, M w , of 700 to 48,000. For the acrylic polymer having the molecular weight, M w , within the above range, the functionalized intermediate disclosed below preferably has a molecular weight, M w , of approximately 300 to 12,000, more preferably from 1,000 to 4,000. Of course, higher molecular weights, M w , are possible for the functionalized intermediate, but such functionalized intermediates are not ideal for curable coating compositions due to an excessive resultant viscosity in the acrylic composition. 
     As stated above, the first compound and the monomer react to form the functionalized intermediate. Assuming the monomer is α,α-dimethyl isopropenyl benzyl isocyanate, i.e., the monomer having the hydroxyl-reactive functionality and the vinyl functionality, with the first compound being glycidyl methacrylate, the functionalized intermediate disclosed below is formed, where INIT. represents the initiator and m ranges from 1 to 80, most preferably from 15 to 30. 
     
       
         
         
             
             
         
       
     
     The functionalized intermediate disclosed above is equivalent to functionalized acrylate branches of the acrylic polymer. That is, this functionalized intermediate functions as the branches for subsequent connection, via condensation, to the core of the acrylic polymer. The functionalized acrylate branches are formed first and the core, i.e., the core molecule, is then condensed with the functionalized acrylate branches. 
     It is to be understood that the above functionalized intermediate is merely one example of many different functionalized intermediates that can be formed during the reaction to form the acrylic composition, and the subject invention is not necessarily limited to this particular functionalized intermediate and subsequent derivatives thereof. For example, when the monomer is di-(1-hydroxycyclohexyl) peroxide, i.e., the monomer having the radical-forming portion and the hydroxyl functionality, and the first compound is glycidyl methacrylate, the functionalized intermediate is formed, where m preferably ranges from 1 to 80, most preferably from 15 to 30. The functionalized intermediate is disclosed below. 
                         
where “*” indicates the free radical. The functionalized intermediate may be terminated, at the free radical, through a number of termination reactions such as through proton extraction from a solvent, reaction with another radicalized compound, decomposition to form a double bond at the free radical site, or any combination of those reactions.
 
     Once the functionalized intermediate is formed, the core molecule is introduced to react with the functionalized intermediate to form the acrylic polymer. The core molecule is selected to provide a functionality that is reactive with the functionality of the monomer that remains unreacted after polymerization with the first compound. As described above, the core molecule is highly branched and is polyfunctional, i.e., has a functionality greater than or equal to 2. For the purposes of this invention, the terminology “highly branched” indicates core molecules that start with a core and branches in at least two, preferably at least three or more, directions. Although extensive branching is not required, it is most preferred that the core molecule, preferably an isocyanate or polyol, is highly branched to achieve desired viscosity benefits. 
     The core molecules may also be described as branched compounds that have a plurality of functionalities. The functionalities can be primary, secondary, and tertiary functionalities. The core molecule is selected from the group of isocyanates, isocyanurates, melamines, polyols, polycarboxylic acid halides, and combinations thereof, with the core molecule reactive with the functionalized intermediate to form the acrylic polymer. However, other potential core molecules could be different than those mentioned above and could provide a functionality other than those described above. For example, the core molecule may also be a melamine-formaldehyde resin. Preferred core molecules when the functionalized intermediate has the hydroxyl-reactive functionality, i.e., wherein the monomer is the α,α-dimethyl isopropenyl benzyl isocyanate having the aliphatic isocyanato functionality, include polyols that are reactive with the functionalized intermediate to form the acrylic polymer. Preferably, the polyols are selected from the group of glycerol, propylene glycol, erythritol, pentaerythritol, dipentaerythritol, trimethylolethane, trimethylolpropane, dulcitol, threitol, and combinations thereof. For descriptive purposes, a chemical representation of pentaerythritol is disclosed below. 
     
       
         
         
             
             
         
       
     
     Preferred core molecules for reacting with the functionalized intermediate that has the hydroxyl functionality, i.e. wherein the monomer is the peroxide having the hydroxyl functionality, include isocyanates, isocyanurates, melamines, carboxylic acid halides, and combinations thereof that are reactive with the functionalized intermediate to form the acrylic polymer. Most preferred core molecules for reacting with the functionalized intermediate that has the hydroxyl functionality include isocyanates. Preferably, the isocyanates are selected from the group of trimethylol propane carbamate with tolylene diisocyanate, pentaerythritol carbamate with tolylene diisocyanate, and combinations thereof. Other preferred isocyanates include Desmodur® or Mondur® polyisocyanate commercially available from Mobay Corporation of Pittsburgh, Pa. For descriptive purposes, a chemical representation of pentaerythritol carbamate with tolylene diisocyanate is disclosed below. 
     
       
         
         
             
             
         
       
     
     The core molecule is condensed with the functionalized intermediate, i.e., with the functionalized acrylate branches. More specifically, the core molecule and the functionalized intermediate are reacted to form the acrylic polymer. Success of the condensation of the core molecule and the functionalized intermediate depends on the observation that when the monomer is used to polymerize the first compound, each one of the polymer strands formed will have one and only one functionality originating from the monomer in most cases. 
     The amount of the core molecule present in the reaction must be balanced with the amount of the functionalized intermediate, i.e., functionalized acrylate branches, that is formed via the reaction of the monomer, the first compound, and, optionally, the second compound. To this end, it is preferred that the molar ratio of the core molecule to the functionalized intermediate is from 1:20 to 1:1, more preferably from 1:10 to 1:3. The core molecule establishes a foundation for the acrylic polymer. Preferably, the core molecule is present in an amount of from 0.1 to 20, more preferably from 0.5 to 10, and most preferably from 0.5 to 1.5, parts by weight based on the total weight of the acrylic polymer. 
     When the monomer is α,α-dimethyl isopropenyl benzyl isocyanate, the first compound is glycidyl methacrylate, the second compound is not present, and the core molecule is pentaerythritol, the acrylic polymer is disclosed below, where INIT. represents the initiator and m ranges from 1 to 80, most preferably from 15 to 30. 
     
       
         
         
             
             
         
       
     
     When the monomer is di-(1-hydroxycyclohexyl) peroxide, the first compound is glycidyl methacrylate, and the core molecule is pentaerythritol carbamate with tolylene diisocyanate, the acrylic polymer is disclosed below, where m ranges from 1 to 80, most preferably from 15 to 30, and the “*” indicates the free radical, which may be terminated as described above. 
     
       
         
         
             
             
         
       
     
     Preferably, the acrylic polymer is present in the acrylic composition in an amount of from 10 to 80 parts by weight based on the total weight of the acrylic composition, more preferably from 30 to 60 parts by weight based on the total weight of the acrylic composition. 
     As alluded to above, the acrylic composition also includes, in addition to the acrylic polymer, carbon dioxide. The carbon dioxide is reactive with the acrylic polymer to form a carbonate-functional acrylic polymer. The reaction between the acrylic polymer and the carbon dioxide may be accomplished under excessive pressure and temperature conditions. More specifically, the reaction between the acrylic polymer and the carbon dioxide preferably occurs at a pressure of about 100 psi and a temperature of about 100° C. Preferably, the reaction also occurs in the presence of a tetraalkylammonium halide catalyst. An example of a suitable catalyst is tetrabutylammonium bromide. For descriptive purposes, a chemical representation of a portion of the carbonate-functional acrylic polymer after carbon dioxide and the epoxy functionality react is disclosed below. 
                         
The “Acrylic Polymer” label corresponds to the structure of either of the acrylic polymers graphically represented above, R corresponds to either the initiator or the free radical, depending on the monomer that is used, m is from 1 to 80, most preferably from 15 to 30, and the arrows labeled “1” and “2” indicate bonds that are reactive through further reaction with the cross-linking agent or with an amine to form carbamate functionality. As illustrated, the carbon dioxide and the epoxy functionality of the acrylic polymer have reacted through a ring-opening reaction, which results in the formation of the carbonate functionality. The above chemical representation is not limited to either of the two specific embodiments of the acrylic polymer as described above.
 
     In one embodiment, the acrylic polymer and carbon dioxide are reacted as soon as those components are combined. Alternatively, the acrylic polymer and the carbon dioxide are combined together under sufficiently high pressure in a leak-free container such that the acrylic polymer and the carbon dioxide remain unreacted until reaction between the acrylic polymer and the carbon dioxide is desired. 
     Preferably, the carbon dioxide is present in the acrylic composition in an amount from 1 to 30, more preferably from 5 to 20, parts by weight based on the total weight of the acrylic composition. 
     In a further embodiment of the subject invention, the acrylic composition further comprises the reaction product of the amine that is reactive with the carbonate-functional acrylic polymer to form carbamate functionality. More specifically, the acrylic composition of the subject invention further includes the reaction product of an ammonia-containing compound. Preferably, the ammonia-containing compound is selected from the group of ammonia, ammonium hydroxide, and combinations thereof. The ammonia-containing compound is reactive with the carbonate functionality in order to modify the carbonate functionality into the carbamate functionality. Use of either ammonia or ammonium hydroxide to convert the carbonate functionality results in a primary carbamate functionality of the general formula NH 2 COO—. Additionally, a primary amine can be used to convert the carbonate functionality into the carbamate functionality. Use of the primary amine results in a secondary carbamate functionality of the general formula NHRCOO—, where R is an alkyl radical. However, in terms of the preferred embodiment of the subject invention, reaction with the primary amine is not preferred because secondary carbamate functionalities exhibit ‘sluggish’ reactions with the preferred cross-linking agents, which will be described below. 
     Preferably, ammonium hydroxide is utilized to convert the carbonate functionality into the carbamate functionality. The ammonia group, NH 3 , of the ammonium hydroxide can modify the carbonate-functional acrylic composition to form a primary carbamate functionality and a primary hydroxyl functionality by reacting at the bond labeled “2”. The reaction is shown schematically below utilizing ammonium hydroxide. 
                         
Alternatively, the ammonia, NH 3 , group of the ammonium hydroxide can form a primary carbamate functionality having a secondary hydroxyl group by reacting at the bond labeled “1”, which is shown schematically below.
 
                         
The “Acrylic Polymer” label corresponds to the structure of either of the acrylic polymers graphically represented above, R corresponds to either the initiator or the free radical, depending on the monomer that is used, and m is from 1 to 80. Preferably, the reaction between the amine and the carbonate functionality occurs at a temperature of from 30° C. to 175° C., and more preferably at a temperature of from 50° C. to 100° C. over a period of from 20 to 30 minutes. The acrylic composition having the carbamate functionality may be cross-linked through further reaction with the cross-linking agent, which will be described in further detail below.
 
     The amount of the amine used in the acrylic composition to modify the carbonate functionality is dependent upon the number of carbonate functionalities on the carbonate-functional acrylic polymer. The total number of moles of the amine is generally equal to the number of carbonate functionalities on the carbonate-functional acrylic polymer, which preferably results in consumption of all carbonate functionality on the carbonate-functional acrylic polymer. Therefore, in the preferred embodiment, the molar ratio of the amine, e.g., ammonia, to the carbonate functionalities on the carbonate-functional acrylic composition is 1:1. It is to be appreciated that the amount of amine to carbonate functionality may be less than 1:1. When the amount of amine to carbonate functionality is less than 1:1, the acrylic composition will have both carbonate and carbamate functionalities. As such, the acrylic composition is capable of “dual” cross-linking, wherein the carbamate functionality will cross-link with cross-linking agents such as aminoplasts, and the carbonate functionality will cross-link with cross-linking agents such as polyamines. 
     As alluded to above, the curable coating composition that includes the acrylic composition also includes the cross-linking agent. In one embodiment, when the acrylic composition includes the carbonate functionality, the cross-linking agent includes a polyamine, i.e., a compound having at least two amino functionalities. Preferably, the polyamine is selected from the group of C 2  to C 20  alkyl compounds that have at least two amino functionalities. Suitable polyamines for the subject invention include, but are not limited to, hexamethylenediamine, triaminononane, and combinations thereof. Most preferably, the polyamine is triaminononane, which has three amino functionalities. For descriptive purposes, triaminononane is the common chemical name, and 4-aminomethyl-1,8-octanediamine is the accepted chemical abstract chemical name. The amino functionality is reactive with the carbonate functionality of the carbonate-functional acrylic polymer. In other words, the carbonate-functional acrylic polymer is combined with the polyamine to form the curable coating composition, which may be cured to form the cured film. 
     When used, the polyamine is preferably present in an amount from 1 to 10, preferably from 3 to 6, parts by weight based on the total weight of the curable coating composition. 
     As shown schematically in the above chemical representation of the carbonate-functional acrylic polymer, the bonds indicated by either “1” or “2” are available for further reaction. The amino functionality, NH 2 , of the polyamine reacts at either “1” or “2” to open the ring and results either in a primary or secondary urethane (—NH—CO—O—) linkage, depending on the bond that is reacted. The resulting primary and secondary urethane linkages established in the curable coating composition of the subject invention are shown respectively in the following chemical representations. 
                         
wherein, for either structure, the “Acrylic Polymer” label corresponds to the structure of either of the acrylic polymers graphically represented above, R corresponds to either the initiator or the free radical, depending on the monomer that is used, m is from 1 to 80, most preferably from 15 to 30, and R 1  is the remainder of the polyamine including the C 2  to C 20  alkyl compound having either at least one remaining amino functionality or another acrylic polymer that has been cross-linked with the remaining amino functionality. The resulting carbonate—amine cross-linking that establishes either of the urethane linkages shown above is ideal for acid etch resistance.
 
     Alternatively, when the acrylic composition has the carbamate functionality, suitable cross-linking agents are selected from the group of, but are not limited to, polyisocyanates, polyisocyanurates, melamine-formaldehyde resins, polycarboxylic acid halides, and combinations thereof. Also suitable for the cross-linking agent are aminoplast resins that are reactive with the carbamate functionality. As understood by those skilled in the art, an aminoplast resin is formed by the reaction product of a formaldehyde and an amine where the preferred amine is a urea or a melamine. In other words, the aminoplast resin may include urea resins and melamine-formaldehyde resins. 
     The melamine-formaldehyde resins of the preferred embodiment include either methylol functionality, CH 2 OH, alkoxymethyl functionality, or both. The alkoxymethyl functionality is of the general formula —CH 2 OR 1 , where R 1  is an alkyl chain having from 1 to 20 carbon atoms. As understood by those skilled in the art, the methylol functionality and the alkoxymethyl functionality are reactive with the carbamate functionality of the acrylic composition. The methylol and alkoxymethyl functionalities are preferentially reactive with the carbamate functionality, as opposed to any hydroxyl functionality, to ‘cross-link’ the curable coating composition upon cure. Examples of suitable aminoplast resins include, but are not limited to, monomeric or polymeric melamine-formaldehyde resins, including melamine resins that are partially or fully alkylated using alcohols that preferably have one to six, more preferably one to four, carbon atoms, such as hexamethoxy methylated melamine; urea formaldehyde resins including methylol ureas and siloxy ureas such as butylated urea formaldehyde resin, alkylated benzoguanimines, guanyl ureas, guanidines, biguanidines, polyguanidines, and the like. Although urea and melamine are the preferred amines, other amines such as triazines, triazoles, diazines, guanidines, or guanamines may also be used to prepare the aminoplast resins. Furthermore, although formaldehyde is preferred for forming the aminoplast resin, other aldehydes, such as acetaldehyde, crotonaldehyde, and benzaldehyde, may also be used. 
     Monomeric melamine-formaldehyde resins are particularly preferred. The preferred melamine-formaldehyde resin includes hexamethoxymethyl melamine (HMMM). HMMM is commercially available from Solutia under its Resimene Amino Crosslinker Resins. HMMM is shown in the following chemical representation. 
     
       
         
         
             
             
         
       
     
     Upon addition of the cross-linking agent to the acrylic composition, the alkoxymethyl functionality of the HMMM, specifically the CH 2 OCH 3  group, and the carbamate functionality of the acrylic polymer react to establish urethane (—NH—CO—O—) linkages. The urethane linkage between the acrylic composition and the cross-linking agent is from the carbamate—melamine reaction and is ideal for resistance to environmental acid etch. 
     In the embodiment of the acrylic composition having carbamate functionality, ether linkages which result from a hydroxyl functionality—aminoplast cure, and which are particularly susceptible to acid etch, can be avoided as the primary cross-linking mechanism because the aminoplast is selectively reactive with the carbamate functionality. To avoid the ether linkages, the amount of the cross-linking agent, i.e., the aminoplast resin in the preferred embodiment, is limited so that the cross-linking agent reacts only with the available carbamate functionality in the acrylic composition. That is, in the preferred embodiment, the aminoplast cross-linking agent reacts preferably with available carbamate functionality before any substantial reaction with the hydroxyl functionality that is present in the acrylic composition. It is therefore possible to control the amount of undesirable ether linkages that are formed when cross-linking the acrylic composition and the cross-linking agent. The amount of cross-linking agent can be increased if cross-linking with the hydroxyl functionality is desired for whatever reason. 
     Although not necessarily preferred, an alternative cross-linking agent for use in the curable coating composition having the acrylic composition with carbamate functionality is the polyisocyanate cross-linking agent. The most preferred polyisocyanate cross-linking agent is a triisocyanurate. The polyisocyanate cross-linking agent can be an aliphatic polyisocyanate, including a cycloaliphatic polyisocyanate, or an aromatic polyisocyanate. The term “polyisocyanate” as used herein refers to any compound having a plurality of isocyanato functionalities on average per molecule. Polyisocyanates encompass, for example, monomeric polyisocyanates including monomeric diisocyanates, biurets and isocyanurates of monomeric polyisocyanates, extended poly-functional isocyanates formed by reacting one mole of a diol with two moles of a diisocyanate or mole of a triol with three moles of a diisocyanate, and the like. Useful examples of suitable polyisocyanates cross-linking agents include, without limitation, ethylene diisocyanate, 1,2-diisocyanatopropane, 1,3-diisocyanatopropane, 1,4-butylene diisocyanate, lysine diisocyanate, 1,4-methylene bis (cyclohexyl isocyanate), isophorone diisocyanate, toluene diisocyanate, the isocyanurate of toluene diisocyanate, diphenylmethane 4,4′-diisocyanate, the isocyanurate of diphenylmethane 4,4′-diisocyanate, methylenebis-4,4′-isocyanatocyclohexane, isophorone diisocyanate, the isocyanurate of isophorone diisocyanate, 1,6-hexamethylene diisocyanate, the isocyanurate of 1,6-hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, p-phenylene diisocyanate, triphenylmethane 4,4′,4″-triisocyanate, tetramethyl xylene diisocyanate, metaxylene diisocyanate, and combinations thereof. Aliphatic polyisocyanates are preferred when the curable coating composition is used as an automotive topcoat composition. 
     Generally, the acrylic composition is present in an amount from 65 to 90, preferably from 75 to 90, parts by weight based on the total weight of the curable coating composition, and the cross-linking agent is present in an amount from 1 to 35, preferably from 5 to 25, and most preferably from 7 to 15, parts by weight based on 100 parts by weight of the curable coating composition. The ratio of effective equivalents of the acrylic composition to the cross-linking agent is from 3:1 to 1:3. 
     The curable coating composition may also include one additive or a combination of additives. Such additives include, but are not limited to, solvents, catalysts, hindered amine light stabilizers (HALs), ultra-violet absorbers (UVAs), rheology control agents, anti-yellowing agents, adhesion promoting agents, and the like. Specific examples of some of the above additives include n-methyl pyrrolidone and oxo-hexyl acetate as solvents to affect such characteristics as pop and sag resistance, and polybutyl acrylate, fumed silica, and silicone as rheology control agents. 
     The following examples illustrating the formation of and the use of the acrylic composition of the present invention, as presented herein, are intended to illustrate and not limit the invention. 
     EXAMPLES 
     In the Examples, Acrylic Polymer A was prepared by adding and reacting the following components, in parts by weight based on the total weight of the acrylic composition, unless otherwise indicated. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Reactant 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 FUNCTIONALIZED MONOMER 
                 4.90 
               
               
                   
                 α,α-dimethyl isopropenyl benzyl isocyanate 
               
               
                   
                 FIRST COMPOUND 
                 19.62 
               
               
                   
                 glycidyl methacrylate 
               
               
                   
                 SECOND COMPOUND A 
                 49.05 
               
               
                   
                 methyl methacrylate 
               
               
                   
                 SECOND COMPOUND B 
                 24.52 
               
               
                   
                 n-butyl acrylate 
               
               
                   
                 INITIATOR 
                 0.98 
               
               
                   
                 tert-butylperoxy-2-ethylhexanoate (TBPO) 
               
               
                   
                 CORE MOLECULE A 
                 0.93 
               
               
                   
                 pentaerythritol 
                   
               
               
                   
                 TOTAL 
                 100.0 
               
               
                   
                 NCO of Functionalized Intermediate, % 
                 1.25 
               
               
                   
                 Number Average Molecular Weight (M n ) of 
                 1970 
               
               
                   
                 Functionalized Intermediate, g/mol 
               
               
                   
                 Weight Average Molecular Weight (M w ) of 
                 3370 
               
               
                   
                 Functionalized Intermediate, g/mol 
               
               
                   
                 Polydispersity Index of Functionalized Intermediate 
                 1.7 
               
               
                   
                 Number Average Molecular Weight (M n ) of Acrylic 
                 2370 
               
               
                   
                 Polymer A, g/mol 
               
               
                   
                 Weight Average Molecular Weight (M n ) of Acrylic 
                 5580 
               
               
                   
                 Polymer A, g/mol 
               
               
                   
                 Polydispersity Index of Acrylic Polymer A 
                 2.4 
               
               
                   
                   
               
            
           
         
       
     
     To form Acrylic Polymer A, 75.0 grams of Solvesso® 100 aromatic hydrocarbon solvent (also referred to as Aromatic 100) were added into a reactor, and the reactor was heated via a conventional heat supply to a temperature of 150° C. Once the reactor reached 150° C., a mixture of the Functionalized Monomer, First Compound, Second Compound A, Second Compound B, and the Initiator were added to the reactor over approximately 3 hours to form the functionalized intermediate. 
     Once the functionalized intermediate was formed, the temperature was lowered until the temperature of the functionalized intermediate reached approximately 100–110° C. Then, the Core Molecule A was added to the reactor along with an additional 11 grams of Solvesso® 100 aromatic hydrocarbon solvent. A drop of dibutyltin dilaurate (DBTDL) catalyst was added. The reaction was maintained at 100° C. until % NCO measured to be less than 0.1 meq on solids. 
     Acrylic Polymer B will be prepared by adding and reacting the following components, in parts by weight based on the total weight of the acrylic composition, unless otherwise indicated. 
     
       
         
           
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Reactant 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 FUNCTIONALIZED MONOMER B 
                 9.17 
               
               
                 di-(1-hydroxycyclohexyl) peroxide 
               
               
                 FIRST COMPOUND 
                 27.51 
               
               
                 glycidyl methacrylate 
               
               
                 SECOND COMPOUND C 
                 18.34 
               
               
                 Styrene 
               
               
                 SECOND COMPOUND D 
                 36.68 
               
               
                 Cyclohexyl methacrylate 
               
               
                 CORE MOLECULE B 
                 8.30 
               
               
                 pentaerythritol carbamate with tolylene diisocyanate 
                   
               
               
                 TOTAL 
                 100.0 
               
               
                 Theoretical OH, % 
                 0.38 
               
               
                 Theoretical Number Average Molecular Weight (M n ) of 
                 2800 
               
               
                 Functionalized Intermediate, g/mol 
               
               
                 Theoretical Weight Average Molecular Weight (M w ) of 
                 4950 
               
               
                 Functionalized Intermediate, g/mol 
               
               
                 Theoretical Polydispersity Index of Functionalized 
                 1.8 
               
               
                 Intermediate 
               
               
                 Theoretical Number Average Molecular Weight (M n ) of 
                 2370 
               
               
                 Acrylic Polymer B, g/mol 
               
               
                 Theoretical Weight Average Molecular Weight (M w ) of 
                 7180 
               
               
                 Acrylic Polymer B, g/mol 
               
               
                 Theoretical Polydispersity Index of Acrylic Polymer B 
                 3.0 
               
               
                   
               
            
           
         
       
     
     To form the acrylic polymer, 75.0 grams of Solvesso® 100 aromatic hydrocarbon solvent (also referred to as Aromatic 100) would be added into a reactor, and the reactor would be heated via a conventional heat supply to a temperature of 121° C. Once the reactor reached 121° C., a mixture of the Functionalized Monomer, First Compound, Second Compound A, and Second Compound B according to Table 2 would be added to the reactor over approximately 3 hours to form the functionalized intermediate. 
     Once the functionalized intermediate is formed, the temperature will be lowered until the temperature of the functionalized intermediate reaches approximately 100–110° C. Then, the Core Molecule will be added to the reactor along with an additional 11 grams of Solvesso® 100 aromatic hydrocarbon solvent. A drop of DBTDL catalyst will also be added and the reaction will be maintained at 100° C. until % NCO measures to be less than 0.02 meq on solids. 
     Acrylic Composition A is prepared, and Acrylic Composition B would be prepared, by adding and reacting the following components, in parts by weight based on the total weight of the acrylic composition, unless otherwise indicated. 
     
       
         
           
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Acrylic 
                 Acrylic 
               
               
                   
                 Composition A 
                 Composition B 
               
               
                 Reactant 
                 Weight, % 
                 Weight, % 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Carbon Dioxide [CO 2 ] 
                 5.7 
                 4.6 
               
               
                 CATALYST 
                 0.04 
                 0.14 
               
               
                 tetraalkylammonium bromide 
               
               
                 ACRYLIC POLYMER A 
                 94.26 
                 None 
               
               
                 α,α-dimethyl isopropenyl benzyl 
               
               
                 isocyanate + glycidyl 
               
               
                 methacrylate + pentaerythritol 
               
               
                 ACRYLIC POLYMER B 
                 None 
                 95.26 
               
               
                 Di-(1-hydroxycyclohexyl) 
               
               
                 peroxide + glycidyl methacrylate + 
               
               
                 pentaerythritol carbamate with 
               
               
                 tolylene diisocyanate 
               
               
                 TOTAL 
               
               
                 ammonium hydroxide (30% in 
                 6.5 
                 4.0 
               
               
                 water), g 
               
               
                 toluene solvent, g 
                 30 
                 30 
               
               
                 amyl acetate solvent, g 
                 100 
                 100 
               
               
                   
               
            
           
         
       
     
     Per the above Table 3, 0.4 grams of the Catalyst and 943 grams of Acrylic Polymer A were heated to a temperature of about 110° C. in a pressure steel reaction flask. Carbon dioxide (CO 2 ) from a tank was fed into the reaction flask at 100 psi to form Acrylic Composition A. The contents of the reaction flask were reacted for about four hours and the pressure was relieved. The contents of the reaction flask were then weighed to determine the weight gain, which was about 57 grams. It was determined through IR Spectroscopy that more than 90% of the epoxide of Acrylic Polymer A reacted. Alternatively, Acrylic Polymer B may be substituted for Acrylic Polymer A to form Acrylic Composition B. 
     After IR Spectroscopy was performed to confirm that most (&gt;90%) of the epoxide has been converted to carbonate, the ammonium hydroxide was charged into the reaction flask and was allowed to react for about one hour at 80° C. IR Spectroscopy confirmed that most of the carbonate had been converted to hydroxy carbamate. In the case of Acrylic Composition B, only 70% of the carbonate would have been converted to hydroxy carbamate, leaving the rest of the carbonate available for cross-linking with cross-linking agents. The total reaction time for the Acrylic Polymer A to react with the carbon dioxide, and then subsequent reaction with the ammonium hydroxide, is about eight hours. The Acrylic Composition A has a non-volatile percentage of about 70 parts by weight based on the total weight of Acrylic Composition A. 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings, and the invention may be practiced otherwise than as specifically described.