Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-08-20
2001-05-08
Wilson, Donald R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S329900, C525S409000, C525S437000, C525S453000, C525S460000, C525S398000
Reexamination Certificate
active
06228953
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved process for preparing carbamate functional polymers via a transcarbamoylation reaction.
BACKGROUND OF THE INVENTION
Aminoplast-cured coating compositions containing polymeric polyols are well known and provide many excellent coating properties. They are inexpensive, durable, and attractive. However, it is widely recognized that such coatings, particularly clear coats, have poor resistance to etching by acid due to the vulnerable ether linkages that are formed between the polyol and aminoplast during curing. Because many geographic areas encounter acidic precipitation, acid etch resistance in coatings is becoming an increasingly desirable property, particularly for automotive coatings.
Coating systems of the prior art which are known to be resistant to acid etch include acid-epoxy curable compositions such as those disclosed in U.S. Pat. No. 4,681,811 and compositions containing hydroxyl functional polymers reacted with isocyanates or polyisocyanates to form polyurethanes. The isocyanates are expensive and the toxicity of the isocyanates is an additional drawback.
Other more recent, promising developments in the field of acid etch resistant coatings include aminoplast-carbamate cured coating compositions, such as those disclosed in U.S. Pat. No. 5,814,410. Carbamate functional polymers are less expensive than isocyanates, do not have the same toxicity drawbacks, and yet provide the same durable urethane bonds in the cured film. A number of processes are available for preparing the carbamate functional polymers, including transcarbamoylation of hydroxyl functional polymers as disclosed in U.S. Pat. No. 5,663,244. Transcarbamoylation of a polymeric polyol using a lower alkyl carbamate is a desirable reaction process because of the relatively low cost, simplicity, and raw material availability. However, high volatility of many lower alkyl carbamates can result in loss of the carbamate from the reaction mixture by sublimation or distillation, leading to poor conversion of hydroxyl to carbamate groups and fouling of the overhead components of the reactor system.
It would be desirable to provide a process for preparing carbamate functional polymers or oligomers via transcarbamoylation using lower alkyl carbamates with improved yields and without loss of reactants.
SUMMARY OF THE INVENTION
In accordance with the present invention, a process for preparing carbamate functional polymers or oligomers is provided. The process comprises: (a) preparing a reaction mixture comprising a lower alkyl carbamate, a hydroxyl functional polymer or oligomer, and an alcohol different from and having a higher boiling point than an alcohol from which the lower alkyl carbamate is derived; and (b) heating the reaction mixture to form a carbamate functional polymer or oligomer.
Also provided is a method of preparing a carbamate functional acrylic polymer by preparing a similar reaction mixture using acrylic monomers containing hydroxyl groups or groups that can be converted to hydroxyl groups and heating the reaction mixture in the presence of a free radical initiator and an esterification catalyst.
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as modified in all instances by the term “about”.
DETAILED DESCRIPTION
The hydroxyl functional polymer or oligomer used to prepare the carbamate functional polymer or oligomer according to the process of the present invention may be any type of polymeric or oligomeric polyol known to those skilled in the art, particularly those commonly used in curable film-forming compositions. The hydroxyl functional polymer or oligomer used in the process of the present invention is most often a polyether polyol, an acrylic polyol, a polyester polyol, or a polyurethane polyol.
Examples of suitable polyether polyols are polyalkylene ether polyols which include those having the following structural formula:
where the substituent R is hydrogen or lower alkyl containing from 1 to 5 carbon atoms including mixed substituents, and n is typically from 2 to 6 and m is from 8 to 100 or higher. Included are poly(oxytetramethylene) glycols, poly(oxytetraethylene) glycols, poly(oxy-1,2-propylene) glycols, and poly(oxy-1,2-butylene) glycols.
Also useful are polyether polyols formed from oxyalkylation of various polyols, for example, glycols such as ethylene glycol, 1,6-hexanediol, Bisphenol A and the like, or other higher polyols such as trimethylolpropane, pentaerythritol, and the like. Polyols of higher functionality which can be utilized as indicated can be made, for instance, by oxyalkylation of compounds such as sucrose or sorbitol. One commonly utilized oxyalkylation method is reaction of a polyol with an alkylene oxide, for example, propylene or ethylene oxide, in the presence of an acidic or basic catalyst.
Preferred polyethers include those sold under the names TERATHANE and TERACOL, available from E. I. Du Pont de Nemours and Company, Inc.
The hydroxyl functional polyether polymer or oligomer used in the process of the present invention preferably has a number average molecular weight of from about 500 to 5000, more preferably from about 1100 to 3200 as determined by gel permeation chromatography using a polystyrene standard, and a hydroxyl number of 35 to 180. Hydroxyl number (or hydroxyl value) is measured using the method of C. L. Ogg, W. L. Porter,
Ind. Eng. Chem. Anal. Ed
., Vol. 17, pp. 394-397, 1945.
The hydroxyl functional acrylic polymers used in the process of the present invention are copolymers of one or more alkyl esters of acrylic acid or methacrylic acid, and, optionally, one or more other polymerizable ethylenically unsaturated monomers. Suitable alkyl esters of acrylic or methacrylic acid (“(meth)acrylates”) include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobutyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, and the like. Suitable other polymerizable ethylenically unsaturated monomers include vinyl aromatic compounds such as styrene and vinyl toluene; nitriles such as acrylonitrile and methacrylonitrile; vinyl and vinylidene halides such as vinyl chloride and vinylidene fluoride and vinyl esters such as vinyl acetate.
The acrylic polymers contain hydroxyl functionality which is most often incorporated into the acrylic polymer through the use of hydroxyl functional monomers such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and 2- or 4-hydroxybutyl (meth)acrylate which may be copolymerized with the other acrylic monomers. Ethylenically unsaturated hydroxyl functional monomers derived from caprolactone, such as those available from Union Carbide Company under the name TONE, may also be used to prepare the hydroxyl functional polymer.
Hydroxyl functional monomers may also be selected from:
a) a reaction product of an ethylenically unsaturated, epoxy functional monomer and a saturated carboxylic acid having about 7 to about 20 carbon atoms; and
b) a reaction product of an ethylenically unsaturated acid functional monomer and an epoxy compound containing at least 5 carbon atoms which is not polymerizable with the ethylenically unsaturated acid functional monomer.
Examples of ethylenically unsaturated, epoxy functional monomers used to prepare the hydroxyl functional monomers of a) above include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, methallyl glycidyl ether, 1:1 (molar) adducts of ethylenically unsaturated monoisocyanates such as meta-isopropenyl-alpa,alpha,-dimethylbenzyl isocyanate with hydroxyl functional monoepoxides such as glycidol, and glycidyl esters of polymerizable polycarboxylic acids such as maleic acid, fumaric acid, and crotonic acid. Preferred are the epoxy-functional acrylates such as glycidyl acrylate, epoxy functional methacrylates such as glycidyl methacrylate
Barancyk Steven V.
Singer Debra L.
Altman Deborah M.
PPG Industries,Ohio, Inc.
Uhl William J.
Wilson Donald R.
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