3  US  6,555,628  B2  4  Other  suitable  epoxy  resins  include  a,  w-diglycidyloxyisopropylidene-bisphenol-based epoxy res› ins (commercially known as D.E.R.™ 300 and 600 series  epoxy  resins),  a,  w-diglycidyloxy  tetrabromoisopropy lidene-bisphenol-based phenoxy resins,  such as D.E.R. 542, both are products of The Dow Chemical  Company. Preferred epoxy resins are the epoxy resins hav› ing an epoxy equivalent weight of from about 100 to about  The diglycidyl esters of dicarboxylic acids are preferably  the diglycidyl esters of terephthalic acid, isophthalic acid,  2, 6 - naphtha  1  en e di car boxy  1  ix  acid,  3, 4’ - biphenyldicarboxylic acid, 4,4’-biphenyldicarboxylic acid,  malonic acid, succinic acid, glutaric acid, adipic acid,  pumelic acid, suberic acid, azaleic acid, sebasic acid, 1,4- cyclohexanedicarboxylic acid, 1,10-decanedicarboxylic  acid, tartaric acid, malic acid, citramalic acid and hydroxy› glutaric acid. The more preferred diglycidyl esters are the  diglycidyl esters of terephthalic acid, isophthalic acid, adipic  acid, 1,4-cyclohexanedicarboxy lie acid and 1, 10- decanedicarboxylic acid.  Strong inorganic and organic acids and the anhydrides and  esters of said acids (including half esters and part esters)  have been found to be particularly effective as reaction  inhibitors. By the term "strong acid" it is meant an organic  acid having a  pKa  value below about 4, preferably below  about 2.5. Representative reaction inhibitors include inor› ganic acids such as hydrochloric acid, sulfuric acid and  phosphoric acid; inorganic acid anhydrides such as phos› phoric acid anhydride; esters of inorganic acids such as  dimethyl sulfate; the organic acids such as alkyl, aryl and  aralkyl and substituted alkyl, aryl and aralkyl sulfonic acids  such asp-toluene sulfonic acid and phenyl sulfonic acid and  stronger organic carboxylic acids such as trichloroacetic  acid and alkyl esters of said acids, such as the alkyl esters of  p-toluene sulfonic acid, e.g., methyl-p-toluene sulfonate,  and ethyl-p-toluenesulfonate, methanesulfonic acid methy› lester and mixtures thereof. An example of an acid anhydride  of a strong organic acid that can be employed herein is  p-toluene sulfonic acid anhydride. Of the reaction inhibitors,  the alkyl esters of sulfuric acid: the aryl or aralkyl sulfonic  acids and the alkyl esters of said acids are preferably  employed herein. Most preferably, an alkyl ester of para› toluene sulfonic acid, particularly methyl or ethyl-p-toluene  sulfonic acid is employed as the reaction inhibitor herein.  A most preferred method for inhibiting the reaction com› prises adding a material to the reaction mixture which  effectively inhibits further reaction such as by deactivating  the catalyst, or by interrupting the reaction mechanism,  thereby inhibiting further reactions between the polyol and  the polyepoxide.  A convenient method for quenching the reaction mixture  comprises the addition of a solvent to the mixture, thereby  diluting the mixture and reducing its temperature. The  amount of organic solvent to be added is dependent on the  reaction temperature and the temperature at which reaction  is effectively terminated. The addition of organic solvent to  the reaction mixture is particularly preferred when the CCR  resin is subsequently to be applied from solution.  The diglycidyl ethers of dihydric phenols are preferably  the diglycidyl ethers of resorcinol, hydroquinone, 4,4’› isop ropy lidene bisphenol (bisphenol A), 4,4’› dihydroxydi pheny le thy lme thane, 3 ,3’ -dihydroxy- diphenyldiethylmethane, 3,4’-dihydroxydiphenyl› methylpropylmethane, 4,4’-dihydroxydiphenyloxide, 4,4’› dihydroxydiphenylcyanomethane, 4,4’-dihydroxy-biphenyl,  4,4’-dihydroxybenzophenone (bisphenol-K), 4,4’› dihydroxydiphenyl sulfide, 4,4’-dihydroxydiphenyl sulfone,  2,6-dihydroxynaphthalene, 1,4’-dihydroxy-naphthalene,  catechol, 2,2-bis( 4-hydroxyphenyl)-acetamide, 2,2-bis( 4- hydroxypheny l)ethanol, 2,2-bis( 4-hydroxyphenyl)-N› methy lacetamide, 2,2-bis( 4-hydroxy-phenyl)-N ,N› dimethylacetamide, 3,5-dihydroxyphenyl-acetamide, 2,4- dihydroxyphenyl-N-(hydroxyethyl)-acetamide, and other  dihydric phenols listed in U.S. Pat. Nos. 3,395,118, 4,438,  254 and 4,480,082 which are hereby incorporated by refer› ence as well as mixtures of one or more of such diglycidyl  ethers. Of these preferred diglycidyl ethers, those of  bisphenol-A, hydroquinone, and resorcinol are more  preferred, with the diglycidyl ether of bisphenol-A being  most preferred.  The reaction is terminated at a point such that the resulting  CCR resin contains the desired amounts of epoxy groups  and terminal hydroxyl groups. In this invention, the CCR  resin will contain at least about 0.25 percent, by weight, of  each of the epoxy and terminal hydroxyl groups. The epoxy  resins which can be employed in the practice of the present  invention for preparing the CCR resins include the digly› cidyl ethers of dihydric phenols, such as those described in  U.S. Pat. Nos. 5,246,751; 5,115,075; 5,089,588; 4,480,082  and 4,438,254, all of which are incorporated herein by  reference, or the diglycidyl esters of dicarboxylic acids such  as those described in U.S. Pat. No. 5,171,820.  Any method which effectively inhibits the reaction upon  reaching the desired degree of conversion can be employed  herein. The reaction is effectively inhibited when the rate of  reaction of the hydroxyl and epoxy group is sufficiently  reduced such that further reaction, if any, does not signifi› cantly and deleteriously affect the product or its handling  characteristics. Preferably, the reaction is sufficiently inhib› ited such that the solution viscosity of the CCR resin remains  essentially constant or increases only marginally with time.  For example, upon reaching the desired degree of  conversion, the reaction mixture can be quenched to stop the  reaction. However, the rapid quenching of the reaction  mixture must be conducted carefully to prevent clotting or  lumping of the CCR resin and to prevent the CCR resin from  forming a large solid mass which cannot subsequently be  used.  The reaction of the dihydric phenol and the epoxy resin,  anhydride or amine is advantageously carried out at an  elevated temperature, preferably, from about 60°  C. to about  200°  C., more preferably from about 100°  C. to about 150°  C. and, more preferably, from about 120°  C. to about 140°  C. The reaction is continued until the desired conversion, as  determined by measuring the residual epoxy and terminal  hydroxyl content in the resin, is achieved, at which point, the  reaction is effectively terminated.  The amounts of reaction inhibitor added to the reaction  mixture are dependent on the specific inhibitor employed  and the catalyst employed in preparing the CCR resin. In  general, the inhibitor is added in an amount sufficient to  overcome the catalytic activity of the catalyst. Preferably, at  least about 0.9, more preferably at least about 2, equivalents  of the inhibitor are added for each equivalent of the catalyst  employed. Although the maximum amount of inhibitor  added to the reaction mixture is dependent on the desired  properties of the resin and the expense of adding excess  inhibitor, the inhibitor is preferably added in an amount not  exceeding about 5 equivalents for each equivalent of catalyst  in the reaction mixture.  thereof. If employed, the organic liquid reaction diluent is  generally employed in an amount from about 5 to about 300  percent based on the total weight of all the reactants. 