Power coatings based on branched oligoesters and non-emissive uretdione polyisocyanates

A process for preparing a branched hydroxyl terminated oligoester polyol, the process comprising:

• blending a hydroxyl terminated oligoester diol and a polyacid having a carboxyl functionality of about 3 or greater, wherein the equivalent ratio of hydroxyl terminated oligoester diol to polyacid is from about 9:1 to about 30:1;
• and
• reacting the hydroxy terminated diol and the polyacid for a time and temperature effective to provide the branched hydroxyl terminated oligoester polyol which has a hydroxyl value in the range of from about 15 to about 250, an acid number of about 1 to about 25, and a number average molecular weight in the range of from about 1500 to about 7500 daltons, the hydroxy terminated oligoester diol being the reaction product of a diol reactant and a diacid reactant selected from the group consisting of an open chain aliphatic dicarboxylic acid, a cycloaliphatic dicarboxylic acid, an aromatic dicarboxylic acid, an open chain aliphatic dicarboxylic acid anhydride, a cycloaliphatic dicarboxylic acid anhydride, an aromatic dicarboxylic acid anhydride, an open chain dicarboxylic acid halide, a cycloaliphatic dicarboxylic acid halide, an aromatic dicarboxylic acid halide and mixtures thereof, the diol reactant and diacid reactant being reacted for a time and temperature to provide a hydroxy terminated diol with a number average molecular weight in the range of from about 400 to about 1500 daltons, cooling the reaction of the diol reactant and diacid reactant at about the time the oligoester diol reaches the number average molecular weight in the range of 400 to about 1500 and before reacting the hydroxy terminated diol with the polyacid,
• wherein the diacid reactant includes a cycloaliphatic diacid reactant where the cycloaliphatic diacid reactant is the cycloaliphatic acid, the cycloaliphatic anhydride or cycloaliphatic acid halide of 1,4-cyclohexane dicaboxylic acid, 1,3-cyclohexane dicarboxylic acid, hexahydrophthalic acid, dimethyl cyclohexane dicarboxylic acid or mixtures thereof.

A branched hydroxyl terminated oligoester polyol comprising the reaction product of a hydroxyl terminated oligoester diol having a number average molecular weight in the range of from about 400 to about 1500 daltons and a polyacid having a carboxyl functionality of about 3 or greater, the branched hydroxyl terminated oligoester polyol having a hydroxyl value in the range of from about 15 to about 250, an acid number of about 1 to about 25, and a number average molecular weight in the range of from about 1500 to about 7500 daltons,

• wherein the hydroxyl terminated oligoester diol is the reaction product of a hydroxyl functional ester compound and a diacid reactant selected from the group consisting of an open chain aliphatic dicarboxylic acid, a cycloaliphatic dicarboxylic acid, an aromatic dicarboxylic acid, an open chain aliphatic dicarboxylic acid anhydride, a cycloaliphatic dicarboxylic acid anhydride, an aromatic dicarboxylic acid anhydride, an open chain dicarboxylic acid halide, a cycloaliphatic dicarboxylic acid halide, an aromatic dicarboxylic acid halide and mixtures thereof,
• wherein the hydroxyl functional ester compound is 3-hydroxy-2,2-dimethylproprionate and the diacid reactant is an aromatic diacid reactant and the aromatic diacid reactant is an aromatic acid, acid anhydride or acid halide of terephthalic acid, phthalic acid, phthalic anhydride, dimethyl terephthalic acid, naphthalene dicarboxylate, tetrachlorophthalic acid, terephthalic acid bisglycol ester, isophthalic acid, t-butyl isophthalic acid, or mixtures thereof.