Processes for preparing polytrimethylene ether glycol esters

A process for preparing a monocarboxylic acid ester of a polytrimethylene ether glycol comprising:

• (a) providing a polytrimethylene ether glycol having a number average molecular weight of about 250 to about 5000 and containing less than about 1 weight % of unreacted diol monomer;
• (b) heating the polytrimethylene ether glycol for at least 5 hours under inert gas at an initial pressure and at a temperature of about 160° C. to about 250° C. in the presence of a molar excess of one or more monocarboxylic acids or monocarboxylic acid equivalents to form a reaction mixture;
• wherein the or monocarboxylic acid or monocarboxylic acid equivalent has the formula R—COOH, wherein R is an a substituted or unsubstituted aromatic, saturated linear or branched aliphatic, unsaturated aliphatic, or cycloaliphatic organic group containing from 6 to 40 carbon atoms;
• and
• (c) further heating the reaction mixture for at least 1 hour at a second pressure of about 50 mm Hg or less and at a temperature of about 160° C. to about 250° C., wherein the second pressure is less than the initial pressure;
• to form a polytrimethylene ether glycol monoester or diester, or mixtures thereof.