An easy and fast direct polyesterification method using Bronsted acid ionic liquids (BAILS) as both reaction medium and catalyst was investigated. High molar mass polyesters of 12-hydroxydodecanoic acid (up to (M) over bar (w) = 50,000 g mol(-1)) were obtained in good yields at atmospheric pressure and low temperature (90-130 degrees C) after 10-120 mm reaction and without any added catalyst, reaction conditions that are much milder than conventional ones Ionic liquids composed of an acidic cation bearing sulfonic acid groups and an acidic anion, such as 3-alkyl-1-(butyl-4-sulfonyl)imidazolium hydrogen sulfates, gave better results than ionic liquids containing only an acidic anion, such as 1-alkyl-3-methylimidazolium hydrogen sulfates. The 1/1 BAIL/12-hydroxydodecanoic acid molar ratio was found to yield polymers of the highest molar mass. (C) 2010 Elsevier Ltd. All rights reserved