The above deficiencies in the art are alleviated by, in an embodiment, a method of preparing a carboxylic acid end-capped oligomer comprising melt reacting a dicarboxylic acid, a dihydroxy compound, a hydroxy end-capped soft block compound, a diaryl carbonate, and a catalyst, wherein the molar ratio of dihydroxy end-capped soft block compound to dihydroxy compound is 1:4 to 1:40, the molar ratio of dicarboxylic acid to the combined molar amounts of dihydroxy compound and hydroxy end-capped soft block compound is 1.01:1 to 2:1, and the molar ratio of diaryl carbonate to the combined molar amounts of dihydroxy compound and hydroxy end-capped soft block compound is 1.5:1 to 3:1. A carboxylic acid end-capped oligomer prepared by the above method is also disclosed. A thermosetting composition comprising the carboxylic acid end-capped oligomer, and an article comprising the thermosetting composition, are also disclosed.