Multicarboxylic aromatic acid core initiator for the synthesis of star-shaped poly(ε-caprolactone) with carboxyl end groups

We successfully carried out the ring-opening polymerization of E-caprolactone with 1,3,5-benzenetricarboxylic acid and 1,2,4,5-benzenetetracarboxylic acid as the core initiators at 225 degrees C in bulk, and three-armed and four-armed star poly(epsilon-caprolactone)s [poly(e-CL)s with carboxy] end groups were obtained. No transesterification, which would have led to a decrease in the molecular weight of poly(e-CL), was found. The effects of the polymerization conditions on the polymerization are discussed; the poly(epsilon-CL)s were characterized by H-1-NMR, gel permeation chromatography, and thermogravimetric analysis in detail. A mechanism of alkyl-oxygen bond scission by the nucleophilic attack of the carboxyl anions via hydrogen proton transfer is presented for this system. (c) 2006 Wiley Periodicals, Inc.