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

We successfully carried out the ring-opening polymerization of ε-caprolactone with 1,3,5-benzenetricar-boxylic acid and 1,2,4,5-benzenetetracarboxylic acid as the core initiators at 225°C in bulk, and three-armed and fourarmed star poly(ε-caprolactone)s [poly(ε-CL)s] with carboxyl end groups were obtained. No transesterification, which would have led to a decrease in the molecular weight of poly(ε-CL), was found. The effects of the polymerization conditions on the polymerization are discussed; the poly(ε-CL)s were characterized by ¹H-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.