Controlled/living ring-opening polymerization of E⟩-caprolactone catalyzed by phosphoric acid

The bulk ring-opening polymerization (ROP) of E >-caprolactone (E >-CL) by various phosphoric acids using phenylmethanol as the initiator was conducted. 1,1'-bi-2-Naphthol (BINOL)-based phosphoric acid was found to be an effective organocatalyst for ROP leading to polyesters at 90A degrees C. The overall conversion to poly(E >-caprolactone) was more than 96% and poly(E >-caprolactone) with M (w) of 8400 and polydispersity index of 1.13 was obtained. H-1 NMR spectra of oligomers demonstrated the quantitative incorporation of the protic initiator in the polymer chains and showed that transesterification reactions did not occur to a significant extent. The controlled polymerization was indicated by the linear relationships between the number-average molar mass and monomer conversion or monomer-to-initiator ratio. In addition, the present protocol provided an easy-to-handle, inexpensive and environmentally benign entry for the synthesis of biodegradable materials as well as polyesters for biomedical applications.