Ring-opening polymerization of e-Caprolactone by iodine charge-transfer complex

DE QUEIROZ,A.A.A.; FRANÇA,E,J.; ABRAHAM,G.A.; SAN ROMAN,J

JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS

John Wiley & Sons, Inc.

Lugar: New York, USA; Año: 2002 vol. 40 p. 714 - 722

0887-6266

The ring-opening polymerization of e-caprolactone (e-CL) catalyzed by iodine (I2) was studied. The formation of a charge transfer complex (CTC) between triiodide, I3-, and e-caprolactone was confirmed by means of UV-Vis spectroscopy. The monomer e-CL was polymerized in bulk using iodine as a catalyst to form the polyester having a molecular weight (Mw) of 35,858 and 45,465 at polymerization temperatures of 25 and 75°C, respectively. The reactivity of both,  e-CL monomer and  e-CL:I2 CTC were interpreted by means of the potential energy surfaces (PES), determined by semi-empirical computations (MNDO-d). The results suggest that the formation  of  the  e-CL:I2 CTC leads to the ring-opening of the e-CL structure with the lactone protonation and the formation of a highly polarized polymerization precursor (e-CL)+. The band gaps approximated from an extrapolation of the oligomeric e-PCL structures were computed.  By semi-empirical quantum chemical calculations, geometries and charge distributions of the protonated polymerization precursor (e-CL)+ were obtained. The calculated band gap (HOMO/LUMO differences) is in good agreement with experiment. The  analysis of the oligomeric e-PCL isosurfaces indicate the existence of a weakly lone pair character of the C=O and C-O bonds suggesting a e-CL ring-opening specificity.