Ring‐Opening polymerization of ε‐caprolactone by rare earth coordination catalysts. I. Characteristics, kinetics, and mechanism of ε‐caprolactone polymerization with nd(acac)3.3H2O‐ALET3 system

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Abstract
Ring‐opening polymerization of ε‐caprolactone has been carried out by using rare earth coordination catalysts for the first time. The rare earth compounds, RE(acac)3.3H2O, Nd(P204)3, Nd(P507)3, Nd(naph)3, Nd(BA)3.2H2O, etc. (where RE = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Lu, Y; acac = acetylacetone; BA = benzoylacetone), combined with trialkyl aluminum, greatly increased the degree of conversion and the molecular weight of poly(ε‐caprolactone) (PCL). The influence of reaction conditions on the polymerization of ε‐caprolactone catalyzed by the Nd (acac)3.3H2O‐AlEt3 system has been examined in detail. The kinetics indicates that the polymerization rate has the first‐order in monomer and a half‐order in catalyst. The overall activation energy of the ring‐opening polymerization amounts to 59.4 kJ/mol. By IR and UV‐Vis spectra, 1H‐ and 13C‐NMR data, it is assumed that the ring‐opening polymerization of ε‐caprolactone catalyzed by the Nd(acac)3.3H2O‐AlEt3 system proceeds via complexation of monomer to catalyst, acyl‐oxygen cleavage insertion propagation mechanism. © 1994 John Wiley & Sons, Inc.