Ring-Opening Copolymerization of 2,2-Dimethyltrimethylene Carbonate and epsilon-Caprolactone Using Rare Earth Aryloxides Substituted by Various Alkyl Groups

A variety of single component rare earth aryloxides substituted by various alkyl groups [Ln(OAr)(3)] such as methyl, isopropyl, tert-butyl have been surveyed in the ring-opening copolymerization of 2,2-dimethyltrimethylene carbonate (DTC) and epsilon-caprolactone (epsilon-CL). It was worthwhile to note that activity of the catalyst varied with both the ligands' structure and the number of alkyl groups on phenyl ring. The stronger ability of electron-donation of alkyl groups on phenyl ring, and the more numbers of alkyl groups on phenyl ring, the higher catalytic activity. The experimental results show that lanthanum tris(2,4,6-tri-tert-butylphenolate) [La(OTTBP)(3)] exhibits highest activity in all lanthanum aryloxides. H-1 NMR spectral data of copolymer obtained showed that the polymerization mechanism is in agreement with the coordination insertion mechanism.