Rare earth aryloxides substituted by various alkyl groups [Ln（OAr）3] such as methyl, isopropyl and tertbutyl, were used as single component catalysts to affect ring-opening polymerization of L-lactide （LLA）. The catalytic activity, polymerization characteristics, polymerization kinetics and the mechanism were studied. It was found that the catalytic activity of rare earth aryloxides is influenced by both the structure and the number of alkyl groups on the phenyl ring. The stronger the electron-donation ability of the alkyl group, the higher the catalytic activity will be. An increase in the number of the substitute group will result in a higher catalytic activity. Lanthanum tris（2,4,6-tri-tert-butylphenolate） [La（OTTBP）3] exhibits the highest activity among all lanthanum aryloxides. According to the ^1H-NMR data, it was proposed that the LLA polymerization proceeded via a coordination-insertion mechanism involving cleavage of acyl-oxygen bond of the laetide.
Single component rare earth aryl oxides substituted by various alkyl groups [Ln(OAr)3] such as methyl,isopropyl,and tertbutyl have been developed to initiate the ring-opening polymerization of 2,2-dimethyltrimethylene carbonate(DTC).The catalytic activity of rare earth aryl oxides,characteristics of the ring-opening polymerization as well as the polymerization kinetics and mechanism were intensively examined.The experimental results turn out that the catalytic activity of Ln(OAr)3 changes in good concordance with variation of ligands' structure and number of alkyl groups on benzene ring.The greater the ability of electron-donation of alkyl groups,the greater the catalytic activity.Moreover,the greater the number of substituted alkyls on benzene ring,the greater the catalytic activity.The results show that rare earth tris(2,4,6-tri-tert-butylphenolate)s [Ln(OTTBP)3](Catalyst 1) exhibit rather great activity in all lanthanide aryl oxides.Investigations of the polymerization mechanism by 1H NMR spectroscopy revealed that the DTC monomer inserted into the growing chains with acyloxygen bond cleavage.
Single component rare earth phenolates substituted by various alkyl groups have been prepared and the correlation between the aryloxides＇ structure and catalytic activity in the ring-opening polymerization of D,L-lactide has also been investigated.The catalytic activity of all rare earth aryloxides,characteristics of the ring-opening polymerization as well as polymerization kinetics and mechanism were investigated.The results showed that both phenolates＇ catalytic activities and polymerization characteristics changed regularly,keeping in good concordance with variations in substitutents＇ number on phenol and structure of aryloxide ligands.The stronger ability of electron-donation of alkyl groups,the higher catalytic activity.Moreover,the more numbers of substituted alkyl on phenyl ring,the higher catalytic activity.The analyses of polymer ends revealed that the polymerization proceeded via a coordination-acyl-oxygen bond cleavage-insertion mechanism.
