| Ring-opening homopolymerization of ε-caprolactone(ε-CL), and copolymerization of ethylene carbonate (EC) and ε-caprolactone, 2,2-dimethyl-trimethylene carbonate (DTC) and ε-caprolactone have been carried out by using rare earth Schiff base complexes: lanthanide tris(N-phenyl-3,5-di-t-butylsalicylaldiminato)s [Ln(OPBS)3] and lanthanide tris[(s)-N-phenethyl-3,5-di-t-butylsalicylaldiminato]s [(s)-Ln(OPBS)3] as single component catalyst for the first time. Characteristics of these homopolymerization and the copolymerization have been examined in detail. The structure and properties of the polymers such as poly(e-caprolactone) (PCL), poly(CL-co-EC), and poly(CL-co-DTC) were characterized and analyzed thoroughly by GPC, DSC, and 1H-NMR.Ln(OPBS)3 were applied to the homopolymerization of CL, the influences of the rare earth element, polymerization time and temperature of polymerization were investigated. It was found that La(OPBS)3 shows the highest activity for CL polymerization in toluene. The optimum conditions are as follows: [CL]=2.0mol/L, [CL]/[La]=2000 molar ratio, 50min, 40℃. Under the conditions, PCL can be prepared with conversion of 99.7%, Mn of 4.94×104 and MWD of 2.31. End-group analysis showed that CL monomer inserted into the growing chains with the acyl-oxygen bond scission.Various (s)-Ln(OPBS)3 were used to the homopolymerization of CL for the first time, and the influences of rare earth and ligand were investigated. It was found that (s)-La(OPBS)3 shows the highest activity for CL polymerization in toluene. The optimum conditions are as follows: [CL]=2.0mol/L, [CL]/[La]=2000 molar ratio, 10min, 40℃. Under the conditions, the conversion of CL is 100%, Mv of PCL is 21×104 and the catalytic efficiency of lanthanum is 232 kg PCL/ mol.La. The results has show somewhat living/controlled polymerization characteristic: The Mn of PCL obtained varied as a linear function of the CL/La molar ratio, andthe Mn of PCL also varied linearly with the conversion of CL monomer. GPC traces showed no bimodal distributions when fresh CL monomer was added to the solution of active polymer. The block copolymer of CL and DTC can be prepared by sequential addition of two monomers.(s)-Ln(OPBS)3 were applied to the copolymerization of CL and EC for the first time. Various rare earths, [CL+EC]/[Ln] molar ratios and polymerization time were investigated. It was found that (s)-La(OPBS)3 shows the highest activity for CL and EC copolymerization in toluene. The optimum conditions are as follows: [CL]/[EC]=7:3, [CL+EC]/[La]=1000, 20min, toluene, 40℃. Under the conditions, the total conversion is 90.8%, Mn is 10.1×104. The monomer reactivity ratios were determined as follows: rCL=1.989, rEC=0.053 for CL and EC copolymerization initiated by (s)-La(OPBS)3 at 40℃. This indicates that CL is preferentially corporated into the copolymer chain. 1H NMR spectra reveal that the structure of P(CL-co-EC) is random copolymer. DSC analysis shows that the Tm of P(CL-co-EC) decrease with the increasing of EC content in copolymer, Tg of P(CL-co-EC) increase with the content of EC in copolymer increasing.
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