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The ring opening polymerization of (-caprolactone (CL) was initiated by glycol and yttrium tri(2,6-di-tert-butyl-4-methylphenolate)s (Y(OAr)3), preparing dihydroxy-capped poly ((-caprolactone) (PCL) with controllable molecular weight.1H NMR and SEC analyses indicate that two kinds of active species and corresponding PCL with different structures exist in the system.Increasing the ratio of glycol to Y(OAr)3 benefits the formation of monofunctional active species.However, poly(ethylene glycol) (PEG)/Y(OAr)3 system only contains sole bifunctional active species to synthesize copolymer of CL with PEG (poly(CL-b-PEG-b-CL)).Dihydroxy- capped PCL as macroinitiator can further initiate the polymerization of 2,2-dimethyltrimethylene carbonate (DTC).Thus, triblock copolymer of CL with DTC (poly(DTC-b-CL-b-DTC)) has been prepared.