Homo- And Block Copolymerization Of Cyclic Carbonates Catalyzed By ITU/MgI₂ Dual Catalysis Systems

In this paper,the homopolymerization of 2,2-dimethyltrimethylene carbonates?DTC?wascarriedoutusingbenzylalcohol?BnOH?astheinitiatorand2,3,6,7-tetrahydro-5H-thiazolo[3,2-a]pyrimidine?ITU?/MgI₂ as the dual catalysis sytems.Secondly,polycaprolactone?PCL?was synthesized by ring-opening polymerization?ROP?of?-caprolactone??-CL?using ITU/MgI₂/BnOH.Then,the PCL-PDTC diblock copolymer was prepared using PCL as macroinitiator for the ROP of DTC.Thirdly,PDTC-PEG-PDTC was synthesized by ROP of DTC catalyzed by ITU/MgI₂ in the presence of PEG.The optimum reaction conditions were summarized by analysis of results.The structure of the polymers was studied using GPC,DSC,IR and NMR.And the possible polymerization mechanism was proposed.The optimum conditions for the ROP of DTC could be described as:[DTC]=1.0 mol/L,[DTC]/[ITU]/[MgI₂]/[I]=300:3:3:1,70?,6 h.The polymer with M_n of 24.96 kg/mol and PDI of 1.31 can be obtained under the optimum conditions.The experiments demonstrated that ITU alone could not induce any polymerization under the same conditions?70?,6 h?.In such polymerization,the cooperativity of the MgI₂ and ITU sites of Lewis pairs was necessary to acquire an effective polymerization system.The kinetic equation of DTC polymerization was:R_P=-d[M]/dt=K_P[DTC][ITU].The optimum conditions for the synthesis of PCL-PDTC copolymer were:[?-CL]=1.0mol/L,[DTC]=1.0 mol/L,[?-CL]/[ITU]/[MgI₂]/[I]=80:1:1:1,in toluene.First stage homopolymerization of?-CL was performed at 30?.After 1 h,DTC was added to the polymerization mixture,and the reaction was continued for 4 h at 70?.In this polymerization condition,the copolymer with M_n of 27.26 kg/mol and PDI of 1.37 was obtained.¹H NMR and ¹³C NMR provided evidence for the well-defined PCL-PDTC block copolymer formation with ITU/MgI₂/BnOH in toluene.In the GPC curves of PCL and PCL-PDTC,compared with the homopolymer,the peak of copolymer obviously moved towards the high molecular weight,which was consistent with the theory.In the presence of PEG,ROP of DTC catalyzed by ITU/MgI₂ cocatalyst has been carried out.The optimum conditions for the synthesis of PDTC-PEG-PDTC copolymer were as follows:[DTC]=1.0 mol/L,[DTC]/[ITU]/[MgI₂]/[PEG]=300:3:3:1,70?,4 h,in toluene.In this polymerization condition,the polymer with M_n of 16.50 kg/mol and PDI of 1.64 was obtained.The structures of PDTC-PEG-PDTC were confirmed by ¹H NMR and ¹³C NMR.In the DSC curves,no clear T_m corresponding to PEG was observed,may be due to the decreased mobility of the PEG chain?no crystallization?in the presence of PDTC chains.