Homo-and Block Copolymerization Of?-caprolactone Catalyzed By ITU/YCl₃ Dual Catalytic Systems

In this thesis,2,3,6,7-tetrahydro-5H-thiazolo[3,2-a]pyrimidine?ITU?was synthesized.Firstly,polycaprolactone?PCL?was obtained by the ring-opening polymerization?ROP?of?-caprolactone??-CL?using ITU combined with yttrium chloride?YCl₃?as cocatalyst and benzyl alcohol?BnOH?as initiator.Secondly,PCL-PEG-PCL triblock copolymer was prepared by using ITU/YCl₃/PEG system to initiate polymerization of?-CL.Finally,the PVL-PCL-PEG-PCL-PVL pentrablock copolymer was synthesized using PCL-PEG-PCL as macroinitiator for ring-opening polymerization of?-valerolactone??-VL?.The experimental results show that the ITU/YCl₃ dual catalyst system is an efficient catalyst for ROP of lactone.The polymerization results under different conditions were discussed emphatically,the structure and property of the obtained polymers was analyzed by ¹H NMR,¹³C NMR,GPC,IR and DSC,and the polymerization mechanism was inferred.The results of homopolymerization of?-CL show that the ITU/YCl₃/BnOH catalytic system has high catalytic activity and good controllability.The optimum conditions obtained through a large number of experiments could be described as:[?-CL]=2.0 mol/L,[?-CL]/[ITU]/[YCl₃]/[I]=100:1:1:1,25?,60 min.PCL having M_n,GPC,GPC of 24.8 kg/mol and PDI of 1.09 was prepared.No polymerization occured when only ITU or YCl₃ acted in?-CL,indicating the combination of two components is essential.The reaction kinetic was further explored and the equation was obtained:R_P=K_P[?-CL][ITU].The DSC scanning curve showed that the melting temperature?Tm?and crystallization temperature?Tc?of PCL are63.2?and 26.4?,respectively.The structure of polymers was confirmed by ¹H NMR spectra and IR.And we proposed the possible polymerization.The PCL-PEG-PCL triblock copolymer was synthesized by ROP of?-CL catalyzed by ITU/YCl₃ in the presence of PEG.After the complete consumption of?-CL in the above system,?-valerolactone??-VL?was added to the mixture,and the PVL-PCL-PEG-PCL-PVL pentrablock copolymer was synthesized.The optimal conditions for the copolymerization can be described as:[?-CL]=2.0 mol/L,[?-CL]/[ITU]/[YCl₃]=100:1:1,[?-CL]/[PEG]=100:1,The reaction temperature of the first stage was 60?,the time was 1 h,under which the conversion rate was up to 97.8%;the polymerization temperature and time of the second stage were 60?,2 h,respectively.According to the GDC test diagram,compared with the triblock copolymer,the peak position of the pentrablock copolymer moved obviously the high molecular weight.The molecular weight is closely related to the feeding ratio of the two monomers,the stepwise increase of[?-CL]/[?-VL]molar ratio resulted in steady growth of the molecular weight of the copolymers.The results of the study on the thermal properties of copolymers showed that the melting temperature and crystallization temperature of the penprablock copolymers were lower than those of triblock copolymers.The structure of copolymers was inferred by detailed analysis of IR,¹H NMR and ¹³C NMR spectra.