Study On Block Copolymerizations Of ?-caprolactone And Polyethylene Glycol

In this study,4-methyl benzo-12-crown-4 imidazole carbene(B12C4imY)and 2,3,6,7-tetrahydro-5H-thiazolo [3,2-a] pyrimidine(ITU)were synthesized.Poly(caprolactone)-poly(ethylene glycol)-poly(caprolactone)(PCL-PEG-PCL)triblock copolymers were successfully prepared by the ring-opening polymerization(ROP)of caprolactone(CL)in the prersece of poly(ethylene glycol)(PEG)employing B12C4 imY and ITU/MgI2 as catalyst,respectively.The influence factors of the reaction had been investigated systematically and the optimum condition was obtained.The triblock architecture,molecular weight and thermal properties of the copolymers were studied through the characterization of NMR,IR spectra,GPC and DSC analyses.And the possible polymerization mechanism was speculated.B12C4imY catalyzed ROP of CL with PEG as the macroinitiator in tetrahydrofuran(THF)was investigated and PCL-PEG-PCL triblock copolymers were synthesized.The effects of polymerization conditions,such as the monomer,initiator and catalyst concentration,as well as polymerization temperature and reaction time have been investigated systematically.Results obtained by several experiments demonstrated that the optimum conditions of the copolymerization with B12C4 imY were : [M] = 3.0 mol/L,[M]/[C]= 300,[M]/[I] = 200,T = 25 ?.The polymerization was terminated after 40 min at 96.8 %monomer conversion to yield a PCL-PEG-PCL triblock copolymer with Mn = 3.68×104g/mol and PDI = 1.47.1H NMR and IR on the polymers demonstrates the ring-opening polymerization of CL proceeds according to “monomer-activated” mechanism.From DSC analysis,we observed that a single melting endothermic peaks of PCL-PEG-PCL copolymer at 64.3 ?.PCL-PEG-PCL triblock copolymers with predictable molecular weights and relatively narrow polydispersity indexs were synthesized by ROP using ITU/MgI2 in the prersece of macroinitiator PEG.The results demonstrated that ITU/MgI2 could efficiently initiate the ROP of CL under mild conditions.The resulting copolymer was characterized using 1H NMR,13 C NMR,IR,GPC and DSC.The main research works are exhibited as follows :1.The ITU/MgI2 was highly active catalyst for the ROP of CL and gave a high molecular weight and relatively narrow molecular weight distribution polymer using PEG.The polymer with molecular weight of about 6.64 ×104 g/mol and molecular weight distribution of 1.43 could be obtained after 12 h at [M] = 2.0 mol/L,[M]/[C] = 80,[M]/[I] =200,in THF at 30 ?.2.The structure of the copolymers and the possible polymerization mechanism were characterized by NMR and IR spectra.The average molecular weight and distribution of PCL-PEG-PCL are obtained from GPC.It could been seen that two tested samples showed single peak and the GPC trace of the PCL-PEG-PCL shifted to higher molecular weights.Research on the crystallization behaviors of PCL,PEG,and PCL-PEG-PCL by DSC showed that the meltling temperature of triblock copolymer was obviously improved.