The Study On Ring-opening Polymerization Of Cyclic Esters By Benzo Crown Ether Bridged N-Heterocyclic Carbene

New supramolecular carbene benzo-12-crown-4bridged N-heterocyclic carbene (B12C4imY) was synthesized as catalyst in the ring-opening polymerization (ROP) of ε-CL and L-lactide (LLA) initiated by benzyl alcohol (BnOH) for the first time in this thesis. This paper focused on the effects of different polymerization conditions on the polymerization results. The kinetics of ring-opening polymerization of ε-CL and LLA catalyzed by B12C4imY/BnOH system were examined in detail. The structures of the polymers were characterized by1H NMR and IR. The possible polymerization mechanism was also speculated.The B12C4imY/BnOH was applied to the ring-opening polymerization of ε-CL. Several factors such as monomer and initiator concentration, polymerization time and temperature were investigated. The optimum conditions obtained for the polymerization could be described as:[ε-CL]=3.0mol/L,[ε-CL]/[C]=600(molar ratio), [ε-CL]/[I]=200(molar ratio),10℃,15min, tetrahydrofuran(THF) assolvent. It could prepare PCL with molecular weight of3.98×104g/moland molecular weight distribution of1.47. The kinetic study indicatedthat the polymerization rate was first-order with respect to monomerand catalyst concentration. The overall activation energy of ε-CLpolymerization amounted to37.8KJ/mol.1H NMR end-group analysesshowed ε-CL polymerization proceeds through monomer-activatedmechanism.The B12C4imY/BnOH was applied to the ring-openingpolymerization of LLA. The influences of monomer concentration,catalyst concentration, initiator concentration, polymerization timeand temperature were investigated systematically, and the optimumconditions could be described as:[LLA]=1.5mol/L,[LLA]/[C]=300(molar ratio),[LLA]/[I]=200(molar ratio),15℃,30min, in THF.PLLA was prepared with the molecular weight of2.64×104g/mol andnarrow polydispersities of1.45.1HNMR terminal group analysisdemonstrated that the ring-opening polymerization of LLA proceedsaccording to activated monomer mechanism. The kinetic studyindicated that the polymerization rate was also first order withrespect to both monomer and initiator concentration.