Ring-opening Polymerization Of Lactones To Prepare Modifiable And Recyclable Polyesters By Organic Base/urea Synergistic Catalysts

Polymer materials bring convenience to people’s life and improve people’s life quality.However,their production and manufacturing are extremely dependent on petrochemical resources,and the resultant wastes also increase day by day.Moreover,the most commercial polymer materials are difficult to degrade in nature and cause white pollution.So degradable polymer materials have sprung up.However,most degradable polymer materials cannot be depolymerized back to monomers to recover the material values.It is the most attractive strategy to develop chemically recyclable polymers to establish a circular plastic economy.Despite the recent advancements,the chemically recyclable polymers still face challenges including high energy cost for polymer preparation or recycling,poor monomer recovery selectivity and efficiency as well as undesired material performances.In this thesis,the chemically selective ring-opening polymerization（ROP）of biomass-derivedα-methylene-δ-valerolactone（MVL）has been realized by using strong base/urea binary catalyst.The research contents and results are as follows:（1）Firstly,the controlled ring-opening polymerization of MVL was realized by using potassium methoxide（KOMe）/urea binary catalyst to prepare unsaturated polyester P（MVL）_ROP.The KOMe/urea binary catalyst showed extremely high catalytic activity and selectivity.The polymerization completed in a short time without forming vinyl addition polymerization products.By using 1-tert-butyl-2,2,4,4,4-penta（dimethylamino）-2Λ~5,4Λ~5-di（phosphonium）（t Bu-P₂）/diurea（U6）as catalyst,a P（MVL）_ROP with molecular weight up to 74.6 k Da was prepared.The kinetics and thermodynamics of the polymerization were investigated.The calculated apparent rate constant(k_app)was 1.9 mol L^-1 min^-1.The enthalpy change（ΔH_p^°）and entropy change（ΔS_p^°）for ROP of MVL was-16.5 k J mol^-1 and-45.1 J mol^-1 K^-1,respectively.（2）The properties of the synthesized P（MVL）_ROPwere investigated.The post-modification of P（MVL）_ROP was achieved through the click reaction between benzyl mercaptan and double bonds to prepare thiolated polyester P（MVL）_ROP-SR.The high-molecular-weight P（MVL）_ROP exhibited comparable mechanical properties with commercial polyolefin plastics with a good tensile strength up to 20.0 MPa.The depolymerization conversion rate can reach up to 98%when the depolymerization of P（MVL）_ROP was mediated by t Bu-P₂/U5 in dilute solution.P（MVL）_ROP can be recycled back to recover the original monomer with a 96%yield by pyrolysis.The recovered monomer can be repolymerized to produce P（MVL）_ROP with almost the same molar mass as the original monomer,thus successfully establishing a closed-loop life cycle.