Efficient And Controlled Sequence Polymerization Of Polar Vinyl Monomers Catalyzed By Lewis Pairs

As a propeller to promote the vigorous development of polymer science and polymer materials,the innovation of polymerization method has always been hotspot of polymer research.Since Chen and Zhang et al.developed Lewis pair polymerization（LPP）,a new polymerization method,LPP has developed rapidly with a"three-step"strategy.1.Clear prove of polymerization mechanism.2.The structure,type and quantity of catalyst and monomer increase explosively.3.Precise synthesis of polymers including molecular weight and distribution control,chemical/regional selectivity,sequence and topological control,etc.These achievements demonstrate LPP’s outstanding talent in the field of precise synthesis of polymers and preparation of functional materials.However,based on the needs of economic and social development,we find that there are still some problems need to be solved in the development of LPP.Firstly,the monomer used in LPP is mainly from non-renewable petrochemical resources,which violates the sustainable development.Secondly,the biomass-based polymer synthesized by LPP lacks of performance advantage and has limited application value.Finally,sequence structure regulation is an important method to synthesize new materials.Traditional synthesis methods with complicated synthetic process hinder the research and application of sequenc-controlled polymer materials.Focusing on the above problems,this paper studies the development of renewable monomers,the precise synthesis of polymer and the construction of functional polymers catalyzed by Lewis pair（LP）.1.The living polymerization of lignin-based monomers catalyzed by LP.In this chapter,five biomass-based methacrylate monomers were synthesized from natural lignin degradation products.After screening,Al（C₆F₅）₃/P（NIⁱPr）Ph₂LP was obtained,which can realize the controllable polymerization of all lignin-based monomers.The living polymerization system has been unequivocally verified by end-group analysis,chain extension and block copolymerization,and the excellent chemical selectivity of Al（C₆F₅）₃/P（NIⁱPr）Ph₂ LP was demonstrated by NMR.By adjusting the structure of the monomer,we can not only regulate the glass transition temperature of the polymer（T_g=91-210°C）,but also obtain the lignin-based polymer with special properties such as heat resistance,post-functionalization,UV crosslinking ability and fluorescence emission phenomenon.Finally,TGA test showed that the lignin-based polymer had good thermal stability（356-365°C）and sufficient processing window.The research covers the synthesis method and polymer properties,and provides a solid foundation for the research and application of lignin-based polymers.2.Synthesis of lignin-based thermoplastic elastomers（TPEs）catalyzed by LP.In this chapter,we design and synthesize a series of new binuclear LB with readily available materials and simple synthesis process.The catalytic system based on binuclear LB can not only efficiently and controllably polymerize lignin-based monomers,but also can synthesize triblock copolymer（tri-block BCP）with lignin-based polymer as hard block and poly（n-butyl acrylate）（PⁿBA）as soft block in one step based on the CSC strategy.The polymer was then characterized in detail.On the one hand,the block structure of the copolymer was clearly demonstrated by GPC,DOSY and kinetic experiments.On the other hand,the existence of microphase separation in the copolymer was demonstrated by DSC,SAXS and AFM.By adjusting the proportion of the soft and hard block of tri-BCP,we obtained a series of TPEs with different mechanical properties.The tensile strength is between 2.2 MPa and 11.5 MPa,the elongation at break is between 643%and 2091%,and the elastic recovery can reach95%,which is much better than poly（methyl methacrylate）（PMMA）based TPEs with the same composition.Finally,we found that lignin-based TPEs have excellent light transmission,UV blocking properties and high-temperature resistance.3.The synthesis of sequence-controlled polymers catalyzed by LP.In this chapter,we focus on the precise and efficient synthesis of sequence-controlled multi-block copolymers（multi-BCP）.The LP composed of mononuclear/binuclear pyridinyl phosphine bases and organoaluminum LA,and monomers including methyl methacrylate（MMA）,?-methyl-α-methylene-?-butyrolactone（MMBL）,butyl acrylate（ⁿBA）and tert-butyl acrylate（^tBA）.Through systematic studies on polymerization kinetics and LA binding ability,we found that when one monomer in the mixed monomer has the advantages of stronger LA affinity and polymerization rate,a well-structured block copolymer（BCP）can be obtained,when one monomer in the comonomer mixtures only has the advantages of LA affinity,a partial random sequence structure will be formed.Based on these findings,we prepared BCP containing 2,3,4 and 7 blocks by adjusting the monomer types in the comonomer mixtures.Further combining with the di-initiating and controllable polymerization of the binuclear pyridinyl phosphine base catalytic system,we realized the chain extension of the comonomer mixtures for the first time,and the four-component comonomer mixture could be synthesized with 63 blocks after 8 times feeding,greatly improving the synthesis efficiency of the multi-BCP.In addition,three multi-BCPs with the same number of blocks（31）and different sequence structures were obtained by adjusting the composition and feeding sequence of the comonomer mixture.Finally,ABC type and ABA type TPEs with the same composition were synthesized.Uniaxial tensile tests showed that the mechanical properties of ABC type TPEs were significantly superior to ABA type TPEs,indicating that the sequence structure is crucial to the regulation of multi-BCP properties.