Study On The Controllable Preparation Of Polymer Materials By Lewis Pair-catalyzed Polymerization

In recent years,the controllable/selective synthesis of polymer materials by Lewis pair polymerization（LPP）has become one of the research hotspots in the field of polymer synthesis.The significance of controllable synthesis of polymers lies in the precise regulation of different dimensional structures of materials,so as to achieve the regulation of their properties and the expansion of their application scope.LPP has developed for 13 years and achieved fruitful results since the concept was proposed,but its controllable/selective synthesis is still in the ascendant,and there are still some unrealized goals or unsolved problems in the system,such as:（1）From the perspective of controllable topology synthesis,the authentic cyclic acrylic polymers that do not contain other non-parent monomer structural units have not yet been synthesized by LPP or other catalytic methods;（2）From the perspective of catalyzed reaction types,there are only a handful of research systems about LP-catalyzed alternating copolymerization and the reaction types are not comprehensive,among which LP-catalyzed epoxide/lactone alternating copolymerization has not been involved;（3）From the perspective of the application of LPP in materials chemistry,the current research focuses on the direct application of Lewis pairs as the main component to improve the performance of the materials,while the synthesis of materials catalyzed by LP is still in its initial stage,in which the application of LPP in the efficient in-situ assembly to obtain nanomaterials has not yet been realized.This thesis aims to continue to expand the controllable/selective synthesis of polymers orrelated materials catalyzed by Lewis pair（LP）.In response to the above problems,the research work mainly focused on development of a new method for the controllable synthesis of cyclic polymer catalyzed by LP.In addition,the controllable alternating copolymerization of lactone and epoxides with LP and in situ controllable synthesis of polymer nanoparticles from LPP have also been explored to a certain extent.The specific contents of these three aspects are as follows:1.The controlled synthesis of cyclic polymer catalyzed by LP.Utilizing a specially designed intramolecular trifunctional B-P-B catalyst,it was firstly realized that the synthesis of an authentic cyclic acrylic polymer without non-parent monomeric structural units,cyclic poly（γ-methyl-α-methylene-γ-butyrolactone）（c-PMMBL）,of which monomeric MMBL is a biobased derivative.A series of detailed studies revealed an unprecedented initiation and propagation mechanism through pairwise monomer enchainment enabled uniquely by cooperative and synergistic initiator/catalyst sites of the trifunctional catalyst.That is,two B-P-B catalysts and two MMBLs firstly form a 16-membered macrocyclic adduct structure through 1,2-P/B addition,which is used as a ring expansion template to realize pairwise monomer enchainment.This is the first application of intramolecular trifunctional catalysts in the field of polymerization of polar vinyl monomer,and the first discovery of this unique"bi-molecular synergistic catalysis"phenomenon in the field of LPP.A new method for the controllable synthesis of cyclic polymers catalyzed by intramolecular trifunctional Lewis pair has been developed,thus realizing the controllable synthesis of an authentic cyclic acrylic monomer polymer mediated by catalyst with specially designed molecular structure.In addition,the cyclic topology of c-PMMBL endows it with a～50°C higher onset thermal degradation temperature as well as a narrower thermal degradation window compared to the linear PMMBL（l-PMMBL）with similar molecular weight and molecular weight distribution,while maintaining high chemical recyclability through pyrolysis.2.Controllable/selective alternating copolymerization of lactone and epoxides catalyzed by LP.In this work,a Lewis pair composed of nitrogen heterocyclic olefin（NHO）and triethyl boron（TEB）was chose as the catalysts,and through their synergistic catalysis effect,the alternating copolymerization of 3,4-dihydrocoumarin（DHC）and epoxides was realized by LPP for the first time.The influence of NHO with different substituent structures on the catalytic activity,the chemoselectivity of alternating copolymerization versus homopolymerization of epoxides,the regioselectivity of epoxides and polymerization mechanism were studied thoroughly.Through the optimizations of polymerization conditions and catalyst structures,the unique NHO-DHC/TEB combination having an ability to obtain linear polyesters that initiated by asymmetric double-head was screened out,which is meaningful for the efficient synthesis of polyester-based triblock polymers,thermoplastic elastomers,etc.;In addition,by the characterizations of active species and MALDI-TOF MS,it also was found that the NHO-DHC/TEB system can completely inhibit intramolecular transesterification,avoid the generation of cyclic polyester by-products,and realize the controllable synthesis of double-head initiated linear polyesters;The system has a wide range of applicability for epoxides,so that various renewable DHC-based polyesters with different structures and functions were synthesized in the high regioselectivity and relatively high polyester selectivity.3.The controllable synthesis of polymer nanomaterials catalyzed by LP.In this work,the processes of Lewis pair polymerization（LPP）and polymerization-induced self-assembly（PISA）were for the first time combined.And it selected NHO as Lewis base（LB）,large sterically hindered organoaluminum reagent Me Al（BHT）₂ as Lewis acid（LA）,equal volumes of mixed toluene and n-hexane as the environmental solvent for the in-situ assembly process,and 2-（dimethylamino）ethyl methacrylate（DMAEMA）and benzyl methacrylate（Bn MA）as the stabilizer chain monomer and core-forming chain monomer,respectively.The polymerization kinetics of Bn MA under these conditions was analyzed and in-situ assembly of the system was correspondingly confirmed to be feasible,thus a new method of Lewis pair polymerization-induced self-assembly（LPPISA）was developed.More importantly,by changing the length of the stabilizer block,various morphologies of polymer nanoparticles from elementary to advanced levels,including spheres,worms and vesicle assemblies have been controllably accessed;and the phase diagram has been constructed when systematically changing the DP of PBn MA block and the total solid content,so that the phase regions of each morphology can be clarified.The development of LPPISA method further facilitates the efficiency of in-situ self-assembly,which is of great significance for the practical application development of polymer nanoparticles.