Synthesis And Characterization Of Single-Layer Two Dimensional Conjugated Polymers

The emergence of polymer materials is a milestone in the history of the development of materials science.It is well known that the polymer materials can be divided into one-dimensional linear structure,two-dimensional layer structure and three-dimensional crosslinked network structure.Among them,two-dimensional layer structures,or two-dimensional polymers,are unstable and very difficult to separate under natural conditions because of its large specific surface area.This led to the development of two dimensional polymers in both synthesis and application is far behind those of one-dimensional polymers and three-dimensional polymers.A two dimensional polymer refers to a plane macromolecule with the thickness of single atom or molecule,in which the repeat unit grew along the two-dimensional direction,and linked by covalent bond.Its special structure makes it have many excellent properties,for example,the typical graphene,which has high specific surface area,super conductivity,thermal conductivity and mechanical strength.However,these excellent properties of graphene can only be presented in the form of a single layer or few layers and the graphene normally exists in the stack state of graphite,which need to be exfoliated.Exfoliation process will damage the structure of graphene more or less and affect its performance and usage.So it will be very meaningful if we can synthesize free-standing two-dimentional polymers like graphene directly.Therefore,development of efficient,convenient preparation method of free-standing two-dimensional polymer is a very important and challenging research subject.Currently,the synthesized two dimensional conjugated polymers mostly were multi-layered covalent organic frameworks.However,single layered conjugated polymers with nanometer thichness were still rarely reported.Therefore,the development of highly efficient and convenient method to prepare single layered conjugated polymer is an extremely important and challenging research topic.In order to explore highly efficient,convenient and versatile method to prepare two dimensional polymer,we proposed the strategy of "solution self-assembly polymerization".By synergetic association of the hydrophobic interactions,π-πstacking interactions and electrostatic repulsion,we have successfully prepared the single layered two dimensional conjugated polymer and two dimensional COFs.The advantage of this solution polymerization method is that we can get single layered or few layered two dimensional polymer directly without using any interfaces.It is an efficient,convenient and versatile method.This dissertation includes three parts as follows:1.We have successfully designed and synthesized two kinds of bolaamphiphiles AM and AM-Br,and investigated their self-assembly behavior in aqueous solution.Then,the supramolecular and covalent two-dimensional polymers were prepared respectively on use of above synthesized small molecules.The TEM results showed that bolaamphiphile AM can self-assemble to form nanosheets directly in pure water with a size of several micrometer,but bolaamphiphile AM-Br self-assemble to form neat supramolecular nanosheets in organic solvent/water mixture.This is because,in different solvent systems,the intermolecular interaction is different for AM and AM-Br,which leads to different self-assembled driving force along the X axis and Y axis.In supramolecular two-dimensional polymer solution formed by AM-Br,the tri-phenyltriboronic acid pinacol ester was added,and the final covalent two-dimensional polymer was obtained by intrastratal Suzuki coupling reaction.The lateral dimension increased with the polymerization time.AFM results demonstrated that the thichness of polymer sheet was about 2-3 layers.2.We developed a strategy for preparation of two dimensional polymers from 1D to 2D,and synthesized a linear amphiphilic conjugated polymer(A-1DP)with diphenyl anthracene and dialkynyl units.The behaviours of A-1DP self-assembled into two-dimensional suramolecular polymer(2D-SP)in aqueous solution were investigated.Then,we studied the kenetis of dialkynyl crosslinking reaction initiated by UV light.The morphology of polymer sheet and chain stacking structure were characterized through the TEM andX-ray diffracton analysis method.The result demonstrated that A-1DP can self-assembled into single layered two dimensional suramolecular polymer without using of any interfaces,which was driven by synergetic association of the hydrophobic interactions,π-π stacking interactions and electrostatic repulsion.After irradiated by UV light,the suramolecular polymer could be easily transformed into covalent two-dimensional polymer(2D-CP).Moreover,in comparison of the supramolecular 2D polymer,the covalent 2D polymer sheets exhibited not only higher mechanical strength,but also higher conductivity,which can be ascribed to the conjugated network within the covalent 2D polymer sheets.3.Based on the fact that boron trifluoride diethyl etherate can not only catalyze the condensation reaction between catechol and boric acid groups,but also can coordinate with tertiary amine,we designed and synthesized the ionic covalent organic frameworks iCOFs-A and non-ionic covalent organic frameworks COFs-B with diphenyl anthracene unit.It was demonstrated that iCOFs-A possesses self-exfoliating property in organic solvents with relative high polarity,but COFs-B does not.The results indicated that the incorparation of ionic moiety into COFs is of great significance for self-exfoliation of the COFs in solution.Moreover,few layered iCONs-A could be well dispersed in polar organic solvents,and showed good film forming characteristic which exhibited explicit electroconductive and photoconductive properties.