Synthesis And Characterization Of Two-dimensional Polymeric Quaternary Ammonium

Due to their unique chemical,physical and biological properties,two-dimensional nanomaterials show outstanding potential in materials science,nanodevices,environmental science,biomedicine and analytical technologies.However,current discussions on two-dimensional nanomaterials mainly involve inorganic two-dimensional nanomaterials,while the research on organic two-dimensional nanomaterials is still relatively rare,mainly due to the lack of effective synthetic methods.Two dimensional(2D)polymers have attracted wide attention due to their large specific surface area and unique mechanical,thermal and electronic properties.2D covalent polymers are planar macromolecules with molecular or atomic thickness formed by a covalent bond.In recent years,a number of preparation strategies have been developed for 2D polymers,however,most of them require external force to obtain mono-or few-layered 2D sheets,for example,graphene monolayer is stripped by Scotch tape.It has rarely been reported to synthesize monolayer 2D polymers directly in solution,mainly because regular monomers tend to react with each other in random directions in solution and form irregular linear or crosslinked aggregates.The difficulty lies in how to control the formation of –2D aggregates in confined space and allow the polymerization reaction to proceed along the 2D space.This thesis proposed to take advantage of the self-assembly of amphiphilic molecules contains quaternary amine in aqueous media to form2 Daggregates and then perform free radical polymerization using redox initiators to form 2D covalent polymers.The 2D polymer possesses ionic groups on the surface,which can suppress interlayer stacking because of electrostatic repulsion and good for the formation of fewlayer or monolayer 2D polymers.Generally,the research in this thesis including the following two parts:(1)We proposed a strategy of “ guided 2D assembly and polymerization”,in which a guide molecule was used to assist the assembly and polymerization of amphiphilic monomers that typically form liner polymers to form two-dimensional polymers.We designed and synthesized Bola amphiphilic molecule D-1as the guide molecule and two single-ended hydrophilic amphiphilic monomers VBA and MVBPy.We investigated the conditions under which guide molecules can direct monomers to assemble into 2D aggregates and polymerize to form 2D covalent polymers.SEM,TEM and AFM were used to characterize the morphological information of 2D polymers,and the results show that we have successful preparation of 2D polymers with lateral size of over 100 micrometers and molecular thickness.Further study revealed that a mixture of guide molecule D-1 and monomer VBA at a mole ratio of 1:1-1:3 range can lead to 2D polymers while monomer MVBPy cannot form 2D polymer at any ratio,properly because of larger space steric hindrance.This study presents for the first time as a convenient method to use guide molecules to guide the assembly of amphiphilic monomers to form a 2D polymer.(2)Based on the "2D assembly and polymerization",two kinds of cationic amphiphilic monomers contain quaternary ammonium groups were designed,synthesized and assembled into 2D nanosheets without the assistance of guide molecules,2D covalent polymers were obtained using free radical polymerization reaction in solution.The amphiphilic monomer was synthesized by alkylation of ethanolamine/diethanolamine and 4-vinylbenzyl chloride;The effects of monomer concentration,solvent,and initiator on the assembly and polymerization behavior were studied.The morphology of 2D polymer was characterized by SEM,TEM,AFM and XRD.The two-dimensional polymer prepared has abundant hydrophilic groups on the surface which is able to form interlayer ion conduction channels.Therefore,we prepared an anion exchange membrane using the 2D polymer and studied the potential in fuel cell application.The experimental results show that the amphiphilic molecules can form 2D nanosheets by self-assembly in polar solvents within the concentration range of 0.2 mg/m L-20 mg/m L,the size of the nanosheets is not affected by the concentration.By AFM characterization,the thickness of 2D polymer is about 2.81 nm.Due to the heavily crosslinked intralayer structure in the 2D polymer,the toughness of the polymer is relatively poor.Therefore,we used a monomer that just contains one polymerizable group to lower the crosslinking density and thus,improved the membrane's mechanical stability.We also found that both temperature and humidity affect the ionic conductivity of the membrane,and the conductivity of the membrane can reach 72.11 m S.cm-1 at 58 ? and RH of 90% iodide ion.