Synthesis And Property Study Of Two Dimensional Poly(Carboxylic Acid) With High Proton Conductivity

Two-dimensional(2D)polymer is generally defined as a covalently linked network of repeating structures with periodic bonding in two orthogonal directions,resulting in a sheet-like macromolecule with atomic or molecular thickness.Due to the unique structural advantages of 2D polymers,which are different from 1D linear polymers and 3D cross-linked polymers,2-D polymers have shown unique properties and potential application prospects in many fields.In this thesis,based on its property that amphiphilic molecules can self-assemble into 2D monomolecular or bimolecular layered structures under suitable conditions,an amphiphilic distyrene amphiphilic monomer was designed and synthesized,and the relationship between its molecular structure and the assembly behavior was studied.Then a new strategy for the preparation of 2D polymers is proposed: Bilayer self-assembly polymerization(BSAP).That is,through the self-assembly of amphiphilic monomers and following free radical polymerization,the crosslinking structure is formed in the double layer,so as to synthesize the 2D polymer with molecular thickness.The method is simple,efficient,pollution-free,and does not require the assistance of substrates or interfaces.2D polycarboxylic acid was used to prepare macroscopic membrane by solution casting method.The electrochemical properties of the membrane were systematically studied,it was found that the membrane has high proton conductivity and good mechanical properties.The detail of the research work is presented in two parts:(1)An amphiphilic distyrene monomer was designed and synthesized.Gram-scale 2D polymer was successfully synthesized by self-assembly of amphiphilic monomer and free radical polymerization in an aqueous solution at room temperature.The polymeric nanosheets are approximately 3-4 nm thick and lateral size ranging from tens to hundreds of microns.We systematically studied the effects of various assembly and polymerization reaction parameters for their influence on the morphology and structure of the polymers,and found that the monomer concentration has a significant effect on the self-assembly and polymerization process,while the type of counterions has little effect.Then we measured and calculated the intrinsic conductivity of 2D polymeric nanosheets and explored the influence of temperature and humidity on the proton conductivity.This thesis not only provides a new strategy for the synthesis of 2D polymers,but also shows the potential of 2D polymers with abundant surface ionizable groups in electrochemical applications.(2)Macroscopic membrane with good mechanical and thermal stability was prepared by solution casting using the2 D polymer.It was found that the membrane has a very high proton conductivity,which is comparable with the best commercial perfluorinated ion-exchange membranes.This can be attributed to a large number of carboxyl groups on large plane surfaces of the2 D polymers,which may contribute to the formation of efficient and stable ion channels.The effects of temperature,humidity and other conditions on the electrochemical properties of 2D polymer membrane were also investigated.Then,to enhance the mechanical stability of the polymeric membrane,we synthesized a monomer with a structure similar to and complementary to the bifunctional monomer but with only one polymerization styrene group.2D copolymer was synthesized by copolymerization.The macroscopic polymer membrane was prepared,which exhibits better mechanical properties and higher proton conduction ability.In addition,the effects of doping additives on the mechanical and electrochemical properties of the films were also investigated.In addition to the proton conductivity,we also measured and calculated the water absorption,swelling rate and ion exchange capacity of the membrane.The results of our study provide a new route for the preparation of macroscopic proton exchange membrane by employing 2D polymers.