Preparation And Properties Of High-performance Polymers Based On Non-covalent Cross-linking Of Imidazole-carboxylic Acids

Supramolecular forces have been widely studied and applied due to their properties such as recognition of self-assembly and reversible reconstruction.In contrast to the traditional method of adding inorganic particles to the matrix,the introduction of non-covalent interactions in the polymer matrix to form a cross-linked network is able to effectively strengthen and toughen the polymer material.Which is not only simple to prepare,but also can give the material good cyclic processing performance by their reversible non-covalent action.High-performance polymers have rigid molecular chains and strong intermolecular forces,exhibiting poor ductility and low toughness,so using non-covalent cross-linking can significantly improve the toughening of high-performance polymer materials.In this paper,aromatic imidazole polymers that can be processed in solution are synthesized as the matrix,and organic small molecules or polymers containing carboxylic acid functional groups are added to the matrix to form a non-covalent cross-linked network for preparing polymer films,and their structure,mechanical properties and recycling properties are investigated.In chapter two,polybenzimidazole(OPBI)was selected as the substrate,and then mixed with different proportions of isophthalic acid(IPA),trimesic acid(TMA),and pyromellitic acid(PMA)in the solution and cast the film respectively.The electrostatic interactions between the carboxylic acid groups and imidazole groups can form cross-linked structures to achieve effective enhancement of OPBI.When 10 wt% PMA is added,OPBI/PMA0.10 composite film achieves the excellent fracture strength of 145 MPa and fracture toughness of 158.4 MJ/m3,which is increased by 100% and 320% compared with pure OPBI film,respectively.Besides,the glass transition temperature of OPBI/PMA0.10 composite film is 5-6 °C higher than that of pure OPBI film,and the composite films can also be recycled with the aid of solvents,showing good recycling performance.In chapter three,5-amino-2-(4-aminophenyl)benzimidazole(M3)and 4,4’-diaminodiphenyl ether(ODA)were condensed with terephthaloyl chloride(TPC)to synthesize solution-processable polymer named M3-POTA at low temperature,and then compounded with different proportions of IPA,TMA and PMA in solution to prepare dense films.The fracture strength and fracture toughness of M3-POTA film can be promoted owing to the electrostatic interactions between the carboxylic acid groups and imidazole groups.When 1 wt% PMA is added,the fracture strength of M3-POTA/PMA0.01 film reaches 252 MPa,and the fracture toughness reaches 151.4 MJ/m3,which is increased by 48% and 110% compared with pure OPBI film,respectively.What’s more,M3-POTA/PMA0.01 film also has better thermal stability and recycling performance,and the film still maintains excellent mechanical properties after multiple solvent recycling.To further enhance the mechanical properties of M3-POTA film,M3-POTA/PMA0.01 film was chosen as the substrate,and Cu2+ was added to form coordination bonds with imidazole groups to prepare composite films,the results of experimental shows the more stable double cross-linked structure.The fracture strength of M3-POTA/PMA0.01/Cu2+ film can reach 310 MPa,and the fracture toughness reaches 185.6 MJ/ m3.The ligand cross-linked structure also gives the films good solvent resistance,which is insoluble in strong polar solvents.However,it is still possible to recover the M3-POTA/PMA0.01/Cu2+ films by adding EDTA to destroy the coordination.In chapter four,we designed and synthesized PDOTA-A and PDOTA-B,aromatic polyamides with different carboxylic acid contents,and then compounded with M3-POTA in solution to prepare M3-POTA/PDOTA composite film.The cross-linked structure is formed by noncovalent interaction between repeating units of M3-POTA and PDOTA molecular chains proved by structural characterization.The mechanical properties test showed that the cross-linking of PDOTAA and PDOTA-B had a good enhancement effect on M3-POTA.M3-POTA/A(5%)has the best mechanical properties,its fracture strength and fracture toughness are 285 MPa and 302.9 MJ/m3,respectively,which is increased by 68% and 310% compared with pure M3-POTA film.In addition,M3-POTA/A film and M3-POTA/B film have outstanding solvent recycling performance,and the mechanical properties of two films were almost unaffected after five recoveries,realizing the complete recycling of the materials.This work provides an idea for the preparation of high-strength and recyclable high-performance polymers.