Study On Polymerization Methods Of Benzo Heterocycles

The research on high-performance materials has long been a national strategy.Benzo heterocyclic polymers have attracted much attention cause their excellent high temperature resistance,oxidation resistance,and dimensional stability.Benzimidazole polymer as a member of the benzoheterocyclic family is an important type of thermoplastic which occupies a certain share in the world's high-performance materials market.It can not only be made into fibers and used in fire-resistant and flame-retardant fabrics,but also processed into thin films and used in permeable membranes and gas separation membranes.The acid-adopped benzimidazole film is used as an excelllent high-temperature proton conductive film.Besides,as a kind of blue fluorescent material,benzimidazole polymer has a potential in the photoelectric field.The classic synthesis of polybenzimidazole is polycondensation of a dibasic acid and an aromatic tetramine but its high cost limits industrial production on a large scale.In recant years,the research on polybenzimidazole mainly focuses on its modification and blending with other materials.As a result,researching a new synthesis method is of great significance for the development of high-performance materials.Hexachloroacetone can react with o-phenylenediamine to form bibenzimidazole.This is an efficient method with easily available raw materials,no by-products,convenient post-processing,mild reaction conditions.When incorporating tetrafunctional monomers,the synthetic knowledge of this method can be easily applied to polymer systems.However,the research on the hexachloroacetone ring formation reaction is insufficient,and its mechanism remains a puzzle.This paper perfected the research on the reaction between hexachloroactone and o-phenylenediamine.First,the reaction conditions were optimized,and it was clear that the solvent had no effect on the reaction,and a green synthesis of using water as the solventwas determined.Applying the method,bibenzthiazole was successfully obtained.Then,the mutual conversion relationship between the two reaction intermediates and their products was determined by liquid phase tracking.The two air and visible light sensitive intermediates were characterized by gas-mass spectrometry and liquid-mass spectrometry.By using hexafluoroacetone as a control experiment to obtain2,3-diaminophenazine,it was confirmed that the leaving of chloride ions played a key role in the ring-formation reaction.Finally,the reaction mechanism was proposed:hexachloroacetone firstly reacted with one molecule of o-phenylenediamine to form intermediate 2-trichloromethylbenzimidazole,and then it reacted with another molecule of o-phenylenediamine to obtain another intermediate N-(2-aminophenyl)-2-benzimidazolecarboxamide after oxidation and leaving.of chloride ion.Then bibenzimidazole was obtained through intramolecule dehydration by light irradiation.With the clarification of the ring-forming reaction mechanism,first,benzene-1,2,4,5-tetraamine was synthesized and then the commercially purchased biphenyltetramine was prepared to react with hexachloroacetone under visible light diversely.Finally,polyphenylene diimidazole was successfully obtained,and its melting point temperature was 310 ° C and its crystallization point temperature was about 360 ° C.In addition,2,5-diaminobenzene-1,4-dithiol was also prepared,but polyphenylene dithiazole was not obtained cause the existence of potassium hydroxide in the system.In this paper,a green and simple hexachloroacetone ring-forming method is proposed to replace the traditional polycondensation method to prepare polybenzimidazole.The polyphenylene diimidazole obtained by this method has the sequence that benzimidazole directly connected in a head-to-head manner.Different with the traditional polybenzimidazole which melted into the benzene ring,this is a benzimidazole polymer dispersed only with a benzimidazole motif.This work can promote the development of high-performance materials.