The Preparation Of Benzophenonetetracarboxylic Dianhydride

Polyimides based on 3,3’,4,4’-benzophenonetetraccarrboxylic dianhydride(4,4’BTDA) are a class of high performance and good adhesion material. However,the polyimides are usually difficult to process because of their poor solubility in organic solvents and high melting temperature. The polyimide based on 2,3’,3,4’benzophenonetetraccarrboxylic dianhydride(3,4’-BTDA) have higher glass transition temperature and better solubility. However,the high cost of the 3,4’-BTDA limits the range of appliction. In this paper we present the comparative study on the preparation of the BTDAs,especially 3,4’-BTDA.Firstly,we synthseised dimethylbenzenesulfonic acid as catalyst to catalyze the condensation reaction between ortho-xylene and formaldehyde. It was found that the catalyst had higher catalytic activity and could be reused several times.Gas chromatography determine the proportion of isomers of the tetramethyldiphenylmethane(TMDM). The proportion of 3,4’-TMDM was 6%. Furthermore the isomer standard sample was prepared. And the standard sample was character-i zed by 1H NMR,13 C NMR,melting point instrument,The result of 3,4’-TMD M consisted with expected results. It was found that diffcult to seperate the isomers by column chromatography,recrystallization,rectification and so on.Secondly,tetramethyldiphenylhydrol prepared with dimethylchlorobenzene and 3,4-dimethyl-benzaldehyde,was diffcult to seperate because of similar properties. TMDM was oxidized into tetramethyldiphenylketone(TMDK) by nitric acid,and to explore the effect of nitric acid concentration,temperature,time and other factors on the yield. The standard sample,which could be obtained by column chromatography,was characterized by 1H NMR,13 C NMR,melting point instrument. The result of 3,4’-TMDK consisted with expected results. 3,4’-T MDK could be obtained by column chromatography,rectification and recrystallize ation.Finally,benzophenonetetraccarrboxylic acid was effcient obtained from TMDM and TMDK by liquid phase oxidation. The yields were more than 90%. The polyimides were prepared by the conventional two-step process. The PIs were characterizated by infrared analyzer,thermogravimetric analyzer,differential sc-aning calorimetry. The glass transition temperature(Tg) of 3,4’-BTDA/ODA was 305℃,and Tg of 4,4’-BTDA/ODA was 285℃,The temperature at loss weight of 3,4’-BTDA/ODA was 495℃,and the temperature at loss weight of 4,4’-BTD A/ODA was 552℃.We found that PIs based on 3,4’-BTDA showed excellent solubility in DMSO, DMF, NMP.