Study on the preparation and properties of copolyimides based on hexafluoroisopropylidene bis(3,4-phthalic anhydride) and 1,12-di(4-aminophenoxy)dodecane

Copolyimides were prepared from hexafluoroisopropylidene his(3,4-phthalic anhydride) (6FDA), 1,12-di(4-aminophenoxy)dodecane and 4,4'-diaminodiphenylether through a solution co-polycondensation reaction followed by a chemical imidization reaction. It was observed that copolyimides prepared with any diamine molar ratio studied (1,12-di(4-aminophenoxy)dodecane/4,4'-diaminodiphenylether = 7/3 similar to 1/9) were soluble in polar organic solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMA), dimethylformamide (DMF) and m-cresol, tetrahydrofuran (THF) and chloroform, while the corresponding homopolyimides were insoluble. Wide angle X-ray diffraction (WAXD) results show a clear relationship between the crystallinity tendency and the solubility of polyimides. High crystallinity tendency leads to low organo-solubility. The glass transition temperature of a copolyimide was in good agreement with Fox's equation for random copolymers. The long flexible chains in the backbone of copolyimides are the least thermally stable part. (C) 1999 Elsevier Science Ltd. All rights reserved.