Synthesis and characterization of new organosoluble polyimides based on flexible diamine

The new five benzene rings-containing diamine, α,α′-bis[3,5-dimethyl-4-(4-aminophenoxy)phenyl]-1,4-diisopropylbenzene (BDAPD) was prepared by the aromatic nucleophilic substitution of α,α′-bis(4-hydroxy-3,5-dimethylphenyl)-1,4-diisopropylbenzene with 1-chloro-4-nitrobenzene, and subsequent hydrogenation of the intermediate dinitro. The diamine was reacted with various aromatic dianhydrides to prepare a series of new polyimides (IPs) via the poly(amic acid) precursors and thermal or chemical imidization. The polyimides were produced with inherent viscosities of 0.60–0.85 dl g−1 by chemical imidization. All the poly(amic acid)s films could be obtained by solution-cast from N,N-dimethylacetamide (DMAc) solutions and thermally converted into transparent, flexible, and tough polyimide films. The wide-angle X-ray diffraction diagrams revealed that all the polyimides showed amorphous character. All of the polyimides, except PI-1, showed excellent solubility in a variety of solvents such as N-methyl-2-pyrrolidinone, DMAc, N,N-dimethylformade, dimethyl sulfoxide, pyridine, cyclohexanone and tetrahydrofuran. Such polyimides had better solubility than those containing only one isopropylidene unit or a hexafluoroisopropylidene linkage in the repeating unit of polyimide backbone. These polyimides had glass transition temperatures (Tg) between 241 and 270°C, which were higher than the Tg value of Ultem 1000 (215°C). The thermogravimetric analyses demonstrated that almost all of the polymers were stable up to 450°C, and the 10% weight loss temperatures were recorded in the range 466–488°C in air atmosphere.