Synthesis and properties of aromatic polyimides based on ether-sulfone-diamines

Two diamine monomers, 4,4′-sulfonylbis(1,4-phenyleneoxy)]dianiline (III _a ) and 4,4′-sulfonylbis(2,6-dimethyl-l,4-phenyleneoxy)]dianiline (III _b ), were prepared by an aromatic nucleophilic substitution of 4,4′-sulfonyldiphenol (I _a ) and 4,4′-sulfonylbis(2,6-dimethylphenol) (I _b ) with p-chloronitrobenzene in the presence of potassium carbonate, followed by hydrazine catalytic reduction of the intermediate dinitro compounds. The diamines III _a and III _b were used as monomers with various aromatic tetracarboxylic dianhydrides (IV _a–f ) to synthesize polyimides. The polymerization was conducted in two steps via the formation of a poly(amic acid) precursor followed by thermal cyclodehydration. The poly(amic acid)s had inherent viscosities above 0.87 and up to 2.56 dL/g. Most poly(amic acid)s could be coated and thermodehydrated into flexible and transparent polyimide films. The polyimides derived from the dianhydrides containing-O-and-SO₂-or-C(CF₃)₂-bridging groups between the phthalic anhydride units were soluble in some organic solvents such as N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF). The glass transition temperatures (T_g) of the polyimides were in the range from 254 to 300 °C. The methyl-substituted polyimides exhibited slightly higher solubility and higher T_g compared to the corresponding unsubstituted polyimides. Thermogravimetric analysis (TG) showed that the polyimides containing methyl substitutents started to lose weight around 450 °C and the unsubstituted ones started to lose weight around 550 °C.