Synthesis and properties of novel polyimides from 3-(4-aminophenylthio)-N-aminophthalimide

A novel, asymmetric diamine, 3-(4-aminophenylthio)-N-aminophthalimide, was prepared from 3-chloro-N-aminophthalimide and 4-aminobenzenethiol. The structure of the diamine was determined via IR and ¹H-NMR spectroscopy and elemental analysis. A series of polyimides were synthesized from 3-(4-aminophenylthio)-N-aminophthalimide and aromatic dianhydrides by a conventional two-step method in N,N-dimethylacetamide and by a one-step method in phenols. These polyimides showed good solubility in 1-methyl-2-pyrrolidinone, m-cresol, and p-chlorophenol, except polyimide from pyromellitic dianhydride, which was only soluble in p-chlorophenol. The 5% weight loss temperatures of these polyimides ranged from 460 to 498°C in air. Dynamic mechanical thermal analysis indicated that the glass-transition temperatures of the polyimides were in the range 278-395°C. The tensile strengths at break, moduli, and elongations of these polyimides were 146-178 MPa, 1.95-2.58 GPa, and 9.1-13.3%, respectively. Compared with corresponding polyimides from 4,4'-diamiodiphenyl ether, these polymers showed enhanced solubility and higher glass-transition temperatures.