Synthesis and properties of aliphatic-aromatic poly(amide-imide)s from sulfonyldianilines and N,N′-bis(ω-carboxyalkyl)pyromellitimides

Seven imide-containing dicarboxylic acids IIa-g were synthesized from pyromellitic dianhydride and amino acids of the formula HOOC—(CH₂)_m—NH₂, with m—1,2,3,4,5,10,11. These diacids were condensed directly with 3,3′- or 4,4′-sulfonyldianiline using triphenyl phosphite in N-methyl-2-pyrrolidone (NMP)-pyridine solution containing calcium chloride and lithium chloride. The resulting poly(amide-imide)s have moderate to high inherent viscosities ranging from 0.47 to 2.02 dL/g in dimethylacetamide. These polymers showed excellent solubility in polar solvents such as NMP, and most of them could be cast into transparent and tough films. Glass transition temperatures (T_gs) of these poly(amide-imide)s were recorded in the range 116–258°C and increased with decreasing number of methylene groups in the repeated unit. The polymers with longer aliphatic chains (e.g., m = 10 and 11) exhibited higher crystallinity, higher initial decomposition temperature, and lower solubility in polar solvents.