Synthesis and properties of soluble alternating copoly(amide–imide)s based on 1,2-bis(4-trimellitimidophenoxy)-4-t-butylbenzene and various aromatic diamines

A new diimide dicarboxylic acid, 1,2-bis(4-trimellitimidophenoxy)-4-t-butylbenzene (I), was prepared by the condensation of 1,2-bis(4-aminophenoxy)-4-t-butylbenzene (1,2-BAP-tBB) and trimellitic anhydride (TMA) at 1:2 molar ratio. The diamine 1,2-BAP-tBB was first synthesized from 4-t-butylcatechol and p-chloronitrobenzene in the presence of potassium carbonate (K2CO3) and then reduced by H2NNH2 and Pd/C. A series of novel poly(amide–imide)s (PAIs) IIIa–IIIk with inherent viscosities of 0.83–1.73 dl/g was prepared from the diimide–diacid I with various aromatic diamines (IIa–IIk) by direct polycondensation in a medium consisting of N-methyl-2-pyrrolidone (NMP) (as a solvent), triphenyl phosphite/pyridine (as condensing agents), and calcium chloride. Most of the polymers show excellent solubility in amide-type solvents such as NMP and N,N-dimethylacetamide (DMAc) and formed a tough, transparent, and flexible film by casting from DMAc solution. The films have tensile strengths of 87–108 MPa, elongations at break of 8–17%, and initial moduli of 2.1–2.6 GPa. The glass transition temperature of these polymers is in the range of 234–276°C and the 10% weight loss temperature is above 475°C in air or in nitrogen.