Synthesis of polyamic acid di‐tert‐butyl esters by direct polycondensation of di‐tert‐butyl esters of tetracarboxylic acids with diamines using diphenyl (2,3‐dihydro‐2‐thioxo‐3‐benzoxazolyl)phosphonate

The direct polycondensation using the activating agent diphenyl (2,3‐dihydro‐2‐thioxo‐3‐benzoxazolyl)phosphonate (1) was successfully applied to the synthesis of polyamic acid tert‐butyl esters, which readily undergo AAL 1 type acid‐catalyzed deesterification. Polycondensations of di‐tert‐butyl esters of tetracarboxylic acids with diamines were conducted in N‐methyl‐2‐pyrrolidone in the presence of triethylamine at room temperature, producing poly(amide‐ester)s with inherent viscosities up to 1,1 dL · g−1. The effects of various factors, such as solvent, amount of solvent, and amount of the activating agent, were studied. The poly(amide‐ester)s are readily soluble in dipolar aprotic solvents and can be cast into uniform films from their solutions. Thermogravimetry of the polymers showed that the deesterification and imidization occur around 150–200°C, giving polyimides.