Studies on polypyromellitimides containing phosphorus^†

The paper describes the synthesis of several polypyromellitimide samples containing phosphine oxide in the backbone and maleimido groups as pendant side chains. These polymers were obtained by solution polycondensation reaction in DMF in three steps. First step involved the reaction of equimolar amounts of maleic anhydride (MA) and tris(3-aminophenyl) phosphine oxide (TAP) in DMF at 60°C for 2 h. Low temperature polycondensation was carried out at 0–5°C by the addition of 4,4'-diaminodiphenyl ether (DADPE) and pyromellitic dianhydride. Cyclodehydration of poly(amide acid) thus obtained was done by chemical means. Various copolymers thus obtained were characterized by intrinsic viscosity measurements, elemental analysis, and IR spectroscopy. Thermal behavior and curing characteristics of copolyimides were evaluated by thermogravimetry and differential scanning calorimetric studies. An increase in the char yield at 800°C was observed on increasing phosphine oxide content of polyimides.