Synthesis and characterization of polyimides by use of metal salts and phosphorous compounds in the presence of solvent

Polyimide precursors and polyamic acid were synthesized by direct polycondensation reaction of the 1,2,3,4-butanetetracarboxylic acid (BTCA) and diamines in the presence of metal salts and phosphorous compounds. The BTCA was reacted with an initiating species, which is the phosphonium salt of metal salts and phosphorous compounds, to form acyloxy phosphonium salt building up at moderated temperatures. The salt reacts with diamine to form polyamic acid. The reaction was markedly affected by several factors: reaction temperature and time, solvent, metal salts, phosphorous compounds, and tertiary amine. The polyamic acid was converted into polyimide by chemico-thermal or thermal methods. The polyimide with a high molecular weight can be prepared from BTCA and diamines and was soluble in polar aprotic solvent.