disclosed is a novel linear urethane - amide - imide copolymer composition obtained from first reacting x mols of diol compound , which had been dissolved in an inert organic solvent , with y mols of diisocyanate compound at room temperature to produce an intermediate reaction product , followed by reacting the intermediate reaction product with z mols of trimellitic anhydride at elevated temperatures , wherein y is greater than x and approximately equals the sum of x plus z . the polyurethane copolymer composition obtained from this process contains urethane , amide and imide groups on the polymer backbone , exhibits excellent mechanical and electric properties and heat resistance , and does not suffer from the phase separation problems observed from polyurethane - polyamideimide blends .