TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (disclosed): 4-Acetoxybenzoic acid and 4,4'-biphenol are esterified, to obtain 4-(4-((4-(acetyloxy)phenyl)carbonyloxy)phenyl)phenyl-4-(acetyloxy)benzoate. Then, the obtained 4-(4-((4-(acetyloxy)phenyl)carbonyloxy)phenyl)phenyl-4-(acetyloxy)benzoate is hydrolyzed, to obtain 4'-((4-hydroxybenzoyl)oxy)-1,1'-biphenyl-4-yl 4-hydroxybenzoate. Then, pyridine and solvent are added and reacted, to obtain 4-(4-(4-((4-((1,3-dioxo-1,3-dihydro-2-benzofuran-5-yl)carbonyloxy)phenyl)carbonyloxy)phenyl)phenoxycarbonyl)phenyl-1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate.    TECHNOLOGY FOCUS - POLYMERS - Preferred Property: The precursor has intrinsic viscosity of 0.1-20 dl/g. Preferred Process: The polyester imide is obtained by polycondensing tetracarboxylic-acid dianhydride and diamine as raw material of polyester-imide precursor in presence of solvent at high temperature, without isolating the precursor. EXAMPLE - Thionyl chloride and 4-acetoxybenzoic acid were refluxed at 80 degrees C in presence of nitrogen for 3 hours, benzene was added, excess thionyl chloride was distilled off, 4-acetoxybenzoyl chloride was obtained, and the obtained 4-acetoxybenzoyl chloride (in g) (19.86) was dissolved in tetrahydrofuran, to obtain a reaction mixture (A). Then, 4,4'-biphenol (9.31), tetrahydrofuran (42 ml) and pyridine (16 ml) were added into a container and mixed, to obtain a reaction mixture (B). The obtained reaction mixture (B) was dripped to the reaction mixture (A), reacted in ice bath for 12 hours, filter-separated, and washed using water and tetrahydrofuran, vacuum-dried at 160 degrees C for 12 hours, to obtain 4-(4-((4-(acetyloxy)phenyl)carbonyloxy)phenyl)phenyl-4-(acetyloxy)benzoate. Then, the obtained 4-(4-((4-(acetyloxy)phenyl)carbonyloxy)phenyl)phenyl-4-(acetyloxy)benzoate (15.3) was added to N,N-dimethylacetamide (100 ml), dissolved, sodium hydroxide aqueous solution (180 ml) containing sodium hydrogen sulfate, stirred at room temperature for 10 minutes, hydrolyzed, washed using hydrochloric acid aqueous solution, vacuum-dried at 80 degrees C for 12 hours and recrystallized, to obtain 4'-((4-hydroxybenzoyl)oxy)-1,1'-biphenyl-4-yl 4-hydroxybenzoate. Then, trimellitic acid chloride (4.2) was added into a flask, dissolved in dimethylacetamide (6.7 ml), 4'-((4-hydroxybenzoyl)oxy)-1,1'-biphenyl-4-yl 4-hydroxybenzoate was added, dissolved in dimethylacetamide (2.3), pyridine (3.2) was added, heat-dissolved, stirred at room temperature for 12 hours, filter-separated, washed using water, vacuum-dried at 160 degrees C for 12 hours and purified, to obtain 4-(4-(4-((4-((1,3-dioxo-1,3-dihydro-2-benzofuran-5-yl)carbonyloxy)phenyl)carbonyloxy)phenyl)phenoxycarbonyl)phenyl-1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate.