TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The polyester imide precursor further has repeating units of formulae (11 and 12) having the molar ratio of 20:80-80:20.B2=bivalent aromatic groups of formulae (13, 14, 15, 16, and/or 17), preferably of formulae (16, 17 or 18), more preferably of formula (16);andR10-R18=1-6C alkyl or H.Preferred property: The weight average molecular weight of polyester-imide precursor is 3-400000. Preferred Process: The polyester-imide precursor is obtaining using ester-group containing tetracarboxylic-acid dianhydride of formula (19). Preferred Condition: The heat of fusion of the polyester-imide precursor is measured using differential scanning calorimeter. The heat of fusion of polyester-imide satisfies the relation: ( Delta )T=((b)-(a)) degrees C, where (a) is peak temperature of heat of fusion and (b) is a temperature of intersection of tangent which uses heat of fusion temperature rises as contact temperature and the straight line which follows the linear portion of the heat-of-fusion peak. Preferred Definitions:    B1=bivalent aromatic group of formula (3 or 4), preferably of formula (4), or of formula (10).    EXAMPLE - N,N-dimethylformamide solution (100 ml) and trimellitic anhydride chloride (200 mmol) were dissolved, cooled at 0 degrees C. Then, 4,4'-biphenol is dripped at 50 ml of N,N-dimethylformamide and pyridine (50 ml), agitated for 2 hours, stirred for 6 hours, filtered and dried to obtain impure tetracarboxylic-acid dianhydride (TABP). The obtained TABP is purified by dissolving TABP (10 g) into ( gamma )-butyrolactone solution, heated at 200 degrees C, stirred for 30 minutes, filtered and heat dried to obtain highly purified TABP yellow crystal. The (tetramethyl piperdin-4-yl)hexane-1-6-diamine (6.42 mmol), diamine (6.42 mmol) having 4 amino-benzoic acid 4-amino-phenyl ester structure, N-methyl-2-pyrrolidone (61 ml), were heated and dissolved at 80 degrees C. Then, TABP (13.38 mmol) was added, stirred for 30 minutes to obtain the transparence and uniform viscous polyester-imide precursor.