A soluble block copolyimide (Bco-PI) was prepared by direct one-pot polycondensation of 2,2-bis-(3-amino-4-hydroxyphenyl)hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, and cyclohexane-tetracarboxylic dianhydride in the presence of gamma-valerolactone and a pyridine catalyst system using gamma-butyrolactone as the solvent. The thermal transmission temperature (T-g) of Bco-PI was 282 degrees C. By having the curing process occur at 250 degrees C, which was below the T-g, colorless and transparent films could be obtained. The film showed excellent optical characteristics. Such properties could not be attained by the conventional high-temperature thermal imidization process of poly(amic acid). The hydroxy groups in the polyimide backbone gave the Bco-PI the potential to become alkaline. To the Bco-PI was added 15 wt % ester of 2,3,4-trihydroxy-benzophenone with 1,2-naphthoquinone-(2) diazide-5-sulfonic acid (NT200) as the photoreactive compound. The system worked as a positive-type photosensitive polyimide (PSPI). The sensitivity and contrast of the PSPI system were 220 mJ/cm(2) and 1.27, respectively, when exposed to UV light, followed by development with a 5% tetramethylammonium hydroxide (TMAH) aqueous solution at room temperature. After curing at 250 degrees C for 1 h, the average refractive index of Bco-PI with and without NT200 was 1.5543 and 1.5563, and the optically estimated dielectric constant of the polyimides was 2.66 and 2.67, respectively. (c) 2006 Wiley Periodicals, Inc.