POLYIMIDES DERIVED FROM 2,2'-BIS(TRIFLUOROMETHYL)-4,4'-DIAMINOBIPHENYL .3. PROPERTY CONTROL FOR POLYMER BLENDS AND COPOLYMERIZATION OF FLUORINATED POLYIMIDES

Fluorinated polyimide blends and copolyimides have been prepared from 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB), 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), and pyromellitic dianhydride (PMDA). The fluorinated polyimide blends are made with two types of poly-(amic acid)s; one is 6FDA/TFDB poly(amic acid) prepared from 6FDA and TFDB, and the other is PMDA/TFDB poly(amic acid) prepared from PMDA and TFDB. On the other hand, fluorinated copolyimides are prepared from TFDB diamine and two dianhydrides, 6FDA and PMDA. The coefficient of thermal expansion (CTE) increases with increasing 6FDA/TFDB content in the polyimide blend and increases with increasing 6FDA/TFDB unit content in the copolyimide. The CTE can be controlled between -5 X 10(-6) and 8.2 X 10(-6) degrees-C-1 by polymer blend or copolymerization techniques. The copolyimide made with a 10 mol % 6FDA/TFDB unit content has almost the same CTE as the silicon substrate and thus has little stress after imidization by heating. On the other hand, the in-plane refractive index of their films decreases with increasing 6FDA/TFDB content in the polyimide blend and decreases with increasing 6FDA/TFDB unit content in the copolyimide. The refractive index can also be controlled between 1.554 and 1.647 at 589.3 nm by polymer blend or copolymerization techniques.