POLYIMIDES DERIVED FROM 2,2'-BIS(TRIFLUOROMETHYL)-4,4'-DIAMINOBIPHENYL .2. SYNTHESIS AND CHARACTERIZATION OF POLYIMIDES PREPARED FROM FLUORINATED BENZENETETRACARBOXYLIC DIANHYDRIDES

A series of new fluorinated rigid-rod polyimides have been synthesized by the reaction of 2,2'-biB(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB) with 1,4-bis(trifluoromethyl)-2,3,5,6-benzenetetra-carboxylic dianhydride (P6FDA), 1-(trifluoromethyl)-2,3,5,6-benzenetetracarboxylic dianhydride (P3FDA), or pyromellitic dianhydride (PMDA). The dielectric constant, refractive index, and water absorption decrease with an increasing number of trifluoromethyl side chains. The polyimide P6FDA/TFDB with the highest fluorine content prepared from TFDB and P6FDA has the lowest dielectric constant of 2.6 at 1 MHz, the lowest refractive index of 1.490 at 589.3 nm, and the lowest water absorption of 0.38%. On the other hand, the coefficient of thermal expansion (CTE) increases with an increasing number of trifluoromethyl side chains. The polyimide PMDA/TFDB prepared from TFDB and PMDA has a negative CTE of -5 X 10(-6)-degrees-C-1 by thermomechanical analysis (TMA) and a high polymer decomposition temperature of 613-degrees-C measured for a 10% weight low in a nitrogen atmosphere by thermogravimetric analysis (TGA).