Effects of addition orders on the properties of fluorine-containing copolyimides

A series of fluorine-containing copolyimides were synthesized by three diff erent orders of addition of monomers. The fluorine-containing copolyimides were prepared by the reaction of 4,4'-diaminodiphenylmethane (DDM) with 2,2 '-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), and pyrome llitic dianhydride (PMDA). The synthesis reactions of the copoly(amic acid) s (PA) were carried out by three different orders of addition of the monome rs with different molar ratios of 6FDA to PMDA. The viscosity of the PA sol ution obtained by DDM-(6FDA+PMDA), that is, 6FDA and PMDA added simultaneou sly to DDM in N-methyl-2-pyrrolidinone (NMP), was higher than the other two addition orders (i.e., DDM-6FDA-PMDA and DDM-PMDA-6FDA). The viscosity dec reased as the relative amount of 6FDA to PMDA increased. The copolyimides f ormed by different addition orders but the same 6FDA-to-PMDA molar ratios c ontained different properties, such as dielectric constant, moisture absorp tion, contact angle, and optical transparency. All of these copolyimides we re insoluble in common organic solvents, such as NMP and tetrahydrofuran. T hermogravimetric analysis showed that the onset temperature of 8% weight lo ss decreased slightly as [6FDA] : [PMDA] increased. (C) 2000 John Wiley & S ons, Inc.