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

Abstract

A series of fluorine-containing copolymides were synthesized by three different 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 pyromellitic dianhydride (PMDA). The synthesis reactions of the copoly(amic acid)s (PA) were carried out by three different orders of addition of the monomers with different molar ratios of 6FDA to PMDA. The viscosity of the PA solution obtained by DDM-(6FDA+PMDA), that is, 6FDA and PMDA added simultaneously 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 decreased as the relative amount of 6FDA to PMDA increased. The copolyimides formed by different addition orders but the same 6FDA-to-PMDA molar ratios contained different properties, such as dielectric constant, moisture absorption, contact angle, and optical transparency. All of these copolyimides were insoluble in common organic solvents, such as NMP and tetrahydrofuran. Thermogravimetric analysis showed that the onset temperature of 8% weight loss decreased slightly as [6FDA]:[PMDA] increased.