Process for producing a low thermally expansive and highly adhesive silicon-containing polyimide and a precursor thereof

Claim 1

A process for producing a silicon-containing polyamic acid having an inherent viscosity of 0.05 to 5 dl/g as measured in a solvent of N-methyl-2-pyrrolidone in a concentration of 0.5 g/dl at 30°±0.01° C., which process comprises reacting (1) anhydrides consisting of -A 1 mols of pyromellitic acid dianhydride (hereinafter abbreviated to PMDA) and -A 2 mols of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (hereinafter abbreviated to BPDA) with (2) B mols of a diamine having the formula ##STR11## and with (3) C mols of an aminosilicon compound selected from the group ##STR12## wherein R 3 represents a methyl group or an ethyl group and -wherein in (2) and (3) R 1 represents a methyl, ethyl, methoxy or ethoxy group or a halogen atom, R 2 represents an alkyl group of 1-6 carbon atoms a phenyl group or a phenyl group substituted by an alkyl group of 7-12 carbon atoms, X represents a hydrolyzable alkoxy group, an acetoxy group or a halogen atom, m represents 0, 1 or 2; n represents 1 or 2; and k represents 1, 2 or 3, the amounts of said reactants being present in quantities to satisfy the expressions: ##EQU7## said silicon-containing polyamic acid having the property that when a solution of said acid in N-methyl-2-pyrrolidone is coated onto a polyester film by means of a coater, followed by drying the resulting film in a dryer at 100° C. for one hour to remove most of the solvent to thereby form a film thereon, stripping off this film from said polyester film, fixing the stripped off film at its periphery by means of two iron plates and baking it at 200° C. for one hour and successively at 350° C. for one hour, then a polyimide film having about 40 μm thick and an average thermal expansion coefficient at 30° C. to 450° C. of 0.8 to 1.8×10 -5 deg -1 is obtained.