Novel silicon-containing copolymer, ultrathin solid membrane composed of said copolymer, use of said solid membrane for concentrating a specified gas in a gaseous mixture, and process for producing said solid membrane

An ultrathin solid membrane capable of producing a concentrated gas from a mixture of two or more gases, especially for obtaining an oxygen-enriched gas from a gaseous mixture containing oxygen gas, said solid membrane having a thickness of from about 50 to about 3,000 A and being composed substantially of a film-forming silicon-containing copolymer consisting substantially of

• (a) at least one recurring unit of the following formula ##STR11## wherein R.sup.1, R.sup.2 and R.sup.3 are identical or different, and each represents an alkyl group having 1 to 10 carbon atoms, or a phenyl group which may be substituted by an alkyl group having 1 to 4 carbon atoms, and
• (b) at least one additional recurring unit selected from recurring units of the formula (II-1) and (II-2):
• ##STR12## wherein R.sup.4 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R.sup.5 represents a hydrogen atom, an alkyl or alkenyl group having 1 to 20 carbon atoms, or a phenyl group which may be substituted by an alkyl group having 1 to 4 carbon atoms;
• and ##STR13## wherein R.sup.6 and R.sup.7 are identical or different, and each represents a hydrogen atom, a chlorine atom, or a methyl group,
• the proportion of said recurring unit of formula (I) being about 5 to about 95 mole% based on the total recurring units of the silicon-containing copolymer and said silicon-containing copolymer having an inherent viscosity, measured at 25.degree. C. for a solution of 0.5 g of the copolymer in 100 cc of cyclohexane, of about 0.5 to about 4.0.