Carbon Molecular Sieve Membranes from Multiring Highly Aromatic Functional Copolymers

A linear, highly aromatic, random (50/50 mol %), film-forming copolymer was synthesized by a one-pot, metal-free, superacid-catalyzed reaction of isatin with multiring aromatic compounds aceanthrenequinone and p-terphenyl (CP-NH). The chemical modification of the copolymer by the reaction of the side oxindole groups with 1-(bromoacetyl)pyrene and tert-butyl bromoacetate afforded copolymers containing thermolabile tert-butyl acetate (CP-Tba) and acetyl pyrene (CP-Prn) moieties. The polymers obtained were completely soluble in common organic solvents NMP, DMF, and THF, and flexible transparent films could be cast from the solutions. Spectroscopic characterization corroborated the structure of the copolymers. Nonporous films from the CP-NH copolymer show high thermal resistance with onset of decomposition, T-d, above 500 degrees C. Substitution of tert-butyl acetate and acetyl pyrene groups in the copolymer increases density and diminishes FFV. Pure gas permeability coefficients are larger for CP-NH and lower for CP-Prn in agreement with FFV. A mixed gas permeability test for a binary gas sample CO2/CH4 (10/90 mol %) shows that P-CO2 and P-CH4 decrease compared to pure gases and also decrease with increasing pressure. Carbon molecular sieve membranes (CMSMs) prepared from film precursors CP-NH, CP-Tba, and CP-Prn at a 600 degrees C final temperature show at least 1 order of magnitude increase in pure gas permeability and around 2 times increase in selectivity for gas pairs O-2/N-2, CO2/CH4, and N-2/CH4. The tert-butyl acetate and acetyl pyrene substitutions in the copolymer precursor increase gas permeability and increase selectivity in CMS membranes. As a result, the performance of pyrolyzed CP-NH, CP-Tba, and CP-Prn CMS membranes is similar to that of other CMSMs reported in the literature in terms of permeability and selectivity.