Effects of molecular structure and thermal annealing on gas transport in two tetramethyl bisphenol‐A polymers

The effects of molecular structure and thermal history on the gas transport properties of tetramethyl bisphenol‐A polycarbonate (TMPC) and tetramethyl bisphenol‐A polysulfone (TMPSF) are reported. The presence of the bulky methyl side groups on the aromatic rings of TMPC and TMPSF inhibits both chain packing and molecular motions in these polymers as compared with standard polycarbonate and polysulfone. The methyl substitution results in significant increases in permeability with little or no loss of selectivity, making these materials promising candidates for membrane‐based gas separations applications. Thermal annealing produces a densification of the materials, resulting in decreased permeabilities. Selectivities remained roughly the same or increased slightly upon annealing at temperatures slightly below the glass transition temperature. Thus, thermal annealing may be useful for “fine‐tuning” a membrane's properties for applications where improved selectivity is desirable, even at the expense of decreased permeability.