Abstract: The invention is a membrane comprising a dense skin of a polyestercarbonate, wherein the diphenolic residue in the backbone of the polyestercarbonate is a tetrabromo diphenolic residue, wherein the membrane has a separation factor for oxygen and nitrogen of 6.5 or greater at about 24.degree. C. In another aspect, the invention is a method of separating oxygen from a mixture of gases comprising nitrogen and oxygen, wherein the method comprises (a) contacting the gas mixture with a thin, non-porous membrane comprising a polyestercarbonate described hereinbefore under conditions such that the oxygen selectively permeates through the membrane to the other side of the membrane; and (b) removing the permeated oxygen from the other side of the membrane, wherein separation factor for the oxygen and nitrogen is 6.5 or greater at about 24.degree. C. The membranes of this invention demonstrate surprisingly high separation factors for oxygen and nitrogen separations.

Abstract: The invention is an improved gas separation membrane comprising a thin, discriminating layer consisting predominantly of a carbonate polymer derived from a bisphenol corresponding to Formula I ##STR1## wherein R at each occurrence is independently H, Cl, Br, or C.sub.1 -C.sub.4 alkyl and R.sup.1 is ##STR2## --S--, --SO.sub.2 --, --O--, or a C.sub.1 -C.sub.6 divalent hydrocarbon or a C.sub.1 -C.sub.6 divalent fluorocarbon radical or inertly substituted hydrocarbon radical, with the proviso that at least 25 weight percent of the moieties derived from the bisphenol of Formula I present in the discriminating layer bear R groups which are exclusively Br or Cl, the gas separation membrane exhibiting a separation factor for oxygen and nitrogen at 24.degree. C. of at least 6.1. In another aspect this invention relates to a process for separating oxygen from nitrogen, or a nitrogen-containing gas.

Abstract: Polyestercarbonate compositions having superior environmental stress crack resistance are obtained by blending with up to about 12 weight percent of a polymer of 4-methyl-1-pentene.

Abstract: Polycarbonate or polyestercarbonate compositions having superior environmental stress crack resistance are obtained by blending with up to about 12 weight percent of a polymer of 4-methyl-1-pentene.