A process for separating two components, A and B, of a gas mixture having a ratio (Rf) of A:B, comprising: (a) passing the gas mixture across a separation membrane having a feed side and a permeate side, the separation membrane having a selective layer comprising a copolymer comprising a perfluorinated dioxolane monomer and a fluorovinyl monomer selected from the group consisting of trifluoroethylene, chlorotrifluoroethylene (CTFE), perfluoro methyl vinyl ether (PFMVE), perfluoroethyl vinyl ether (PFEVE), perfluoropropyl vinyl ether (PFPVE), vinyl fluoride, and vinylidene fluoride; wherein the copolymer has a glass transition temperature Tg(c) that is at least 5°C, preferably 10°C, higher than the glass transition temperature of a homopolymer, Tg(h), of the dioxolane monomer, or wherein the copolymer has a glass transition temperature Tg(c) that is at least 5°C, preferably 10°C, lower than the glass transition temperature of a homopolymer, Tg(h), of the dioxolane monomer; and wherein Tg(c) is calculated using the Flory-Fox equation: 1 T g = w 1 T g, 1 + w 2 T g, 2 wherein Tg is the glass transition temperature Tg(c) of the copolymer; w 1 is the weight fraction of the dioxolane monomer; w 2 is the weight fraction of the fluorovinyl monomer; T g,1 is the glass transition temperature of the homopolymer, Tg(h), of the dioxolane monomer; and T g,2 is the glass transition temperature, Tg(h), of the homopolymer of the fluorovinyl monomer; and wherein the copolymer does not have more than two different monomer units; (b) providing a driving force for transmembrane permeation; (c) withdrawing from the permeate side a permeate stream having a ratio (Rp) of A:B, where Rp > Rf; and (d) withdrawing from the feed side a residue stream having a ratio (Rr) of A:B, where Rr < Rf. (a) passing the gas mixture across a separation membrane having a feed side and a permeate side, the separation membrane having a selective layer comprising a copolymer comprising a perfluorinated dioxolane monomer and a fluorovinyl monomer selected from the group consisting of trifluoroethylene, chlorotrifluoroethylene (CTFE), perfluoro methyl vinyl ether (PFMVE), perfluoroethyl vinyl ether (PFEVE), perfluoropropyl vinyl ether (PFPVE), vinyl fluoride, and vinylidene fluoride; wherein the copolymer has a glass transition temperature Tg(c) that is at least 5°C, preferably 10°C, higher than the glass transition temperature of a homopolymer, Tg(h), of the dioxolane monomer, or wherein the copolymer has a glass transition temperature Tg(c) that is at least 5°C, preferably 10°C, lower than the glass transition temperature of a homopolymer, Tg(h), of the dioxolane monomer; and wherein Tg(c) is calculated using the Flory-Fox equation: 1 T g = w 1 T g, 1 + w 2 T g, 2 wherein Tg is the glass transition temperature Tg(c) of the copolymer; w 1 is the weight fraction of the dioxolane monomer; w 2 is the weight fraction of the fluorovinyl monomer; T g,1 is the glass transition temperature of the homopolymer, Tg(h), of the dioxolane monomer; and T g,2 is the glass transition temperature, Tg(h), of the homopolymer of the fluorovinyl monomer; and wherein the copolymer does not have more than two different monomer units; wherein the copolymer has a glass transition temperature Tg(c) that is at least 5°C, preferably 10°C, higher than the glass transition temperature of a homopolymer, Tg(h), of the dioxolane monomer, or wherein the copolymer has a glass transition temperature Tg(c) that is at least 5°C, preferably 10°C, lower than the glass transition temperature of a homopolymer, Tg(h), of the dioxolane monomer; and wherein Tg(c) is calculated using the Flory-Fox equation: 1 T g = w 1 T g, 1 + w 2 T g, 2 wherein Tg is the glass transition temperature Tg(c) of the copolymer; w 1 is the weight fraction of the dioxolane monomer; w 2 is the weight fraction of the fluorovinyl monomer; T g,1 is the glass transition temperature of the homopolymer, Tg(h), of the dioxolane monomer; and T g,2 is the glass transition temperature, Tg(h), of the homopolymer of the fluorovinyl monomer; and (b) providing a driving force for transmembrane permeation; (c) withdrawing from the permeate side a permeate stream having a ratio (Rp) of A:B, where Rp > Rf; and (d) withdrawing from the feed side a residue stream having a ratio (Rr) of A:B, where Rr < Rf.