Gas separation membranes from bisphenol AF polycarbonates and polyestercarbonates

The invention relates to a gas separation membrane comprsing a thin discriminating layer of bisphenol AF polycarbonate or polyestercarbonate. The invention further relates to a method of separating gases comprising PA0 (a) contacting with a feed gas mixture under pressure one side of a semi-permeable membrane comprising a thin discriminating layer of polycarbonate or polyestercarbonate, wherein the diphenolic residue in the polymer backbone is based on bisphenol AF; PA0 (b) maintaining a pressue differential across the membrane under conditions such that a component(s) of the feed gas selectively permeates through the membrane from the high pressure side to the low pressure side of the membrane; PA0 (c) removing the permeated gas which is enriched in the faster permeating component(s) from the low pressure side of the membrane; PA0 (d) removing the nonpermeated gas which is depleted in the faster permeating component(s) from the high pressure side of the membrane.

BACKGROUND OF THE INVENTION 
This invention relates to semi-permeable membranes substantially derived 
from bisphenol AF polycarbonates and polyestercarbonates. This invention 
further relates to the use of these membranes to separate gases. 
The use of membranes to separate gases is well known in the art. Membranes 
have been used to recover or isolate a variety of gases, including 
hydrogen, helium, oxygen, nitrogen, carbon dioxide, methane, and light 
hydrocarbons. Particular applications of interest include the separation 
of carbon dioxide from light hydrocarbons or other crude oil components as 
part of the tertiary oil recovery process. In other embodiments, nitrogen 
or helium is separated from natural gas. Other applications include the 
recovery of an enriched oxygen stream from air for use in enhanced 
combustion processes. Alternately, an enriched nitrogen stream may be 
obtained from air for use as an inert atmosphere over flammable fluids or 
for food storage. 
Such membrane separations are based on the relative permeability of two or 
more gaseous components through the membrane. To separate a gas mixture 
into two portions, one richer and one leaner in at least one component, 
the mixture is brought into contact with one side of a semi-permeable 
membrane through which at least one of the gaseous components selectively 
permeates. A gaseous component which selectively permeates through the 
membrane passes through the membrane more rapidly than the other 
component(s) of the mixture. The gas mixture is thereby separated into a 
stream which is enriched in the selectively permeating component(s) and a 
stream which is depleted in the selectively permeating component(s). The 
stream which is depleted in the selectively permeating component(s) is 
enriched in the relatively nonpermeating component(s). A relatively 
nonpermeating component permeates more slowly through the membrane than 
the other component(s). An appropriate membrane material is chosen for the 
mixture so that some degree of separation of the gas mixture can be 
achieved. 
Membranes for gas separation have been fabricated from a wide variety of 
polymeric materials, including cellulose triacetate; polyolefins such as 
polyethylene, polypropylene, and poly-4-methylpentene-1; and polysulfone. 
An ideal gas separation membrane is characterized by the ability to 
operate under high temperature and/or pressure while possessing a high 
separation factor (selectivity) and high gas permeability. The problem is 
finding membrane materials which possess all the desired characteristics. 
Polymers possessing high separation factors generally have low gas 
permeabilities, while those polymers possessing high gas permeabilities 
generally have low separation factors. In the past, a choice between a 
high separation factor and a high gas permeability has been unavoidably 
necessary. Furthermore, some of the membrane materials previously used 
have suffered from the disadvantage of poor performance under high 
operating temperatures and pressures. A membrane which possesses high 
selectivity, high gas permeability, and ability to operate under extreme 
conditions of temperature and pressure is needed. 
SUMMARY OF THE INVENTION 
The invention relates to a gas separation membrane comprising a thin 
discriminating layer of polycarbonate or polyestercarbonate, wherein the 
diphenolic residue in the polymer backbone is based on bisphenol AF. 
The invention further relates to a method of separating gases comprising 
(a) contacting with a feed gas mixture under pressure one side of a 
semi-permeable membrane comprising a thin discriminating layer of 
polycarbonate or polyestercarbonate, wherein the diphenolic residue in the 
polymer backbone is based on bisphenol AF; 
(b) maintaining a pressure differential across the membrane under 
conditions such that a component(s) of the feed gas selectively permeates 
through the membrane from the high pressure side to the low pressure side 
of the membrane; 
(c) removing the permeated gas which is enriched in the faster permeating 
component(s) from the low pressure side of the membrane; and 
(d) removing the nonpermeated gas which is depleted in the faster 
permeating component(s) from the high pressure side of the membrane. 
The membranes of this invention possess high selectivities for 
oxygen/nitrogen separation and carbon dioxide/methane separation. The 
membranes of this invention also possess good mechanical properties so as 
to enable operation of the membranes at high temperatures and pressures. 
DETAILED DESCRIPTION OF THE INVENTION 
The gas separation membranes of this invention are prepared from 
polycarbonates or polyestercarbonates, wherein the diphenolic residue in 
the polymer backbone is based on bisphenol AF. Polyestercarbonates contain 
both ester and carbonate linkages as functional groups in the polymer 
backbone. The polyestercarbonates of this invention are randomized 
copolymers, in which the ester and carbonate functional groups occur in a 
random arrangement along the polymer backbone. 
The polycarbonates or polyestercarbonates used in the invention preferably 
correspond to Formula 1: 
##STR1## 
wherein R is independently in each occurrence hydrogen, a halogen, a 
C.sub.1-6 alkyl, a C.sub.1-6 haloalkyl, or a C.sub.1-4 alkoxy; 
R.sup.1 is independently in each occurrence a divalent unsubstituted or 
halo-substituted C.sub.1-20 hydrocarbon; 
x is a positive real number from about 0.05 to 1.0, 
y is a positive real number from 0 to about 0.95, with the proviso that the 
ratio of ester to carbonate groups is between about 50 to about 0 percent; 
and 
n is a positive real number of about 20 or greater. 
In Formula 1, R is preferably hydrogen, chlorine, bromine, fluorine, a 
C.sub.1-4 alkyl, a C.sub.1-4 haloalkyl, methoxy, ethoxy; R is more 
preferably hydrogen, chlorine, bromine, fluorine, methyl, ethyl, methoxy, 
or ethoxy. 
In Formula 1, R.sup.1 is preferably a divalent unsubstituted or 
halo-substituted C.sub.1-18 aliphatic, a divalent unsubstituted or 
halo-substituted C.sub.5-20 cycloaliphatic, or a divalent unsubstituted or 
halo-substituted C.sub.6-20 aromatic. More preferably, R.sup.1 is 
described by Formulas 2-5: 
##STR2## 
wherein R.sup.3 independently in each occurrence a halogen, an 
unsubstituted or halo-substituted C.sub.1-4 alkyl, or phenyl; and m is 
independently in each occurrence a positive integer from 0 to 4. R.sup.4 
is a C.sub.1-6 divalent unsubstituted or halo-substituted alkyl. Most 
preferably, R.sup.1 is described by Formula 3: 
##STR3## 
In Formula 1, x is preferably from about 0.67 to 1.0, more preferably from 
about 0.75 to 1.0. y is preferably from 0 to about 0.33, more preferably 
from 0 to about 0.25. The ratio of ester to carbonate groups in the 
polyestercarbonates is preferably from about 50 to about 0 percent, more 
preferably from about 40 to about 0 percent. 
n preferably is about 20 or greater, more preferably about 50 or greater. 
The polycarbonates and polyestercarbonates useful in this invention are 
prepared from bisphenol AF, that is 
1,1,1,3,3,3-hexafluoro-2,2-bis-(4-hydroxyphenyl)propane, or its 
substituted derivatives, which correspond to Formula 7: 
##STR4## 
wherein R is independently in each occurrence hydrogen, a halogen, a 
C.sub.1-6 alkyl, a C.sub.1-6 haloalkyl, or a C.sub.1-4 alkoxy. 
R is preferably hydrogen, chlorine, bromine, fluorine, a C.sub.1-4 alkyl, a 
C.sub.1-4 haloalkyl, methoxy, ethoxy; R is more preferably hydrogen, 
chlorine, bromine, fluorine, methyl, ethyl, methoxy, or ethoxy. The 
manufacture of bisphenol AF and its derivatives is known in the art. See 
U.S. Pat. Nos. 4,358,624 and 4,649,207, incorporated herein by reference. 
The polycarbonates useful in this invention may be prepared by any process 
known in the art which results in polycarbonates with suitable membrane 
formation properties. For example, polycarbonates may be produced by the 
reaction of phosgene and the appropriate bisphenol in the presence of an 
HCl acceptor such as pyridine. Polycarbonates may also be prepared by a 
transesterification reaction between the appropriate bisphenol and a 
carbonate ester such as diphenyl carbonate. See Kirk-Othmer Encyclopedia 
of Chemical Technology, 3rd edition, John Wiley & Sons, New York, 1982, 
Vol. 18, pp. 479-494 and Ferdinand Rodriguez, Principles of Polymer 
Systems, 2nd edition, Hemisphere Publishing Corporation, McGraw-Hill Book 
Company, 1982, pp. 433-436; the relevant portions incorporated herein by 
reference. 
The polyestercarbonates useful in this invention may be prepared by 
reacting the appropriate bisphenol with a difunctional ester forming agent 
in the presence of phosgene. Preferred ester forming agents are 
dicarboxylic acids or dicarboxylic acid halides such as C.sub.1-20 
hydrocarbons substituted with two carboxylic acid or carboxylic acid 
halide moieties. More preferred dicarboxylic acids or dicarboxylic acid 
halides include C.sub.1-20 aliphatic dicarboxylic acids, C.sub.1-20 
aliphatic dicarboxylic acid halides, C.sub.5-20 cycloaliphatic carboxylic 
acids, C.sub.5-20 cycloaliphatic carboxylic acid halides, C.sub.6-20 
aromatic carboxylic acids, C.sub.6-20 aromatic carboxylic acid halides, 
C.sub.1-20 aliphatic dicarboxylic acids, C.sub.1-20 aliphatic dicarboxylic 
acid halides, C.sub.5-20 cycloaliphatic carboxylic acids, C.sub.5-20 
cycloaliphatic carboxylic acid halides, C.sub.6-20 aromatic carboxylic 
acids, and C.sub.6-20 aromatic carboxylic acid halides. 
The most preferred class of ester forming agents is the dicarboxylic acid 
halides. Preferred dicarboxylic acid halides include those corresponding 
to Formulas 8-11: 
##STR5## 
wherein X is a halogen and R.sup.3 and m are as previously defined. 
Preferred dicarboxylic acid halides useful in this invention include 
1,4-cyclohexane dicarboxylic acid chloride, 1,4-cyclohexane dicarboxylic 
acid bromide, 1,3-cyclohexane dicarboxylic acid chloride, or 
1,3-cyclohexane dicarboxylic acid bromide, terephthaloyl chloride, 
terephthaloyl bromide, isophthaloyl chloride, isophthaloyl bromide, 
2,6-naphthylene dicarboxylic acid chloride, or 2,6-naphthylene 
dicarboxylic acid bromide. The more preferred class of dicarboxylic acid 
halides is the dicarboxylic acid chlorides. Preferred acid chlorides are 
terephthaloyl chloride, isophthaloyl chloride, 1,4-cyclohexane 
dicarboxylic acid chloride, and 2,6-naphthylene dicarboxylic acid 
chloride. The most preferred diacarboxylic acid chlorides are 
terephthaloyl chloride, isophthaloyl chloride, or mixtures thereof. 
In a preferred embodiment in which a mixture of terephthaloyl chloride and 
isophthaloyl chloride is used as the ester forming agent, the ratio of 
terephthaloyl chloride to isophthaloyl chloride may be from 100:0 to 
0:100, preferably from about 80:20 to about 20:80. 
Generally a chain stopping agent is added to the reaction mixture to 
control molecular weight and viscosity. The molecular weight of the 
polymers useful in this invention is preferably greater than about 7,500, 
more preferably greater than about 10,500. The inherent viscosity of the 
polymers useful in this invention is preferably from about 0.2 to about 
1.5, more preferably from about 0.25 to about 0.80. 
The polyestercarbonates of this invention may be prepared by techniques 
known in the art. The solution process is one preferred process for the 
manufacture of the polyestercarbonates which are the subject of this 
invention. In the solution process, the bisphenol in a chlorinated solvent 
in the presence of a tertiary amine acid acceptor is contacted with a 
dicarboxylic acid or acid chloride in the presence of phosgene with 
agitation. See U.S. Pat. Nos. 3,028,365; 4,194,038; and 4,310,652; all 
incorporated herein by reference. See also P. W. Morgan, Condensation 
Polymers: By Interfacial and Solution Methods, Interscience, 1965, pages 
325-393, the relevant portions incorporated herein by reference. 
In another preferred process for preparing polyestercarbonates, the 
interfacial process, an aqueous bisphenolate solution with a pH of at 
least about 8 is mixed with phosgene and an organic solution of an acid 
halide which solution is immiscible with the aqueous bisphenolate 
solution. The said components are agitated for a sufficient time at a 
temperature so as to react the phosgene and the acid halide with the 
bisphenolate to form an amorphous polymer. The aqueous phase containing 
the amorphous polymer is separated from the organic phase. The organic 
phase is then washed with an aqueous liquid. An amorphous, 
melt-processable polyestercarbonate polymer is recovered from the washed 
organic phase. The organic phase may be based upon any conventional 
organic solvent for the product polymer. A preferred group of solvents 
includes chlorinated aliphatic C.sub.1-4 hydrocarbons such as methylene 
chloride, dichloromethane, chloroform, carbon tetrachloride, 
dichloroethane, trichloroethane, trichloroethylene, tetrachloroethylene, 
and mixtures thereof. Another preferred group of solvents includes 
chlorinated and non-halogenated aromatic hydrocarbons such as toluene, 
chlorobenzene, dichlorobenzene, and mixtures thereof. Preferred solvents 
are the chloromethanes, especially dichloromethane. The bisphenols useful 
in this invention are converted to bisphenoates by dissolving the 
bisphenol in water with an inorganic base, especially in an aqueous or 
alkaline earth metal hydroxide, preferably an alkali metal hydroxide, and 
more preferably sodium hydroxide. Further descriptions of the interfacial 
processes can be found in U.S. Pat. Nos. 3,169,121; 3,030,331; 3,028,364; 
4,137,128; 4,156,069; 3,207,814; 4,255,556; and 4,311,822; all 
incorporated herein by reference. See also P. W. Morgan, supra. 
The ratio of acid halide to phosgene generally controls the relative ratio 
of ester to carbonate units, with a higher ratio of acid halides resulting 
in a higher ester content and a lower ratio of acid halides resulting in a 
lower ester content. Generally, the molar ratio of phosgene to acid halide 
or carboxylic acid is between about 0.02:1 to about 20:1. 
The membranes of this invention may be homogenous, composite, or asymmetric 
membranes. Preferably, the membranes of this invention are asymmetric or 
composite. In addition, the membranes may be shaped in the form of flat 
sheets, hollow fibers, or hollow tubes. 
Homogeneous membranes are prepared by forming a thin discriminating layer 
which is dense and free of voids and pores. Such membranes generally have 
the same structure and composition throughout the membrane. In one 
preferred embodiment, the polycarbonate and polyestercarbonates of this 
invention are dissolved in a water-miscible solvent, for example, 
dimethylformamide or dimethylacetamide. Additional solvents suitable for 
forming membranes include chlorinated hydrocarbons such as methylene 
chloride, chloroform, trichloroethane, trichloroethylene, 
tetrachloroethylene, and the like. The configuration into which the 
membrane is to be formed determines the membrane solution composition. To 
form a flat sheet membrane, a solution with about 10 to 20 weight percent 
of polymer is preferred, with about 15 to 20 weight percent of polymer 
being more preferred. To form a hollow fiber membrane, a solution with 
about 30 to 80 weight percent polymer is preferred, with about 50 to 80 
weight percent of polymer being more preferred. 
The polymer solution should be homogeneous and possess sufficient viscosity 
to allow casting of the solution onto a flat surface. The casting surface 
is such that the finished membrane may thereafter be readily separated. 
One way of carrying out this operation is by casting the polymer solution 
onto a support surface which may be dissolved away from the finished 
membrane following drying and curing. Alternately, the membrane may be 
cast onto a support having a low surface energy, such as silicone, coated 
glass, or a surface to which the membrane will not adhere, such as 
mercury. Casting is performed by pouring the solution onto the appropriate 
surface and drawing down the polymer soluting using an appropriate tool to 
form a solution of the appropriate thickness. 
Thereafter, the cast solution is exposed to drying or curing conditions. 
Such conditions are used to remove the solvent, thereby leaving a thin 
discriminating layer of polymer which is homogeneous. The solution may be 
dried by exposing the solution to a vacuum, exposing the solution to 
elevated temperatures, allowing the solvent to evaporate from the solution 
over time, or a combination thereof. Generally, it is preferable to expose 
the cast solution to elevated temperatures. Any temperature at which the 
solvent evaporates in a reasonable period of time and below the glass 
transition temperature is suitable, preferably less than about 100 degrees 
Celsius, more preferably less than about 80 degrees Celsius. In one 
preferred embodiment, such exposure is done under vacuum at elevated 
conditions. This drying is performed over a period sufficient to remove 
the solvent, preferably between 24 to 48 hours. 
Homogeneous polycarbonate and polyester-carbonate membranes may alternately 
be formed by the melt extrusion process. The polymers may be extruded and 
drawn down into films using conventional extrusion equipment. Typically, 
the polymers of this invention may be extruded at temperatures from about 
220.degree. to about 300.degree. C. 
In a composite membrane, the thin discriminating layer of the membrane is 
supported on a porous substructure or substrate. The porous substrate 
generally does not greatly impede the transport of components through the 
membrane. To prepare a composite membrane, a homogeneous, thin 
discriminating layer can be formed and thereafter adhered to a porous 
support after formation. Alternatively, the porous support can be the 
surface upon which the membrane is cast or laminated. In one embodiment, 
the composite membrane is prepared by casting or laminating a forming 
solution as a uniform coating on the porous support which forms the 
support layer for the finished membrane. Penetration of the polymer into 
pores of the porous support layer is operable so long as the desired 
thickness of the semi-permeable membrane is not exceeded. In one 
embodiment, the support layer may be a metal or polymeric plate with a 
plurality of holes drilled into it. However, such a drill plate is not 
advantageous because it can significantly reduce the effective surface 
area of the membrane. In a preferred embodiment, the porous support layer 
is a very porous polymer membrane. Illustrative of such polymeric support 
layers are porous cellulose ester and microporous polysulfone membranes. 
Such membranes are commercially available under the tradenames MILLIPORE, 
PELLICON, and DIAFLOW. Where such support membranes are thin or highly 
deformable, a screen or other support frame may also be necessary to 
adequately support the semi-permeable membrane. In one especially 
perferred embodiment, the polymeric support layer is in the form of a 
hollow fiber of a microporous polymer such as cellulose ester or 
polysulfone. The hollow fiber itself provides adequate support for the 
thin discriminating layer coated on the inside or the outside of the 
hollow fiber. After the thin discriminating layer is coated onto the 
porous support, the composite membrane is exposed to conditions for 
removal of the solvent so as to form the dense skin. Such conditions are 
similar to those hereinbefore described for the formation of homogenous 
membranes. 
To form an asymmetric membrane, a solution is cast as hereinbefore 
described, and thereafter the cast solution is partially cured to remove a 
portion of the solvent. Thereafter, one or both surfaces of the partially 
dried membrane is contacted with a quench liquid such as water so as to 
form a thin discriminating layer on one or both sides of the membrane, 
under conditions such that the solvent away from the dense layer 
communicates to the dense layer forming pores in the remainder of the 
membrane, thereby forming an asymmetric membrane. Such porous layer is 
present to provide support for the thin discriminating layer without 
impeding the transport of the fluid containing the components to be 
separated by the semi-permeable, thin discriminating layer. The parital 
curing step is performed in a manner similar to the curing step described 
with respect to the formation of homogeneous membranes. 
Hollow fiber membranes can be formed by spinning fibers from an appropriate 
solution of the polycarbonate or polyestercarbonate in a water-miscible 
solvent or by melt extrusion. Such spinning processes are well known to 
those skilled in the art, and the formation of homogeneous, asymmetric, or 
composite membranes requires the adaptation of the hereinbefore described 
procedures to the hollow fiber membrane form. Such adaptations are well 
within the skill of the art. 
The membranes used in the invention are relatively thin. The thickness of 
such homogeneous membranes is preferably greater than about 5 microns and 
less than about 500 microns. More preferably, the membrane thickness for a 
homogeneous membrane is between about 10 and about 300 microns. In the 
case of composite or asymmetric membranes, the active discriminating layer 
is preferably between about 0.05 and 10 microns, more preferably between 
about 0.05 and 5 microns. 
The membranes are fabricated into flat sheet, spiral, tubular, or hollow 
fiber devices by methods described in the art. The membranes are sealingly 
mounted in a pressure vessel in such a manner that the membrane separates 
the vessel into two fluid regions wherein fluid flow between the two 
regions is accomplished by fluid permeating through the membrane. For 
examples of conventional membrane device designs and fabrication methods 
see U.S. Pat. Nos. 3,228,876; 3,433,008; 3,455,460; 3,475,331; 3,526,001; 
3,538,553; 3,690,465; 3,702,658; 3,755,034; 3,801,401; 3,872,014; 
3,966,616; 4,045,851; 4,061,574; 4,080,296; 4,083,780; 4,220,535; 
4,235,723; 4,265,763; 4,430,219; 4,352,092; 4,337,139; and 4,315,819; all 
incorporated herein by reference. 
The membranes are used to isolate or recover gases from gas mixtures. The 
feed gas mixture may contain gases such as hydrogen, helium, oxygen, 
nitrogen, carbon dioxide, methane, light hydrocarbons, and the like. One 
side of the membrane is contacted with a feed gas mixture under pressure, 
while a pressure differential is maintained across the membrane. At least 
one of the components in any given gas mixture selectively permeates 
through the membrane more rapidly than the other component(s). A stream is 
obtained on the low pressure side of the membrane which is enriched in the 
faster permeating component(s). The permeated gas is removed from the low 
pressure (downstream) side of the membrane. A stream depleted in the 
faster permeating gas is withdrawn from the high pressure (upstream) side 
of the membrane. 
The separation process should be carred out at pressures which do not 
adversely affect the membrane. In the case where oxygen is separated from 
nitrogen, the pressure differential across the membrane is preferably 
between about 10 and 350 psig, more preferably between about 50 and 250 
psig. In the case where carbon dioxide is separated from methane, the 
pressure differential across the membrane is preferably between about 50 
and 1000 psig, more preferably between about 50 and 500 psig. The 
separation process should be carried out at temperatures which do not 
adversely affect membrane integrity. Under continuous operation, the 
operating temperature is preferably from about 0 to 100 degrees Celsius, 
more preferably from about 0 to 50 degrees Celsius. 
##EQU1## 
A standard permeability measurement unit is the barrer, which is 
##EQU2## 
The reduced flux is defined as (permeability) (membrane thickness). A 
standard reduced flux unit is 
##EQU3## 
The separation factor (selectivity) is defined as the ratio of the 
permeability of the faster permeating gas to the permeability of the 
slower permeating gas. 
In the embodiment where oxygen is separated from nitrogen, the membrane 
preferably has a separation factor for oxygen/nitrogen at about 25 degrees 
Celsius of about 3.5 or greater, more preferably of about 4.0 or greater. 
The permeability of oxygen at about 25 degrees Celsius is preferably of 
about 2.0 Barrers or greater, more preferably of about 2.5 Barrers or 
greater. The reduced flux of oxygen at about 25 degrees Celsius is 
preferably about 
##EQU4## 
In the embodiment where carbon dioxide is separated from methane, the 
membrane preferably has a separation factor for carbon dioxide/methane at 
about 25 degrees Celsius of at least about 16, more preferably of at least 
about 21. The permeability of carbon dioxide at about 25 degrees Celsius 
is at least about 9 Barrers, more preferably at least about 12 Barrers. 
The reduced flux of carbon dioxide at about 25 degrees Celsius is 
preferably about 
##EQU5##

SPECIFIC EMBODIMENTS 
The following examples are included to illustrate the invention and are not 
intended to limit the scope of the invention or claims. 
EXAMPLE 1 
Bisphenol AF Based Polycarbonate Polymerization 
A three neck, 2.0 liter round bottom flask, equipped with a thermometer, 
stirrer, and glass funnel, is charged with 1.2 liters of methylene 
chloride, 185.6 grams (0.55 moles) of 
1,1,1,3,3,3-hexafluoro-2,2-bis-(4-hydroxy phenyl)propane (bisphenol AF), 
and 116.8 cc (1.44 moles) of pyridene. The resultant clear, pale pink 
solution is stirred under a nitrogen atmosphere for 10 minutes. Moderate 
stirring is continued while a total of 68 grams (0.69 moles) of phosgene 
is bubbled into the solution over a period of 41 minutes. 
The creamy, pale yellow solution is then scavenged with methanol, 
neutralized with dilute hydrochloric acid, and washed a second time with 
dilute hydrochloric acid. The colorless, slightly hazy solution is 
clarified by passing it through an MSC resin bed, further diluted with 
methylene chloride, and precipitated in 4 volumes of n-heptane. The 
precipitated polymer is dried under vacuum at 80 degrees Celsius for 48 
hours. The resultant polymer has an inherent viscosity of 0.67 dL/g at 25 
degrees Celsius in methylene chloride. 
Film Preparation and Testing 
2 grams of dried polymer are dissolved in 18 grams of methylene chloride to 
form a casting solution. The casting solution is passed through a fritted 
glass filter onto a clean glass plate and drawn down with a casting blade. 
The film is covered until dry, removed from the glass plate, and annealed 
under vacuum at 80 degrees Celsius for 48 hours. 
From the cast film, a small disc is cut to provide a sample for gas 
permeability evaluation. The mean thickness and standard deviation are 
determined and the sample is placed in a gas permeation test cell of a 
fixed volume-variable pressure gas permeability test apparatus. Both sides 
of the membrane are evacuated overnight. One side of the membrane is then 
pressurized with oxygen at 150 kPaG and the downstream pressure increase 
is monitored with a pressure transducer and recorded on a single-pen 
recorder. Gas permeability coefficients and standard deviation are 
calculated from the slope of the time-pressure curve. 
The same procedure is followed for each of the following gases: nitrogen, 
methane, helium, and carbon dioxide. The results are listed in Tables IA, 
IB, and II. 
EXAMPLE 2 
Bisphenol AF Based Polyestercarbonate 
The polymerization step is similar to that of Example 1, except that 50% of 
the phosgene (0.345 moles) is replaced with an 80:20 mixture of 
terephthaloyl chloride:isophthaloyl chloride. A film is prepared in a 
manner similar to that described in Example 1 and gas permeabilities are 
determined for oxygen, nitrogen, methane, helium, and carbon dioxide. 
Results are listed in Tables IA, IB, and II. 
EXAMPLE 3 
Bisphenol A Based Polycarbonate 
This Example does not illustrate the invention but is meant to compare the 
gas separation performance of bisphenol AF polycarbonates with that of 
bisphenol A polycarbonates. 
The procedure of Example 1 is used except that bisphenol A is used in place 
of the 1,1,1,3,3,3-hexafluoro-2,2-bis(4-hydroxy phenyl)propane (bisphenol 
AF). 
The results of gas permeability measurements for oxygen, nitrogen, methane, 
and carbon dioxide are listed in Tables IA, IB, and II. 
EXAMPLE 4 
Bisphenol A Based Polyestercarbonate 
This Example does not illustrate the invention but is meant to compare the 
gas separation performance of bisphenol AF polyestercarbonates with that 
of bisphenol A polyestercarbonates. 
The procedure of Example 2 is used except that bisphenol A is used in place 
of the 1,1,1,3,3,3-hexafluoro-2,2-bis(4-hydroxyphenyl)propane (bisphenol 
AF). 
The results of gas permeability measurements for oxygen and nitrogen are 
listed in Tables IA, IB, and II. 
TABLE IA 
______________________________________ 
GAS PERMEABILITIES.sup.1 
Membrane 
Ex- Thickness Oxy- Nitro- 
Meth- Carbon 
ample (mils) gen gen ane Dioxide 
Helium 
______________________________________ 
1 2.10 3.37 0.69 0.51 14.2 31.9 
2 1.92 3.96 0.95 0.77 17.7 31.4 
3 5.14 1.06 0.20 0.23 5.54 -- 
4 2.04 1.16 0.26 -- -- -- 
______________________________________ 
.sup.1 Gas permeability values in units of barrers (cm.sup.3cm/(cm.sup.2 
cm Hg) .times. 10.sup.10 
TABLE IB 
______________________________________ 
REDUCED FLUX.sup.1 
Ex- Membrane 
am- Thickness 
ple (mils) Oxygen Nitrogen Methane 
______________________________________ 
1 2.10 6.32 .times. 10.sup.-8 
1.29 .times. 10.sup.-8 
9.56 .times. 10.sup.-9 
2 1.92 8.12 .times. 10.sup.-8 
1.95 .times. 10.sup.-8 
1.58 .times. 10.sup.-8 
3 5.14 8.12 .times. 10.sup.-9 
1.53 .times. 10.sup.-9 
1.76 .times. 10.sup.-9 
4 2.04 2.24 .times. 10.sup.-8 
4.93 .times. 10.sup.-9 
-- 
______________________________________ 
Carbon 
Dioxide Helium 
______________________________________ 
2.66 .times. 10.sup.-7 
5.98 .times. 10.sup.-7 
3.63 .times. 10.sup.-7 
6.44 .times. 10.sup.-7 
-- -- 
______________________________________ 
##STR6## 
TABLE II 
______________________________________ 
SEATION FACTORS 
Example O.sub.2 /N.sub.2 
CO.sub.2 /CH.sub.4 
He/CH.sub.4 
______________________________________ 
1 4.9 27.8 62.3 
2 4.2 23.0 41.0 
3 5.3 24.1 -- 
4 4.6 -- -- 
______________________________________