GB2139237A - Selective permeable membrane for gas separation - Google Patents

Abstract

A selectively permeable membrane for gas separation, comprising a polyphosphazene having a repeating unit represented by the general formula <IMAGE> wherein X and X' are each independently a group selected from an alkoxy group, an amino group, an aryloxy group, a group having an organosilane unit, a group having an organosiloxane unit, an etheroxy group, an alkyl group, an alkenyl group and an aryl group.

Description

SPECIFICATION Selectively permeable membrane for gas separation BACKGROUND OF THE INVENTION The present invention relates to a selectively permeable membrane for gas separation and more particularly to a selectively permeable membrane for gas separation suitable for concentrating oxygen from air.

It has long been known that a specific component can be separated and concentrated from a gaseous mixture by using a membrane formed of a polymeric material. This has recently attracted considerable attention from the standpoint of resources saving and energy saving.

Particularly, if oxygen-enriched air with a high oxygen concentration can be obtained from air easily, inexpensively and continuously according to the membrane separation method, it is of great value. At present, the oxygen used for medical purposes such as the use thereof for incubators for immature infants or for therapy of patients suffering from diseases of the respiratory system is a pure oxygen filled in a cylinder. However, serious drawbacks are encountered in the use of such oxygen, for example, a troublesome operation is required and the oxygen cannot be fed continuously and must be diluted before use.But, if a highly efficient membrane capable of feeding oxygen in a concentrated state from air is obtained, the above drawbacks will be overcome, and it will become possible to use such oxygen even at home with the aid of an apparatus of a simple structure, and thus a great improvement an be expected in the medical field.

Further, if oxygen-enriched air can be fed easily and continuously by using a membrane also in various combustion systems presently in use such as, for example, industrial boilers and furnaces, iron manufacturing blast furnaces, internal combustion engines for vehicles, and household heaters, then the consumption of fuel can be reduced at a higher combustion efficiency, that is, energy saving can be attained, and at the same time the problem of environmental pollution caused by incomplete combustion can be overcome. Moreover, if oxygen-enriched air can be fed easily and inexpensively by the use of a membrane, a further development can be expected also in other fields such as the food industry, aquaculture and waste disposal.

Polymeric materials presently known are more or less gas permeable, but in order to obtain an oxygen enriching membrane employable industrially, such materials must permit a sufficiently high permeation speed of oxygen and exhibit a large selectivity of oxygen against nitrogen. It has been known that the gas permeation speed is proportional to the permeation coefficient (usually represented by P in the unit of cm3 (STP)cm/cm2~sec~cmHg) peculiar to polymeric substances, a differential pressure between both sides of a membrane and the surface area of the membrane and is inversely proportional to the membrane thickness. The selectivity of oxygen against nitrogen depends on the ratio (PO2/PN2) of the permeation coefficient of oxygen (to2) to that of nitrogen (PN2) which are peculiar to polymeric substances.Therefore, in order to obtain a practical permeation speed, it is necessary to select a material having a large P02, or else it will become necessary to enlarge the differential pressure or the surface area of a membrane, thus resulting in increased size and complicated structure of the apparatus which employs the membrane. Moreover, in order to obtain a sufficient oxygen concentration, it is necessary to select a polymeric material having a high PO2/PN2 ratio. Further, the membrane thickness must be reduced in order to obtain as high a permeation speed as possible, and to this end the material strength must be high. Additionally, it is also required for the membrane material to have a durability high enough to stand long use and an oxidation stability high enough for contact continually with a highly concentrated oxygen.Thus, oxygen enriching membrane materials employable industrially are required to have large P02 and PO2/PN2 and be superior in strength, durability and oxidation stability.

However, there is scarcely any known polymeric substance that satisfies the above requirements. Although there have been made many attempts for improving polymeric substances, none of them have fully attained the purpose. The following table shows examples of P02 and PN2 of known polymeric substances.

Polymeric Material P02(cm3(STP)cm/cm2.s.cmHg) PO2/PN2 Polydimethylsiloxane 3.5 x 10-8 1.9 Poly-4-methylpentene-1 3.O X 10~9 2.9 Natural rubber 2.3 x 10-9 2.4 Low density 2.9 x 10-'0 2.9 polyethylene Cellulose acetate 4.3X10-11 3.0 There are only an extremely limited number of known polymeric substances as polymeric substances having a P02 of 10-9 or more, examples of which are merely polydimethylsiloxane, poly-4-methylpentene-1 and natural rubber.Most other polymeric substances exhibit a P02 of 10-10 or less, so it is impossible to obtain a membrane having a practical permeation speed from those materials unless the membrane area is made extremely large. Even among high polymers having a P02 not less than 10be, such a high polymer as natural rubber is poor in durability (especially in oxidation stability) because it has -C = C- double bond in the main chain, and is insufficient also in mechanical strength.

Poly-4-methylpentene-1 exhibits a high strength because it is polyolefin, but is poor in oxidation stability because it has a tertiary carbon in the main chain, so its use under severe industrial conditions (for example, under a high temperature condition) involves problems.

Polydimethylsiloxane has the highest gas permeability among the polymeric substances presently known, but its strength is poor so it is extremely difficult to form a membrane below 20# in thickness, and thus a practical permeation speed is not attainable despite a large P02 of the material. If it is reinforced with a filler and crosslinked, it strength can be enhanced to some extent, but since these treatments impair the membrene-forming property, it is difficult to obtain a very thin membrane. Further, polydimethylsiloxane has the essential drawbacks that its PO2/PN2 ratio is small and the selectivity of oxygen against nitrogen is poor.In order to make the most of the large gas permeability of polydimethylsiloxane, there have been made several attempts to improve its strength by copolymerization with another component. For example, a block copolymer of polydimethylsiloxane and a polycarbonate is proposed in U.S. Patent No.3,189,662. This block copolymer is somewhat improved in strength because of the introduction of polycarbonate units, but not only it is apt to be deteriorated by pump oil or the like because of lowering of its solvent resistance, but also there arises such a problem as lowering of P02 in comparison with a single use of polydimethylsiloxane. There have been made many other attempts to make modification by the reaction of organopolysiloxanes as base materials with other components and to thereby remedy the above-mentioned drawbacks.But, all of these attempts have encountered a dilema that as the siloxane content of the polymer is decreased, the feature of polyorganosiloxanes, namely, a large P02, is lost although an improvement is recognized in point of strength. Thus, the known high polymers and their modified high polymers have not yet satisfied the foregoing requirements.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel selectively permeable membrane for gas separation.

It is another object of the present invention to provide an oxygen enriching permable membrane having a large P02 and PO2/PN2 and superior strength, durability, resistance to chemicals and oxidation stability.

The selectively gas permeable membrane of the present invention comprises a polyphosphazene having a repeating unit represented by the following general formula:

wherein X and X', which may be alike or different, are each independently a group selected from an alkoxy group, an amino group, an aryloxy group, a group having organosilane unit and a group having organosiloxane unit, and n, which represents a number average polymerization degree, is usually in the range of 20 to 70,000.

DESCRIPTION OF PREFERRED EMBODIMENTS First, the X and X' in the above general formula (1) will be explained below.

As alkoxy groups there preferably may be used those represented by the general formula -OR wherein R is an alkyl group having 1 to 20 carbon atoms. Preferred examples are methoxy, ethoxy, propoxy, butoxy, sec-butoxy, pentyloxy, 2-methlypentyloxy, neopentyioxy, hexyloxy, decyloxy and dodecyloxy. Alkoxy groups in which one or more hydrogen atoms have been substituted by one or more of halogen atoms such as chlorine, bromine and fluorine, amino, phenyl, nitro, methoxy and mercapto, are also preferred. Particularly, those wherein hydrogen in any other position than a-position has been substituted are preferred. Alkoxy groups referred to herein include these substituted alkoxy groups.Examples of substituted alkoxy groups are 2chloroethoxy, 3-chloropropoxy, 2-bromoethoxy, 2-fluoroethoxy, phenylmethoxy, p-chlorophenylmethoxy, 2-phenylethoxy, 3-phenylpropoxy, p-sec-butylphenylmethoxy, 2-dimethylaminoethoxy, 2-methylaminoethoxy, 4-methoxybutoxy, 2-mercaptoethoxy and 2-nitroethoxy.

Fluoroalkoxy groups represented by the general formula -OCG2tCF2)mZ wherein m is an integer of 1 to 10 and Z is hydrogen or fluorine are also preferred, suitable examples of which are 2,2, 2-trifluoroethoxy, 2,2,3,3, 3-pentafluoropropoxy, 2,2,3, 3,4,4,4-heptafluorobutoxy, 2,2, 3,3-tetrafluoropropoxy, 2,2,3,3,4,4,5,5-octafluoropentyloxy, and 2,2,3,3,4,4,5,5,6,6,7,7- dodecafluoroheptyloxy.

Amino groups which may be used in the present invention are those represented by the general formula -NR1R2 wherein Rt and R2, which may be alike or different, are preferably each independently hydrogen; alkyl of C1 to CtO; substituted alkyl of C, to C10 in which one or more hydrogen atoms have been substituted by one or more of halogen atoms such as fluorine, chlorine and bromine, phenyl, alkoxy groups of C, to C4, nitro, cyano, alkylamino groups of Ct to C4 and alkylacetoxy groups of Cl to C4; phenyl; substituted phenyl in which one or more hydrogen atoms have been substituted by one or more of halogen atoms such as fluorine, chlorine and bromine, alkyl groups of Ct to C20, alkoxy groups of C1 to C4, phenoxy, phenyl, nitro, cyano and alkylamino groups of C, to C4; cyano; nitro; alkylamino of C, to C4; alkylcarbamate; pyridyl; or imidazolyl.

Preferred examples of amino groups are amino; alkylamino groups such as methylamino, ethylamino, n-propylamino, n-butylamino, sec-butylamino, n-hexylamino, cyclohexylamino, octylamino, decylamino, dimethylamino, diethylamino, methylethylamino and piperidino; substituted alkylamino groups such as benzylamino, 2-phenylethylamino, 2,2,2-trifluoroethylamino, 2,2,3, 3,4,4,4-heptafluorobutylamino and ethylacetoxyamino; arylamino groups such as pheny amino, 34luorophenylamino, 4-fluorophenylamino, 3-chlorophenylamino, 4-chlorophenylamino, 3-methylphenylamino, 4-methylphenylamino, 4-ethylphenylamino, 4-n-butylphenylamino, 4-methoxyphenylamino, perfluorophenylamino, perchlorophenylamino and biphenylamino; pyridylamino groups such as 2-pyridylamino and 5-methyl-2-pyridylamino; imidazolyl; alkylcarbazate groups such as methylcarbazate and ethylcarbazate; amino groups derived from methylhydrazine and ethylhydrazine; cyano group-containing amino groups such as cyanamide and dicyanamide; and nitro group-containing amino groups.

Preferred examples of aryloxy groups are phenoxy and substituted phenoxy in which one or more hydrogen atoms have been substituted by one or more of straight-chain or branched alkyl groups of Ct to C20, straight-chain or branched alkoxy groups of C1 to C20, aryl groups, halogen atoms, alkylamino groups having straight-chain or branched alkyl groups of C, to C10, cyano and nitro.

More concrete preferred examples of aryloxy groups are phenoxy; ss-naphthoxy; alkylsubstituted aryloxy groups such as 4-methylphenoxy, 3-methylphenoxy, 2, 6-dimethylphenoxy, 4-ethylphenoxy, 4-n-propylphenoxy, 4-iso-propylphenoxy, 4-sec-butylphenoxy, 4-tert-butylphenoxy, 2, 4-di-tert-butylphenoxy, 3, 5-di-tert-butylphenoxy, 4-n-pentylphenoxy, 4-2-ethylhexylphenoxy, 4-nonylphanoxy, 4-n-dodecylphenoxy, 4-hexadecylphenoxy, 4-phenyl methylphenoxy and 4-trifluoromethylphenoxy; alkoxy-substituted aryloxy groups such as 4-methoxyphenoxy, 3methoxyphenoxy, 4-ethoxyphenoxy, 4-n-butoxyphenoxy, 4-sec-butoxyphenoxy and 4-hexyloxyphenoxy; aryl-substituted aryloxy groups such as 4-phenylphenoxy; halogen-substituted aryloxy groups such as 4-chlorophenoxy, 4-bromophenoxy, 4-fluorophenoxy, 3-chlorophenoxy, 2,4dichlorophenoxy, 2,4-dibromophenoxy, 2,4, 6-trichlorophenoxy, 2-chloro-4-methylphenoxy, perchlorophenoxy and perfluorophenoxy; alkylamino-substituted aryloxy groups such as 4-dimethylaminophenoxy, 4-diethylaminophenoxy, 4-propylaminophenoxy and 4-butylaminophenoxy; cyano-substituted aryloxy groups such as 4-cyanophenoxy; and nitro-substituted aryloxy groups such as 2-nitrophenoxy, 2-nitro-4-methylphenoxy, 4-nitrophenoxy and 2-chloro-4-nitrophenoxy.

The group having an organosilane unit is represented by the following general formula (2): -A-SiR1R2R3 (2) wherein A is an atom or group which connects the organosilane unit represented by the general formula -SiR1R2R3 with the phosphorus atom in the polyphosphazene main chain, and is not specially limited provided it can connect the organosilane unit with the phosphorus atom, typical examples of which are -0-, -NH-, -S-, -O-(-CH2-)m-, -O-(-CH2-)m-O-,

wherein m and I are each an integer of 1 to 4.

In the above general formula -SiR1R2R3, R1, R2 and R3, which may be alike or different, are each independently hydrogen, alkyl of C, to C4; substituted alkyl of C1 to C4 in which one or more hydrogen atoms have been substituted by one or more of halogen atoms such as fluorine, chlorine and bromine, cyano, nitro and alkylamino groups of C, to C4; phenyl; substituted phenyl in which one or more hydrogen atoms have been substituted by one or more of halogen atoms such as fluorine, chlorine, and bromine, cyano, nitro and alkylamino groups of C, to C4; halogen atom such as chlorine, fluorine, or bromine; alkylamino of C, to C4; cyano; or vinyl.

Preferred examples of the organosilane unit include various organosilyl groups such as dimethylsilyl, trimethylsilyl, triethylsilyl, t-butyld imethylsilyl, chloromethyldimethylsilyl, trifluoropropyldimethylsilyl, cyanoethyldi methylsilyl, dimethylaminoethyldimethylsilyl, cyanopropyldimethylsilyl, phenyldimethylsilyl, perfluorophenyldimethylsilyl, 4-dimethylaminophenyldimethylsilyl, dimethylaminodimethylsilyl, methylchlorodimethylaminosilyl, dimethylchlorosilyl and vinyldimethylsilyl, with dimethylsilyl and trimethylsilyl being particularly preferred.

The group having an organosiloxane unit is represented by the following general formula (3):

wherein B is an atom or group which connects the organosiloxane unit with the phosphorus atom in the polyphosphazene main chain, and is not specially limited provided it can connect :he organosiloxane unit with the phosphorus atom, typical examples of which are -0--NH-,

wherein m and I are each an integer of 1 to 4.

In the organosiloxane unit represented by the general formula

R4, R5, R8 and R7, which may be alike or different, are each hydrogen; alkyl of C, to C4; halogenated alkyl of C, to C4 in which one or more hydrogen atoms have been substituted by one or more of halogen atoms such as fluorine, chlorine and bromine; phenyl; or vinyl, Y is hydrogen; alkyl of C, to C4; halogenated alkyl in which one or more hydrogen atoms have been substituted by one or more of halogen atoms such as fluorine, chlorine and bromine; hydroxyalkyl; phenyl; vinyl; halogen such as fluorine, chlorine, or bromine; hydroxyl; amino, alkylamino of C1 to C4; epoxy; -(-CH2-)rn-O-Si(CH3)3; or~(~CH2-)m-NH-Si(CH3)3 in which m is an integer of 1 to 4, and p is an integer of 1 to 1,000.The following are typical preferred examples of the group containing the organosiloxane unit:

The X and X' in the general formula (1) may be the same or different, but in the case where these substituent groups have organosilane units or organosiloxane units, the ratio of the total of organosilane units and/or organosiloxane units to the entire polymer is suitably in the range of 10 to 90%, more preferably 20 to 80%, by weight. If the above ratio is lower than 10%, the purpose of improving the gas permeability will not be attained, and if the ratio is higher than 90%, the resultant polymer will be poor in strength and unable to afford a thin membrane.

Thus, at those ratios outside the range just specified above, it is impossible to overcome the same drawbacks as those of silicone rubber, and the objects of the present invention cannot be attained.

Polyphosphazenes affording a particularly superior oxygen enriching membrane, that is, having a high selective permeability for oxygen, i.e. PO2/PN2, are those wherein 10 to 90% of the substitutent groups are alkoxy and the remaining 90 to 10% comprises amino, aryloxy, etheroxy, alkyl, alkenyl and/or aryl. The alkoxy, amino and aryloxy groups are as previously defined.

The etheroxy group is represented by the general formula R(OR')nO- wherein R is C1 -C20 alkyl, aryl, alkylaryl or arylalkyl and R' is C,-C, alkylene. Preferred examples are

and

wherein m and n are integers of 1 to 12 and 1 to 70, respectively.

As the alkyl group, it is preferable to use a straight-chain or branched alkyl group of Ct to C12, examples of which are methyl, ethyl, propyl, butyl, sec-butyl, t-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, decyl and dodecyl.

As the alkenyl group, it is preferable to use one represented by the general formula -CH = CCIR" wherein R" is hydrogen or a straight-chain or branched alkyl or aryl group of C, to C,2, examples of which are 2-chloroethenyl, 2-chloropropenyl, 2-chloro-1-butenyl, 2-chloro-3 methyl-1-butenyl, 2-chloro-1-hexenyl, 2-chloro-3-methyl-1 -heptenyl, 2-chloro-1 -octenyl, 2-chloro 1 -decenyl, 2-chloro-2-phenylethenyl, 2-chloro-2-(4-tert-butylphenyl)ethenyl and 2-chloro-2-naphthylethenyl.

As the aryl group there may be used a substituted or unsubstituted aryl group. Preferred examples are phenyl, 4-methylphenyl, 3-ethylphenyl, 4-tert-butylphenyl, 3-methoxyphenyl, 4 butoxyphenyl and 4-phenylphenyl.

In the general formula (1), n is an integer of 20 to 70,000, at which the polymer is usually in the form of a rubbery or flexible solid. If n is smaller than 20, the polymer will be too poor in strength and not afford a membrane strong enough for practical use. If n is larger than 70,000, it is difficult to prepare the polymer because of a too large molecular weight and it is difficult to form a membrane because of a too high viscosity of the membrane forming solution. Even when n is not smaller than 20, there may be obtained an oily liquid according to some particular kind of substituent, but polyphosphazene partially containing such substituent is employable, of course, and a membrane obtained by impregnating the liquid polymer into a porous substance is also employable.

The polyphosphazene of the present invention can be prepared by known methods (for example, see Allcock et al, Inorg. Chem., 5, 1716 (1966)). As an example, polydichlorophosphazene obtained by heat-polymerizing a cyclic chlorophosphazene such as hexachlorocyclotriphosphazene or octachlorocyclotetraphosphazene or a linear chlorophosphazene of low molecular weight in a thoroughly water-excluded system in the presence or absence of a catalyst, is reacted with reactant for forming the X and/or X' group.

Alkoxy-containing polyphosphazene may be prepared by the reaction of polydichlorophosphazene with an alkali metal (such as sodium, potassium or lithium) alkoxide of the corresponding alcohol. Alternatively, it may be prepared by heating polydichlorophosphazene and the corresponding alcohol in the presence of a tertiary amine such as triethylamine.

Likewise, the amino, aryloxy and other groups are introduced in the polyphosphazene molecule in the following manner.

Amino Group Polydichlorophosphazene and the corresponding amine are reacted in the presence or absence of a tertiary amine such as triethylamine.

Aryloxy Group Polydichlorophosphazene is reacted with an alkali metal (such as sodium, potassium or lithium) alkoxide of the corresponding phenol or substituted phenol. Alternatively, polydichlorophosphazene is reacted with the corresponding phenol or substituted phenol under heating in the presence of a tertiary amine such as triethylamine.

Organosilane unit-containing Group Method in which part or the whole of the chlorine atoms of polydichlorophosphazene is substituted directly by hydroxyl, amino.or mercapto group, or polyphosphazene substituted by a substituent having hydroxy, amino or mercapto group on a site other than the connection with phosphorus atom is silylated with a silane coupling agent having the corresponding organosilyl group.

Method in which part or the whole of the chlorine atoms of polydichlorophosphazene is substituted by an alkoxide of the corresponding silyl alcohol.

Method in which the alkoxy groups of polyalkoxyphosphazene are subjected to ester interchange with an alkoxide of the corresponding silyl alcohol in the presence of an alkali catalyst.

Organosiloxane unit-containing Group Method in which part or the whole of the chlorine atoms of polydichlorophosphazene is substituted by an alkoxide of polyorganosiloxane having terminal hydroxyl groups or by a polyorganosiloxane having terminal amino or epoxy groups.

Method in which part or the whole of the alkoxy groups of polyalkoxyphosphazene is subjected to ester interchange with an alkoxide of polyorganosiloxane having terminal hydroxyl groups.

Method in which polyphosphazene containing a substituent group having unsaturated bond is first prepared and then polyhydrosiloxane having an active hydrogen is attached to the unsaturated bond by using such a catalyst as chloroplatinic acid.

Etheroxy Group Polydichlorophosphazene is reacted with an alkali metal (e.g. sodium, potassium or lithium) alkoxide of the corresponding ether alcohol (R(OR')nOH), or reacted with the corresponding ether alcohol under heating in the presence of a tertiary amine such as triethylamine.

Alkenyl Group Polydichlorophosphazene and the corresponding alkyne are reacted in the presence of a tertiary amine such as triethylamine.

Alkyl and Aryl Groups Alkyl- or aryl-substituted cyclophosphazene trimer or tetramer (e.g. rnonomethylpentachlorncy- clotriphosphazene) is polymerized under heating. Alternatively, polydifluorophosphazene derived from hexafluorocyclotriphosphazene is reacted with an organometallic compound having the alkyl or aryl group to be incorporated (e.g. aryllithium or dialkylmagnesium).

In the case of using one kind of reactant, e.g. alcohol, there is obtained a homopolymer represented by ~ [ -NPX2- ] n-, and in the case of using two kinds of reactants, there is obtained a copolymer with the following three kinds of repeating units distributed randomly,

Further, in the case of using three kinds or more, there is obtained a copolymer with these three or more substituents distributed randomly.

For example, in order to prepare a polyphosphazene containing 10 to 90% of alkoxy group and 90 to 10% of other substituent group, there may be adopted a method in which first a polyphosphazene containing a desired amount of alkoxy group is prepared according to the above method and then the remaining unsubstituted chlorine atoms are subs:itu':ed by a desired substituent group according to the above method. There also may be adopted a method in which a polyphosphazene containing a substituent group other than alkoxy is first prepared and then the remaining chlorine atoms are substituted by alkoxy. According to a further method which may be adopted, the material for introducing alkoxy and the material for introducing a substituent other than alkoxy are simultaneously reacted with polydichiorophosphazene. Since a preferred method depends on the reactivity of the starting materials used, there may be chosen a method best suited for the copolymer to be obtained.

In the polyphosphazene of the present invention, part of the substituent groups X and X' may be substituted by a crosslinkable group such as an allylalkoxy or allylphenoxy group so as to permit crosslinking with peroxide, sulfur, etc. Alternatively, part of the chlorine atoms of polydichlorophosphazene may be allowed to remain for crosslinking purpose. It goes without saying that these polymers are also included in the polyphosphazenes of the present invention.

The selectively permeable membrane for gas separation comprising the polyphosphazene of the present invention exhibits a high gas permeation speed and a superior selectivity. For example, in enriching oxygen from air, P02 is as large as 10-9 to 10-8. High polymers having such a large P02 are not known except polyorganosiloxanes. Besides, the PO2/PN2 value not less than 2.0, preferably not less than 3.0, is larger than 1.9 of polyorganosiloxanes. Further, the polyphosphazene as the material of the gas separating membrane of the present invention can vary in its state from rubbery to plastic, depending on the kind or proportion of substituent groups. In any of such gates the polyphosphazene is superior in solvent resistance, heat resistance and oxidation stability.Therefore, there do not arise such problems as the deterioration of the membrane performance caused by pump oil, deterioration in use under a high temperature condition and an oxidative deterioration of the membrane caused by a continual contact with a highly concentrated oxygen. This is also an outstanding feature of the present invention. Further, the polyphosphazene of the present invention is superior in film forming ability, and this fact affords a great merit in using it as a gas separating membrane.

The gas separating membrane comprising the polyphosphazene of the present invention having such superior features can be easily obtained by any of membrane forming methods known in this field, for example, by the casting method. The solubility in solvent differs according to the kind of substituent group, so by preparing a casting solution using a solvent suitable for the polyphosphazene used, then casting the solution onto a glass plate or the like, followed by drying and removal of the solvent, there can be obtained a homogeneous membrane.Examples of suitable solvents, which differ according to the kind of substituent group as mentioned above, are aromatic hydrocarbons such as benzene and toluene as well as alcohols in the case of polydiethoxyphosphazene, and ketones and ethers such as methyl ethyl ketone and tetrahydrofuran in the cases of polydifluoroethoxyphosphazene and polybisphenoxyphosphazene. The concentration of the casting solution is in the range of suitably 0.5 to 30%, preferably 1 to 20%, at which there is obtained a membrane having a thickness in the range of 0.01 to 200 #. In order to attain a large amount of gas permeation, the thinner the membrane, the better, and in this sense a membrane thickness range from 0.05 to 30 y is preferable.A thin membrane below 1,u can be obtained by adopting a method known in this industry in which method a solution using a hydrophobic solvent is developed on the water surface and then, after evaporation of the solvent, the resultant thin film is dipped up onto an organic or inorganic porous support.

The membrane of the present invention may be used directly as a homogeneous membrane, or may be used in a strengthened composite form by putting it on a polymeric porous support such as cellulose acetate, polyamide, polycarbonate, polysulfone, polyether sulfone or polyolefin, or an inorganic porous support such as glass or alumina, or a woven or non-woven cloth.

Further, the membrane of the invention can exhibit its performance in a sheet-like, tubular, hollow, or any other form. The polyphosphazene type membrane of the present invention as it is can exhibit its features, but there also may be used a membrane formed from a blend polymer obtained by mixing the polyphosphazene with other high polymer, e.g. polyolefin or polyorganosiloxane.

As set forth hereinabove, the selectively permeable membrane for gas separation comprising the polyphosphazene of the present invention is a superior membrane having large P02 and PO2/PN2 as an oxygen enriching membrane and exhibiting high strength, solvent resistance, heat resistance and oxidative stability, and is employable in various combustion systems for medical, industrial and household use. Moreover, the membrane of the present invention is employable not only for oxygen enriching from air but also for the separation of mixtures of various gases such as hydrogen, carbon monoxide, carbon dioxide, helium, argon, hydrogen sulfide, ammonia, as well as lower hydrocarbons such as methane, ethane, propane, butane, ethylene, propylene and butene.

The present invention will be described more concretely hereinunder on the basis of its working examples, but it is to be understood that the invention is not limited thereto.

Example 1 Hexachlorocyclotriphosphazene was heated at 250 C in a glass ampoule in vacuo for 20 hours. Then, a solution of the resultant polydichlorophosphazene in benzene was dropwise added to a solution of sodium trifluoroethoxide in tetrahydrofuran at room temperature, and thereafter refluxing was continued for 30 hours to obtain polydifluoroethoxyphosphazene, which was then thoroughly purified by removing by-produced sodium chloride, unreacted monomer and low molecular weight oligomer. The polydifluoroethoxyphosphazene thus purified was then measured for weight average molecular weight by the light scattering method, which was found to be about 1 500,000. This value corresponds to about 6,100 in terms of average polymerization degree (n in the formula (1)).

The polymer was then dissolved in methyl ethyl ketone to prepare a 15% solution thereof.

Then, this solution was cast over a glass plate so as to give a cast thickness of 0.4 mm by means of a doctor blade knife. After standing for a day at room temperature, there was obtained a translucent membrane having a thickness of 12cm~ This membrane having such a small thickness exhibited a high strength sufficient to resist stretching. It was set in a gas permeability measuring cell.Air was passed to the primary side of the membrane at a pressure of 2 kg/cm2G and the flow rate and composition of oxygen-enriched air permeating through the membrane was analyzed to determined P02 and PN2. The following results were obtained, which shows that the polydifluoroethoxyphosphazene membrane has a superior oxygen enriching ability: Po2 7.1 X 10 - cm2(STP)cm/cm2#scmHg PN2 2.7X10-8 PO2/PN2 2.6 Example 2 A solution of polydichlorophosphazene in benzene prepared in the same way as in Example 1 was dropwise added to a solution of sodium methoxide in methanol at room temperature over a period of 2 hours, and then refluxing was continued for 38 hours to obtain polydimethoxyphosphazene.The polymer was thoroughly purified by removing by-produced sodium chloride, unreacted monomer and low molecular weight oligomer, and then measured for weight average molecular weight by the light scattering method, which was found to be 950,000. This value corresponds to 8,900 in terms of average polymerization degree (n in the formula (1)).

The polymer was then dissolved in methanol to prepare a 1% solution thereof. This solution was applied thinly onto a 7.4cm-dia. porous plate of sintered alumina pre-impregnated with liquid paraffin, and dried. Then, the resultant membrane was immersed in n-hexane together with the support to remove the liquid paraffin.After drying for a day at room temperature, the oxygen permeability of the membrane was determined in the same manner as in Example 1, the results of which are as follows: Oxygen permeating speed 5.0 X 10-6 cm3 (STP)/cm2scmHg Nitrogen permeating speed 1.9 X 10-6 Using an approximate membrane thickness of 1 .O,u obtaned by the gravimetric method and in consideration of the porosity of 45% of the sintered alumina support, P02, PN2 and PO2/PN2 were determined, the results of which are as follows, which results show that the polydimethoxyphosphazene membrane has a superior oxygen enriching ability:: P02 1.1 X 10~9 cm3(STP)cm/cm2.s.cmHg PN2 4.2X10-10 PO2/PN2 2.6 Example 3 Polydichlorophosphazene was prepared by polymerization for 30 hours in the same way as in Example 1, and a solution thereof in benzene was dropwise added to a solution of sodium ethoxide in ethanol at room temperature over a period of 2 hours. Thereafter, refluxing was continued for 30 hours to prepare polydiethoxyphosphazene. The polymer was thoroughly purified by removing by-produced sodium chloride, unreacted monomer and low molecular weight oligomer, and then determined for weight average molecular weight by the light scattering method, which was found to be 2,800,000. This value corresponds to about 20,000 in terms of average polymerization degree (n in the formula (1)).

The polymer was then dissolved in toluene to prepare a 6% solution thereof, and this solution was cast over a glass plate so as to give a cast thickness of 1 mm by means of a doctor blade knife. After standing for a day at room temperature, the resultant film was stripped carefully from the glass plate, which film was a transparent film having a thickness of 35it. P02, PN2 and PO2/PN2 were determined in the same manner as in Example 1.The results, which are as follows, show that the polydiethoxyphosphazene membrane has a superior oxygen enriching ability: Po, 1.4 x 10-8 cm3(STP)cm/cm2 s cmHg PN2 5.8x10-9 PO2/PN2 2.4 Example 4 Polydichlorophosphazene was prepared in the same way as in Example 3, and a solution thereof in benzene was dropwise added to a tetrahydrofuran solution containing equimolar amounts of sodium 2, 2,2-trifluoroethoxide and sodium 2,2,3,3,4,4,4-heptafluorobutoxide at room temperature over a period of 3 hours. Thereafter, refluxing was continued for 20 hours to prepare a fluoroalkoxyphosphazene copolymer.After a thorough purification by the removal of by-produced sodium chloride, unreacted monomer and low molecular weight oligomer, the copolymer was determined for weight average molecular weight by the light scattering method, which was found to be 5,100,000. This value corresponds to about 15,000 in terms of average polymerization degree (n in the formula (1)).

The copolymer was then dissolved in a mixed (9:1) solvent of trichlorofluoroethane and acetone to prepare a 2% solution thereof. Then, using this solution, a film was formed on a porous plate of sintered alumina in the same manner as in Example 2 and determined for oxygen permeability. The results, which are as follows, show that the fluoroalkoxyphosphazene copolymer membrane has a superior oxygen enriching ability: Po2 1.7 X 10-8 cm3(STP)cm/cm2scmHg PN2 7.4X10-8 PO2/PN2 2.3 Example 5 A 1% solution in toluene of the polydiethoxyphosphazene prepared in Example 3 was dropped one droplet onto the surface of water filled in a glass vessel and held at 1 0 C. The droplet immediately spread to form a liquid film on the water surface.Benzene was evaporated while keeping the liquid surface as stationary as possible, and the resultant thin film was dipped up while pushing thereonto a porous polypropylene film (trade name: Juraguard 2500, a product of Polyplastics Co.).

After standing for a day to drain off water, the membrane was set in the cell described in Example 1, and a gaseous mixture of carbonic acid gas and nitrogen was passed to the primary side of the membrane at a pressure of 2 kg/cm2G to determined PCO2/PN2, which was found to be 18.5. Likewise, the separating performance for a gaseous mixture of helium and nitrogen was checked; as a result, the PHe/PN2 was 10.6. Next, by way of comparison, a 30# thick membrane of silicon rubber (polydimethylsiloxane) crosslinked with bis-2,4-dichlorobenzoyl peroxide was formed and checked for PCO2/PN2 and PHe/PN2, which were found to be 6.5 and 1.2, respectively.This result shows that the polydiethoxyphosphazene membrane has a far superior gas separating ability as compared with the silicone rubber membrane.

Example 6 Hexachlorocyclotriphosphazene was heatpolymerized at 250 C in a glass ampoule in vacuo for 24 hours, and a solution of the resultant polydichlorophosphazene in benzene was dropwise added to a solution of dimethylamine in benzene over a period of 4 hours while maintaining the temperature at a level not higher than 5 C. Further, reaction was continued at 25 C for 24 hours to prepare polybisdimethylaminophosphazene. The polymer was purified by removing unreacted amine, dimethylamine hydrochloride and low molecular weight oligomer, and then determined for average molecular weight by the light scattering method, which was found to be 780,000, corresponding to 5,800 in terms of average polymerization degree (n in the formula (1)).

Then, a 2% solution of the polymer in trifluoroethanol was prepared and applied onto a porous polypropylene film (Juraguard 2500, a product of Polyplastics Co., thickness: 25#, porosity: 45%), followed by drying for a day at room temperature. The resultant composite membrane was set in a gas permeability measuring cell, and air was passed to the primary side of the membrane at a pressure of 3 kg/cm2G, under which condition the flow rate and composition of oxygen-enriched air at atmospheric pressure permeating through the membrane were measured, the results of which are as follows: Oxygen permeation speed 3.1 X 10-6 cm3(STP)/cm2#s#cmHg Nitrogen ,, O.82X10-6 PO2/PN2 3.8 The above results show that the dimethylaminophosphazene membrane has a good oxygen enriching ability.

Example 7 A solution in benzene of polydichlorophosphazene prepared in the same way as in Example 6 was dropwise added to a solution of aniline in tetrahydrofuran at room temperature over a period of 4 hours, and then reaction was continued for 4 hours at the reflux temperature to prepare phenyiaminophosphazene. The polymer was purified by removing unreacted aniline, aniline hydrochloride and low molecular weight oligomer and then determined for average molecular weight by the light scattering method, which was found to be 1,720,000, corresponding to 7,500 in terms of average polymerization degree (n in the formula (1)). Then, a 2% solution of the polymer in benzene was prepared and applied onto Juraguard 2500 in the same manner as in Example 6.The resultant composite membrane was measured for oxygen and nitrogen permeation speed, the results of which are as follows: Oxygen permeation speed 6.3 x 1O-6 cm2(STP)/cm2scmHg Nitrogen ,, 1.5X10-6 PO2/PN2 4.2 The above results show that the polybisphenylaminophosphazene membrane has a superior oxygen enriching ability.

Example 8 A solution in tetrahydrofuran of polydichlorophosphazene prepared in the same way as in Example 6 was dropwise added to a solution of diethylamine in tetrahydrofuran at room temperature over a period of 2 hours. Further, reaction was continued for 2 days at room temperature. The resultant polymer was purified thoroughly and determined for composition by elementary analysis. As a result, the polymer proved to have a structure in which 50% of the chlorine atoms of the starting polydichlorophosphazene had been substituted by diethylamino group and the residual 50% chlorine remained unsubstituted.Then, a solution of the polymer in tetrahydrofuran was dropwise added to a solution of n-butylamine in tetrahydrofuran at room temperature over a period of 2 hours, and thereafter reaction was continued for 2 days at room temperature to obtain an n-butylaminodiethylaminophosphazene copolymer with diethylamino and n-butylamino groups introduced in equal amounts. The polymer after purification by removal of unreacted amine, n-butylamine hydrochloride and low molecular weight oligomer proved to have an average molecular weight of 170,000 and an average polymerization degree of 890.

Then, a 2% solution of the polymer in benzene was prepared and dropped one droplet with a micropipet onto the surface of a clean water held at 5 C in a vessel to allow a thin film to be formed on the water surface. Then, the thin film was dipped up carefully while pushing Juraguard 2500 film thereagainst. The resultant composite membrane was measured for oxygen and nitrogen permeation speed in the same manner as in Example 6, the results of which are as follows: Oxygen permeation speed 4.7 X 10-4 cm2(STP)/cm2.s.cmHg Nitrogen ,, 1.2X10-4 P02/PN2 3.9 The above results show that the n-butylaminodiethylaminophosphazene copolymer membrane has a superior oxygen enriching ability.

Example 9 Into a solution in toluene of polydichlorophosphazene prepared in the same way as in Example 6 was added triethylamine as a reaction accelerator. To this solution was further aded a solution of 2-amino-4-picoline dropwise at room temperature over a period of 4 hours, and then reaction was continued for 5 days at the reflux temperature to prepare a 2-amino-4-picolinesubstituted polyphosphazene. The polymer was purified by removing unreacted amine, triethylamine, hydrochlorides of these amines and oligomer, and a 10% solution of the purified polymer in dioxane was prepared and then cast onto a glass plate so as to give a cast thickness of 0.3 mm by means of a doctor blade knife, followed by air-drying for a day at room temperature, to obtain a strong, transparent, homogeneous film having a thickness of 20eel. The flow rate and composition of oxygen-enriched air permeating through this film were analyzed in the same manner as in Example 6 to determine P02 and PN2, the results of which are as follows:: P02 1.3 X 10-9 cmNSTP)cm/cm2'scmHg PN2 3.2 x 10-10 ,, PO2/PN2 4.1 The above results show that the polyaminophosphazene membrane has a superior oxygen enriching ability.

Example 10 The membrane prepared in Example 8 was set in the cell described in Example 6 and a gaseous mixture of carbonic acid gas and nitrogen was passed to the primary side of the membrane at a pressure of 2 kg/cm2G and PCO2/PN2 was determined, which was found to be 24.3. Likewise, the separating performance for a gaseous mixture of helium and nitrogen was checked; as a result, there was obtained the value of 13.7 in terms of PHe/PN2. Next, by way of comparison, a 30y thick membrane of silicone rubber (polydimethylsiloxane) crosslinked with bis-2,4-dichlorobenzoyl peroxide was formed and determined for PCO2/PN2 and PHe/PN2 which were found to be 6.5 and 1.2, respectively.The results thus obtained show that the polydiethoxyphosphazene membrane has a superior gas separating ability as compared with the silicone rubber.

Example 11 Hexachlorocyclotriphosphazene was heated at 250 C in a glass ampoule in vacuo for 24 hours, and a solution of the resultant polydichlorophosphazene in toluene was dropwise added to a solution of sodium 4-ethylphenoxide in diglym at 90 C over a period of 1 hour. Then, the temperature was raised to 11 5 C and reaction was continued for 30 hours to prepare polybis(4ethylphenoxy)phosphazene.The polymer was purified by removing by-produced sodium chloride, unreacted phenoxide and low molecular weight oligomer and then determined for molecular weight by the gel permeation chromatography (using polystyrene calibration curve), which was found to be 1,200,000, corresponding to about 4,200 in terms of average polymerization degree (n in the formula (1)).

Next, the polymer was dissolved in tetrahydrofuran to prepare a 15% soplution thereof, which was then cast over a glass plate so as to give a cast thickness of 0.3 mm by means of a doctor blade knife. After drying for a day at room temperature, the resultant film was stripped from the glass plate carefully.It was transparent and strong and had a thickness of 25cm. This film was set in a gas permeability measuring cell, and air was passed to the primary side of the membrane at a pressure of 2 kg/cm2G, under which condition the flow rate and composition of oxygenenriched air permeating through the membrane were analyzed to determine P02 and PN2, the results of which are as follows: P02 2.0 x 10-9 cm3(STP)cm/cm2.s.cmHg PN2 5.9 x " PO2/PN2 3.4 The above results show that the polybis(4-ethylphenoxy)phosphazene membrane has a superior oxygen enriching ability.

Example 12 Polybisphenoxyphosphazene was prepared in the same way as in Example 11 except that sodium phenoxide was used in place of sodium 4-ethyl phenoxide. The molecular weight and the average polymerization degree (n) were 9ûO,OOO and 3,900, respectively. The polymer was dissolved in tetrahydrofuran to prepare an 18% solution thereof, which was then applied onto a porous polypropylene film (Juraguard 25û0, a product of Polyplastics Co., thickness: 25,u, porosity: 45%) and allowed to stand overnight for drying. The thickness of the resultant composite film was calculated to be 22# on the basis of the weight, area and specific gravity of the applied polymer.Then P02 and PN2 were determined in the same manner as in Example 11, the results of which are as follows: P02 7.1 X 10~9 cm3(STP)cm/cm2.s.cmHg PN2 2.0x10-9 3.5 The above results show that the polybisphenoxyphosphazene membrane has a superior oxygen enriching ability.

Example 13 Polybis(4-chlorophenoxy)phosphazene was prepared in the same way as in Example 11 except that the polymerization time of hexachlorotriphosphazene was changed to 48 hours and sodium 4-chlorophenoxide kvass used in place of sodium 4-ethylphenoxide. The molecular weight and the average polymerization degree were 3,500,000 and 1 2,~00, respectively.The polymer was dissolved in tetrahydrofuran to prepare a 5% solution thereof, which was then applied onto a glass plate in the same manner as in Example 11 to obtain a strong membrane having a thickness of 1 0y. Using this membrane, P02 and PN2 were determined in the same manner as in Example 11, the results of which are as follows: P02 5.3 > < 10-9 cm3(STP)cm/cm2scmHg FN2 1.4x10-9 PO2/PN2 3.8 The above results show that the polybis(4-chlornphenoxy)phosphazene membrane has a superior oxygen enriching ability.

Example 14 Hexachlorocyclotriphosphazene was heated at 250 C in a glass ampoule in vacuo for 30 hours to prepare polydichiorophosphazene. Then, a solution of this polymer in toluene was dropwise added to a diglym solution containing equimolar amounts of sodium phenoxide and sodium 4-sec-butyl phenoxide, at 30 C over a period of 2 hours. Then, the temperature was raised to 115"6 and reaction was continued for 30 hours to prepare a polyaryloxyphosphazene copolymer containing phenoxy and 4-sec-butylphenoxy groups in the ratio of 1:1. The average molecular weight and the average polymerization degree (n) were 1,800,000 and 6,200, respectively.

The copolymer was dissolved in tetrahydrofuran to prepare a 10% solution thereof, which was then applied onto Juraguard 2500 film in the same way as in Example 12, followed by drying for a day at room temperature, to obtain a composite film. The film thickness calculated on the basis of the weight of the polymer supported on the support film was 24#. The P02 and PN2 of this composite membrane were determined in the same manner as in Example 11, the results of which are as follows: P02 2.5 X 10~9 cm3(STP)cm/cm2.s.cmHg PN2 6.7X10-' P02/PN2 3.7 The above results show that the polyaryloxyphosphazene copolymer membrane has a superior oxygen enriching ability.

Example 15 A composite membrane comprising the polyaryloxyphosphazene copolymer prepared containing 4-methoxyphenoxy and 4-tert-butylphenoxy groups in the ratio of 1:1 and supported on Juraguard 2500 was set in the cell described in Example 11, and a gaseous mixture of carbonic acid gas and nitrogen was passed to the primary side of the membrane at a pressure of 2 kg/cm2G, under which condition PCO2/PN2 was determined and found to be 20.1. Likewise, the separating performance for a gaseous mixture of helium and nitrogen was checked; as a result, PHe/PN2 was 12.3. By way of comparison, a 30y thick membrane of silicone rubber (polydimethylsiloxane) crosslinked with bis-2,4-dichlorobenzoyl peroxide was prepared and determined for PCO2/PN2 and PHe/PN2, which were 6.5 and 1.2, respectively. The results thus obtained show that the above composite membrane has a far superior gas separating ability as compared with the silicone rubber membrane.

Example 16 Hexachlorocylotriphosphazene was heated at 250 C in a glass ampoule in vacuo for 20 hours to prepare polydichlorophosphazene. Then, a solution of the polymer in toluene was dropwise added at 95 C to a diglym solution of bisphenol A monosodium salt which had been prepared from bisphenol A and sodium in amounts corresponding respectively to 4 and 3 mols based on dichlorophosphazene units. Thereafter, the temperature was raised to 11 5 C and reaction was continued for 30 hours to prepare polyphosphazene of the following structure,

The average polymerization degree (n) was 9,700.

Then, the polymer was reacted slowly with an excess amount of trimethylchlorosilane in tetrahydrofuran containing triethylamine to trimethylsilylate the hydroxyl groups of the polyphosphazene. The polymer after purification was subjected to determination of silicon to determine the trimethylsilyl content thereof, which was found to be 19 wt.%.

The polymer was then dissolved in tetrahydrofuran to prepare an 8% solution thereof, which solution was cast over a glass plate to a thickness of 0.2 mm, followed by air-drying for a day, to obtain a 7s thick film. This film was set in a gas permeability measuring cell, and air was passed to the primary side of the membrane at a pressure of 2 kg/cm2G, under which condition the flow rate and composition of oxygen-enriched air permeating through the membrane were analyzed to determine P02 and PN2, the results of which are as follows:: Po, 2.3 x 10-8 cm2(STP)cm/cm2scmHg PN2 9.1x10-g P02!PN2 2.5 The above results show that the polymer prepared above can be easily thinned as compared with polydimethylsiloxane and that the membrane formed therefrom is a superior oxygen enriching membrane having a larger PO2/PN2 value than that of 1.9 of polydimethylsiloxane.

Example 17 A t-butyldimethylsilylated polyphosphazene was prepared in the same was as in Example 16 except that the polymer

prepared in Example 16 was used as the starting polymer and t-butyldimethylchlorosilane was used as a silane coupling agent. The t-butyldimethylsilyl content of the polymer was 29%. The polymer was dissolved in tetrahydrofuran to prepare a 10% solution thereof, which solution was then cast over a glass plate to form a 1 5,u thick film.The film was determined for P02 and PN2 in the same manner as in Example 16, which were found to be as follows: P02 1.6 x 1O-8 cm3(STP)cm/cm2.s.cmHg PN2 5.7X1O-9 PO2 / PN2 2.8 Example 18 A solution in benzene of polydichlorophosphazene prepared in the same way as in Example 16 was dropwise added at room temperature to a solution in tetrahydrofuran of sodium trifluoroethoxide in an amount equimolar to dichlorophosphazene units, then reaction was continued for 30 hours at the reflux temperature to prepare a partially trifluoroethoxy-substituted polyphosphazene.Then, a solution of the polymer in tetrahydrofuran was dropwise added to a tetrahydrofuran solution containing monosodium alkoxide of 1,4-butanediol and unreacted 1,4butanediol in excess amounts relative to the remaining chlorine of the polymer, and heatrefluxed to prepare a polyphosphazene of the structure [ NP(OCH2CF3) (O-C4H8-OH) ] n. The average polymerization degree of this polymer was 5,300. The polymer thus prepared was reacted slowly with an excess amount of 3,3,3-trifluoropropyldimethylchlorosilane in tetrahydrofuran containing triethylamine to obtain a trifluoropropyldimethylsilylated polymer having a trifluoropropyldimethylsilyl content of 38%.

Then, the polymer was dissolved in tetrahydrofuran to prepare a 2% solution thereof, which solution was applied onto a porous polypropylene film (Juraguard 2500, a product of Polyplastics Co.) and air-dried for a day to obtain a composite film. On the basis of results obtained by measurement in the same manner as in Example 16 and in consideration of the film thickness (2,u) calculated from the weight of the polymer supported on Juraguard and the porosity of Juraguard. P02 and PN were determined as follows:: P02 1.3 X 10-8 cm3(STP)cm/cm2scmHg PN2 5.2X10-9 PO2/PN2 2.5 Example 19 Polydichlorophosphazene prepared in the same way as in Example 1 6 and diethylamine were reacted in tetrahydrofuran to prepare polydiethylaminochlorophosphazene. Then, a tetrahydrofuran solution of this polymer was dropwise added to a tetrahydrofuran solution of ammonia, and after subsequent removal of unreacted ammonia, reaction was allowed to proceed at oec for 4 hours to prepare polyaminodiethylaminophosphazene. Then, the amino groups of this polymer were trimethylsilylated with trimethylchlorosilane in tetrahydrofuran containing triethylamine.

The average polymerization degree and trimethylsilyl content of the resultant polymer were 670 and 35%, respectively.

The polymer was dissolved in tetrahydrofuran to prepare a 10% solution thereof, which solution was then applied onto a glass plate to a thickness of 0.1 mm and then air-dried for a day to obtain an 81u thick film. The P02 and PN2 of the membrane were determined in the same manner as in Example 16, the results of which are as follows: P02 1.1 X 10-8 cm3(STP)cm/cm2scmHg PN2 3.7X10-9 Po2 / PN2 3.0 Example 20 A solution in toluene of polydichlorophosphazene prepared in the same way as in Example 16 was dropwise added at 95 C to a diglym solution containing equimolar amounts of sodium phenoxide and sodium orthoallylphenoxide.Thereafter, the temperature was raised to 95 C and reaction was allowed to proceed for 24 hours to prepare a polyphosphazene of the structure

The average polymerization degree of the polymer was 9,200. Then, this polymer and pentamethyldisiloxane were reacted in toluene using chloropiatinic acid as catalyst to prepare a polymer with siloxane group added to allyl group. The siloxane units content of the polymer was 34 wt.%.

The polymer thus obtained was dissolved in tetrahydrofuran to prepare a 10% solution thereof. Using this solution, an extremely thin film was formed on the water surface in the same way as in Example 19 and then it was dipped up onto Juraguard. Oxygen and nitrogen permeation speeds of the resultant thin membrane were as follows: Oxygen permeation speed 7.8 X 1 0-4 cm3(STP)/cm2scmHg Nitrogen ,, 3.0X10-4 PO2 / PN2 2.6 The above results show that the polyphosphazene prepared above can easily afford an ultra-thin membrane which exhibits superior performances such as a high oxygen permeation speed and a large PO2/PN2 ratio.

Example 21 Polydichlorophosphazene prepared in the same way as in Example 16 was reacted with an alkoxide which had been prepared by the reaction of sodium and a silanolternainated polydimethylsiloxane (molecular weight: 3,200) with one hydroxyl group blocked with trimethyl clllorosilane, in tetrahydrofuran under reflux for 30 hours to introduce polydimethylsiloxane group into the polymer. Then, unreaczed chlorine remaining in the polymer was substituted by trifluoroethoxy group through its reaction with sodium trifluoroethoxide. The average polymerization degree and the polydimethysiloxane units content of the polymer were 11,000 and 73%, respectively.

Then, the polymer was dissolved in 1 2-dichloroethane to prepare a 10% solution thereof, which solution was cast over a glass plate to a thickness of 0.2 mm and then air-dried for a day to form a 20IL thick film. The P02 and PN2 of this membrane were determined in the same manner as in Example 16, the results of which are as follows: Po, 2.9 X 10-8 cm3(STP)cm/cm2scmHg PN2 1.2X10-8 P02/PN2 2.4 Example 22 Polyphosphazene containing polydiphenylsiloxane and trifluoroethoxy groups was prepared in the same way as in Example 21 except that there was used a silanol-terminated polydiphenylsiloxane. The polysiloxane units content of the polymer was 59%.From a 10% solution of this polymer there was formed a film on a glass plate, which film was 1 5it in thickness and exhibited the following P02 and PN2 values: P02 1.1 X 10-8 cm3(STP)cm/cm2.s.cmHg PN2 4.2 x 10-9 PO2/PN2 2.6 Example 23 Polydichlorophosphazene prepared in the same way as in Example 16 was reacted with monoalkoxide prepared from sodium and one hydroxyl group of a carbinol-terminated polydimethylsiloxane (molecular weight: 2,400), in tetrahyfrofuran under heat-reflux for 30 hours to introduce polydimethylsiloxane group with carbinol group remaining on the opposite side. Then, unreacted chlorine remaining in the polymer was substituted by trifluoroethoxy group through its reaction with sodium trifluoroethoxide.The average molecular weight and the polydimethylsiloxane units content of the polymer were 10,300 and 48%, respectively. The polymer was dissolved in tetrahydrofuran to prepare a 10% solution thereof, and using this solution, a 1 OIL thick film was formed on a glass plate.The P02 and PN2 of this membrane were determined in the same manner as in Example 16, the results of which are as follows: P02 2.0 x 10-8 cm3(STP)cm/cm2.s.cmHg PN2 8.1 X 10-9 P02/PN2 2.5 Example 24 The trimethylsilylated polyphosphazene membrane obtained in Example 16 was set in the cell described in Example 16, and a gaseous mixture of carbonic acid gas and nitrogen was passed to the primary side of the membrane at a pressure of 2 kg/cm2G, under which condition the PCO2/PN2 ratio was determined, which was 15.1. Likewise, the separating performance for a gaseous mixture of helium and nitrogen was checked; as a result, the PHe/PN2 ratio was found to be 7.4.By way of comparison, a 30y membrane of silicone rubber (polydimethylsiloxane) crosslinked with bis-2,4-dichlorobenzoyl peroxide was formed and determined for PCO2/PN2 and PHr/PN2, which were found to be 6.5 and 1.2, respectively. The results thus obtained show that the polydiethoxyphosphazene membrane has a far superior gas separating ability as compared with the silicone rubber membrane.

Example 25 The polyphosphazene membrane obtained in Example 23 with polydimethylsiloxane units introduced in the side chain was determined for PCO2/PN2 and PHe/PN2 in the same way as in Example 24, which ratios were found to be 10.3 and 4.9, respectively. These values are extremely larger than those obtained in the use of polydimethylsiloxane, showing that the above membrane has a good gas separating ability.

Example 26 Hexachlorocyclotriphosphazene was heated at 250 C in a glass ampoule in vacuo for 20 hours. Then, a solution of the resultant polydichlorophosphazene in tetrahydrofuran was dropwise added at room temperature to a tetrahydrofuran solution containing excess diethylamine, and thereafter reaction was allowed to proceed at room temperature for 3 days to prepare a diethylamino-substituted polymer. As a result of elementary analysis, this polymer proved to have a structure in which a half quantity of chlorine in the polydichlorophosphazene had been substituted by diethylamino group. Then, a solution of this intermediate polymer in tetrahydrofuran was dropwise added at room temperature to a tetrahydrofuran solution containing an excess amount of sodium trifluoroethoxide, and then refluxing was performed for 20 hours to complete the reaction.As a result of elementary analysis, the polymer after purification proved to be of a structure having such substituent group proportions as 30% trifluoroethoxy, 50% diethylamino and 20% chlorine. The average polymerization degree of the polymer was 1 200.

Then, the polymer thus prepared was dissolved in tetrahydrofuran to prepare a 2% solution thereof, which solution was applied onto a porous polypropylene film (trade name: Juraguard 2500, a product of Polyplastics Co.) and then dried for a day to obtain a composite membrane.

This membrane was set in a gas permeability measuring cell, and air was passed to the primary side of the membrane at a pressure of 2 kg/cm2G, under which condition the flow rate and composition of oxygen-enriched air permeating through the membrane were analyzed and the following results were obtained: Oxygen permeation speed 5.3 X 10-8 cm3(STP)/cm2.s.cmHg Nitrogen ,, 1.5X10-8 PO2/PN2 3.5 Example 27 Into a benzene solution of polydichlorophosphazene prepared in the same way as in Example 26 was slowly added at room temperature a tetrahydrofuran solution containing 60 mol% based on dichlorophosphazene units of an alkoxide which had been prepared from 4-hydroxybiphenyl and sodium, and then refluxing was coritinued for 4 hours.To the reaction mixture was dropwise added a tetrahydrofuran solution containing an excess amount of sodium ethoxide, and then refluxing was continued for 35 hours to complete the reaction. As a result of elementary analysis, the polymer after purification proved to be of a structure having such substituent group proportions as 70% ethoxy and 30% 4-phenylphenoxy. The average polymerization degree of the polymer was 4,800.

Then, using a 2% solution of the polymer in tetrahydrofuran, a film was formed on Juraguard in the same manner as in Example 26, and oxygen and nitrogen permeation speeds were measured, the results of which are as follows: Oxygen permeation speed 6.2 x 1 0 ~ 5 cm2(STP)/cm2scmHg Nitrogen 1.8 1.6X10-5 PO2/PN2 3.8 Example 28 Polyphosphazene containing phenoxy and butoxy groups each 50% as substituent groups was prepared in the same way as in Example 27. The average polymerization degree of the polymer was 5,200.A membrane formed on Juraguard from a 2% solution of this polymer exhibited the following performances: Oxygen permeation speed 8.1 X 10-5 cm3(STP)/cm2#s#cmHg Nitrogen 2.2 2.2x10-5 PO2/PN2 3.6 Example 29 Polydichlorophosphazene was prepared in the same way as in Example 1 except that the polymerization time was changed to 40 hours. Then, it was dissolved in a tetrahydrofuran solution containing excess trifluoroethanol and 2(2-phenoxyethoxy)ethanol in equimolar amounts, then triethylamine was added as a reaction accelerator and reaction was allowed to take place at 1 20 C for 40 hours. As a result of analysis, the polymer proved to have a structure with 48% trifluoroethoxy and 52% 2(2-phenoxyethoxy)ethoxy introduced as substituent groups. The average polymerization degree of the polymer was 11,000.

Then, the polymer was dissolved in tetrahydrofuran to prepare a 2% solution thereof, which solution was dropped one droplet onto the surface of a clean water held in a vessel to form a thin film. The film was then dipped up carefully onto Juraguard and dried. Oxygen and nitrogen permeation speeds were measured in the same manner as in Example 26, the results of which are follows: Oxygen permeation speed 2.1 X 10-4 cm3(STP)/cm2scmHg Nitrogen ,, 6.2X10-5 PO2/PN2 3.4 Example 30 Polydichlorophosphazene prepared in the same way as in Example 29 was reacted in chloroform with phenylacetylene and trifluoroethanol in equimolar amounts in excess of the dichlorophosphazene units in the presence of triethylamine as a reaction accelerator.As a result of elementary analysis, the resultant polymer proved to be of a structure having such substituent group proportions as 39% 2-chloro-2-phenylethenyl and 61% trifluoroethoxy.

A 20,u thick membrane was formed from this polymer and determined for oxygen and nitrogen permeation speed, from which P02 and PN2 were found to be as follows: Po2 7.8 X 10~9 cm2(STP)cm/cm2scmHg PN2 2.0x10-9 PO2/PN2 3.9 Example 31 Monoethylpentachlorocyclotriphosphazene was polymerized at 250 C in vacuo for 24 hours.

Then, a solution of the resultant polymer in tetrahydrofuran was dropwise added at room temperature to a tetrahydrofuran solution containing sodium 2,2,3,3-tetrafluoropropoxide and sodium trifluoroethoxide in excess and equimolar amounts, and thereafter refluxing was continued for 24 hours to complete the reaction. The resultant polymer proved to have an average polymerization degree of 2,200 and have a structure with such substituent group proportions as 17% methyl, 40% fluoropropoxy and 43% fluoroethoxy.

Then, using a 3% solution of the polymer in tetrahydrofuran, a thin film was formed on Juraguard in the same manner as in Example 26 and determined for oxygen and nitrogen permeation speed, the results of which are as follows: Oxygen permeation speed 1.2 X 10-4 cm3(STP)/cm2.s.cmHg Nitrogen ,, 3.9 x 10-5 " PO2/PN2 3.1 Example 32 Polydifluorophosphazene prepared according to the Alcock et al's process (see Inorg. Che., 11, 11 20 ('72)) and phenyllithium were reacted in tetrahydrofuran at room temperature. Then, a solution of sodium hexyloxide in tetrahydrofuran was dropwise added to the reaction mixture at room temperature, and thereafter refluxing was continued for 60 hours.Lastly, sodium methoxide was added to the reaction mixture and refluxing was further continued for 24 hours to complete the reaction. As a result of analysis, the resulant polymer proved to have an average polymerization degree of 2,600 and have a structure with such substituent group proportions as 50% phenyl, 16% hexyloxy, 30% methoxy and 4% chlorine.

Then, from a 3% solution of the polymer in tetrahydrofuran there was formed a thin film on Juraguard in the same manner as in Example 26, and oxygen and nitrogen permeation speeds were measured, the results of which are as follows: Oxygen permeation speed 7.8 X 10-5 cm3(STP)/cm2scmHg Nitrogen ,, 2.1 X 10-8 PO2/ PN2 3.7 Example 33 The membrane obtained in Example 32 was used for the separation of a gaseous mixture of carbonic acid gas and nitrogen, and the value of 19.3 was obtained as PCO2/PN2. Likewise, the separation of a gaseous mixture of helium and nitrogen was performed and the value of 12.2 was obtained as PHs/PN2.

Claims (26)

1. A selectively permeable membrane for gas separation, comprising a polyphosphazene having a repeating unit represented by the general formula

wherein X and X' are each independently a group selected from an alkoxy group, an amino group, an aryloxy group, an etheroxy group, an alkyl group, an alkenyl group, an aryl group, a group having an organosilane unit and a group having an organosiloxane unit.

2. A selectively permeable membrane as claimed in claim 1, wherein the number average polymerization degree of said polyphosphazene is in the range of 20 to 70,000.

3. A selectively permeable membrane as claimed in claim 1 or claim 2 wherein X and X' are each an alkoxy group.

4. A selectively permeable membrane as claimed in claim 1 or claim 2 wherein X and X' are each an amino group.

5. A selectively permeable membrane as claimed in claim 1 or claim 2 wherein X and X' are each an aryloxy group.

6. A selectively permeable membrane as claimed in claim 1 or claim 2 wherein some of X and X' are groups having an organosilane unit and the remainder are groups selected from alkoxy groups, amino groups, aryloxy groups, groups having an organosilane unit and groups having an organosiloxane unit.

7. A selectively permeable membrane as claimed in claim 1 or claim 2 wherein some of X and X' are groups having an organosiloxane unit and the remainder are groups selected from alkoxy groups, amino groups, aryloxy groups, groups having an organosilane unit and groups having an organosiloxane unit.

8. A selectively permeable membrane as claimed in claim 1 or claim 2 wherein the alkoxy group accounts for 10 to 90% of all substituent groups.

9. A selectively permeable membrane as claimed in claim 8, wherein the alkoxy group accounts for 10 to 90% of all substituent groups and one or more groups selected from an amino group, an aryloxy group, an etheroxy group, an alkyl group, an alkenyl group and an aryly group for 90 to 10%.

10. A selectively permeable membrane as claimed in claim 1, 2, 3, 6, 7, 8 or 9, wherein the alkoxy group is a group having the general formula -OR in which R is an alkyl group of C to C20.

11. A selectively permeable membrane as claimed in claims 1, 2, 3, 6, 7, 8 or 9, wherein the alkoxy group is a fluoroalkoxy group having the general formula -OCH2(CF2)mZ in which m is an integer of 1 to 10 and Z is hydrogen or fluorine.

12. A selectively permeable membrane as claimed in claim 10, wherein the alkoxy group is methoxy, ethoxy, propoxy, butoxy, sec-butoxy or neopentyloxy.

13. A selectively permeable membrane as claimed in claim 11, wherein the fluoroalkoxy group is -OCH2CF3, -OCH2CFs, -OCH2C2F7 or -OCH2(CF2)3CF2H.

14. A selectively permeable membrane as claimed in claim 1, 2, 4, 6, 7 or 9, wherein the amino group is a group having the structure -NR,R2 wherein R, and R2 are each hydrogen or an alkyl group of C, to C4.

15. A selectively permeable membrane as claimed in claim 14, wherein the amino group is -NHCH3, -NHC2H5, -N(C2H5)2, -NHC3H7, -NHC4H9, or

16. A selectively permeable membrane as claimed in claim 1, 2, 5, 6, 7 or 8, wherein the aryloxy group is a phenoxy group or a phenoxy group substituted with an alkyl group of C1 to C20.

17. A selectively permeable membrane as claimed in claim 16, wherein the alkyl-substituted phenoxy group is t-butyl phenoxy group.

18. A selectively permeable membrane as claimed in claim 6, wherein the organosilane unit accounts for 10 to 90 weight percent of the polymer.

1 9. A selectively permeable membrane as claimed in claim 7, wherein the organosilane unit accounts for 10 to 90 weight percent of the polymer.

20. A selectively permeable membrane as claimed in claim 6 or 7, wherein the total of the organosilane unit and organosiloxane unit accounts for 10 to 90 weight percent of the polymer.

21. A selectively permeable membrane as claimed in claim 1, 2, 6, 7, 18, 19 or 20, wherein the group having an organosilane unit is a group having the general formula -A-SiR,R2R3 in which A is an atom or group which connects the organosilane unit with the phosphorus atom in the polyphosphazene main chain, and R,, R2 and R2 are each hydrogen or an alkyl group of C1 to C4.

22. A selectively permeable membrane as claimed in claim 21, wherein A is -o-(-CH2-)m-, NH#(#CH2#)rn#,

in which m is an integer of 1 to 4.

23. A selectively permeable membrane as claimed in claim 18, 20 or 21, wherein the organosilane unit having the general formula -SiR1R2R2 is -Si(CH3)2.

24. A selectively permeable membrane of claim 1, 2, 6, 7, 18, 19 or 20, wherein the group having an organosilane unit is a group having the general formula

in which B is an atom or group which connects the organosiloxane unit with the phosphrous atom in the polyphosphazene main chain, R4, R5, R8 and R7 are each hydrogen or an alkyl group of C1 to C4 or a hydroxyl group, and p is an integer of 1 to 1,000.

25. A selectively permeable membrane as claimed in claim 24, wherein B is -O-(-CH2-)m-, ~NH~(~CH2~)m~t

in which m is an integer of 1 to 4.

26. A selectively permeable membrane as claimed in claim 24, wherein the organosiloxane unit having the general formula

or