CA1226389A

CA1226389A - Miscibile polymer blends containing poly(2-alkyl-2- oxazoline)

Info

Publication number: CA1226389A
Application number: CA000467740A
Authority: CA
Inventors: Kathleen M. Mccreedy; Henno Keskkula; James C. Pawloski; Edward H. Yonkers
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1983-11-15
Filing date: 1984-11-14
Publication date: 1987-09-01
Also published as: DE3469549D1; JPS60130646A; EP0152551A1; AU3537384A; US4547530A; EP0152551B1

Abstract

Abstract of the Invention Miscible blends of poly-2-oxazolines and thermoplastic polymers are disclosed herein. These blends exhibit a single glass transition point indicative of a miscible blend. The blends of this invention are useful as membranes, particularly separation membranes for mixtures of organic com-pounds or organic compounds and water and a per-evaporation process.

Description

:~L22~3~

MISCIBILE POLYMER BLENDS
CONTAINING POLY(2-OXAZOLINE) This invention relates to blends and alloys of polymers of 2-oxazolines, and to articles, partic-ularly membranes, prepared therefrom.

There are two well known, general types of S oxazoline polymers. One type is the result of the addition polymerization of an oxazoline substituted in the 2-position with an unsaturated moiety. The other is the result of a ring-opening polymerization.
This invention deals with the ring-opening polymers.

Polymers of 2-oxazolines are generally hydro-philic water-soluble materials. Such oxazoline polymers have proven utilities as adhesion promoters and viscosity modifiers in similar applications. Unfortunately, however, such oxazoline polymers when formed into solid articles such as films exhibit very poor mechanical properties and show sensitivity to atmospheric moisture.
tried films of oxazoline polymers are too brittle to be useful in most applications. Water causes dissolution of such articles and films.

32,280-F -1-63~

Despite these mechanical problems which limit the utility of oxazoline polymers, saicl polymers have many desirable properties such as hydrophilicity which would be advantageous in many solid articles such as films. It would therefore be desirable -to prepare solid articles containing oxazoline polymers which exhibit good mechanical and physical properties.

Oxazoline polymers have previously been employed in small amounts as additives in water--insoluble polymer compositions. In addition, polymers of oxazoline have been blended with polyolefins to form immiscible blends. However, it is not heretoore been attempted to prepare blends or alloys of oxazoline polymers and other polymers comiscible therewith.

In one aspect, the present invention ls a blend or alloy of a first polymer which is a polymer of a 2-oxazoline and at least one other polymer which is not a polymer of a 2-oxazoline, wherein said other polymer it miscible with said oxazoline polymer in the relative proportions thereof present in said blend or alloy, and wherein the weight ratio said oxazoline polymer to said other polymer present in said blend or alloy is from 19:1 to 1:19, preferably from 9:1 to 1:9.

In another aspect, this invention is a semi-permeable membrane comprising a blend or alloy of afirst polymer which is a polymer of a 2-oxazoline, at least one other polymer which is not a polymer of a

2-oxazoline and which other polymer is miscible with said oxazoline polymer in relative proportions thereof present in said blend or alloy and wherein the weight ratio of said oxazoline polymer to said other polymer 3Z,280-F -2~

63~

-3 present in said blend or alloy is from 19:1 to 1:19, preferably from 9:1 to 1:9.

Surprisingly, it has been found that miscible blends of 2-oxazoline polymers are prepared with a variety of other polymers. The miscibillty of 2-oxazoline polymers with such polymers is unexpected in light of the diverse structures and properties of the component polymers, especially the differences in solubility characteristics.

Also surprising is that even though these blends contain substantial amounts of 2-oxazoline polymers, the 2-oxazoline polymer is not extractable from the blend in siynificant quantities when the blend is contacted with water. Accordingly, these blends can be used in applications which require contacting the blend with an aqueous environment.

In addition, in many cases the blends of this invention exhibit improved physical properties as compared to the 2-oxazoline polymer alone.

The blends of this invention exhibit utility as membranes, particularly as pervaporation membranes for use in separating components of liquid mixtures such as water/ethanol or ethanol/hexane mixtures.
membranes comprising the blends of this invention exhibit particularly high selectivities and/or fluxes as compared to corresponding conventional permeation membranes.

The 2-oxazoline polymers employed herein are polymers containing pendant N-acyl groups, as repre-sented by the structure (I).

32,280-F -3-~2~3l3~

4N- ( CHR ) - C~2 C=O
S Rl Such 2-oxazoline polymers are readily prey pared by the ring opening polymerization of 2-oxazolines or like compounds, represen-ted by the structure (II) N
(CHR)~ / C-R (II) wherein each R is independently hydrogen or an inertly substituted C1 to C4 moiety, pxeferably hydrogen; each R is independently hydrogen or an inertly substituted hydrocarbon moiety, preferably hydrogen, phenyl, or a Cl to C6 moiety, more preferably a Cl to C4 moiety, most preferably ethyl; and x is 1 or 2, preferably 1.
The 2-o~azoline is most preferably 2-ethyl-2-oxazoline.
The most preferred 2-oxazoline polymer is poly(2-ethyl-2-oxazoline) which is non-hydrolyzed. The term "inertly substituted" means that the moiety referred to contains no substituent group which interferes with the polymerization of the 2-oxazoline, or to the ability of the polymer to form a miscible blend with said other polymer. In the 4-position (R) steric hinderence by groups larger than C4 greatly interfere with poly-merization of the monomer. However, in the 2-position (Rl), steric hinderence does not cause polymerization problems. The term 2-oxazoline is used herein to describe compounds having the general structure as defined by II, including species wherein x is 2, even though they would not strictly be named oxazolines.

32,280-F -4-3~3~
- --5~

Illustrative inert substituents include alkenyl, hydrocarbyl, alkoxy and the like. Exemplary R
substituents include hydrogen, methyl, ethyl, and N-propyl; and exemplary Rl substituents lnclude hydrogen, methyl, ethyl, propyl, pentyl, cyclohexyl, and the like. The ring-opening polymerization of 2-oxazoline monomers is generally conducted in the presence of a cationic polymerization catalyst at a reaction tempera-ture of 0-20~C. Typical catalysts include strong I0 mineral acids, organic sulfonic acids and their esters, acidic salts such as ammonium sulfate, Lewis acids such as aluminum trichloride, stannous tetrachloride, boron trifluoride and organic diazoniumfluoroborates, dialkyl sulfates and other like catalysts. This ring-opening polymerization is further described by Tomalia et al., J. Polymer Science, 4, 2253 (1966); Bassiri e-t al., Polymer Letters, 5, 871 (1967); Seeliger, Ger. 1,Z06,585;
30nes and Roth, U.S. Patent No. 3,640,909; and Litt et al., U.S. Patent No. 3,483,141.

The polymer obtained in the polymerization of 2-oxazoline is linear, N-acylated polyalkyleneimine having a molecular structuxe consis-ting of repeating units (I). If desired, a portion of said N-acyl groups may be hydrolyzed. Generally, hydrolysis of such N-acyl groups tends to decrease the miscibility of the 2-oxazoline polymer with the other polymer employed herein. Accordingly, it is typically not desirable to employ a 2-oxazoline polymer having greater than 25 - number percent of such N-acyl groups hydrolyzed.
Preferably, fewer than 10 number percent of such N-acyl groups are hydrolyzed.

32,280-F -5-~63~3~
.

Typically, the 2-oxazoline polymer has a molecular weight within the range of 1,000 to 1,000,000.
In the present invention, it is preferable to use a 2-oxazoline polymer having a molecular weight within the range of about 100,000 to about 600,000.

The 2-oxazoline polymer is incorporated into the other polymer by any known blending technique such as conventional melt blending equipment, including compounding extruders, Banbury mixers, roll mills and the like, as well as by solution blending in a suitable solvent.

The oxazoline polymer is blended with at least one other polymer which is not a polymer of a 2-oxazoline. Said other polymer is watex-insoluble and capable of forming a miscible blend with the oxazoline polymer.

A "miscible blend" as that term is used herein refers to a blend of an oxazoline polymer and at least one other polymer which blend exhibits only one glass transition temperature ~Tg). By contrast, blends of polymers which are immiscible exhibit the charac-teristic Tgls of each component of the blend. If such polymers form a miscible blend, the Tg of the individual components are not exhibited by the blend. Instead, the blend exhibits a characteristic T of its own.
g Procedures for determining the Tg of polymers or blends of polymers are well known in the art.

Diffexential Scanning Calorimetry (DSC) is an especially suitable technique for measuring Tg.

32,280-F -6-The other polymer employed herein does not necessarily form mlscible blends with the oxazoline polymer in all proportions. It is recognized that certain polymers form miscible blends with oxazoline polymers only when blended therewith within a limited range of proportions. Blends of 2-oxazoline polymers with such other polymers are considered to be within the scope of this invention when such blends are miscible blends as defined herein.

Exemplary polymers which form comiscible blends with polymers of 2-oxazoline in a wide range of proportions include certain styrene/acrylonitrile copolymers; rubber modified styrene/acrylonitrile polymers; phenoxy resins; certain styrene/acrylic acid copolymers and the like. Polymers which form miscible blends with polymers of 2-oxazoline in a narrower range of proportions include, for example, polyvinylidiene chloride; copolymers of vinylidiene chloride and vinyl chloride; and styrene/acrylic acid copolymers containing small amounts of acrylic acid.

Styrene/acrylonitrile copolymers ~SAN polymers) which are prepared from a monomer mixture containing from about 18 to about 50 percent by weight acrylonitrile form miscible blends with polymers of 2-oxazolines in all proportions. Any of such SAN copolymers having such acrylonitrile content may be employed herein.
Exemplary SAN polymers are commercially available from The Dow Chemical Company under the TYRIL~ brand name.

In addition, rubbex-modified SAN polymers are useful herein. Such rubber modified SAN polymers typically comprise a continuous matrix of SAN polymer 32,280-F -7-3~3 having colloidially sized rubber particles dispersed therein. Said rubber particles generally have a volume average particle diameter of less than 1 em, perferably less than about 0.5 em, more preferably between 0.05 and 0.5 em. Said rubber particles comprise a natural or synthetic elastomeric polymer which is preferably a polymer of a conjugated diene monomer such as isoprene or butadiene. More preferably, the rubber particle is a polybutadiene. In said more preferred embodiment, the rubber modified SAN polymer is a so-called ABS
(acrylonitrile/butadiene/styrene) terpolymer. Generally, the continuous SAN matrix can be prepared from a monomer mix containing from 15 to 50 percent by weight acryloni-trile based on the weight of monomers. The rubber content of the rubber modified SAN polymer can range from about 0.1 to about 50, preferably from about 5 to about 20 percent by weight of the rubber modified polymer.

Suitable styrene/acrylic acid copolymers include those which are polymers of a monomer mixture containing from 15 to 50 percent acrylic acid based on weight of monomers. Such polymers form miscible blends with the oxazoline polymer in all proportions.

Diverse epoxy or phenoxy resins form miscible blends with the o~azoline polymer in a wide range of proportions. Most generally, epoxy resins are oxirane-containing monomers or prepolymers comprising the reaction product of epichlorohydrin and an active hydrogen containing compound. Such epoxy resins pre-pared from bisphenol A typically have have molecularstructures as represented by the structures 32,280-F -8-:~22~i33~3~
g O OH
O-CH2-bH-C~2- (III) CH2-C~-CH2-O -o-C~2-C~2 C~2 (IV) Those epoxy resins having structures corresponding to structure III, or similar structures, are generally high molecular weight thermoplastic resin. Blends prepared from such thermoplastic resins are also thermo-plastic. Epoxy resins having terminal oxirane groups, such as depicted in structure IV, are curable with heating and the addi-tion of a curing agent such as a polyamine, oxyalkylated short chain polyarnine, poly-amidoamine and the like. Blends of this inventioncontaining such curable epoxy resin are usually cross-linkable t-thermoset-table) by incorporating such a curing agent into the blend. In addition, the so-called phenol novalac and epoxy cresol novalac resins are useful herein. Preferably, however, the epoxy is a high molecular weight polymer thermoplastic polymer as described herein.

Such epoxy and phenoxy resins are widely commercially available. Methods for -the preparation, curing and use of such epoxy resins are described in Sherman et al. "Epoxy xesins" Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Ed., Vol. 9, pages 267-290 (1980).

32,280-F -9-ti3~

Vinylidiene chloride polymers and copolymers thereof, especially copolymers thereof with vinyl chloride, form miscible lends with oxazoline polymers when said blend contains at leas-t 45 percent by weight of oxazoline polymer based on the combined weight of the vinylidiene chloride and oxazoline polymer.

Similarly, styrene/acrylic acid (SAA) polymers which are polymerized from a monomer mixture containing from 5 to 15 weight percent acrylic acid form miscible blends with oxazoline polymers when the blend contains up to 60 weight percent of oxazoline polymer. It is noted, however, that as the acrylic acid content of the SAA copolymer decreases, the copolymer forms miscible blends only with decreasing amounts of oxazoline polymer.
For example, a SAA polymer containing 8 percent acrylic acid forms miscible blends containing up to 60 percent of the oxazoline polymer. By contrast, a SAA polymer containing 5 percent acrylic acid forms a miscible blend only when the blend contains 25 percent or less of the oxazoline polymer.

In addition to the polymers specifically described herein, the blends of this invention may comprise any other polymer which is capable of forming a miscible blend with the oxazoline polymer. The ability of any particular polymer to form a miscible blend with the oxazoline polymer is easily tested by blending a small quanity of the polymer being tested with the oxazoline polymer in the desired proportions and determining the Tg of the blend so obtained.

In addition to the oxazoline polymer and at least one other comiscible polymer, the blends of this 32,280-F -10-.~2~i3~5~

invention may further contain or be blended with diverse materials such as other polymers, inert fillers, plasti-cizers, pigments, antioxidants, mold release agents, preservatives, and the like. The benefical use of such materials is well understood by those skilled in the relevant arts.

Crosslinking agents are also beneficially, but optionally, employed in the blends of this invent tion. Various materials are known to crosslink oxazoline polymers including diisocyanates, as described in U.S.
Patent No. 4,087,413 to Kelyman et al. In addition, crosslinking agents which crosslink the other polymer contained in the blend are usefully employed in this invention When an epoxy or other thermosetting resin is employed herein, the blend advantageously contains a curing agent therefor.

The blends of this invention exhibit desirable physical and chemical properties which make said blends useful in a variety of applications, particularly membrane applications. Often, the physical properties of these blends are better than those exhibited by the oxazoline polymer alone. In addition, these blends usually exhibit increased water wettability as compared to the nonoxazoline polymer alone.

A surprising aspect of the blends of this invention is that little or none of the oxazoline polymer contained therein is extractable from the blends with water. This property is unexpected in that oxazoline polymers are known to be readily soluble in 32,280-F -11-~63~1~

water and are extractable from blends with another polymer which is not miscible with the oxazoline polymer.
Generally, less than 25, preferably less than 10, weigh-t percent of the oxazoline polyme:r in the blend is extractable with water. Most preferably, less than 5 weight percent of the oxazoline polymer is extractable from the blend.

Because -the oxazoline polymer is not readily extracted from the blends of this invention, the blends are suitable for use in agueous environments or in contact with mixtures of water and alcohols or other polar organic molecules which are not solvents for the other polymers in the blend. It is noted, however, that 2-oxazoline polymers are sometimes extractable from miscible blends with alcohol or mixtures of alcohol and a minor amount of waker.

The blends of this invention typically exhibit a refractive index intermediate to those of the component polymers. Accordingly, the blends of this inven-tion can often be prepared such that the blend has a certain desired refractive index. This is especially significant in the preparation of certain rubber-modified polymers, where clarity is improved by employing a polymer and rubber which have the same refractive index. Using the blends of this invention, the refractive indices of the polymer matrix and the rubber particles can be matched to yield a rubber-modified polymer with improved clarity.
In particular, blends of 2-oxazoline polymers and a SAN
polymer may be employed to form such higher clarity rubber-modified polymers.

The blends of this invention are especially useful as semi-permeable membranes. Semi-permeable 32,280-F -12-:~Z2~3~1~
~13-membranes are those which are readily permeated by certain materials but which are substantially imper-meable to other materials accordingly, said membranes are useful for separating or concentrating the com-ponents of a fluid mixture (i.e., mixtures of liquidsor gases).

More particularly, the blends of this inven-tion are useful for separating the components of a fluid mixture of two or more organic compounds in a pervaporation process. In said pervaporation process, one side of the membrane (the feed side) is contacted with a fluid mixture containing two or more components.
A pressure gradiant is provided across the membrane so that the permeate side of the membrane is at a lower pressure than the feed side. From the permeate side of the membrane is withdrawn a vaporous permeate which contains a higher concentration of one component than is contained in feed mixture. General procedures for such pervaporation process are described in U.S. Patent ~os. 3,950,247 and 4,035,291 to Ch.iang et al. Generally, the permeate side of the membrane is maintained at a pressure lower than the vapor pressure of the major component of the permeate. The permeate side of the membrane may be subjected to pressure as low as 0.1 mm of mercury (13 Pa). In addition, superatmospheric pressure may be applied to the feed side of the membrane.
The temperature at which the separations are conducted affects both the selectivity and permeation rate. As the temperature increases, the permeation ra-te rapidly increases while selectivity decreases slightly. This increase in rate, however, may be compensated for by the increase in energy needed to maintain the system at an elevated temperature. In general, the temperature 32,280-F -13-i31~

is sufficiently high that the components of the permeate have a substantial vapor pressure at the temperature at which the separation is effected and sufficiently low that the membrane is stable. Advantageously, the temperature is from -10C to 95c.

The membrane of this invention is useful in separating waxer from organic compounds which are miscible with water. exemplary water-miscible com-pounds include, but are not limited to, aliphatic alcohols, such as methanol, ethanol, propanol, hexanol, and the like; ketones, such as ethylmethyl ketone, acetone, diethyl ketone, and the like; aldehydesl such as formaldehyde, acetaldehyde and the like; alkyl esters of organic acids such as ethylacetate, methyl propionate, and the like; p-dioxane; alkyl and cycloalkyl amines and other water-miscible oryanic compounds which do not chemically react with or dissolve the membrane of this invention. In addition, the organic compound may be one in which water has limited solubility, such as chlorinated alkanes like chloroform and carbon tetrachloride. Preferably, the organic compound is an aliphatic alcohol, a ketone or an aldehyde, with lower alcohols, especially ethanol, being preferred.

In addition, the membrane of this invention is useful in separating mixtures of organic compounds particularly mixtures of a relatively polar organic compound with a less polar organic compound. The organic compounds in said mixture are preferably comis-cible compounds but may be only partially miscible.
Exemplary organic mixtures which can be separated with the membrane of this invention include, for example, mixtures of aliphatic alcohols with aromatics or alkanes, 3~-,280-F -14-3~

such as ethanol/benzene, ethanol/hexane, methanol/hexane, propanol/toluene mixtures; methanol/methyl acetate, isopropanol/ethyl acetate, methanol/acetone, ethanol/-ethyl acetate and like mixtures. A wide range of mixtures of compounds may be separated using the membrane of this invention provided that such mixture does not substantially dissolve or react with the membrane under the conditions at which the separation is effected.

The following examples are provided to illus-trate the invention and are not intended to limit thescope thereof. All parts and percentages are by weight unless otherwise indicated.

Example 1 This example illustrates miscible blends of polyethyloxazoline (PEOX) with a rubber-modified styrene/-acrylonitrile (ABS) resin. The resin employed is a polybutadiene modified resin containing 13.5 weight percent rubber dispersed in a continuous SAN matrix.
The average size of the rubber particles is 0.5 microns.
The continuous SAN matrix is prepared from a monomer mixture containing 25 weight percent acrylonitrile.

Blends are prepared by melting the ABS and PEOX polymers together in an oil-heated Brabender mixer at 190C for 10 minutes. In this manner, blends contain-ing 0, 20, 40, 60 and 80 percent PEOX are prepared.

The glass transition temperature (Tg) of eachof the blends is determined using a Perkin-~lmer DSC 2 calorimeter. The heating rate is 20 per minute. The Tg is defined as the intersection of the heat capacity slopes of the glassy and transition regions. In prepar-ing samples for the DSC, a weighed amount of the blend 32,280-F -15-~2;~;3~

is placed in a tared DSC aluminum dish and then heated on a hot plate at about 200~-230C for 30 seconds to melt the blends. The melted sample is then cooled in the DSC dish and evaluated in the calorimeter.

Moldings are prepared from the blends by grinding, followed by compression molding. The ground polymer is preheated for 3 minutes at lg0C in the compressisn mold followed by heating for 3 minutes under full pressure. The molding is cooled under pressure.

The molded blends are all clear or only slightly hazy Each of the blends exhibits only one Tg, indicating that such blends of PEOX and ABS resins are miscible in all propOrtiQns.

In addition, a blend containing 10 percent PEOX and 90 percent ABS resin is prepared and molded as described above. This molding exhibits a tensile strength at rupture of 5500 psi (38MPa), 33 percent elongation at rupture, a tensile modulus of 3.2 x 105 psi (Z.2 MPa) and a notched Izod impact strensth of 3.2 lb/in (0.571 kg/mm~

Example 2 Blends of a styrene/acrylic acid (SAA) copolymer (20 percent acrylic acid) and PEOX containing 0, 20, 40, 60 and 80 percent PEOX are prepared and molded as described in Example 1. In each case a clear molding is obtained. The To of each of the blends is determined by DSC as described in Example l. In each instance, the blend exhibits only one Tg.

32,280~F -16-Blends of an SAA polymer (containing 8 percent acrylic acid) are prepared containing 0, 20, 40, 60 and 8V percent PEOX. The blends containing 40 percent or less PEOX are clear. Those containing 60 and 80 percent PEOX are hazy. The Tg of each of the blends is deter-mined. Those blends containing 60 percent or less PEOX
exhibit a single Tg and are accordingly examples of this invention. Those containing greater than 60 percent PEOX exhibit two Tg's and are, therefore, not miscible blends. Accordingly, these immiscible blends are not examples of this invention.

A SAA polymer containing 5 percent acrylic acid is blended with PEOX at varying proportions as descr.ibed herein. Miscible blends are formed when the blend contains less than about 30 weight percent PEOX.

Example 3 Blends of polyethyloxazoline and vinylidene chloride/vinyl chloride copolymer (13.5 percent vinyl chloride; Mw = 10,100) containing 0, 20, 40, 60 and 80 percent PEOX are prepared by dissolving the PEOX and vinylidene chloride copolymer in tetrahydrofuran (THF) at 60C with stirring. The polymers are precipitated with n-heptane and dried under vacuum at 60C for 5 days. The blends containing greater than 50 percent PEOX exhibit a single Tg and are accordingly examples of this invention. The blends containing less than 50 percent PEOX exhibit two Tg and are, therefore, not miscible blends.

Example 4 Blends are prepared by dissolving PEOX and a thermoplastic phenoxy resin sold as TKHH resin by Union Carbide Corporation in THF at room temperature. Blends 32,280-F -17-:~2~3~

containing 20, 40, 60 and 80 percent PEOX are prepared in this manner. Films are prepared from such blends by casting a film of the dissolved blend and then evaporating the solvent. The blends all exhibit a single To indi-cating that the PEOX and the phenoxy resin are misciblein all proportions.

ExamE~e 5 In this example, polyethyloxazoline (Mw equal 400,000) is melt blended with diverse SUN resins having various AN contents. The resulting blends are compres-sion molded as described hereinbefore and the Tg of the molded blends is determined by DSC. The polymer employed in the blends and the results obtained are as described in the following table.

TABLE

(Miscible 1 2 3 Blends) Polymer% AN PEOX Miscibility C
20 SAN-8 8 Immiscible in all proportions*
SAN-16 16 Immiscible in all proportions*
SAN-21 21 25 Yes 95.5 SAN-21 21 50 Yes 76.4 SAN-21 21 75 Yes 70.3 25 SAN-25 25 20 Yes 85 SAN-2S 25 40 Yes 70 SAN-25 25 60 Yes 62 SAN 25 25 80 Yes 58 SAN-40 40 20 Yes 90 30 SAN-40 ~0 40 Yes 78 SAN-40 40 60 Yes 69 SAN-40 ~0 ao Yes 62 *Not an example of the invention Weight % Acrylonitrile repeating units in SAN polymer 32,280-F -18-;3~3~

2Weight percent polyethyloxazoline in blend. The poly-ethylo~azoline has a molecular weight of 400,000, except those blended with SAN 16 and 21 which have a molecular weight of 606,000.
3"Yes" indicates that the blend exhibits only one Tg.

From the foregoing Table it is seen that SAN
polymers form miscible blends with Pox in all pro-portions provided the SAN polymer contains at least about 18 percent acrylonitrile repeating units.

The sample of the blend containing 60 percent SAN (24 percent AN) and 40 percent PEOX is extracted with water in an attempt to remove the PEOX content therefrom. A weighed dry sample of the molded blend ~1.25 by 1.25 by .01 cm) is extracted with 10 g of water for 3 days at room temperature under mild agitation.
The thus treated sample is then dried and weighed to determine the amount of PEOX which is extracted from the water. Under these conditions, no PEOX is extracted from the blend. Substitution of 10 percent of the water with ethanol leads to extraction of 8 weight percent of the PEOX in the blend. Forty-four percent of the PEOX is extracted with a 50/50 ethanol water solution.

A membrane is prepared from the blend containing 60 percent SAN (24 percent AN) and 40 percent PEOX by melt blending and compression molding as described above. The membrane has a thickness of S mils (O.127 mm).

The membrane is placed onto an in-line filter holder so that a 14.2 cm2 section of the membrane is open to feed solution The membrane is supported with 32,280-F -19-3~3~

Whatman #50 filter paper. The permeate end of the filter holder is connected to a vacuum pump with two cold traps placed in line to collect the permeate by condensation. The membrane and holder are then immersed in a closed flask containing the mixtuxe to be separated.
The flask is equipped with thermometer for measuring temperature and a reflux condenser to prevent feed loss due to evaporation.

Separation is effected by pulling a vacuum of 0.lmm Hg (13 Pa) on the permeate side of the membrane and collecting the permeate in the cold trap. The tempera-ture of the feed solution is maintained at 35C. The permeation rate is calculated by periodically weighing the collected permeate. The permeate composition is determined by gas chromatography using a ~ewlett-Packard 5840A gas chromatograph eguipped with a thermal conduc-tivity detector.

The membrane is used to separate various ethanol/hexane mixtures. Each separation is effected until a steady state condition is obtained (typically about 25 hours. Once a steady state is reached, the content of the permeate and permeation rate are deter-mined. The feed solution is a mixture of 7.3 percent ethanol and 92.7 percent hexane. The permeate contains 97.7 percent ethanol. The separation factor ae defined as:

_ ~O ETOH/% Hexane in permeate e % ETOH/% Hexane in feed is determined to be 539. The permeation rate of this membrane is 174 g mil/m2 hr (4.42 g mm/m hr).

32,280-F -20-The foregoing separation is repeated, this time employing a membrane which is a blend of 60 weight percent SAN resin (40 percent AN) and 40 percent PEOX.
In this case, the feed contains 7.5 percent ethanol and 5 92.5 percent hexane and the permeate contains 99.5 percent ethanol, yielding an ye of 2,454. The permea-tion rate is 31 g mil/m2 hr (O.787 g mm/m2 hr).

For comparison, the foregoing separation is repeated this time employing a membrane comprising lO0 percent SAN resin (40 percent AN). The feed contains 7.4 percent ethanol and 92.6 percent hexane and the permeate contains 2 percent ethanol yielding an ye f 0.2. The permeation rate is 24 g mil/m hr ~0.610 g mm/m2 hr). These data clearly demonstrate the surprising effect caused by the presence of PEOX
in the separation membrane. The SAN resin alone exbibits a modest selectivity for hexane over ethanol. By con-trast, the modified membrane of this inven-tion exhibits a very high selectivity for ethanol over hexane~ Moreover, the permeation rates obtained with the membrane of this invention are significantly higher than those obtained with the SAN membrane alone. The a values for the e membranes of this invention are extremely high. By con-trast, the highest reported literature value for ye in an ethanol/hexane seperation for any membrane i6 a . o.

32,280-F -21-

Claims

WHAT IS CLAIMED IS:

1. A blend comprising a first polymer which is a polymer of a 2-oxazoline and at least one other water-insoluble polymer which is not a polymer of 2-oxazoline and which other polymer is miscible with said oxazoline polymer in the relative proportions thereof present in said polymeric composition, wherein the weight ratio of said oxazoline polymer to said other polymer in said composition is from 19:1 to 1:19.

2. The blend of Claim 1 wherein the oxazoline is represented by the formula:

wherein each R is independently hydrogen or an inertly substituted C1 to C4 group, each R1 is hydrogen or an inertly substituted hydrocarbon group, and x is 1 or 2.

3. The blend of Claim 2 wherein the oxazoline is 2 ethyl-2-oxazoline.

4. The blend of Claim 1 wherein said other polymer is a thermoplastic resin.

5. The blend of Claim 4 wherein said thermo-plastic resin is a polymer of styrene and acrylonitrile containing from 18 to 50 weight percent repeating acrylonitrile unit, a butadiene rubber modified styrene/-acrylonitrile resin, a high molecular weight phenoxy resin, a styrene/acrylic acid copolymer containing at least 15 weight percent repeating acrylic acid units, or a homopolymer or copolymer of vinylidenechloride.

6. The blend of Claim 1 wherein the blend contains from 10 to 60 weight percent of the oxazoline polymer based on the combined weight of the oxazoline polymer and other polymer.

7. The blend of Claim 1 wherein the polymers are crosslinked after blending.

8. A semipermeable membrane comprising a film of the blend of Claim 1.

9. A process for separating mixtures of 2 or more organic compounds, or a mixture of water and an organic compound miscible therewith, comprising (a) contacting one side of a membrane comprising the blend of Claim 1.
(b) withdrawing from the other side of said membrane a permeate in vapor form, said permeate containing a higher concentration of one component of the feed mixture than is present in the feed mixture.

10. The process of Claim 9 wherein the feed mixture comprises hexane and ethanol, or water and ethanol.