A CROSS-LINKING METHOD AND ARTICLES PRODUCED THEREBY
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] Embodiments of the present invention relate to a cross-linking method and
articles produced thereby, particularly to a method for cross-linking styrenic polymers and
articles produced thereby.
Description of the Prior Art
[0002] Cation-exchange polymers have wide applications in industry. Ion exchange
capacity (IEC) is one of the most important parameters, which have high effects on polymer
properties. High IECs impart high ionic conductivity to cation-exchange polymers.
However, polymers with high IECs often cause excess swelling or even dissolution in water.
From viewpoint of practical use, it is strongly desired to develop cation-exchange polymer
with high IEC, low swelling degree and high thermal stability. Cross-linking is a common
and effective method to suppress swelling degree and to improve stability.
BRIEF DESCRIPTION
[0003] In one aspect, embodiments disclosed herein relate to a method for
cross-linking a styrenic polymer, comprising: providing a partly sulphonated styrenic polymer,
and cross-linking the partly sulphonated styrenic polymer in the presence of a polyphosphoric
acid.
[0004] In one embodiment, the styrenic polymer is selected from a group consisting
of a homopolymer of a styrenic monomer, a copolymer of a styrenic monomer with one or
more comonomers, and a combination thereof.
[0005] In one embodiment, the cross-linking is carried out at a temperature of about
100°C or greater, in particular at a temperature in the range from about 0 °C to about
200 C .
[0006] In one embodiment, the partly sulphonated styrenic polymer has a degree of
sulfonation of about 10%-80%, preferably about 20%-70%.
[0007] In one embodiment, the cross-linking is carried out by forming a composition
comprising the partly sulphonated styrenic polymer to obtain a molding, and immersing the
molding into the polyphosphoric acid. In another embodiment, the molding is selected from
a group consisting of a film, an ion exchange resin and a hollow fiber.
[0008] In another aspect, embodiments disclosed herein relate to an article which
comprises at least one component comprising a cross-linked polystyrene produced by the
method of the disclosure.
[0009] In another aspect, embodiments disclosed herein relate to a water treatment
apparatus, which comprises at least one component comprising a cross-linked polystyrene
produced by the method of the disclosure.
[0010] In another aspect, embodiments disclosed herein relate to an ion exchange
membrane, which comprises a cross-linked polystyrene produced by the method of the
disclosure. In one embodiment, the ion exchange membrane has an Ion Exchange Capacity
(IEC) of from about 1.9 to about 2.5 meq/g.
[0011] In another aspect, embodiments disclosed herein relate to a process for treating
water, which comprises contacting the water with the ion exchange membrane of the
disclosure.
[0012] These and other features, aspects, and advantages of the disclosure may be
understood more readily by reference to the following detailed description.
DETAILED DESCRIPTION OF THE INVENTION
[0013] In the following specification and the claims, which follow, reference will be
made to a number of terms, which shall be defined to have the following meanings.
[0014] The singular forms "a", "an", and "the" include plural referents unless the
context clearly dictates otherwise.
[0015] "Optional" or "optionally" means that the subsequently described event or
circumstance may or may not occur, and that the description includes instances where the
event occurs and instances where it does not.
[0016] Approximating language, as used herein throughout the specification and
claims, may be applied to modify any quantitative representation that could permissibly vary
without resulting in a change in the basic function to which it is related. Accordingly, a value
modified by a term or terms, such as "about" and "substantially", are not to be limited to the
precise value specified. In at least some instances, the approximating language may
correspond to the precision of an instrument for measuring the value. Here and throughout
the specification and claims, range limitations may be combined and/or interchanged, such
ranges are identified and include all the sub-ranges contained therein unless context or
language indicates otherwise.
[0017) As used herein, "Polymer" means a polymeric compound prepared by
polymerizing monomers, whether of the same or a different type. The generic term
"polymer" embraces the terms "homopolymer," "copolymer," and the like.
[0018] As used herein, "Copolymer" means a polymer prepared by the
polymerization of at least two different types of monomers. The generic term "copolymer"
includes the term "bipolymer" (which is usually employed to refer to a polymer prepared
from two different monomers) as well as the term "terpolymer" (which is usually employed
to refer to a polymer prepared from three different types of monomers). It also encompasses
polymers made by polymerizing four or more types of monomers.
[0019) In a first aspect, the disclosure relates to a method for cross-linking a styrenic
polymer, comprising:
providing a partly sulphonated styrenic polymer, and
cross-linking the partly sulphonated styrenic polymer in the presence of a polyphosphoric
acid.
[0020] As used herein, the term "styrenic polymer" refers to a polymer comprising a
styrenic monomeric unit, which may include a homopolymer, a copolymer, and a
combination thereof.
[0021] As used herein, the term "styrenic monomer" includes styrene represented by
the formula C H5CH=CH2, and its derived compounds such as, for example, styrenic
derivatives. In one embodiment, the styrenic monomer can be of the following formula:
wherein each of Ri to R is independently selected from the group consisting of a hydrogen, a
C1-C20 alkyl or alkoxy, and a halogen, with the proviso that at least one of R \ to R 5 is a
hydrogen. n one embodiment, the C1-C20 alkyl or alkoxy includes, but is not limited to
methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-hexyl, methoxy, ethoxy,
i-propoxy, t-butyloxy, and hexyloxy. In one embodiment, examples of the halogen include,
for example, fluoro, chloro, and bromo. In a preferred embodiment, each of i to is a
hydrogen, i.e. the styrenic monomer is styrene.
[0022] In one embodiment, the styrenic polymer is selected from a group consisting
of a homopoiymer of a styrenic monomer, a copolymer of a styrenic monomer with one or
more comonomers, and a combination thereof.
[0023] Suitable comonomers that may be used in embodiments disclosed herein
include various compounds, as known in the art, polymerizable with the styrenic monomer.
The comonomers include, but are not limited to a-olefins such as ethylene, propylene and
butylene; dienes including conjugated dienes such as ,3-butadiene and isoprene, and
non-conjugated dienes such as 1,2-butadiene and 1,4-pentadiene; other comonomers such as
acrylonitrile, and the like.
[0024] In one embodiment, the styrenic polymer is selected from a group consisting
of a homopoiymer of styrene, a copolymer of a styrene with one or more comonomers, and a
combination thereof. In a preferred embodiment, the styrenic polymer is a homopoiymer of
styrene, i.e. polystyrene. When the styrenic polymer is polystyrene, cross-linked
polystyrene is obtained by the method of the disclosure.
|0025] In one embodiment, styrenic polymer useful for the disclosure can have a
number average molecular weight of at least about 5,000 atomic mass units, specifically at
least about 8,000 atomic mass units. In another embodiment, styrenic polymer useful for
the disclosure can have a number average molecular weight up to about 5,000,000 atomic
mass units, specifically up to about 2,000,000 atomic mass units. In one embodiment,
styrenic polymer useful for the disclosure can have a number average molecular weight of
about 10,000 to about 1,000,000 atomic mass units, specifically about 20,000 to about
800,000 atomic mass units.
[0026] In one embodiment, styrenic polymer useful for the disclosure is selected from
polystyrene, which has a number average molecular weight of about 10,000 to about
2,000,000 atomic mass units, specifically about 20,000 to about 800,000 atomic mass units.
[0027] Styrenic polymer can be prepared in a continuous or batchwise manner by any
method known to those skilled in the art, including solution polymerization, emulsion
polymerization, and suspension polymerization.
[0028] For example, styrenic polymer can be prepared by a solution polymerization
method as follows: the styrenic monomer, a solvent, an initiator, and optionally one or more
comonomer(s) are introduced into a reactor, and heated to allow the polymerization reaction.
In the solution polymerization, a single reactor, or multiple reactors with at least 2, at least 3
reactors, and so on can be used. Solvent can be used to control the viscosity and control the
molecular weight as a chain transfer agent, whose amount depends on the structure of the
reactor(s) and the desired molecular weight of the product. The temperature of the reactor(s)
can be selected as desired, for example, about 90-200°C.
[0029] Styrenic polymer useful for the disclosure can be commercially available.
[0030] In the preparation of sulphonated styrenic polymer, a phenyl ring in the repeat
units of styrenic monomer is typically substituted by one sulfonic acid group, and rarely
substituted by multiple sulfonic acid groups. As used herein, the term "partly sulphonated
styrenic polymer" refers to a sulphonated styrenic polymer with a sulfonation degree of less
than 100%, in other words, in the partly sulphonated styrenic polymer, some phenyl rings in
the repeat units of styrenic monomer are substituted by sulfonic acid groups, whereas others
are un-substituted by any sulfonic acid group. Sulfonation degree is defined as the
percentage of sulphonated phenyl rings (i.e. phenyl ring attached to a sulfonic acid group) in
the structure of a sulphonated styrenic polymer based on the total number of phenyl rings.
[0031J Sulfonation degree can be calculated as follows:
Sulfonation Degree= n- So H P henyi ring* 00%
wherein n_so3H and np nyi ring represent the moles of sulfonic acid groups and the moles of
benzene rings, respectively.
[0032] f each benzene ring is substituted by one sulfonic acid group, the sulfonation
degree will be equal to 100%. Sulfonation degree can be determined according to any
known method in the art, such as titration and - R.
[0033] Partly sulphonated styrenic polymer used in the disclosure can be obtained by
sulfonation of a styrenic polymer with a sulphonating reagent.
[0034] In the sulfonation process, a solvent may be usually used. The solvent can
include various solvents known to the person skilled in the art, for example, halogenated
hydrocarbons such as chlorinated alkanes, and cycloalkanes such as cyclohexane. In
addition, concentrated sulfuric acid can be used as a solvent, and in this case, it also serves as
the sulfonating reagent itself.
[0035] In one embodiment, sulfonating reagents useful for the disclosure can include,
but are not limited to, concentrated sulfuric acid, oleum, SO3, acyl sulfate. In another
embodiment, sulfonating reagents can be selected from acyl sulfates. Examples of acyl
sulfates include, but are not limited to, acetyl sulfate, propionyl sulfate and butyryl sulfate.
[0036] In one embodiment, the sulfonation of styrenic polymer can be carried out as
follows: styrenic polymer is dissolved in an appropriate solvent such as 1,2 - dichloroethane,
followed by adding acyl sulfate such as acetyl sulfate, propionyl sulfate and butyryl sulfate,
in particular, acetyl sulfate, to allow the reaction; the reaction can be quenched by alcohol
(for example ethanol). After removing the solvent, washing and drying, partly sulphonated
styrenic polymer is obtained. The sulfonation degree of the partly sulphonated styrenic
polymer so obtained is in a linear relationship with the amount of sulfonating reagent within a
certain range, resulting in an easy control of the sulfonation degree.
[0037] In one embodiment, acyl sulfate can be prepared as follows: fatty acid with a
high molecular weight is dissolved in cyclohexane, then treated with SO3 in a certain ratio
(for example, the molar ratio of acid to SO3 = 1.6: 1) . Although SO3 is not soluble in
cyclohexane, it can quickly dissolve and form a homogeneous solution in the presence of
carboxylic acid at room temperature. For example, C12 and Cis fatty acids are mixed with
SO3, resulting in lauroyl sulfate and stearoyl sulfate, respectively. The reaction of fatty acid
and SO3 can be expressed as:
RCOOH+SOs RCOOS03H ( 1)
[0038] In another embodiment, acyl sulfate can be prepared by the reaction of acyl
chloride and sulfuric acid. The reaction of acyl chloride and sulfuric acid can be expressed
as:
RCOCI+H2SO4 ► RCOOSO3H + HC1 (2)
[0039] In another embodiment, acyl sulfate can be prepared by the reaction of
anhydride and concentrated sulfuric acid. The reaction of anhydride and sulfuric acid can
be expressed as:
(RCO)20+H S0 4 ► RCOOSO3H + RCOOH (3)
[0040] In the above three equations, R can be selected from C1.20 alkyls, including,
for example, methyl, ethyl, propyl, n-undecyl, and n-heptadecyl.
[0041] By selecting appropriate conditions and sulfonating reagents, partly
sulphonated styrenic polymers with various sulfonation degrees can be obtained. In one
embodiment, the partly sulphonated styrenic polymer useful for the disclosure has a degree of
sulfonation of about 10%-80%. In another embodiment, the partly sulphonated styrenic
polymer useful for the disclosure has a degree of sulfonation of about 20% -70%. If the
degree of sulfonation is too low, IEC of the resulting final product will be relatively small,
which may limit the applicability of the final product. If the degree of sulfonation is too
large, the partly sulphonated styrenic polymer may have a great solubility in water, negatively
affecting the stability of the final product.
[0042] In a method of the disclosure, polyphosphoric acid is used as a catalyst for the
crosslinking of partly sulphonated styrenic polymer.
[0043] As used herein, the term "polyphosphoric acid" refers to compounds with the
following formula,
[0044] wherein n represents the number of phosphoric acid units in the molecule,
which is an integer greater than or equal to 2. Polyphosphoric acid can be obtained by
condensation of two or more ortho-phosphoric acid molecules through dehydration. For
example, dehydration of two ortho-phosphoric acid molecules results in polyphosphoric acid
with n equal to 2 (i.e. pyrophosphoric acid). For example, dehydration of three
ortho-phosphoric acid molecules results in polyphosphoric acid with n equal to 3 (i.e.
triphosphoric acid). Similarly, dehydration of four ortho-phosphoric acid molecules results
in polyphosphoric acid with n equal to 4 (i.e. tetraphosphoric acid).
[0045] Pyrophosphoric acid, tripolyphosphoric acid and tetrapolyphosphoric acid
have the following formula, respectively:
HO— P—O— P—OH
I I
OH OH
pyrophosphoric acid
O O O
HO— P— O— P—O— P— OH
OH OH
tripolyphosphoric
HO— P—O— P—O— P—O— P —OH
OH OH OH OH
tetrapolyphosphoric acid
[0046] , Polyphosphoric acid is typically formed by dehydration of phosphoric acid,
for example, through heating and evaporation to remove water. Thus the obtained
polyphosphoric acid is usually a mixture of polyphosphoric acids with different values of n.
Polyphosphoric acid is also commercially available.
[0047] Polyphosphoric acid can be characterized by the phosphorus amount in the
form of phosphorus pentoxide (P2O5). In one embodiment, the polyphosphoric acid used in
the disclosure has a phosphorus amount by phosphorus pentoxide (P2O5) of at least about
30wt%, based on the total weight of the polyphosphoric acid. In a preferred embodiment,
the polyphosphoric acid used in the disclosure has a phosphorus amount by phosphorus
pentoxide (P 0 5) of about 60wt% to about 90%, particularly about 75wt% to about 85%,
based on the total weight of the polyphosphoric acid.
[0048] Under the conditions used in a method of the disclosure, the polyphosphoric
acid is present in a liquid form. Therefore, in one embodiment, a method of the disclosure
can be carried out by immersing the partly sulphonated styrenic polymer into the
polyphosphoric acid.
[0049| In one embodiment, the method of the disclosure can be carried out by
forming the partly sulphonated styrenic polymer (or a composition comprising the partly
sulphonated styrenic polymer) to obtain a molding, and immersing the molding into the
polyphosphoric acid. The forming can be performed by any processes known to those
skilled in the art, including, but not limited to, injection molding, compression molding, blow
molding, casting, or extruding. Those skilled in the art can select the form of the molding if
desired, including, but not limited to, a film, an ion exchange resin and a hollow fiber, or the
like.
[0050| In one embodiment, the cross-linking of the partly sulphonated styrenic
polymer can be carried out at a temperature of about 100°C or greater, preferably at least
about 120°C, more preferably at least about 140°C. Generally, the cross-linking temperature
should not be too high. In another embodiment, the cross-linking can be carried out at a
temperature of at most about 250°C, preferably at most about 220°C, more preferably at most
about 200°C. In a preferable embodiment, the cross-linking can be carried out at a
temperature of from about 120°C to about 200°C(preferably from about 140°C to about
190°C).
[0051] Those skilled in the art can select the cross-linking time depending on the
factors, such as the cross-linking conditions (the temperature, or the like), the dimension of
the molding, and the properties of the end products. For example, when the cross-linking
temperature is low, a longer time can be selected. In one embodiment, the cross-linking
time can be in a range of from about 5 minutes to about 5 hours. In another embodiment,
the cross-linking time can be less than or equal to about 2 hours, less than or equal to about
1.5 hours, or less than or equal to about 1.2 hours.
[0052] The inventors of the disclosure have found that the partly sulphonated styrenic
polymer may be dissolved well in a lot of solvents such as ethanol, dimethyl sulfoxide
(DMSO), or the like prior to being treated with the method of the disclosure. After the
treatment, the polymer becomes completely insoluble in these solvents, which implies that
the partly sulphonated styrenic polymer is cross-linked. The inventors presume that the
sulfonic group in the partly sulphonated styrenic polymer reacts with the active hydrogen
atom on the non-sulfonated benzene rings in the polymer to form a highly stable sulfonyl
bond due to the effect of the polyphosphoric acid, whereby the cross-linking is formed by
connecting the different styrenic polymer chains with the stable sulfonyl bond.
[0053] The second aspect of the disclosure relates to a method of treating an article
comprising, providing an article comprising a composition containing a partly sulphonated
styrenic polymer, and treating the article in the presence of a polyphosphoric acid.
[0054] In one embodiment, the article is selected from a group consisting of an ion
exchange membrane, an ion exchange resin and a hollow fiber used in water treatment.
[0055] In one embodiment, the treating is carried out by immersing the article into the
polyphosphoric acid. In one embodiment, the treating is carried out at a temperature of
about 00°C or greater. In a preferable embodiment, the treating is carried out at a
temperature in the range from about 120°C to about 200°C, preferably from about 140°C to
about 190°C. The treatment time can be selected according to the treatment conditions
(such as temperature), the types, dimensions and/or the desired properties of the article.
[0056] The embodiments described above in the first aspect of the disclosure can be
also suitable for the second aspect.
[0057] The third aspect of the disclosure relates to a method for producing an article,
comprising: providing a composition comprising a partly sulphonated styrenic polymer,
forming the composition to obtain a molding, and treating the molding in the presence of a
polyphosphoric acid to obtain the article.
[0058] In one embodiment, the article is selected from a group consisting of an ion
exchange membrane, an ion exchange resin and a hollow fiber used in water treatment.
[0059] The forming can be performed by any processes known to those skilled in the
art, including, but not limited to, injection molding, compression molding, blow molding,
casting, or extruding. Those skilled in the art can select the form of the molding if desired,
including, but not limited to, a film, an ion exchange resin and a hollow fiber, or the like.
[0060] In one embodiment, the treating is carried out by immersing the molding into
the polyphosphoric acid. In one embodiment, the treating is carried out at a temperature of
about 100°C or greater. In a preferable embodiment, the treating is carried out at a
temperature in the range from about 120°C to about 200°C, preferably from about 140°C to
about 190°C. The treatment time can be selected according to the treatment conditions
(such as temperature), the types, dimensions and/or the desired properties of the article.
[0061] The embodiments described above in the first aspect of the disclosure can be
also suitable for the third aspect.
[0062] The fourth aspect of the disclosure particularly relates to a method for
manufacturing a cation exchange membrane used in water treatment, comprising providing a
composition comprising a partly sulphonated polystyrene, forming the composition into a
film, and treating the film by immersing the film into a polyphosphoric acid to obtain the
cation exchange membrane.
[0063] In one embodiment, the partly sulphonated polystyrene has a degree of
sulfonation of about 10%-80%, preferably about 20-70%.
[0064] In a embodiment, the treating is carried out at a temperature in the range from
about 120°C to about 200°C, preferably from about 140°C to about 190°C.
[0065] In one embodiment, the forming is carried out by casting the composition.
The thickness of the film prepared by casting can be selected according to the requirements.
[0066] The resultant cation exchange membrane, having good properties per se, such
as a high ion exchange capacity, a low water uptake and a low swelling ratio, can be used
directly without a substrate. In one embodiment, the resultant cation exchange membrane
has an 1EC of from about 1.9 to 2.5 meq/g.
[0067] In one embodiment, the membrane can be provided on a substrate such as a
non-woven fabric, so as to improve the properties of the membrane. The membrane can be
pressed on the substrate.
[0068] The fifth aspect of the disclosure relates to an article, comprising at least one
component comprising the cross-linked polystyrene prepared according to the method
described in the first aspect of the disclosure.
[0069] The article can be any form known in the art, such as a membrane, an ion
exchange resin, or the like. In one embodiment, as noted above, the sulphonated
polystyrene can be formed to obtain a film, which is subsequently immersed into the
polyphosphonc acid to be treated according to the method described in the first aspect of the
disclosure. Thereby, an ion exchange membrane can be obtained.
[0070] In another embodiment, the sulphonated polystyrene can be granulated to
obtain a particulate, which is subsequently immersed into the polyphosphoric acid to be
treated according to the method described in the first aspect of the disclosure. Thereby, an
ion exchange resin can be obtained.
[0071] The sixth aspect of the disclosure relates to a water treatment apparatus,
comprising at least one component comprising a cross-linked polystyrene produced by the
method described in the first aspect of the disclosure.
[0072] The seventh aspect of the disclosure relates to an ion exchange membrane,
comprising a cross-linked polystyrene produced by the method described in the first aspect of
the disclosure. The membrane can also be prepared according to the method of the fourth
aspect. The membrane has an Ion Exchange Capacity (IEC) of from about 1.9 to 2.5 meq/g.
[0073] The eighth aspect of the disclosure relates a method for treating water, said
method comprising contacting the water with the ion exchange membrane of the seventh
aspect. The method for treating water can be performed according to the conventional
procedure in the art. For example, water can be treated by passing through the ion exchange
membrane under a pressure. Those skilled in the art can select the parameters for treating
water according to the properties of the membrane, such as the pressure, the temperature, the
flow rate, or the like.
[0074] In the prior arts, the cross-linked polystyrene is generally prepared by adding a
cross-linker, divinylbenzene, during the synthesis of the polystyrene. The resultant
cross-linked polystyrene is hard to be processed since it has been cross-linked. Furthermore,
the prior art processes involve complex synthesis procedures, and an additional cross-linking
group is introduced into the polymer structure. t is also difficult to control the cross-linking
procedure.
[0075] In the method of the disclosure, the styrenic polymer is cross-linked after it is
synthesized. Furthermore, the partly sulphonated styrenic polymer may be formed to obtain
a molding, which is then cross-linked directly. Thus, comparing with the prior art processes,
the method has advantages such as simple operation, and it is easy to control the cross-linking
procedure according to the requirements. The partly sulphonated styrenic polymer before
being cross-linked, having a good processabiiity, can be easily formed to obtain a variety of
moldings if desired. A variety of cross-linked articles can be obtained by utilizing the
method.
[0076] It has been proved that, the polyphosphoric acid and a phosphorus pentoxide
solution, two kinds of different catalysts in the term of catalyzing the cross-linking of a
sulphonated polymer, may be not exchanged simply. In addition, the structure of the
sulphonated polymer may also greatly affect the type of the suitable catalyst.
[0077] For example, the sulphonated poly(sulphide sulphone) having the following
formula can be cross-linked only with the polyphosphoric acid as a catalyst,
(x = 0.4, SPSSF-40)
(x = 0.5, SPSSF-50)
(x = 0.6, SPSSF-60) J
[0078] The sulphonated poly(sulphide sulphone) was cross-linked well by using the
polyphosphoric acid as the catalyst at 180 °C for a very short period of time (e.g. 0.5-5 h).
After the solubility was test, the resultant product was completely insoluble in DMSO.
However, if a phosphorus pentoxide/methanesulfonic acid solution (phosphorus pentoxide/
methanesuifonic acid=l / 10, wt/wt)) was used as the catalyst, the sulphonated poly(sulphide
sulphone) can not be cross-linked well even at the optimal use temperature of the phosphorus
pentoxide/methanesulfonic acid solution, 80°C , for a very long period of time (>48h). After
the solubility was test, the resultant product was still partially (mostly) soluble in DMSO.
[0079] The method of cross-linking the sulphonated styrenic polymer (especially the
sulphonated polystyrene) with the polyphosphoric acid as the catalyst is non-obvious, and the
effects thereof are unexpected.
[0080] The method where the polyphosphoric acid is used as the catalyst for
cross-linking the partly sulphonated styrenic polymer, can be easily operated, and it is hardly
to pollute the environment, since the polyphosphoric acid is a non-volatile acid. The
hydrolysate of the polyphosphoric acid during the cross-linking of the partly sulphonated
styrenic polymer is phosphoric acid, which is not a strong acid, has a relatively low causticity,
and will not adversely affect the properties of the final cross-linked products.
[0081] Contrarily, when the phosphorus pentoxide solution is used as the catalyst for
cross-linking the sulphonated polymer, a solvent such as methanesuifonic acid must be used.
The solvent such as methanesuifonic acid is very volatile, resulting in easily polluting the
environment. Methanesuifonic acid also is a strong caustic solvent, which will greatly erode
the device used in the method. Furthermore, methanesuifonic acid is a strong acid, which
will degrade the sulphonated polymer during the cross-linking of the polymer, resulting in the
deterioration of the properties of the cross-linked products.
[0082] In addition, the polyphosphoric acid may be reused many times. Under the
similar cross-linking conditions, the polyphosphoric acid may be reused for about 5 times
higher than the phosphorus pentoxide solution.
[0083] The disclosure comprises the following embodiments:
[0084] Embodiment 1. A method for cross-linking a styrenic polymer, comprising:
providing a partly sulphonated styrenic polymer, and
cross-linking the partly sulphonated styrenic polymer in the presence of a
polyphosphoric acid.
[0085] Embodiment 2. The method of Embodiment 1, wherein the styrenic polymer is
selected from a group consisting of a homopoiymer of a styrenic monomer, a copolymer of a
styrenic monomer with one or more comonomers, and a combination thereof.
[0086] Embodiment 3. The method of any one of Embodiments 1 to 2, wherein the
cross-linking is carried out at a temperature of about 100°C or greater.
[0087] Embodiment 4. The method of any one of Embodiments 1 to 3, wherein the
cross-linking is carried out at a temperature in the range from about 120°C to about 200 °C.
[0088] Embodiment 5. The method of any one of Embodiments 1 to 4, wherein the
partly sulphonated styrenic polymer has a degree of sulphonation of about 10%-80%.
[0089] Embodiment 6. The method of any one of Embodiments 1 to 5, wherein the
partly sulphonated styrenic polymer has a degree of sulphonation of about 20%-70%.
[0090] Embodiment 7. The method of any one of Embodiments 1 to 6, wherein the
cross-linking is carried out by forming a composition comprising the partly sulphonated
styrenic polymer to obtain a molding, and immersing the molding into the polyphosphoric
acid.
[0091] Embodiment 8. The method of Embodiment 7, wherein the molding is
selected from a group consisting of a film, an ion exchange resin and a hollow fiber.
[0092] Embodiment 9. The method of any one of Embodiments 1 to 8, wherein the
providing the partly sulphonated styrenic polymer comprises the steps of :
providing a styrenic polymer;
contacting acetic anhydride with concentrated sulfuric acid to form acetyl sulfate; and
reacting the acetyl sulfate with the styrenic polymer to obtain the partly sulphonated
styrenic polymer.
[0093] Embodiment 10. An article comprising at least one component comprising a
cross-linked polystyrene produced by the method of any one of Embodiments 1 to 9.
[0094] Embodiment 11. A water treatment apparatus, comprising at least one
component comprising a cross-linked polystyrene produced by the method of any one of
Embodiments 1 to 9.
[0095] Embodiment 12. An ion exchange membrane, comprising a cross-linked
polystyrene produced by the method of any one of Embodiments 1 to 9.
i s
[0096] Embodiment 13. The ion exchange membrane of Embodiment 12, wherein the
membrane has an Ion Exchange Capacity (IEC) of from about 1.9 to 2.5 meq/g.
[0097] Embodiment 14. A method for treating water, said method comprising
contacting the water with the ion exchange membrane of Embodiment 12 or 13.
[0098] Embodiment 15. A method for treating an article, comprising:
providing an article comprising a composition comprising a partly sulphonated styrenic
polymer;
treating the article in the presence of a polyphosphoric acid.
[0099] Embodiment 16. The method of Embodiment 15, wherein the article is
selected from a group consisting of an ion exchange membrane, an ion exchange resin and a
hollow fiber for water treatment.
[00100] Embodiment 17. The method of any one of Embodiments 15-16, wherein the
treatment is carried out by immersing the article into the polyphosphoric acid.
[00101] Embodiment 18. The method of any one of Embodiments 15-17, wherein the
treatment is carried out at a temperature of about 100°C or greater.
[00102] Embodiment 19. The method of any one of Embodiments 15-18, wherein the
treatment is carried out at a temperature in the range from about 120°C to about 200 °C.
[00103] Embodiment 20. The method of any one of Embodiments 15-19, wherein the
partly sulphonated styrenic polymer has a degree of sulphonation of about 20%-80%.
[00104] Embodiment 21. The method of any one of Embodiments 15-20, wherein the
styrenic polymer is selected from a group consisting of a homopolymer of a styrenic
monomer, a copolymer of a styrenic monomer with one or more comonomers, and a
combination thereof.
[00105] Embodiment 22. The method of any one of Embodiments 15-21, wherein the
styrenic polymer is selected from a group consisting of a homopolymer of a styrenic, a
copolymer of a styrenic with one or more comonomers, and a combination thereof.
[00106] Embodiment 23. The method of any one of Embodiments 15-22, wherein the
providing the partly sulphonated styrenic polymer comprises the steps of :
providing a styrenic polymer;
contacting acetic anhydride with concentrated sulfuric acid to form acetyl sulfate; and
reacting the acetyl sulfate with the styrenic polymer to obtain the partly sulphonated
styrenic polymer.
[00107] Embodiment 24. A method for manufacturing an article, comprising:
providing a composition comprising a partly sulphonated styrenic polymer;
forming the composition to obtain a molding; and
treating the molding in the presence of a polyphosphoric acid to yield the article.
[00108] Embodiment 25. A method of Embodiment 24, wherein the article is selected
from a group consisting of an ion exchange membrane, an ion exchange resin and a hollow
fiber for water treatment.
[00109] Embodiment 26. A method of any one of Embodiments 24-25, wherein the
treatment is carried out by immersing the molding into a polyphosphoric acid.
[001 10] Embodiment 27. A method of any one of Embodiments 24-26, wherein the
treatment is carried out at a temperature of about 00°C or greater.
[001 11] Embodiment 28. A method of any one of Embodiments 24-27, wherein the
treatment is carried out at a temperature in the range from about 120°C to about 200 °C.
[001 12] Embodiment 29. A method of any one of Embodiments 24-28, wherein the
partly sulphonated styrenic polymer has a degree of sulphonation of about 20%-80%.
[001 13] Embodiment 30. A method of any one of Embodiments 24-29, wherein the
forming of the composition is carried out by injection, compression, blow, casting or
extrusion molding.
[001 14] Embodiment 31. A method for manufacturing a cation exchange membrane,
comprising:
providing a composition comprising a partly sulphonated polystyrene;
forming the composition into a membrane; and
treating the membrane by immersing it into a polyphosphoric acid to yield the cation
exchange membrane.
[001 15] Embodiment 32. The method of Embodiment 31, wherein the partly
sulphonated styrenic polymer has a degree of sulphonation of about 20%-80%.
[001 16] Embodiment 33. The method of Embodiment 31 or 32, wherein the treatment
is carried out at a temperature in the range from about 20°C to about 200 °C.
[001 17] Embodiment 34. The method of any one of Embodiments 31-33, wherein the
forming of the composition is carried out by casting molding.
[00118] Embodiment 35. The method of an one of Embodiments 31-34, wherein the
providing the partly sulphonated polystyrene comprises the steps of :
providing a polystyrene;
contacting acetic anhydride with concentrated sulfuric acid to form acetyl sulfate; and
reacting the acetyl sulfate with the polystyrene to obtain the partly sulphonated styrene.
Examples
[001 19] The invention is illustrated in more details by virtue of examples below.
However, it is to be understood that these examples are merely exemplary, and shall not be
construed as limiting. Unless otherwise indicated, all materials used are commercially
available.
[00120] Measurement Process
[00121 ] 1. Measurement of the degree of sulphonation
[00122] The degree of sulphonation was measured as followed: weighing a sample of
dry sulphonated polystyrene film with a mass of Wsps(e g . g); immersing it into 200ml
saturated sodium chloride solution; stirring at room temperature for 3 days; taking out the
membrane, washing thoroughly with deionized water; combining the aqueous solution;
titrating with a NaOH solution whose molar concentration is known (CNaOH, mol/L) to
equivalent point (phenolphthalein turns red and the color does not fade within a minute);
recording the volume of NaOH consumed (VNa0 H, in L). The degree of sulphonation were
calculated from the following equation:
[00123] degree of sulphonation = 104-CNaoH aoH ( sps - 80 CNao H VNaOH) -
[00124] 2. Measurement of Ion Exchange Capacity (IEC)
[00125] IEC was measured by a titration method.
[00126] For membranes of Example 1 and Comparative Example 1, dry membranes
(0.2-0.8 g) were cut into small pieces and immersed into saturated sodium chloride solution
with stirring for 1 day. The resulting solution was titrated with 0.01 N sodium hydroxide
solution using phenolphthalein as the indicator. EC was reported in meq/g. Since the
membranes of Example 1 and Comparative Example 1 did not have substrate, IEC thereof
could be directly calculated.
[00127] For the GE CR61CMP membrane of Comparative Example 2, it was first
immersed in HC1 solution for 24 hours to form a -SO 3H type membrane. The H+ type
membrane was immersed into saturated sodium chloride solution with stirring for 1 day.
The resulting solution was titrated with 0.01 N sodium hydroxide solution using
phenolphthalein as the indicator. IEC was reported in meq/g. Since the GE CR61CMP
membrane had non-woven fabrics as substrate, weight thereof was taken out in the
calculation.
[00128] 3. Water uptake (WU)
[00129] Water uptake was measured as followed: three sheets of films (20-80 mg per
sheet) of each film were immersed into water at a given temperature for 5 hours;
subsequently the films were taken out, wiped with tissue paper, and quickly weighed on a
microbalance. WU of the films was calculated from the following equation:
WU( ) = , x 100
where W and Ws are the weight of dry and corresponding water swollen film sheets
respectively. Water uptake of each film was estimated from the average value of WU of
each sheet.
[00130] 4. Swelling ratio
Dimensional changes were measured by immersing the membranes into deionized water at a
given temperature for 7 h. The area change was calculated from the following equations:
A A =
A
Where Ao and A are the area of membrane before and after soaking treatment, respectively.
[00131] Preparative Example 1: Synthesis of sulphonated polystyrene (SPS)
[00132] 1.7mL concentrated sulfuric acid, 3.1mL acetic anhydrate and 6.0mL
1,2-dichloroethane (DCE) were added into a 5mL dry beaker pre-chilled in an ice bath under
nitrogen flow. The mixture was stirred magnetically for 2 hours. Acetyl sulfate was
formed in DCE. The solution mixture was transferred to a dropping funnel to be used as a
sulphonating agent in the next step.
[00133] 5.2g polystyrene (Mn = 140,000, available from Aldrich) and 150mL DCE
were added into a 250mL dry beaker under nitrogen flow. The mixture was stirred
magnetically throughout the reaction. After the polystyrene fully dissolved, the mixture was
heated to 50°C, and the acetyl sulfate/DCE solution prepared above was added dropwise.
The reaction was continued at that temperature for 24 hour. Precipitates appeared and were
isolated, washed with DCE, then washed with n-hexane, and dried under vacuum to yield the
solfonated polystyrene (SPS). Degree of sulphonation thereof was determined to be 51%.
[00134] Preparative Example 2 Forming the membrane
[00135] SPS of Preparative Example 1 was dissolved in ethanol to give a concentration
of about 8% (g/lOOml). The SPS solution was cast to a Teflon plate, and dried at 50°C for 8
hours. Subsequently, it was cooled to room temperature. The membrane was stripped
from the Teflon plate and dried under vacuum at 100 °C for 10 hour to yield the SPS
membrane.
[00136] 1EC of the SPS membrane of Preparative Example 2 was determined as
described above to be 3.55 meq/g; swelling ratio was determined to be 195% at 50°C; water
uptake was not measured due to lack of mechanical strength.
[00137] Comparative Example 1: Cross-linking SPS membrane using P2O5 solution as
catalyst
[00138] The dry membrane produced in Preparative Example 2 was completely
immersed into Eaton's reagent ^Os/methanesulfonic acid solution, wherein
P20 /methanesulfonic acid = l/10(wt/wt)) at 80°C (due to the volatility of methanesulfonic
acid, 80°C is the optimal temperature for Eaton's reagent) for 30 minutes. Subsequently,
the membrane was taken out, washed thoroughly with de-ionized water to remove the
residual acid, and dried under vacuum at 100-120°C for 24 hours to give the cross-linked
SPS membrane of Comparative Example 1. IEC of the cross-linked SPS membrane of
Comparative Example 1 was determined to be 2.1 meq/g.
[00139] Comparative Example 2: CR61CMP membrane
[00140] CR61CMP membrane was a cation exchange membrane available from GE
Inc, which was formed by a polystyrene cross-linked with divinylbenzene, with non-woven
fabrics as substrate.
[00141] IEC of CR61CMP membrane of Comparative Example 2 was determined to
be 1.9 meq/g; swelling ratio thereof was 6.9±1.0% at 50°C; and water uptake was 50.2±0.3%
at 50°C.
[00142] Example 1 Cross-liriking SPS membrane using polyphosphoric acid as catalyst
[00143] The dry membrane produced in Preparative Example 2 was completely
immersed into polyphosphoric acid (the phosphorus amount in the form of P2O5 is 80wt%
based on the weight of the polyphosphoric acid, available from SinoPharm, China) for 30
minutes. Subsequently the membrane was taken out washed thoroughly with de-ionized
water to remove the residual acid, and dried under vacuum at 100-120°C for 24 hours to give
the cross-linked SPS membrane (CSPS) of Example 1.
[00144] As mentioned above, sulphonated polystyrenes (SPS) have good solubility in
ethanol. However, the cross-linked SPS membrane produced in Example 1 was completely
insoluble in ethanol, which proved that the treatment in the polyphosphoric acid cross-linked
the sulphonated polystyrene.
[00145] IEC of the cross-linked SPS membrane of Example 1 was determined to be
2.45 meq/g; swelling ratio thereof was 21% at 50 °C; and water uptake was 48% at 50 °C.
[00146] It had been found by comparison between the cross-linked SPS membrane of
Example 1 and the SPS membrane of Preparative Example 2 that the former possessed
significantly reduced swelling ratio and water uptake, as well as significantly increased
stability, which further proved that the treatment of the disclosure cross-linked sulphonated
polystyrene. Moreover, it took only 30 minutes at 170 °C to yield a cross-linked SPS
membrane with a satisfying stability using polyphosphoric acid as catalyst, and the resulting
cross-linked SPS membrane had very good ion exchange property with an IEC up to 2.45
meq/g.
[00147] For an ion exchange membrane, ion exchange capacity is one of the most
important properties. Generally, it is desirable that the ion exchange capacity is as high as
possible insofar as it does not affect stability, while the swelling ratio and water uptake is
relatively low.
[00148] The inventors also surprisingly found that the ion exchange capacity of the
cross-linked SPS membrane of Example 1 was significantly higher than the cross-linked SPS
membrane of Comparative Example 1 (about 5% higher). This indicates that compared to
the cross-linked membrane resulting from the cross-linking with P20 5as catalyst, the method
using a phosphoric acid as catalyst is able to provide a cross-linked SPS membrane with
significantly better performance.
[00149] Even the comparison between the cross-linked SPS membrane of Example 1
and the CR6 CMP membrane of Comparative Example 2 could demonstrate that the ion
exchange capacity of the cross-linked SPS membrane of Example 1 was significantly higher
than the CR6 1CMP membrane, while water uptake thereof was also slightly lower than that
of the CR6 1CMP membrane. The CR6 1CMP membrane had a lower swelling ratio because
it had non-woven fabrics as substrate, which essentially did not swell in the water to limit the
swelling of the membrane so as to give a lower swelling ratio. If a substrate were also
provided for the cross-linked SPS membrane of Example 1, a similarly good swelling ratio
would be obtained. The results indicate that the stability of the cross-linked SPS membrane
of Example 1 is already comparable to a successful commercial cation exchange membrane.
Moreover the cross-linked SPS membrane also has a significantly higher ion exchange
capacity, thus better performance.
[00150] The foregoing examples are merely illustrative, serving to illustrate only some
of the features of the disclosure. The appended claims are intended to claim as broadly as it
has been conceived and the examples herein presented are illustrative of selected
embodiments from a manifold of all possible embodiments. Accordingly, it is applicants'
intention that the appended claims are not to be limited by the choice of examples utilized to
illustrate features of the disclosure. As used in the claims, the word "comprises" and its
grammatical variants logically also subtend and include phrases of varying and differing
extent such as for example, but not limited thereto, "consisting essentially of and "consisting
of." Where necessary, ranges have been supplied, those ranges are inclusive of all sub-ranges
there between. t is to be expected that variations in these ranges will suggest themselves to a
practitioner having ordinary skill in the art and where not already dedicated to the public,
those variations should where possible be construed to be covered by the appended claims. It
is also anticipated that advances in science and technology will make equivalents and
substitutions possible that are not now contemplated by reason of the imprecision of language
-and these variations should also be construed where possible to be covered by the appended
claims.
CLAIMS
What is claimed is:
1.A method for cross-linking a styrenic polymer, comprising:
providing a partly sulphonated styrenic polymer, and
cross-linking the partly sulphonated styrenic polymer in the presence of a
polyphosphoric acid.
2. The method of claim 1, wherein the styrenic polymer is selected from a group
consisting of a homopolymer of a styrenic monomer, a copolymer of a styrenic monomer
with one or more comonomers, and a combination thereof.
3. The method of claim 1, wherein the cross-linking is carried out at a temperature of
about 100°C or greater.
4. The method of claim 1, wherein the cross-linking is carried out at a temperature in the
range from about 120°C to about 200 °C.
5. The method of claim 1, wherein the partly sulphonated styrenic polymer has a degree
of sulfonation of about 10%-80%.
6. The method of claim 1, wherein the partly sulphonated styrenic polymer has a degree
of sulfonation of about 20%-70%.
7. The method of claim 1, wherein the cross-linking is carried out by forming a
composition comprising the partly sulphonated styrenic polymer to obtain a molding, and
immersing the molding into the polyphosphoric acid.
8. The method of claim 1, wherein the molding is selected from a group consisting of a
film, an ion exchange resin and a hollow fiber.
9. The method of claim 1, wherein the providing the partly sulphonated styrenic polymer
comprises the steps of :
providing a styrenic polymer;
contacting acetic anhydride with concentrated sulfuric acid to form acetyl sulfate; and
reacting the acetyl sulfate with the styrenic polymer to obtain the partly sulphonated
styrenic polymer.
10. An article comprising at least one component comprising a cross-linked polystyrene
produced by a method for cross-linking a styrenic polymer, the method comprising:
providing a partly sulphonated styrenic polymer, and
cross-linking the partly sulphonated styrenic polymer in the presence of a
polyphosphoric acid.
11. A water treatment apparatus comprising at least one component comprising a
cross-linked polystyrene produced by a method for cross-linking a styrenic polymer, the
method comprising:
providing a partly sulphonated styrenic polymer, and
cross-linking the partly sulphonated styrenic polymer in the presence of a
polyphosphoric acid.
12. An ion exchange membrane comprising a cross-linked polystyrene produced by a
method for cross-linking a styrenic polymer, the method comprising:
providing a partly sulphonated styrenic polymer, and
cross-linking the partly sulphonated styrenic polymer in the presence of a
polyphosphoric acid.
13. The ion exchange membrane of claim 12, wherein the membrane has an Ion
Exchange Capacity (IEC) of from about 1.9 to 2.5 meq/g.
14. A method for treating water, the method comprising contacting the water with an ion
exchange membrane comprising a cross-linked polystyrene produced by a method for
cross-linking a styrenic polymer comprising:
providing a partly sulphonated styrenic polymer, and
cross-linking the partly sulphonated styrenic polymer in the presence of a
polyphosphoric acid.
15. The method of claim 14, wherein the ion exchange membrane has an Ion Exchange
Capacity (IEC) of from about 1.9 to 2.5 meq/g.