Ultrafine porous polymer article and method of making

IP =

2 ν ·

cos

In the AP, the pressure difference between the opposite sides of the porous body, γ is the surface tension of the monomer solution, θ is the wetting angle and radius of the pores to be wetted, after which the solvent is evaporated off and the monomer or monomers are polymerized in situ.

Second A method according to claim 1, characterized in that one post-treated such a porous polymer body, which has been crosslinked prior to treatment.

The invention relates to a process for the aftertreatment of cell bodies by impregnation with polymerizable monomers and polymerization of these monomers, in order to produce in this way new cell bodies with uitrafeinen pores having a predetermined maximum pore radius.

Articles having a porous structure have already been produced by various methods. Thus, it is well known that such porous structure articles can be made by subjecting a selectively soluble, solid material to a heterogeneous mixture of the soluble, solid material, e.g. As sodium chloride, urea, sodium carbonate or sodium bicarbonate, and a polymer selectively dissolves. However, the substances mentioned do not give articles with ultrafine pores. Rather, the polymer must be present in sufficient amount so that a linking network of the polymer is formed between the pores so that the structure does not collapse when the soluble material is extracted. When extracting the soluble solid material, uneven large pores are obtained because it is not possible to obtain a uniform mixture during mixing, and because unfilled voids are trapped into a sheet during milling and shaping.

Another well-known method for producing porous products is that a thermally decomposable material is incorporated into a polymer and then heated to cause decomposition of the thermally decomposable material and expansion of the polymer into a porous structure structure. Such a process requires the careful composition of the mixture to avoid premature decomposition, as well as the careful control of the amount of material that is placed in the containers in which the material is to be molded, so that just enough material is added to the molded article to completely fill and mold porous object. In addition, thermally decomposable materials are generally hazardous to handle and relatively expensive and are commonly used to form closed pores.

From the Belgian patent 6 29 652 it is finally known to post-treat cell body by impregnation with polymerizable monomers and polymerization of these monomers to give these cell bodies a soft velvety surface.

However, none of these prior art methods make it possible to produce polymeric articles having an ultrafine pore structure and a predetermined maximum pore radius.

It is therefore an object of the present invention to provide a method for post-treatment of cell bodies, with which the production of such cell bodies with ultrafine pores is possible, which have a predetermined maximum pore radius.

This object is achieved by a method of the type described above, which is characterized in that a porous, thermoplastic cell body of a monoethylenically unsaturated hydrocarbon or a mixture of polyphenylene oxide and polystyrene with a solution of neutral unsaturated monomers, unsaturated acids, unsaturated amines or mixtures of such substances brings together and a pressure difference between the opposite sides of the porous body, wherein only a wetting of such pores by the Monomyre occurs whose radius is greater than the predetermined pore radius, wherein a pressure difference according to the formula:

IF =

2γ ■ cos (-) r

where ΔΡ is the pressure difference between the opposite sides of the porous body, γ is the surface tension of the monomer solution, θ is the wetting angle and the radius of the pores to be wetted, followed by the solvent

b^r> Evaporates and the monomer or monomers polymerized in situ.

In carrying out the process according to the invention may be any porous thermoplastic

Polymer body of a monoethylenically unsaturated hydrocarbon can be used.

Examples of such materials are the various polymers and copolymers which are initially prepared by polymerization of monoethylenically unsaturated hydrocarbons containing aryl substituents, e.g. As phenyl, tolyl, dimethylphenyl or naphthyl may be substituted formed. Preferably, the monoethylenically unsaturated hydrocarbon has 2 to 8 carbon atoms in the unbranched part of the olefin chain and, preferably, the ethylenically unsaturated bond is between a terminal and its adjacent carbon atom, that is, according to the grouping

15

CH, = C

20

These unsaturated hydrocarbons are known as 1-alkenes or α-olefins.

Specific examples of those in the inventive 2^r> Materials which can be employed in the process are the polymers and copolymers of two or more of the following monoethylenically unsaturated hydrocarbons: ethylene, propylene, 1-butylene, 1-isobutylene, 4-methyl-1-pentene, 4-ethyl-1-hexene, 1 Octen, 1-witches, _{J (}) Styrene, vinyltoluene and vinylnaphthalene. The preferred polymers are the polymers of alkenes in the range of C ^ -s-alkene-1-compounds, in particular polymers of ethylene and of propylene. Mixtures of two or more of these polymers in place of j, copolymers may also be used, or a mixture of polyphenylene oxide and polystyrene may be used.

It is also possible to use various amounts of polymerizable monomers other than the monoethylenically unsaturated hydrocarbons, such as, for example, 1,3-eutadiene, 2,4-dimethyl-1,3-butadiene, 1,4-hexadiene, isoprene, acrylic acid and their esters, Methacrylic acid and its esters, vinyl esters, vinyl ethers, vinyl chloride, vinyl pyridine and vinyl quinoline, with the monoethylenically unsaturated ₍₎ Hydrocarbons are copolymerized or the polymers of the former substances can be mixed with the polymers of monoethylenically unsaturated hydrocarbons. In selecting the copolymers or polymer blends, it is readily apparent that either the properties or the amount of the other monomer blended in the copolymer or other blended with the monoethylenically unsaturated hydrocarbon polymer does not compromise the stiffness of the resulting gamma porous body that is, the cold flow properties should decrease so much that the porous body becomes unsuitable, to produce ultrafine pore articles according to the invention. In other words, the properties of the porous body should be as close as possible_w) the properties which the polymers and copolymers of the monoethylenically unsaturated hydrocarbon have. Accordingly, such compositions also fall under the concept of polymers of a monoethylenically unsaturated hydrocarbon, ·; serstoff.

The process according to the invention can be carried out with many different thermoplastic polymer bodies, which are produced from said material, which are then shaped into porous polymers or polymer bodies. A method for shaping such porous bodies is described in US Pat. No. 3,378,507.

According to this patent microporous polymers of momoäthylenisch unsaturated hydrocarbons are prepared by heating a mixture of the polymer and a water-soluble anionic surfactant to a temperature at which a homogeneous solution of the two components is obtained, and then the mixture to a Temperature at which the surfactant and the polymer form two separate phases mixed together, and then dissolving out the phase of the surfactant from the polymer. These preparations have a fibrillar structure with extremely fine pores. Such materials are useful as filters, filter media or as binders for ion exchange resins.

Other porous state-of-the-art porous polymers made porous by the initial addition of materials such as sodium carbonate and sodium chloride and their subsequent removal gave porous coarse pore polymers of average size in the range of 1 to ΙΟμίη. These porous polymer bodies can be crosslinked by irradiation with high energy electrons before or after leaching or removal of the leachable material, forming an insoluble crosslinked structure.

Irradiation with high-energy electrons is determined as a total dose, which is defined as the total number of X-ray units that are expended during the irradiation process. An X-ray unit is, according to the usual definition, the amount of irradiation which is one electrostatic charge unit per cm³ Produces air under standardized temperature and pressure conditions. In the present case, it refers to the amount of electron radiation measured with an ionization chamber equivalent to the free air at the point where the surface of the polymer is located. While the total dose may vary, according to the invention, a total dose of 20 × 10 is preferred⁶ X-ray units to use at room temperature. Another discussion of high energy electron beam irradiation and suitable devices therefor is described, for example, in US Pat. Nos. 2,763,609 and 2,858,259.

Neutral monomers that can be used in the method according to the invention for the aftertreatment of cell bodies are, for. As isopropylacrylamide, methacrylamide, methyl methacrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate. Unsaturated acids include e.g. As acrylic acid, methacrylic acid and 4-allylphthalic acid. Unsaturated amines include e.g. Vinylpyridine, vinylquinoline, dimethylaminomethacrylate, t-butylaminomethacrylate and the quaternized derivatives of tertiary amines.

Such a monomer solution contacts the porous body by applying a pressure difference between the opposite sides of the porous body, thereby printing the monomer through the pores of the body. The monomer solution only wets the pore walls of such pores which have at least one pore radius which is greater than the selected pore radius. When a monomer solution is used, it may be desirable to contact it

To repeat the monomer solution with the porous body once or more often because the liquid is under conditions in which it evaporates

The pressure difference is as already mentioned according to the formula:

AP =

2- / · cos θ

where AP is the pressure difference between the opposite sides of the porous body, γ

the surface tension of the monomer, the wetting angle and y the radius of the pores to be wetted

Table I below sets forth the pressure differential in atmospheres required to fill pore radii of 100, 200, 500 and 1000A when particular monomers are used in the practice of the process. Particular monomers and the concentrations of these solutes in aqueous solutions are also given. The surface tension of the monomer solution and the contact or wetting angles are also listed.

Table I

<p><tgroup cols="8"><tbody><row><entry>Dissolved monomer</entry><entry>pore radius</entry><entry>200 Ä</entry><entry>15,8</entry><entry>500 Ä</entry><entry>1000 Ä</entry><entry>upper</entry><entry>Berüh</entry></row><row><entry></entry><entry></entry><entry></entry><entry>19,8</entry><entry></entry><entry></entry><entry>areas</entry><entry>rungs-</entry></row><row><entry></entry><entry>100 A</entry><entry>Pressure difference (AP) </entry><entry>23,7</entry><entry>in atmospheres</entry><entry></entry><entry>tension</entry><entry>corner</entry></row><row><entry></entry><entry></entry><entry>31,6</entry><entry>8,7</entry><entry>6,3</entry><entry>3,2</entry><entry> (Y) </entry><entry> (Θ) </entry></row><row><entry></entry><entry></entry><entry>39,6</entry><entry>13,0</entry><entry>7,9</entry><entry>3,9</entry><entry>Dyn / cm</entry><entry>Degree</entry></row><row><entry>1) 1m allylamine</entry><entry>47,4</entry><entry>23,0</entry><entry>9,5</entry><entry>4,7</entry><entry>52,4</entry><entry>72,5</entry></row><row><entry>2) 2m allylamine</entry><entry>17,4</entry><entry>23,9</entry><entry>3,5</entry><entry>1,7</entry><entry>45,1</entry><entry>64</entry></row><row><entry>3) 3m allylamine</entry><entry>26,0</entry><entry></entry><entry>5,2</entry><entry>2,6</entry><entry>39,3</entry><entry>53</entry></row><row><entry>4) 1 M acrylic acid</entry><entry>46,0</entry><entry></entry><entry>9,2</entry><entry>4,6</entry><entry>50,1</entry><entry>80</entry></row><row><entry>5) 1.5 M acrylic acid</entry><entry>47,8</entry><entry>9,6</entry><entry>4,8</entry><entry>47,1</entry><entry>74</entry></row><row><entry>6) 2 m acrylic acid</entry><entry></entry><entry>42,3</entry><entry>57</entry></row><row><entry>7) 1.35 m isopropylacrylamide</entry><entry></entry><entry>36,3</entry><entry>49</entry></row></tbody></tgroup></p>

Several porous thermoplastic polymer bodies made of polyethylene were prepared for use in the process of the invention. Each body was in the form of a membrane or film about 0.1 mm thick. The average properties of these bodies were the following:

<p><tgroup cols="2"><tbody><row><entry>Porosity:</entry><entry>50 ±2%</entry></row><row><entry>Mass:</entry><entry>97 ± 4 mg</entry></row><row><entry>Nitrogen flow through the</entry><entry></entry></row><row><entry>Membrane at:</entry><entry></entry></row><row><entry>0.37 kg / cm²:</entry><entry>5.1 ± 1.4 ml / min / cm²</entry></row><row><entry>4.57 kg / cm²:</entry><entry>20.7 ± 4.4 ml / min / cm²</entry></row><row><entry>Conductivity in aqueous</entry><entry></entry></row><row><entry>In-KCL solution:</entry><entry>3.3 ± 03millionths</entry></row></tbody></tgroup></p>

cm-¹

The porosity of the polymeric material is readily determined by determining the difference in density between the initially opaque polymer and the porous polymer and dividing by the density of the initial impermeable polymer and multiplying the quotient by 100.

The gas flow measurements were made so that gaseous nitrogen at a pressure of 1.4 kg / cm² and 5.6 kg / cm² was passed through a fixed experimental setup, the 13.5 cm² of the porous polymer material. This gave a measure of the gas permeability expressed in ml of gas per minute through one centimeter² Surface of the material flowed through.

A porous polymer that has both a high porosity and a high gas-flow permeability is a multi-pore structure that does not have an ultrafine pore structure. A polymer that exhibits low porosity and low gas flow permeability is a structure that has very few pores that are neither continuous nor interconnected. A high porosity of about 50% or higher with the above-mentioned low flow rates of gas and a relatively high conductivity indicates. in that the porous polymer article has a pore structure in which there are generally uniformly distributed continuous and interconnected pores, thereby providing a structure having a controlled pore size or a predetermined maximum pore radius

When a membrane of the above type is brought to a high pressure of 68 atmospheres, many of the fine pores are destroyed, resulting in lower porosity, permeability and conductivity when the membrane is returned to atmospheric pressure. As mentioned above, this can be avoided if the polyolefin is crosslinked and reinforced by irradiation prior to processing. The source of free radical generator (s) used to polymerize these monomers may be, besides electrons, still y radiation, ultraviolet radiation, peroxides such as methyl ethyl ketone peroxide coupled with metal activators, soluble azo compounds or persulfates, and the like.

The effect of this irradiation is shown in the following Table II, wherein three such porous polymer membranes of the above type with respect to the percentage of porosity and weight in mg before and after the irradiation, the maximum pressure before the application of a pressure difference and the flow rate of nitrogen after are specified the application of the pressure difference.

Table II

<p><tgroup cols="6"><tbody><row><entry>Mem</entry><entry>Before irradiation</entry><entry>After irradiation</entry><entry>Nitrogen flow at</entry><entry>4,57</entry><entry>In</entry></row><row><entry>bran</entry><entry></entry><entry></entry><entry></entry><entry>kg / cm²</entry><entry>expended</entry></row><row><entry>No.</entry><entry>Porosity weight</entry><entry>Porosity weight</entry><entry>0,37</entry><entry>ml / min /</entry><entry>Maximum</entry></row><row><entry></entry><entry>did</entry><entry>did</entry><entry>kg / cm²</entry><entry>cm²</entry><entry>pressure</entry></row><row><entry></entry><entry>% mg</entry><entry>% mg</entry><entry>ml / min /</entry><entry>kg / cm²</entry></row><row><entry></entry><entry></entry><entry></entry><entry>cm²</entry><entry></entry></row><row><entry></entry></row></tbody></tgroup></p>

51 51 49

97,2 93,1 93,5

49

5,2 4,7 5,3

25,1 19,6 24,0

5,6 70 70

Membranes 1 and 2 in Table II were not irradiated prior to applying the maximum pressure. The smaller flow rate in Example 2 when applying a pressure of 70 kg / cm² results from the comparison with the value of 4.57 kg / cm² of Example 1. However, Example 3 had been irradiated prior to applying the maximum pressure. A high flow rate is shown by Example 3 over Example 2 because Example 3 prior to the application of a pressure of 70 kg / cm² had been irradiated.

Other membranes which can be used for the process according to the invention have the following properties:

Membrane No. 4

This membrane was 0.1 mm thick, had a porosity of 51%, a weight of 96.6 mg and a nitrogen permeability of 5, OmI / min / cm² at 0.37 kg / cm² and 23.8 ml / min / cm² at 4.57 kg / cm², The conductivity, the measurement of which was described above, was 3.1 milliohm¹ · Cm- '. The membrane had not been irradiated initially.

Membrane No. 5

This membrane was 0.1 mm thick, had a porosity of 50%, a weight of 95.8 mg, and showed a nitrogen flow rate of 5.8 ml / min / cm² at 0.37 kg / cm² and 27.2 ml / min / cm² at 4.57 kg / cm², The conductivity, whose measurements were described above, was 3.1 milliohm¹ · Cm- '. This membrane was initially not irradiated.

The invention will now be explained in more detail by the following examples:

example 1

In this example, a No. 6 membrane was used, initially irradiated and treated by the method of the invention, to give an ultrafine pore polymer article having a predetermined maximum pore radius. The membrane had a porosity of 51% and a weight of 96.6 mg. It was at pressure differences of 037 kg / cm² and 4.57 kg / cm²² subjected to a stream of nitrogen gas and showed a flow rate of 5.1 ml / min / cm² at 037 kg / cm² and 23.8 ml / min / cm² at 4.57 kg / cm².

For post-treatment according to the invention, the membrane was contacted with 135 m-isopropylacrylamide as a monomer. A pressure difference of 68 atmospheres was applied between the opposite sides of the porous body, passing through

the monomer has only been wetted with pores having a radius greater than the predetermined maximum pore radius of 70 f. The membrane impregnated with the monomer was then crosslinked by irradiation of 20Mr, whereby the monomer was polymerized in situ to obtain a micro-ultrafine pore polymer article, in which the second polymer filled those pores whose radii! greater than 70 A was.

Subsequently, this membrane was allowed to flow through again at the same initial pressure differences of nitrogen gas. The Durchströmmeng «at 0.37 kg / cm² was 0.60 ml / min / cm²while di (flow rate at 4.57 kg / cm² 3.73 ml / min / cm^: scam. The conductivity was 0.86 milliohm¹ -cm- 'The flow drop at 0.37 kg / cm² was 87% while the flow drop was 4.57 kg / cm² 84 ° / (was.

The efficiency of the inventive method for closing larger pores in a pore structure results from the drop in the amount of nitrogen flowing through, which results in a structure having a predetermined maximum pore radius

Example 2

In this example, a membrane No. / was used which was initially irradiated and subsequently treated according to the present invention to provide an ultrafine pore polymer article having a predetermined maximum pore radius. This membrane had a porosity of 51% and a weight of 97.1 mg ,

so The membrane was at pressure differences before 037 kg / cm² and 4.57 kg / cm² exposed to a Stickstoffgasstrorr The membrane showed a flow rate of 5.9 ml / min / cm² at 037 kg / cm² and before 25.1 ml / min / cm² at 4.57 kg / cm².

For aftertreatment according to the present invention, the membrane was contacted with 3m-allylamine as a monomer solution. A pressure difference of 34 atmospheres was applied between the opposite sides of the porous body, only the pores were wetted by the monomer solution whose radius was greater than the predetermined maximum pore radius of 139 A was. The membrane impregnated with the Monomei was then crosslinked by irradiation of 20M, thereby polymerizing the monomer in situ and yielding an ultrafine pore polymer article, with a second polymer filling the pores with a radius greater than 139A. Then this membrane became one again

Nitrogen gas stream exposed with the same initial pressure difference. The gas atmosphere at 0.37 kg / cm² was 3.8 ml / min / cm²while the gas flow at 4.57 kg / cm² 21.1 ml / min / cm² scam. The conductivity was 3.01 milliohm-cm.¹, The flow drop at 0.37 kg / cm² was 35%, while the flow drop was 4.57 kg / cm²16%.

Step Example! 3

In this example, a No. 8 membrane was used which was initially irradiated and then treated according to the present invention to provide an ultrafine pore polymer article having a predetermined maximum pore radius. This membrane had a porosity of 51% and a weight of 97.3 mg. The membrane was at pressure differences of 0.37 kg / cm² and 4.57 kg / cm² exposed to a nitrogen gas stream. The membrane showed a of 5.9 ml / min / cm² at 0.37 kg / cm² and of 25.7 ml / min / cm² at 4.57 kg / cm².

For the aftertreatment according to the invention, the membrane was brought into contact with 2 M acrylic acid as monomer solution. A pressure difference of 34 atmospheres was applied between opposite sides of the porous body, with only those pores having a radius larger than the predetermined maximum pore radius of 135 A wetted by the monomer solution. The membrane impregnated with the monomer was then crosslinked by irradiation of 20M r, whereby the monomer was polymerized in situ and an ultrafine pore polymer article was obtained in which a second polymer filled the pores whose radius was greater than 135A.

Subsequently, this membrane was again exposed to a flow of nitrogen gas at the same initial pressure differences. The gas flow at 0.37 kg / cm² was 4.4 ml / min / cm²while the gas flow at 4.57 kg / cm² 23.7 ml / min / cm² scam. The conductivity was 3.38 milliohm¹ -cm-'. The flow drop at 0.37 kg / cm² was 15%, while the flow drop was 4.57 kg / cm² 8%.

Example 4

In this example, a No. 9 membrane was used which was initially irradiated and treated according to the present invention to provide an ultrafine pore polymer article having a predetermined maximum pore radius. This membrane had a porosity of 51% and a weight of 99.4 mg. The membrane was at pressure differences of Q_r37 kg / cm² and 4.57 kg / cm² exposed to a nitrogen gas flow The membrane showed a flow rate of 5.6 ml / min / cm² at 037 kg / cm² and 24.9 ml / min / cm² at 4.57 kg / cm².

For the aftertreatment according to the invention, the membrane was contacted with 2m-acrylic acid as monomer solution. Between opposite sides of the porous body, a pressure difference of 68 atmospheres was applied, whereby only those pores were wetted by the monomer solution whose radius is larger than the predetermined maximum pore radius of 68 Å was. The membrane impregnated with the monomer was then crosslinked by irradiation with 20Mr, whereby the monomer polymerized in situ and a polymer article with ultrafine

A second polymer was filled with a second polymer filling the pores with a radius greater than 68 Å.

Subsequently, this membrane was again exposed to a nitrogen gas flow at the same initial pressure differences. The gas flow at 0.37 kg / cm² was 4.5 ml / min / cm²while the gas flow at 4.57 kg / cm² 19.6 ml / min / cm² scam. The conductivity was 2.78 milliohm¹ -cm-¹, The flow drop at 0.37 kg / cm² was 31% while the flow drop was 4.57 / kg / cm²19%.

From the drop in the flow of nitrogen gas, the effectiveness of the method of the invention for closing larger pores in a pore structure results, thereby providing a structure having a predetermined maximum pore radius without closing through pores of smaller diameters.

The above examples show that the ultra-fine pores obtained according to the invention are unique. Because of their adjusted porosity and physical and chemical properties, the ultrafine pore polymers obtained by the process of the present invention can find many diverse applications. You can z. B. for the production of moldings of any desired kind, alone or in admixture with various fillers, such as wood flour, diatomaceous earth, clay, carbon black, silica, fibrous materials, such as glass fibers, asbestos fibers and cotton fibers, or used to make sealed moldings which are lifted up by the water be swimming in water. They may also be used to make filters or filter media for use in solution clarification or cigarette filter production or may be used as a matrix for absorbing liquids such as dye solutions, printing inks and the like. used as a reservoir z. B. can serve in the production of ink pads.

These polymers may also be used to coat one or more surfaces of a substrate, e.g. B. fiber fleece or other fiber material, or a solid surface, for. As metal sheets or wood, to laminate, coat or impregnate or they can be used to over another material, eg Wire yarn or tubes to extrude a coating leaving a coating on these ultrafine pore articles which provides excellent thermal insulation. Ultra-fine pore plastic webs or blocks may also be used to thermally insulate other articles such as tubes or refrigerators , Fabrics and laminates are ideal partitions for batteries. Metal powders, conductive solids, e.g. B. conductive carbon species, metallized dielectrics and the like may be incorporated into the polymer to produce an ultrafine pore conductive article, e.g. B. a surface formed for electrodes in galvanic cells, eg. As fuel elements, is suitable for decorative objects and electrical conductors Such a structure would be ideally suited for applications such. B. the water treatment and the production of a solid electrolyte for fuel elements, which

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