Ultrafine porous polymer article and method of making

1638-RD-277O

GENERAL ELECTRIC COMPAIiY 1, River Road

Schenectady, HY, USA

"Ultrafine Pore Polymer Articles and Methods for their Preparation"

The invention relates to novel ultrafine pore polymer articles having a predetermined maximum pore radius and to a method of making these polymeric articles. More particularly, the invention relates to a novel process for the preparation of an ultrafine pore polymer article having a predetermined maximum pore size, characterized by comprising a porous thermoplastic polymer body of a monoethylenically unsaturated hydrocarbon with a solution of neutral unsaturated monomers, unsaturated acids, unsaturated amines or mixtures of such substances and on opposite sides of the porous body with wetting only those pores whose radius is greater than the predetermined pore radius, with the monomer solution, a pressure difference according to the formula:

AF = 2y »cos Q

- 2-

1 (J 9! 'IM / 20 5

where ΔΡ is the pressure difference between the opposite sides of the porous body, f is the surface tension of the monomer solution, θ is the wetting angle and r is the radius of the pores to be wetted, the solvent evaporates and the monomer (s) are polymerized in situ.

Porous structure articles have already been prepared by selectively dissolving a soluble solid material from a heterogeneous mixture of the soluble solid, eg, sodium chloride, urea, sodium carbonate or sodium bicarbonate, and a polymer. However, the substances mentioned do not give articles with ultrafine pores. The polymer must be present in sufficient amount to form a linking network of the polymer between the pores so that the structure does not collapse when the soluble material is extracted. When extracting the soluble solid, nonuniform large pores are obtained because it is not possible to obtain a uniform mixture during mixing and because unfilled voids become trapped during milling and shaping.

Another method of making porous products is to incorporate a thermally decomposable material into a polymer and then heat it to cause decomposition of the thermally decomposable material and expansion of the polymer into a porous 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 brought into the container in which the material is to be molded, such as a mold, so that just a sufficient amount of material is added to completely fill and mold the molded, porous article. In addition, thermally decomposable substances

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generally dangerous to handle and relatively expensive and commonly used to form closed pores.

Other methods have already been used, for example, volatilization of a solvent, use of an extractable plasticizer, sintering, bonding with an adhesive, and the like. However, these methods do not give the very uniform ultrafine pore structure with a predetermined maximum pore radius, which is obtained according to the invention.

There has been found a process for producing ultrafine pore polymer articles which substantially eliminates all the disadvantages of the prior art processes In the practice of the invention, 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 formed by polymerization of monoethylenically unsaturated hydrocarbons which may be substituted with aryl substituents, eg, phenyl, tolyl, dimethylphenyl or naphthyl radicals. 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 lies between a terminal and its adjacent carbon atom, ie according to the grouping OH₂ »C <^. These unsaturated hydrocarbons are known as 1-alkenes or ot-olefins.

Specific examples are the polymers and copolymers of 2 or more of the following monoethylenically unsaturated hydrocarbons: ethylene, propylene, 1-butylene, 1-isobutylene, 4-methyl-1-pentene, 4-ethyl-1-hexene, 1-octene , 1-hexene, styrene, vinyltoluene and vinylnaphthalene. The preferred polymers are

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the polymers of alkenes in the range of C₂_g-alkene-1 compounds, in particular polymers of ethylene and of propylene. Mixtures of two or more of these polymers instead of copolymers may also be used, or a mixture of polyphenylene oxide and polystyrene may be used.

There may also be various amounts of polymerizable monomers except the monoethylenically unsaturated hydrocarbons, such as 1,3-butadiene, 2,4-dimethyl-1,3-butadiene, 1,4-hexadiene, isoprene, acrylic acid and its 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 into the copolymer or the other polymer blended with the monoethylenically unsaturated hydrocarbon polymer does not compromise the stiffness of the resulting porous body, ie Cold flow properties, should decrease so much that the porous body is unsuitable, to produce ultrafine pore articles according to the invention. In other words, the properties of the porous body should come as close as possible to the properties of the polymers and copolymers of the monoethylenically unsaturated hydrocarbon. Accordingly, such compositions also fall within the definition of polymers of a monoethylenically unsaturated hydrocarbon.

The process according to the invention can be carried out with many different thermoplastic polymer bodies, which are produced from said material, which are subsequently

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be formed 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 monoethylenically 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 dissolves 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 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 Λ to 10 / μm. These porous polymer bodies can be crosslinked by irradiation with high-energy electrons before or after the leaching or removal of the leachable material, forming an insoluble crosslinked structure.

High-energy electron irradiation is determined as the total dose defined as the total number of X-ray units used in the irradiation process. An X-ray unit is, according to the usual definition, the amount of irradiation which an electrostatic charge unit Je cur air under standardized temperature and pressure conditions.

10 9819/2054

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, it is preferred according to the invention to use a total dose of 20 × 10 X-ray units at room temperature. Another discussion of high energy electron irradiation and suitable devices therefor is, for example in U.S. Pat. Nos. 2,763,609 and 2,858,259.

Surprisingly, it has been found that an ultrafine pore polymer article having a predetermined maximum pore radius can be prepared by reacting a porous thermoplastic polymer body of a monoethylenically unsaturated hydrocarbon with a solution of a monomer selected from the group consisting of neutral unsaturated monomers, unsaturated acids, the unsaturated amines and mixtures of these compounds is brought together and a pressure difference between the opposite sides of the porous body is applied, whereby only a wetting of the pores by the monomer whose radius is greater than the predetermined maximum pore radius, wherein the pressure difference according to the equation

AP = 2y »cos 0

where ΔP is the pressure difference between the opposite sides of the porous body, f is the surface tension of the monomer, O is the wetting angle, and r is the radius of the pores to be wetted, after which the solvent is evaporated and the monomer is polymerized in situ.

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It has been found that the porous thermoplastic body used as the starting material can be contacted with a liquid or solid monomer from the group of the neutral unsaturated monomers, the unsaturated acids, the unsaturated amines and mixtures of these compounds, wherein the monomer can then be polymerized in situ in the pores leaving at least a predetermined maximum radius. Neutral monomers are, for example Isopropylacrylamide, methacrylamide, methyl methacrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate. Unsaturated acids include, for example, acrylic acid, methacrylic acid and 4-allylphthalic acid. Unsaturated amines include, for example, vinylpyridine, vinylquinoline, dimethylamino dimethacrylate, t-butylaminomethacrylate, and the quaternized derivatives of tertiary amines.

Such a monomer solution contacts the porous body by applying a pressure differential between the opposite sides of the porous body, thereby forcing the monomer through the pores of the body.

The monomer solution only wets the pore walls of such pores having at least one pore radius greater than the predetermined pore radius, if a monomer solution is used, it may be desirable to contact the monomer solution with the porous body

repeat once or more often because the liquid "

under conditions where it evaporates.

The pressure difference is calculated according to the formula; AP «2γ .cos θ

where ΔP is the pressure difference between the opposite sides of the porous body, γ is the surface tension of the monomer, the wetting angle and r

1 ü 8 8 1 9/2 0 5 k

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 1000 pounds when using particular monomers in the practice of the process. Particular monomers and the concentrations of the respective 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

pore radius

Dissolved monomer

100 2

200 1 500 & Λ

Pressure difference (ΔΡ) in atmospheres

1) 1m allylamine

2) 2m allylamine

3) 3m allylamine

4) 1 M acrylic acid

5) 1.5 M acrylic acid

6) 2 M acrylic acid

7) 1.35 m isopropyl

acrylamide

<p><tgroup cols="4"><tbody><row><entry>31.6</entry><entry>15.8</entry><entry>6.3</entry><entry>3.2</entry></row><row><entry>39.6</entry><entry>19.8</entry><entry>7.9</entry><entry>3.9</entry></row><row><entry>47.4</entry><entry>23.7</entry><entry>9.5</entry><entry>4.7</entry></row><row><entry>17.4</entry><entry>8.7</entry><entry>3.5</entry><entry>1.7</entry></row><row><entry>26.0</entry><entry>13.0</entry><entry>5.2</entry><entry>2.6</entry></row><row><entry>46.0</entry><entry>23.0</entry><entry>9.2</entry><entry>4.6</entry></row><row><entry>47.8</entry><entry>23.9</entry><entry>9.6</entry><entry>4.8</entry></row></tbody></tgroup></p>

Surface tension (γ) dynes / cm

<p><tgroup cols="2"><tbody><row><entry> D </entry><entry>52.4</entry></row><row><entry>2)</entry><entry>45.1</entry></row><row><entry>3)</entry><entry>39.3</entry></row><row><entry>4)</entry><entry>50.1</entry></row><row><entry>5)</entry><entry>47.1</entry></row><row><entry>6)</entry><entry>42.3</entry></row><row><entry>7)</entry><entry>36.3</entry></row></tbody></tgroup></p>

Contact angle (0) degrees

72.5 64

53 80 74

49

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For use in the practice of the invention, a plurality of porous thermoplastic polymer bodies of polyethylene have been prepared. Each body was in the form of a membrane or sheet about 4 mils thick. The average properties of these bodies were the following:

Porosity: 50 - 2% Weight: 97 * 4 mg

Nitrogen flow through the membrane at:

0.37 kg / cm² (5.3 psi): 5.1-1.4 ml / min / cm² 4-57 kg / cm² (65.3 psi): 20.7-4.4 ml / min / cm²

Conductivity in aqueous _Λ _ ^

1n KCL solution: 3.3 * 0.3 milliohms cm

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 / cm (20 psi) and

2 m

5.6 kg / cm (80 psi) through a fixed experimental setup "

which released 13.5 cm of the porous polymeric material. This gave a measure of gas permeability

expressed in ml of gas flowing through one cm of material per minute.

A porous polymer having both a high porosity and a high gas-permeable transmittance is a structure having many large pores, but having no ultrafine pore structure. A polymer that has low porosity and low permeability

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for a gas stream 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 relatively high conductivity indicates that the porous polymer article has a pore structure, with 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 generators used to polymerize these monomers may include, in addition to electrons, gamma radiation, ultraviolet radiation, peroxides such as methyl ethyl ketone peroxide coupled with metal activators, soluble azo compounds or persulfates, and the like. be.

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.

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Example no.

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TABLE II

Before after

radiotherapy

Porosity Weight Porosity Weight% mg% mg

<p><tgroup cols="3"><tbody><row><entry>1</entry><entry>51</entry><entry>97.2</entry></row><row><entry>2</entry><entry>51</entry><entry>93.1</entry></row><row><entry>3</entry><entry>49</entry><entry>93.5</entry></row></tbody></tgroup></p>

93.8

Example no.

Nitrogen flow at 0.37 kg / cm² 4.57 kg / cm²

(5.3 psi) ρ (65.3 psi) ml / min / cm

5.2 4.7 5.3

25.1 19.6 24.0

he applied maximum pressure kg / cm² (Psi)

5,6 (80) (1000) (1000)

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 / cm results from the comparison with the value

of 4.57 kg / cm 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, because Example 3 prior to the application of a pressure

ο of 70 kg / cm was irradiated.

The invention is further illustrated by the following examples.

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10981 9 / 205Ä

- 12 Example 1

In this example, a membrane of the above type was used, which was 0.1 ml (4 mils) thick. This membrane, designated membrane # 4, had a porosity of 51%, a weight of 96.6 mg, and a throughflow capability

ο ρ

of nitrogen of 5.0 ml / min / cm at 0.37 kg / cm and

ρ ρ

23.8 ml / min / cm at 4.57 kg / cm. The conductivity, the measurement of which was described above, was 3.1 milliohm cm. This membrane was initially not irradiated.

Example 2

In this example, a membrane of the above type was used, which was 0.1 mm (4 mils) thick. This membrane, designated membrane no. 5, had a porosity of 50%, a weight of 95.8 mg and exhibited a flow-through

2 2

amount of nitrogen of 5.8 ml / min / cm at 0.37 kg / cm and

2 2

27.2 ml / min / cm at 4.57 kg / cm. The conductivity, the measurement of which was described above, was 3.1 milliohms "cm"¹, This membrane was initially not irradiated.

Example 3

In this example, another membrane, designated membrane # 6, was used. This membrane was initially irradiated and treated by the method of the present invention to give an ultrafine pore polymer article having a predetermined maximum pore radius. This membrane had a porosity of 51% and a weight of 96.6 mg. This membrane was used at pressure

separated from 0.37 kg / cm and 4.57 kg / cm^c~ subjected to a stream of nitrogen gas. The membrane showed a

2 2

flow rate of 5.1 ml / min / cm at 0.37 kg / cm and 23.8 ml /

2 2

min / cm at 4.57 kg / cm.

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The membrane was contacted with 1.35 m isopropyl acrylamide as a monomer. A pressure differential of 68 atmospheres was applied between the opposite sides of the porous body, with the monomer wetting only pores having a radius greater than the predetermined maximum pore radius of 70 pounds. The membrane impregnated with the monomer was then crosslinked by irradiation of 20M r, thereby polymerizing the monomer in situ and obtaining an ultrafine pore polymer article in which a second polymer filled those pores whose radius was greater than 70 S was.

Subsequently, this membrane was again at the same |

allowed to flow through the initial pressure differences of nitrogen gas. The flow rate at 0.37 kg / cm

ο was 0.60 ml / min / cm, while the flow rate at

ρ ρ

4.57 kg / cm 3.73 ml / min / cm. The conductivity was 0.86 milliohm · cm.s .. The flow drop at

0.37 kg / cm was 87%, while the flow drop was 4.57 kg / cm² 84%.

From the drop in the amount of nitrogen flowing through, the effectiveness of the method according to the invention for closing larger pores in a pore structure results, whereby a structure is created which has a predetermined maximum pore radius. \

Example 4

In this example, another membrane, designated membrane no. 7, was used. This membrane 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 97.1 mg.

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1 f} Ti β 1 3/2 0 S Λ

ν * ρ

The membrane was at pressure differences of 0.37 kg / cm

and 4.57 kg / cm ^ exposed to a nitrogen gas stream. The

Membrane showed a flow rate of 5 »9 ml / min / cn ρ? ?

at 0.37 kg / cm and 25.1 ml / min / cm at 4.57 kg / cm.

The membrane was contacted with 3 M allylamine as a monomer solution. A pressure difference of 34 atmospheres was applied between the opposite sides of the porous body, with only those pores having a radius larger than the predetermined maximum pore radius of 139 S being wetted by the monomer solution. The membrane impregnated with the monomer 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 Hadius greater than 139 Å.

Subsequently, this membrane was again subjected to a nitrogen gas flow with the same initial pressure difference

2

exposed. The gas flow at 0.37 kg / cm was 3.8 ml / min / cm ",

ρ ρ

while the gas flow at 4.57 kg / cm was 21.1 ml / min / cm.

-1 -1 The conductivity was 3.01 milliohm · cm. The flow

waste at 0.37 kg / cm was 35%, while the flow drop at 4.57 kg / cm² 16%.

Example 5

In this example, another membrane, designated membrane no. 8, was used. This membrane was initially irradiated and then treated according to the 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

ρ ρ

0.37 kg / cm and 4.57 kg / cm exposed to a nitrogen gas stream. The membrane showed a flow rate of 5.9 ml /

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19/2054

ρ ο ρ ρ

min / cm "at 0.37 kg / cm ^ and from 25.7 ml / min / cm" at 4.57 kg / cm

The membrane was contacted with 2 M acrylic acid as a monomer solution. A pressure difference of 34 atmospheres was applied between opposite sides of the porous body, only the pores whose radius was greater than the predetermined maximum pore radius of 135 ° were 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 135S. ™

Subsequently, this membrane was again exposed to a flow of nitrogen gas at the same initial pressure differences. The gas flow was 0.37 kg / cm

ο ρ

4.4 ml / min / cm¹"while the gas flow at 4.57 kg / cm

o 23.7 ml / min / cm¹The conductivity was 3.38

-1 -1 2

milliohms * cm. The flow drop at 0.37 kg / cm was

15 / 'o, while the flow drop at 4.57 kg / cm was 8%.

Example 6

In this example, another membrane, called membrane # 9, was used. This membrane was initially irradiated and was 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

excluded

2 ο

0.37 kg / cm and 4.57 kg / cm exposed to a nitrogen gas stream. The membrane showed a flow rate of 5.6 ml / min / cm^c

- 16 -

p ^w p

at 0.37 kg / cm and 24.9 ml / min / cm at 4.57 kg / cm.

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The membrane was contacted with 2m-acrylic acid as a monomer solution. A pressure difference of 68 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 68 pounds being wetted by the monomer solution. The Monpmer-impregnated membrane was then crosslinked by irradiation with 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 with an eadius greater than 68S.

Subsequently, this membrane again became a nitrogen gas stream at the same initial pressure differences

2

exposed. The gas flow at 0.37 kg / cm was 4.5 ml / min / cm, while the gas flow at 4.57 kg / cm was 19.6 ml / min / cm,; never ''

-1 1 conductivity was 2.78 milliohm cm. The flow

waste at 0.37 kg / cm was 31%, while the flow drop at 4.57 / kg / cm² 19%.

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 such a structure with 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 of the invention can have many different applications. You can eg for the production of shaped articles of any desired shape, alone or in admixture with various fillers, such as wood flour, diatomaceous earth, clay, carbon black, silica, fibrous materials, such as glass fibers, asbestos

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fibers or cotton fibers are used, or used for the production of sealed moldings that are lifted from the water to float 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. can be used, where they can serve as a reservoir eg in the production of ink pads.

These polymers can be used to laminate, coat, or impregnate one or more I surfaces of a substrate, such as nonwoven or other fibrous material, or a solid surface, such as metal sheets or wood, or they can be used to coat over another material , eg Wire, yarn or tubes to extrude a coating, leaving a coating on these ultrafine pores, which provides excellent thermal insulation. Sheets or blocks of ultra-fine pore plastic can also be used to thermally insulate other objects such as tubes or refrigerators. Fabrics and laminates are ideal partitions for -

Batteries dar. Metal powder, conductive solids, eg ™

Conductive carbon species, metallized dielectrics, and similar materials can be incorporated into the polymer to produce an ultrafine pore conductive article, eg, a sheet suitable for electrodes in galvanic cells, eg, fuel elements, decorative objects, and electrical conductors. Such a structure would be ideally suited for applications such as water treatment and the production of a solid electrolyte for fuel elements operating at low temperatures.

PATENT CLAIMS:

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10981 9/2054