WO2003104312A1

WO2003104312A1 - Method for producing porous silicone materials

Info

Publication number: WO2003104312A1
Application number: PCT/FR2003/001709
Authority: WO
Inventors: Michel Feder; Yves Giraud; Fernando Leal-Calderon; Nadia Martin; Frédéric Placin
Original assignee: Rhodia Chimie
Priority date: 2002-06-10
Filing date: 2003-06-06
Publication date: 2003-12-18
Also published as: AU2003250353A1; FR2840617A1; FR2840617B1

Abstract

The invention concerns a method for producing porous silicone materials, comprising the following steps: (1) introducing in a receptacle, a silicone phase-in-water emulsion, comprising the silicone phase constituents, an anionic, cationic or nonionic surfactant and water; (1') optionally, inducing a pre-crosslinking of the silicone phase; (2) destabilizing the emulsion using a triggering factor which inhibits the action of the surfactant, initiating coalescence of the silicone phase drops, and leading to a homothetic retraction of the gel; (3) bringing about crosslinking of the silicone phase, thereby congealing development of the coalescence and retraction of the gel; if step (1') is performed, proceeding with crosslinking of the silicone phase; (4) drying the resulting material to obtain the porous silicone material.

Description

PROCESS FOR PRODUCING POROUS SILICONE MATERIALS

The invention relates to a new process for producing porous silicone materials. It also relates to the porous silicone materials thus obtained.

In a different technical field, J. Philippe et al. (Physical Review Letters 2000, 84: 2018-2021) have caused the destabilization of a bitumen emulsion using an appropriate chemical agent. The destabilization of the emulsion induces the formation of a gel by fusion of the bitumen drops, and this gel contracts while substantially retaining the geometry of the container that contains it. This phenomenon of gel removal with substantial maintenance of the initial shape is known as homothetic contraction. Bitumen gel contraction is interrupted when the volume fraction of bitumen in the gel is around 95%.

Porous silicone materials can potentially be used in various applications, such as artificial skin and bone substitutes, hydrophobic or waterproof-breathable textiles (waterproof and permeable to water vapor), filters and filter membranes , porous networks for catalysis, silicone foams, in particular as thermal and mechanical insulator.

There are two main ways of obtaining silicone foams: • The implementation of a condensation reaction with release of volatile by-products. This is particularly the case for polyaddition systems based on polyorganosiloxane carrying ethylenic and / or acetylenic unsaturation (s), eg carrying SiVi units (Vi = vinyl), of polyorganosiloxane carrying units SiH, platinum and compounds with accessible ROH bonds (R = H, alkyl, organosiloxane). Platinum is both the catalyst for the SiH + SiVi addition reaction and the catalyst for the SiH + SiOH condensation reaction which generates hydrogen.

• The use of pore-forming agents or additives, added to the silicone matrix, which, under the action of heat, expand the material either by decomposition with release of gas - in particular the case of AZO derivatives - or by change of phase (gas liquid) - particularly in the case of water or solvents with a low boiling point. The essential characteristics of porous materials are their porosity, their density and their microscopic morphology, which are the result of the geometry, distribution, number and dimensions of the pores.

One of the main difficulties is to produce porous materials while controlling these essential characteristics, in particular their porosity, their microscopic morphology and their density.

The present invention aims to provide a method for producing porous silicone materials, and more particularly such a method for controlling in particular the porosity, microscopic morphology and density of the final material.

The Applicant has found that it is possible, by suitable means, to destabilize emulsions of highly viscous silicone oil in water, thereby causing a phenomenon of coalescence, which results in the formation of a contracted gel. homothetic. The Applicant has also found a way to control and stop the contraction of the gel, before a final drying leading to the porous silicone material.

The subject of the invention is therefore a method for producing a porous silicone material, comprising the following steps:

(1) there is introduced into a container, an emulsion of silicone phase in water, comprising

- (A) at least one polyorganosiloxane (POS) crosslinkable by polyaddition, by polycondensation, by cationic route or by radical route;

- (B) optionally at least one crosslinking organosilicon compound;

- (C) optionally at least one catalyst or initiator of the crosslinking reaction;

- (D) an anionic, cationic or nonionic surfactant;

- (E) water; (1 ') optionally, a pre-crosslinking of the silicone phase is induced;

(2) the emulsion is destabilized using a triggering factor which inhibits the action of the surfactant (D), initiating the coalescence of drops of silicone phase, and leading to a homothetic retraction of the gel;

(3) crosslinking of the silicone phase, that is to say of the constituents (A) and (B) when the latter is present, thus freezing the evolution of the coalescence and the retraction of the gel; in the case where step (1 ′) is carried out, the crosslinking of the silicone phase is continued;

(4) the material obtained is dried to obtain the porous silicone material. The invention can be applied to the various known types of silicone compositions, namely those which crosslink by polyaddition, by polycondensation, by cationic route or by radical route. The oil-in-water emulsion can be formed according to conventional methods known to those skilled in the art (e.g. WO-A-94/09058). A preferred method consists in preparing an oil in coarse water emulsion, by direct route or by phase inversion, starting from a mixture of silicone oil (with the other ingredients intended to form the silicone phase) and an aqueous solution. surfactant. The emulsion obtained can then be refined in an appropriate device.

The emulsion comprises one or more silicone phases, dispersed in an aqueous phase formed of an aqueous solution of the surfactant (D). The emulsion can comprise from 5 to 85%, in particular from 5 to 60%, preferably from 5 to 30%, e.g. about 10% (v / v) of silicone phase. The emulsion can be prepared by mixing a silicone phase and an aqueous solution of surfactant representing from 4 to 15% (v / v). When possible, preference is given to surfactant solutions with a viscosity identical or similar to that of the silicone phase considered and the person skilled in the art is perfectly capable of determining the optimum concentration as a function of this silicone phase and of the surfactant (s) used. As a general rule, the aqueous solution can comprise from 20 to 70%, for example approximately 50% by weight of surfactant (s). The nature of the catalyst or of the photoinitiator (C) is adapted to the type of silicone composition used. It is a catalyst usually used for crosslinking the type of silicone composition used.

The surfactant (D) can be an anionic surfactant. In this case, it can in particular be chosen from: i. the alkyl esters sulfonates of formula R-CH (S0 ₃ M) -COOR ', where R is an alkyl radical in C ₈ -C ₂ o, preferably in Cι ₀ -Cι ₆ , R' is an alkyl radical in C Cβ, preferably in CrC ₃ and M is an alkali cation (eg sodium, potassium, lithium), a substituted or unsubstituted ammonium (methyl-, dimethyl-, trimethyl-, tetramethyl-ammonium, dimethylpiperidinium, etc.), or a derivative of an alkanolamine (eg mono-, di- or tri-ethanolamine).

Mention may very particularly be made of methyl ester sulfonates whose radical R is C ₁₄ -C ₆ ; ii. alkyl sulfates of formula ROS0 ₃ M where R is a C ₅ -C ₂₄ alkyl or hydroxyalkyl radical, preferably in

M is H or corresponds to the same definition as under i. ; eg SDS iii. ethoxylenated (OE) and / or propoxylenated (OP) derivatives of the alkyl sulphates defined in ii., having on average from 0.5 to 30 units, preferably from 0.5 to 10 OE and / or OP units; iv. sulfated alkylamides of formula RCONHR'OS0 ₃ M where R is a C ₂ -C ₂₂ , preferably C ₆ -C ₂ , alkyl radical, R 'is a C ₂ -C ₃ alkyl radical, M is a radical as defined under i. or H; v. ethoxylenated (OE) and / or propoxylenated (OP) derivatives of sulphated alkylamides defined under iv., having on average from 0.5 to 60 OE and / or OP units; vi. salts of C ₈ -C _24, preferably C ₄ -C ₂ o saturated or unsaturated fatty acids, C ₉ -C ₂ o alkylbenzenesulfonates, C ₈ -C ₂₂ primary or secondary alkyl sulfonates, alkyl glycerol sulfonates, sulfonated polycarboxylic acids such as those described in GB-A-1 082 179, paraffin sulfonates, N-acyl N-alkyltaurates, alkylphosphates, isethionates, alkylsuccinamates, alkylsulfosuccinates, monoesters or diesters of sulfosuccinates , N-acyl sarcosinates, alkyl glycoside sulfates, polyethoxycarboxylates; the cation being an alkali metal (eg sodium, potassium, lithium), a substituted or unsubstituted ammonium residue (methyl-, dimethyl-, trimethyl-, tetramethyl-ammonium, dimethylpiperidinium, etc.), or a derivative of an alkanolamine (eg mono-, di- or tri-ethanolamine); vii. rosin salts. The surfactant (D) can in particular comprise or consist of sodium dodecyl sulphate (SDS).

The surfactant (D) can be a cationic surfactant. In this case, it can in particular be chosen from: a) primary amine salts b) tertiary amine salts c) substituted diamine salts d) quaternary ammonium salts, of formula N ⁺ RR'R "R '" Y ^" in which the radicals R, R ', R" and R'", which are identical or different, are hydrocarbon radicals, optionally hydroxylated, and Y ^" is an anion of a strong acid such as the halide, sulphate and sulphonate anions ; e) amino-amine salts f) quaternary ammonium salts of amino-amides g) salts and derivatives of imidazolines h) salts and derivatives of amino-alcohols.

In particular, the surfactant (D) comprises or consists of a salt from group d), e.g. trimethyltetradecylammonium bromide (TTBA).

When the surfactant (D) is an anionic or cationic surfactant, the destabilization of the emulsion in step (2) can be carried out by adding a destabilizing agent which neutralizes the surfactant activity of the surfactant (D). In particular, a solution of a metal salt, in particular an alkali metal salt, eg potassium salt, preferably potassium iodide, or NaOH or KCI as monovalent salts, or bivalent salts can be used. or trivalent such as Ca salts and AI salts, eg Ca or AI sulfate. Those skilled in the art are able to find other destabilizing agents on the basis of their general knowledge and possible routine tests.

It has been found that by adding the potassium salt or similar agent when hot, the emulsion remains stable, but is destabilized when the temperature decreases. Thus, to ensure, before precipitation, a homogeneous distribution of the potassium salt or of another destabilizing agent within the emulsion, the emulsion and the saline solution or the like can be advantageously heated, in particular between 40 and 100 °. C, preferably between 60 and 80 ° C, and mixed and homogenized at this temperature. The activity of the surfactant (D) is then neutralized and the emulsion is destabilized, cooling the mixture, in particular to a temperature less than or equal to 25 ° C. This cooling can be carried out in air, in water or in ice.

Preferably, the salt used to destabilize the emulsion is used in molar excess relative to the surfactant (D). It has been found that the cooling rate influences the contraction and the porosity of the final material. It has also been found that the contraction is faster in ice or in water than in air. Compared to rapid cooling, slow cooling causes more gradual contraction and the final material is more porous. Those skilled in the art can therefore play on these parameters to obtain various ranges of porosity.

When the surfactant (D) is a cationic or anionic surfactant, the destabilization of the emulsion in step (2) can also be carried out:

- By adding an anionic surfactant when the surfactant (D) is a cationic surfactant, or - by adding a cationic surfactant when the surfactant (D) is an anionic surfactant.

This destabilizing surfactant is preferably added in an equimolar amount relative to the surfactant (D). In order to allow a homogeneous distribution of the destabilizing surfactant in the emulsion, it is preferably introduced in step (2) in the form of a suspension of crystals, at a temperature below its Kraft point. Generally, the destabilizing surfactant is introduced at a temperature which is approximately 5 to 20 ° C. lower than its Kraft point, while nevertheless avoiding temperatures too low for the integrity of the emulsion. The surfactant is mixed and gradually dissolves in the emulsion, which is preferably kept at room temperature. Next, the destabilizing surfactant is activated by heating the emulsion above this Kraft point. This heating can be more or less rapid, which also makes it possible to vary the porosity of the final material. This destabilizing surfactant can be chosen in particular from the groups defined above for the surfactant (D) and more particularly from those whose Kraft point is greater than or equal to 15 or 20 ° C.

Preferably, when the surfactant (D) is cationic, the destabilizing surfactant comprises or consists of SDS, the Kraft point of which is located around 20 ° C. An SDS solution is therefore introduced at a temperature below 20 ° C., in particular between 1 and 15 ° C., typically of the order of 4 or 5 ° C.

The surfactant (D) can finally be a nonionic surfactant. As nonionic surfactant, there may be mentioned: I. polyoxyalkylenated (eg polyoxyethylenated, polyoxypropylenated, polyoxybutylenated) alkylphenols in which the alkyl substituent is Cβ-Cι ₂ and containing from 5 to 25 oxyalkylene units; II. polyoxyalkylenated C ₈ -C ₂₂ aliphatic alcohols having from 1 to 25 oxyalkylene units (eg oxyethylenes, oxypropylenes); III. alkoxylated terpene hydrocarbons such as ethoxylated and / or propoxylated alpha- or beta-pinenes, having from 1 to 30 oxyethylene and / or oxypropylene units;

IV. the products resulting from the condensation of ethylene oxide or propylene oxide with propylene glycol or ethylene glycol, of molecular weight of the order of 2000 to 10,000;

V. products resulting from the condensation of ethylene oxide or propylene oxide with ethylenediamine;

VI. fatty acids ethoxylated and / or propoxylated at Cβ-Ciβ, having from 5 to 25 ethoxylated and / or propoxylated units; VII. ethoxylated fatty amides having 5 to 30 ethoxylated units;

VIII. ethoxylated amines having from 5 to 30 ethoxylated units;

IX. alkoxylated amidoamines having from 1 to 50, preferably from 1 to 25 and more particularly from 2 to 20 oxyalkylene units (preferably oxyethylene); X. ethoxylated tristyrylphenols;

Among these surfactants, those whose cloud point is less than 100 ° C. are preferred.

For each of the types of surfactants, other surfactants are known that can be used to form silicone emulsions, and, among them, mention may be made of silicone surfactants, that is to say comprising a polydimethylsiloxane chain.

When the surfactant (D) is a nonionic surfactant, the destabilization of the emulsion in step (2) can be carried out by heating, in particular by heating in the vicinity or beyond the cloud point of the surfactant, preferably by heating to a temperature 5 to 50 ° C higher than this cloud point.

In general, it is recommended not to use an excess of surfactant (D) in the emulsion in order to facilitate complete and homogeneous neutralization. Preferably the concentration of surfactant (D) is close to the critical micellar concentration of this surfactant.

One of the advantageous features of the invention is to be able to control the contraction process and at the same time avoid complete coalescence and therefore complete separation of the phases of the emulsion. Several means linked to the crosslinking of the silicone phase make it possible to stop the contraction, in order to preserve the porosity of the final material.

For a two-component silicone composition, the destabilization of the emulsion, which leads to the coalescence of the drops of silicone phase, makes it possible to initiate crosslinking during this coalescence. The mother emulsion is then a double emulsion, formed of two separate silicone phases, none of these phases comprising all of the reactive species leading to crosslinking. In other words, the emulsion comprises two different silicone phases comprising together all of the reactive species, with the condition that the catalyst (C) is not present in the same phase at the same time as (A) and B). The coalescence of the drops makes it possible to put these reactive species and the catalyst in the presence, which initiates crosslinking.

For a two-component silicone composition crosslinking by polyaddition, it is preferable to have a silicone phase comprising an unsaturated polyorganosiloxane POS A, in particular vinylated, and the hydrosilylation catalyst, and a silicone phase comprising POS A and a polyorganosiloxane POS B hydrogenated. The composition can comprise a catalyst inhibitor and / or any other usual additives. The amounts of each of the constituents and therefore of each of the two silicone phases are adjusted so as to obtain crosslinking in accordance with usual practice, e.g. with an SiH / SiVi ratio greater than or equal to 1.5.

This practice can be transposed to other types of silicone compositions. For example, for a two-component silicone composition crosslinking by polycondensation, a double emulsion is prepared to avoid bringing into contact, in a single phase, the hydroxylated polyorganosiloxane, the silane or analog and the polycondensation catalyst, eg tin catalyst. Polycondensation is generally slower than polyadition. It is therefore preferred to use polycondensation compositions of high viscosity, in particular greater than or equal to 1000, preferably 10 000 mPa.s. For single-component compositions, in particular those which crosslink by polycondensation, it is preferable to start from the partially crosslinked silicone phase (the crosslinking of which began during a so-called ripening phase) and therefore comprising a substantially hardened part limiting the contraction and a fluid part allowing the coalescence. A third means consists in causing crosslinking during contraction using an external triggering factor, for example UV radiation for a cationic crosslinking silicone composition (epoxy polyorganosiloxane) in the presence of a cationic initiator or by radical route (in particular polyorganosiloxane with acrylic or methacrylic group) in the presence of a radical initiator. It is therefore preferable to use a very viscous silicone phase, in particular with a viscosity greater than 1000, preferably greater than 10 000 mPa.s, eg an epoxy silicone gum.

This third means can also be applied to single-component compositions which crosslink by polyaddition, comprising a catalyst inhibitor (C). These inhibitors are perfectly known to those skilled in the art, as are the means to be used to eliminate their inhibitory action, e.g. by heating.

Controlling the contraction process makes it possible to modulate certain properties of the final porous material, such as porosity, density and microscopic morphology.

The addition of solid particles (in particular mineral fillers or crosslinked silicone) in an emulsion according to the invention will increase the level of solid material in the gel and therefore limit the contraction of the material, which makes it possible to modulate properties such as porosity, density and microscopic morphology. We have already seen above that the cooling rate in the case of an emulsion based on cationic or anionic surfactant destabilized by a potassium salt or the like, also makes it possible to modulate these properties.

The drying in step (4) can be carried out by any method. It is preferably carried out by lyophilization. The contracted and crosslinked silicone material can thus be immersed in liquid nitrogen, in particular for a few minutes, then placed in a freeze-dryer for a sufficient time, eg from 30 min to 2 h, in particular of the order of 1 h. Drying can also be carried out by hot air. In the latter case in particular, it may be advantageous to add to the aqueous phase of the emulsion, an additive for protecting the porous structure, such as a glycerol, a polyol, a polyether glycol or one of their derivatives.

In accordance with a first embodiment corresponding to a mode of crosslinking of the silicone phase by polyaddition, that is to say by hydrosilylation reaction, the following products are chosen as constituents of the silicone phase: - POS A ': Polyorganosiloxane having units of formula:

^ SiO ^ (AM)

2 in which:

W is an alkenyl group, preferably vinyl,

Z is a monovalent hydrocarbon group, free from any unfavorable action on the activity of the catalyst (C) and chosen, preferably, from alkyl groups having in particular from 1 to 8 carbon atoms included, preferably from 1 to 5, advantageously, among the methyl, ethyl, propyl and 3,3,3-trifluoropropyl groups and also among the aryl groups and, advantageously, among the xylyl and tolyl and phenyl radicals,

- a is 1 or 2, b is 0, 1 or 2 and a + b is between 1 and 3, possibly at least some of the other units are units of average formula:

Z _c SiO ^ (A \ 2)

2 in which Z has the same meaning as above and ca a value between 0 and 3, for example between 1 and 3; dimethylpolysiloxanes with dimethylvinylsilyl ends, methylvinyldimethylpolysiloxanes with trimethylsilyl ends, copolymers methylvinyldimethyl-polysiloxanes with dimethylvinylsilyl ends, the cyclic methyl-vinylpolysiloxanes being more especially selected;

- POS B ': Polyorganosiloxane having siloxyl units of formula:

H _d L _c SiO _{±; l £ Î ± £}} (BU)

2 in which:

- L is a monovalent hydrocarbon group, free from any unfavorable action on the activity of the catalyst (C) is preferably chosen from alkyl groups having in particular from 1 to 8 carbon atoms included and, advantageously, from methyl groups , ethyl, propyl and 3,3,3-trifluoropropyl and also among the aryl groups and, advantageously, among the xylyl and tolyl and phenyl radicals, - d is 1 or 2, c is 0, 1 or 2, d + ca a value between 1 and 3,

- optionally, at least some of the other motifs being motifs of medium formula:

^si0 z (B \ 2)

2 in which L has the same meaning as above and g has a value between 0 and 3, and the poly (dimethyl-siloxane) (methylhydrogenosiloxy) (α, ω- dimethylhydrogen) -siloxane, being more specially selected.

These POS crosslinkable by polyaddition can be of two types, namely on the one hand those which crosslink at room temperature (but whose crosslinking can be accelerated when hot) called RTV ("Room Temperature Vulcanizing") or Cold Vulcanizable Elastomers (EVF ), and on the other hand those which crosslink hot called EVC which is the abbreviation of "hot vulcanizable elastomer".

In the case of silicone compositions which can be vulcanized hot (EVC) by polyaddition, the POS A 'have in particular a viscosity at least equal to 5.10 ⁵ mPa.s, preferably between 1.10 ⁶ and 1.10 ⁷ mPa.s. In the case of silicone compositions which can be vulcanized hot by polyaddition of the liquid silicone elastomer (LSR) type, the POS A 'have in particular a viscosity preferably between 1.10 ⁴ and 5.10 ⁵ mPa.s.

In the case of silicone compositions which can be vulcanized at room temperature by polyaddition or RTV, the POS A 'have in particular a viscosity of between 100 and 10 ⁴ mPa.s, preferably between 1000 and 5000 mPa.s.

The POS B 'generally have a viscosity of between 10 and 10,000 mPa.s, preferably between 50 and 1,000 mPa.s.

Throughout the description, the viscosities are measured using a BROOKFIELD viscometer according to the indications of standard AFNOR NFT 76 106 of May 1982. All these viscosities correspond to a quantity of dynamic viscosity at 25 ° C called "Newtonian" ", that is to say the dynamic viscosity which is measured, in a manner known per se, at a sufficiently low shear speed gradient so that the viscosity measured is independent of the speed gradient.

The composition further comprises a conventional metal catalyst for hydrosilylation reaction. Hydrosilylation catalysts are well known to those skilled in the art. These are generally platinum complexes, in particular the platinum / unsaturated siloxane complexes, in particular the platinum / vinylsiloxane complexes, in particular those obtained by reaction between a platinum halide and an unsaturated organosilicon material such as an unsaturated silane or a unsaturated siloxane, eg according to the teaching of US-A-3,775,452 to which a person skilled in the art can refer. Preference is given to the Karstedt solution or complex, as described in US Pat. No. 3,775,452. As another additive, it is possible in particular to incorporate a catalyst inhibitor in order to delay crosslinking. These inhibitors are known. In particular, organic amines, silazanes, organic oximes, diesters of dicarboxylic acids, acetylenic ketones, acetylenic alcohols (cf. for example FR-A-1,528,464, 2,372,874 and 2,704,553) can be used. and cyclic polydiorganosiloxanes consisting essentially of units (I) where Y = vinyl and where a = b = 1, possibly associated with units (II) where c = 2. The inhibitor, when one is used, can be used to from 0.005 to 5 parts by weight, preferably 0.01 to 3 parts by weight, per 100 parts of POS A. Phosphines, phosphites and phosphonites also form part of the inhibitors which can be used in the invention. Mention may in particular be made of the compounds of formula P (OR) ₃ in US-A-6 300 455 (incorporated here by reference), and in particular those of formula Pi:

in which :

- R ¹ , R ² , R ³ , R ⁴ , R ⁵ = H, C _n H _{2n +} ι and n = 1 to 15, C _m H _2m -ι and m = 3 to 15 and / or -C _n F _{2n +} ι, and

- R ¹ , R ² , R ³ , R ⁴ and R ⁵ can be identical or different and these radicals do not all represent H.

These inhibitors are added in an amount by weight of between 1 and 50,000 ppm relative to the weight of the total silicone composition, in particular between 10 and 10,000 ppm, preferably between 20 and 2,000 ppm.

Mention may also be made of the inhibitors corresponding to the following formula P ₂ (described in patent application PCT / FR03 / 01305 incorporated here by reference):

in which :

R, R ¹ , R ² , R ³ and R ⁴ , identical or different, represent a linear, branched or cyclic alkyl radical, or an aryl radical substituted or not, in particular:

a linear or branched alkyl radical, in particular having from 2 to 30 carbon atoms (C), preferably from 2 to 12 C, an alkyl radical comprising one or more rings, in particular 1 or 2, a cycle which may in particular have from 4 to 14 C, preferably from 5 to 8 C, or - an aryl or alkylaryl radical, comprising one or more aromatic rings joined or not joined together, in particular 1 or 2 cycles, a cycle possibly comprising from 4 to 14 C, preferably from 6 to 8 C, optionally substituted by 1 or more, in particular from 1 to 2, linear alkyl (s) or branched (s), in particular having from 1 to 12 C, preferably from 4 to 12 C. In the formula PR is advantageously a cyclic alkyl radical, and even better an alryl radical, in particular bi-phenyl. R ¹ , R ² , R ³ and R ⁴ are advantageously cyclic alkyl radicals, and even better aryl radicals and more preferably alkylaryl radicals, in particular substituted phenyl, eg tert-butyl-phenyl. R ¹ , R ² , R ³ and R ⁴ are preferably identical. Two-component or one-component RTV or EVC polyaddition compositions are described, for example, in US Patents 3,220,972, 3,284,406, 3,436,366, 3,697,473 and 4,340,709.

According to a second embodiment, the silicone phase can crosslink by polycondensation of OH groups and / or of hydrolysable groups, in the presence of a catalyst such as a tin catalyst. This relates to two-component or single-component POS compositions which crosslink at room temperature by polycondensation reactions, generally in the presence of a metal catalyst, for example a tin compound (RTV polycondensation). The POSs (A ") which can be used in the compositions according to the invention are more particularly those corresponding to the formula:

Y _n Si _3-n 0 (SiR ₂ 0) _x SiR ₃ .n Yn (A ")

in which :

R represents identical or different monovalent hydrocarbon radicals, Y represents identical or different hydrolyzable or condensable groups, or hydroxy groups, n is chosen from 1, 2 and 3 with n = 1, when Y is hydroxy, and x is an integer greater than 1, preferably greater than 10.

The viscosity of the oils of formula (A ") is between 50 and 10 ⁶ mPa.s at 25 ° C. As examples of radicals R, mention may be made of alkyl radicals having from 1 to 8 carbon atoms such as methyl, ethyl , propyl, butyl, hexyl and octyl, vinyl radicals, phenyl radicals.

As examples of substituted radicals R, mention may be made of 3,3,3-trifluoropropyl, chlorophenyl and betacyanoethyl radicals.

In the products of formula (A ") generally used industrially, at least 60% by number of the radicals R are methyl radicals, the other radicals generally being phenyl and / or vinyl radicals.

As examples of hydrolyzable groups Y, mention may be made of amino, acylamino, aminoxy, ketiminoxy, iminoxy, enoxy, alkoxy, alkoxy-alkyleneoxy, acyloxy and phosphato groups. As hydrolysable groups Y, mention may be made of hydrogen atoms and halogen atoms, preferably chlorine.

When in formula (A ") above n is equal to 1, it is necessary, to prepare polyorganosiloxane elastomers from the polymers of formula (A") above, to use, in addition to the condensation catalysts , crosslinking agents (B ") which are polyhydroxylated or polyalkoxylated silanes or silicone resins. These agents (B") may also be present in the case where n is different from 1.

The silanes correspond in particular to the general formula:

R ₄ -aSiY ' _a (B ") in which:

R has the meanings given above in formula (A ") and Y 'represents hydrolysable or condensable groups, identical or different, a is equal to 3 or 4. The examples given for the groups Y are applicable to the groups

Y '.

It is desirable to use silanes of formula (B ") even in the case where in POS (A") Y is not a hydroxy group. In this case it is desirable to use Y groups of POS (A ") identical to Y 'of silane (B").

The compound (B ") is preferably a polyhydroxylated or polyalkoxylated silicone resin. These silicone resins are those having, per molecule, at least two different siloxy units chosen from those of type M, D, T and Q, at least one being a T or a Q, resins of the MQ, MDQ, TD and MDT type being particularly preferred.

Advantageously, these silicone resins have a content by weight of hydroxyl or alkoxyl group of between 0.1 and 10% by weight.

The alpha-omega dihydroxylated diorganopolysiloxanes of formula (A ") are generally oils whose viscosity varies from 300 to 2,000,000 mPa.s at 25 ° C, preferably from 100,000 to 1,000,000 mPa.s at 25 ° C .

These compositions are described for example in US Patents 3,065,194, 3,542,901, 3,779,986, 4,417,042 and in Patent FR-2,638,752

(single-component compositions), in US Patents 3,678,002, 3,888,815,

3,933,729 and 4,064,096 (two-component compositions), and more particularly in WO-A-94/09059.

It is also possible to use a crosslinking system by dehydrocondensation between SiH units and SiOH units.

According to a third embodiment of a composition of the type which can be crosslinked cationically, in the presence of a photoinitiator and under actinic activation. More specifically, such a composition may comprise: -A- at least one POS A ′ "carrying functional crosslinking groups, the latter preferably being chosen from groups comprising at least one ethylenically unsaturated function - advantageously acrylate and / or methacrylate and / or alkenyl ether - and / or epoxide and / or oxethane, -B- optionally at least one silane and / or a POS B '"carrying functional groups of the same nature or not as the functional crosslinking groups of POS A'", -C- at least one photoinitiator system preferably chosen from onium salts of an element from groups 15 to 17 of the periodic table or of an organometallic complex of an element from groups 4 to 10 of the periodic table, the crosslinking functional groups being preferably chosen from groups comprising at least one ethylenically unsaturated function - advantageously acrylate and / or methacrylate and / or alkenyl ether - and / or epoxy and / or oxethane.

The present invention also relates to porous silicone materials obtained by the method of the invention, and articles formed in whole or in part, e.g. covered, with such a material. These articles can in particular be artificial skin and bone substitutes, hydrophobic or waterproof-breathable textiles (waterproof and permeable to water vapor), filters and filtering membranes, porous networks for catalysis, silicone foams, in particular thermal and mechanical insulators.

The present invention will now be described in more detail with the aid of embodiments taken by way of nonlimiting examples and referring to the drawing in which:

FIG. 1 is a graph showing the evolution of the porosity as a function of the volume fraction of silicone in the emulsion,

- Figure 2 is a graph showing the change in porosity as a function of the inverse of the volume fraction.

Example 1

Emulsion formulation

(1) polydimethylsiloxane oil carrying at its two ends hydroxydimethylsilyl groups, titrating about 300 ppm of OH and having a viscosity of 135,000 mPa.s at 25 ° C

(2) hydroxylated MDT resin before 0.5% of OH by weight and consisting of 62% by weight of CH ₃ Si0 _{3 2 units} , 24% by weight of (CH ₃ ) ₂ Siθ2 / 2 units and 14% by weight of motifs (CH ₃ ) ₃ SiO-ι ₂ .

To 100 g of oil (1) were mixed 7 g of resin (2) and 0.5 g of tin catalyst. This preparation was then dispersed by phase inversion in 10.3 g of aqueous sodium dodecylsulphate (SDS) solution at 30%. This coarse emulsion was sheared in a Couette type apparatus at 680 rpm in an air gap of 100 micrometers thick and with a radius of 20 mm, i.e. shear gradients of 14,200 s-1 during a few seconds. Then the monodisperse emulsion obtained was diluted to 10% in silicone with water and left to mature for one week in order to initiate the polycondensation. This emulsion titers 10mM in SDS.

Destabilization of the emulsion

2 ml of emulsion were brought to 70 ° C, then 0.5 ml of a 1M solution of potassium iodide (KI) and at 70 ° C was added. The mixture was cooled to below 30 ° C so that destabilization and contraction were initiated.

This test was repeated by varying the silicone dilution so as to vary the final volume fraction φ of silicone in the diluted formulation. 7.5, 15, 20, 30 and 45% emulsions were prepared.

Drying

The drying of the gels was carried out by lyophilization. A silicone composition crosslinked in the absence of blowing agent, noted 100%, was also prepared.

Measuring methods

For each porous material obtained, the porosity or average pore diameter was measured.

The average porosity is measured by extrapolation of the flow rate of a column of water through the porous. The flow rate is proportional to the pressure of the height of the water column according to Darcy's law:

Φr ²

With) P: pressure relative to the water height, 0: viscosity of the continuous phase, L: length of the porous, M (phi): volume fraction of the porous and r mean radius of the pores.

The density of the final porous material is measured by weighing before and after lyophilization, taking into account the respective densities of the silicone and of the water.

Table Results:

These results have been reported in Figures 1 and 2.

The variation in the percentage of silicone in the emulsion makes it possible to control the average porosity of the porous. A linear variation of the porosity in 1 / φ is observed (fig. 2).

Example 2: Contraction of emulsions based on a two-component system

Two emulsions were produced according to the previous protocol:

100 g of silicone mixture were dispersed in 9.6 g of 30% aqueous SDS solution. The coarse emulsion obtained was sheared in a Couette type device with a shear gradient of 14200 s-1. The calibrated emulsion obtained was then diluted with water until reaching 10% in a silicone mixture and an SDS concentration of 10 mM.

An emulsion A was prepared with a homogeneous mixture of 99.5% by weight of vinylated silicone oil (oil V, vinylated T-polydimethylsiloxane at the end of the chain, of viscosity of 200 mPa.s) and of 0.5% in weight of Karstedt catalyst at 10% platinum metal An emulsion B was prepared with a mixture of 100g of the same vinylated silicone oil and 14g of hydrogenated silicone oil (hydrogenated polyorganosiloxane oil with Me ₂ SiO and MeHSiO units, viscosity of 30 mPa.s and containing 1% by weight H). A mixture of emulsion A and emulsion B was produced in the proportions of 99% of A and 1% of B.

The destabilization of the final mixture was initiated by adding at a temperature above 65 ° C 20% of a solution of KI at 1 mole / liter, then cooling to room temperature. After drying by lyophilization, a porous silicone material was obtained.

It should be understood that the invention defined by the appended claims is not limited to the particular embodiments indicated in the description above, but encompasses variants thereof which do not depart from the scope or the spirit of the present invention.

Claims

1. Method for producing a porous silicone material, comprising the following steps:

(A) at least one polyorganosiloxane (POS) crosslinkable by polyaddition, by polycondensation, by cationic route or by radical route; (B) optionally at least one crosslinking organosilicon compound;

(C) optionally at least one catalyst or initiator of the crosslinking reaction;

(D) an anionic, cationic or nonionic surfactant;

(E) water; (1 ') optionally, a pre-crosslinking of the silicone phase is induced;

(2) the emulsion is destabilized using a triggering factor which inhibits the action of the surfactant (D), initiating the coalescence of the drops of silicone phase, and leading to a homothetic retraction of the gel;

(3) crosslinking of the silicone phase, that is to say of the constituents (A) and (B), causes the evolution of the coalescence and the retraction of the gel to be frozen; in the case where step (1 ′) is carried out, the crosslinking of the silicone phase is continued;

(4) the material obtained is dried to obtain the porous silicone material.

2. Method according to claim 1, characterized in that the surfactant (D) is an anionic or cationic surfactant.

3. Method according to claim 2, characterized in that, in step (2), the emulsion is destabilized by adding a saline solution leading to the coalescence of the drops of silicone oil.

4. Method according to claim 3, characterized in that it is a saline solution of a potassium salt, preferably potassium iodide, or also using NaOH, KCI or a salt of Ca or AI.

5. Method according to claim 3 or 4, characterized in that the emulsion and the saline solution are heated between 40 and 100 ° C, preferably between 60 and 80 ° C and mixed and homogenized at this temperature, then the mixture is cooled, in particular to a temperature less than or equal to 25 ° C.

6. Method according to claim 5, characterized in that during cooling, one plays on the parameters cooling medium and / or temperature.

7. Method according to claim 6, characterized in that the cooling is carried out in air, in water or in ice.

8. Method according to claim 1, characterized in that the surfactant (D) is a cationic surfactant and in that, in step (2), the emulsion is destabilized by adding an equimolar amount of a surfactant anionic.

9. Method according to claim 1, characterized in that the surfactant (D) is an anionic surfactant and in that, in step (2), the emulsion is destabilized by adding an equimolar amount of a surfactant cationic.

10. Method according to claim 8 or 9, characterized in that the surfactant used to destabilize the emulsion is introduced in step (2) in the form of a suspension of crystals at a temperature below the Kraft point of this surfactant.

11. Method according to one of claims 1 to 8 and 10, characterized in that the cationic surfactant (D) is sodium dodecyl sulfate.

12. Method according to one of claims 1 to 7 and 9, 10, characterized in that the anionic surfactant (D) is trimethyltetradecylammonium bromide.

13. Method according to claim 1, characterized in that the surfactant (D) is a nonionic surfactant and in that, in step (2), the emulsion is destabilized by heating.

14. Method according to any one of claims 1 to 13, characterized in that the emulsion comprises:

(A ') a diorganopolysiloxane oil having alkenyl groups, preferably vinyl, (B') a diorganopolysiloxane oil carrying hydrogen atoms, (C) a hydrosilylation reaction catalyst, optionally a catalyst inhibitor (C).

15. Method according to any one of claims 1 to 13, characterized in that the emulsion is a mixture of emulsions none of which contains together the three constituents (A), (B), (C), and in that these constituents are: (A ') a diorganopolysiloxane oil having alkenyl groups, preferably vinyl, (B') a diorganopolysiloxane oil bearing atoms of hydrogen, (C) a hydrosilylation reaction catalyst, and in that the crosslinking in step (3) results from the bringing together of the constituents (A '), (B') and (C) during coalescence of the drops.

16. Method according to any one of claims 1 to 13, characterized in that the emulsion comprises:

(A ") a diorganopolysiloxane oil having condensable, hydrolysable or hydroxy end groups,

(B ") a silane with condensable or hydrolyzable groups or a polyhydroxylated or polyalkoxylated silicone resin, (B) a polycondensation catalyst.

17. Method according to claim 16, characterized in that the crosslinking between the constituents (A ") and (B") is triggered before the destabilization in step (2).

18. Method according to any one of claims 1 to 17, characterized in that the container serves as a mold for the final porous silicone material.

19. Method according to any one of claims 1 to 18, characterized in that, in step (4), the drying is carried out by lyophilization.

20. Method according to any one of claims 1 to 19, characterized in that the container serves as a mold for the final porous silicone material.

21. Porous silicone material capable of being obtained by implementing the method according to any one of claims 1 to 20.

22. Article made of porous silicone material capable of being obtained by implementing the method according to any one of claims 1 to 20.