WO2004031200A1

WO2004031200A1 - Silanoxyl phosphates, preparation thereof and use thereof in linear polyorganosiloxane synthesis

Info

Publication number: WO2004031200A1
Application number: PCT/FR2003/002727
Authority: WO
Inventors: José MARTINS; Rémi THIRIA
Original assignee: Rhodia Chimie
Priority date: 2002-10-01
Filing date: 2003-09-16
Publication date: 2004-04-15
Also published as: AU2003276345A1; FR2845089A1; FR2845089B1

Abstract

The invention concerns silanoxyl phosphate mixtures useful in synthetic polymerization reactions of long-chain linear POS, optionally bearing at their ends functional groups such as hydroxyl and vinyl groups. The invention aims at providing a neutralizing agent based on silanoxyl phosphates, which is more efficient and enables to render more smooth and easier processes for synthesis of long POS by basic polymerization and neutralization, so as to make them simple, economical and to reduce the amounts of harmful by-products. Therefor the inventive method consists essentially in reacting in smooth conditions, phosphoric acid or derivatives thereof A with hexaorganotricyclosiloxane D3, to obtain a silanoxyl phosphate mixture of general formula (I), wherein m + n = 3, x ≥ 3. Said silanoxyl phosphate mixtures can be used as neutralizing solution in synthesis by chain elongation in base catalysis, of linear or branched POS oils and POS resins.

Description

SILANOXYL PHOSPHATES, THEIR PREPARATION AND THEIR USE IN THE SYNTHESIS OF POLYORGANOSILOXANES

LINEAR

The field of the invention is that of the synthesis of linear poly (di) organosiloxanes (POS), which are among the essential components of multiple known silicone compositions, such as compositions of hot-vulcanizable silicone elastomers (ENC) by the free-radical using peroxide, single-component silicone sealants (ENF1) vulcanizable by hydrolysis and condensation, with atmospheric water vapor and in the presence of that of tin, two-component silicones crosslinkable by condensation (ENF II and CAF) presence of tin salts or silicone compositions crosslinkable by ≡SiH / ≡Si-vinyl (RTV) polyaddition, in the presence of platinum.

More specifically, the invention relates to mixtures of silanoxyl phosphates useful in synthesis reactions by polymerization of linear POSs with long chains, optionally carrying at their ends functional groups such as hydroxyls or vinyls.

The invention also relates to the synthesis of long chain linear POSs in which it is possible to have recourse to these silanoxyl phosphates.

Conventionally, access to the linear polydiorganosiloxane chains, forming the low viscosity silicone oils as well as the high viscosity silicone gums is achieved by elongation of the siloxane oligomers resulting from the hydrolysis of organochlorosilanes.

Thus, these linear long chain POSs are most often obtained by polymerization of linear or cyclic oligoorganosiloxanes, in the presence of a basic catalyst which can be chosen from alkali metal hydroxides and / or from alkali metal silanolates (eg hydroxides of sodium, potassium, cesium, lithium and their corresponding silanolates and / or siloxanates).

These strong bases which catalyze anionically the polymerization of siloxanes (preferably at a temperature above 100 ° C.) must be perfectly neutralized. Most often this neutralization occurs when the polymerization reaction has reached its thermodynamic equilibrium (85% linear POS / 15% cyclic and linear POS of low molar masses). The neutralization of the basic catalyst (s) must be rapid and effective so as to put an end to any catalytic activity as soon as possible. Indeed, to avoid, in the final linear POS, the presence of POS compounds, linear or cyclic, of low molar masses, which could largely alter the final performances of the linear POS, it is essential to carry out a devolatilization at a temperature at less than 100 ° C, of the reaction medium. Part of the volatile compounds is then eliminated. But under these conditions of devolatilization, the slightest trace of catalyst, and a fortiori of the basic type, has a harmful influence. Indeed, in parallel with the loss by devolatilization of cyclic and linear POS compounds of low molecular weights, to maintain the thermodynamic equilibrium (85% linear POS / 15% cyclic and linear POS of low molecular weights), the basic catalyst has preferentially catalyzed chain breaks to generate cyclic and linear POS of low molecular weights from linear POS. Consequently, the properties of the linear POS of high molar mass can then be greatly altered.

The neutralization of these alkaline catalysts is most commonly carried out using one or more acid compounds, more especially chosen from the group comprising hydrochloric, acetic, phosphoric and toluene-sulfonic acids.

All neutralizing agents work with varying degrees of success. Phosphoric acid is particularly suitable since it is a triacid which, when used to neutralize an alkali metal hydroxide, forms potassium dihydrophosphate, dipotassium hydrophosphate and tripotassium phosphate. These salts act as a buffer in the system, which makes it possible to protect the polymers from traces of acid or basic impurities and to tolerate small errors when adding the theoretical amount of phosphoric acid. This acid is inexpensive and relatively non-toxic.

However, phosphoric acid has a drawback: it is insoluble in siloxanes and therefore requires constant stirring for long periods and a relatively high temperature to obtain a homogeneous and perfectly neutralized mixture.

In order to improve the solubility of phosphates in a mixture of siloxanes, one of the widely studied routes has been the preparation of silylated phosphates from phosphoric acid and organosiloxane derivatives. The resulting silylated phosphate is soluble in the siloxane medium and has good neutralization properties.

The prior art on silylated phosphates useful in the neutralization of alkaline catalysts in the synthesis of siloxanes, includes patent applications and patents, a number of which are discussed below by way of illustration. French patent application FR-A-2 410 004 describes silylated phosphates useful as neutralizing agents in the preparation of silicone and their manufacturing processes. These silylated phosphates are obtained from hexamethyldisiloxanes (M ₂ ) or polydimethylsiloxanes α, ra-di- (trimethylsilyl): {M (D) _x = _2. ₂ o}, on the one hand, and oxybromide (Br) ₃ P = O or chloride (Cl) ₃ P == O phosphorus, on the other hand, the reaction temperature for the preparation of these silylphosphates is 120 ° C. At the end of the reaction of the organohalosilanes, addition reaction products are removed by distillation (at a temperature above 150 ° C). European patent EP-B-0 299 640 relates to a process for the production of a polydiorganosiloxane substantially free of hydroxyl groups in which the neutralization is carried out by an agent obtained by reacting hexamethyldisilazane and phosphoric acid. There is no provision for cooling the reaction medium, the temperature of the latter being on the contrary maintained for a time sufficient to allow the elimination of the OH groups. The volatile compounds are finally eliminated by evaporation. The performance of this neutralizing agent remains to be demonstrated.

European patent EP-B-0 708 780 discloses a catalyst for manufacturing POS, this catalyst being characterized in that it is obtained by transforming phosphonitrile chloride with tris (trimethoxysiloxy) phosphate. The latter compound is obtained by reaction of:

H ₃ PO ₄ + ClMe ₃ This is not a neutralizing agent for an alkaline polymerization catalyst for silicone oligomers but a new polymerization catalyst. This invention is therefore outside the scope of the present invention.

European patent EP-B-0 742 263 describes silylated phosphonates used as stabilizing agents during the synthesis by basic polymerization of polydiorganosiloxanes. The silylated phosphonate can be a vinyl bis (trimethoxysilyl) - phosphate which is placed in the presence of octamethylcyclotetrasiloxane (D) and of vinylated polydimethylsiloxane, to form a gum after reaction at 250 ° C., in the presence of a catalyst alkaline stabilized by silylated phosphonate.

The stabilizing performances of these silylated phosphonates are entirely perfectible. The patent documents mentioned above constitute a distant technological background which is irrelevant to the present invention. French patent application FR-A-2 416 898 relates to a process for the manufacture of silylated phosphate compounds from octamethyltetracyclosiloxane (D), hexamethyldisiloxane (M), phosphoric acid H ₃ PO ₄ and a silyl phosphate foot. The addition of the latter makes it possible to improve the miscibility of the reagents. At the end of the synthesis of these silylated phosphates, the temperature of the reaction medium is 196 ° C. The neutralization performance of these silylated phosphates in the context of basic POS polymerization is not evaluated in this document. These neutralizing agents based on silylated phosphate comprise a chain stopper M ₂ , capable of counteracting the titer of terminal functional groups in the synthesized POS polymers. In addition, this neutralization mixture may contain by-products harmful to the polymerization. In addition, the preparation of this mixture of silylated phosphates includes a final devolatilization step which makes the process cumbersome. Finally, this neutralizing mixture does not overcome the cooling operation during the neutralization of the basic polymerization of POS. European patent EP-B-0 488 490 relates to a process for the preparation of a mixture of silylated phosphates, the mixture itself and the use of this mixture in the stabilization of metal silanolates, during the basic polymerization of POS. This mixture of silylated phosphates comprises: o 10 to 30% of monosilyl phosphates [(CH ₃ ) ₃ SiO] (HO) ₂ P =, o 65 to 85% by weight of a disilyl phosphate of formula [CH ₃ ) ₃ SiO] ₂ (HO) P = O, o and 2 to 7% by weight of a trisilyl phosphate of formula [(CH ₃ ) ₃ SiO] ₃ P = O. This mixture is obtained by reacting phosphoric acid and hexamethyldisiloxane M ₂ , trapping the water formed and allowing the temperature to rise to 150-190 ° C. This stabilizing silyl phosphate mixture can be combined with CO ₂ gas, for the neutralization of the alkaline catalyst during the basic polymerization of POS.

Patent EP-B-0 528 508 relates to a mixture of silanoxyl phosphates and its use in the stabilization of metal silanolates, during the basic polymerization of linear POS. This mixture of silanoxyl phosphates is obtained by reacting hexamethyldisiloxane M ₂ with H ₃ PO ₄ , as described in document EP-B-0488 490, in order to obtain a mixture of silylated phosphates. The latter is then placed in the presence of cyclopolydimethylsiloxane comprising from 3 to 7 dimethylsiloxane units (D. ₇ ), at ambient temperature or at 170 ° C., to obtain the desired mixture of silanoxyl phosphates. This mixture of silanoxyl phosphates, useful as an agent for neutralizing the basic polymerization of POS, has the same drawbacks as those mentioned against the mixture of neutralizing silyl phosphates according to document EP-B-0 488 490 .

It appears from this second extract of the prior art that the silylated phosphates which relate to it, always imply the use of siloxy groups M (M: R ₃ SiOι _{/ 2} -, with R = H, alkyl or OH, for example) supplied by compounds M ₂ which act as chain limiters. However, if the introduction of these groups M is not too problematic in the synthesis of non-reactive POS oils, it is not the same for the synthesis of functionalized POS of the polydimethylorganosiloxane a, w-dihydroxy type. In fact, during the neutralization step, these entities M replace the silanol functions, thus reducing the reactivity of the silicone chains, as well as the physicochemical properties sought for these silicones in the final applications.

It is also clear that this prior art is fishing in the supply of a neutralizing agent, which is more efficient and which makes it possible to soften and lighten the processes for the synthesis of long POSs by basic polymerization and neutralization, for the sake of simplification, economy and reduction of the quantities of harmful by-products. In this context, one of the essential objectives of the present invention is to provide new neutralizing agents constituted by silanoxyl phosphates which, by themselves and through their preparation processes, remedy the drawbacks noted in the prior art . Another essential objective of the present invention is to provide a process for preparing mixtures of silanoxyl phosphates, which is economical, easy to implement and in which no precursor chain precursors of M siloxy units are used, in order to to preserve, during the neutralization step of silicone oils polymerized by basic catalysis, the reactivity of the ends of the siloxane chains. Another essential objective of the present invention is to provide a process for the preparation of mixtures of silanoxyl phosphates, during which little or no harmful by-products are generated, capable of causing instability of the polymers formed after neutralization, in particular during the final devolatilization treatment (distillation) or during storage. Another essential objective of the present invention is to provide a process for the preparation of mixtures of siloxanyl phosphates, which is efficient in terms of yield and conversion rate, under mild conditions (temperature, pressure) of implementation.

Another essential objective of the present invention is to provide a process for the preparation of mixtures of silanoxyl phosphates, which does not require devolatilization step (s), so that the mixture of siloxanyl phosphates obtained can be used directly under crude form, as a neutralizing agent in basic POS polymerizations.

Another essential objective of the present invention is to provide a process for the preparation of mixtures of silanoxyl phosphates, which makes it possible to simplify the neutralization in the processes of synthesis of POS by basic catalysis.

Another object of the present invention is to provide a mixture of silanoxyl phosphates having low polydispersity indices, that is to say a high level of polymers and a reduced rate of volatiles. Another essential objective of the present invention is to provide mixtures of siloxanyl phosphates free of M siloxy units capable of disturbing the reactivity and the functionalities of the ends of the polyorganosiloxane chains obtained by basic catalysis and neutralized using said mixture of silanoxyl phosphates. Another essential objective of the present invention is to provide a process for the synthesis of linear polydiorganosiloxanes involving basic catalysis and neutralization using silanoxyl phosphates, this process comprising simplified operating conditions, economical and suitable for not harm qualities intrinsic POS obtained, especially in terms of chemical functionalization, stability and physicochemical properties as expected in silicone applications.

These objectives, among others, are achieved by the present invention which firstly relates to a process for the preparation of a mixture of silanoxyl phosphates comprising compounds of general formula (I) below:

K ₃

VS ,

(I) with m + n = 3, x> 3; characterized in that it essentially consists in reacting phosphoric acid or its derivatives A with hexaorganotricyclosiloxane Dj of formula (II) below:

(II) with R independently representing hydrogen - or a hydrocarbon group, preferably a Cι-C ₂₀ alkyl (and more preferably linear or branched Cι-C ₆ ), or a C ₂ -C o alkenyl (and more preferably still a vinyl or an allyl).

Thus, the inventors have had the merit of highlighting, in a completely surprising and unexpected manner, that it is possible to carry out a synthesis of siloxanyl phosphates, without the introduction of siloxy M units, by polymerization of D ₃ and phosphoric acid or derivative A, under mild conditions.

Besides the fact that it makes it possible to dispense with the use of siloxy M units, which preserves the reactivity of the ends of the siloxane chains during neutralization, the method according to the invention is also advantageous in that hexamethyltrisiloxane D ₃ has a reaction kinetics such that the polymerization proceeds perfectly, without the formation of by-products capable of damaging the neutralizing and stabilizing properties of the silanoxyl phosphates. Thus, the production of the latter from D ₃ + H ₃ PO ₄ , is simple, rapid and selective. It therefore does not require the use of a post-polymerization treatment for purifying the reaction medium (distillation).

The preparation of silanoxyl phosphates according to the invention has another advantage which is due to the fact that D ₃ is a readily available raw material, posing no handling and economic problem.

Another advantage of this process, based on the polymerization reaction of D ₃ with H ₃ PO ₄ , is due to the relatively loose temperature / pressure conditions, so that the secondary reactions such as gel formation or the uncontrolled increase in molar mass due to polycondensation. In this regard, and according to a preferred characteristic of the process according to the invention, the temperature T (in ° C.) of the reaction A + D ₃ is fixed as indicated below:

T <80 preferably 40 <T <70 and even more preferably 55 <T <65

Finally, the process according to the invention which provides for the polymerization by opening of D at a temperature below 80 ° C. and preferably at atmospheric pressure, is therefore easy and simple to implement, in particular in terms of control, kinetics, but also manipulation and security.

The derivatives dΗ ₃ PO ₄ are designated by the reference A in the context of the invention, may in particular be monoalkylphoshates.

Preferably, the quantities of Dj and A used are such that the molar ratio Dj 1 A is defined as follows:

0.1 ≤ Ds / A ≤ lO preferably 0.5 <D ₃

7 and more preferably still 1 <Dj / A_ <5

According to a preferred embodiment, the reaction A + Dj is carried out in the presence of at least one polyorganocyclosiloxane D _E of formula (TLI) below:

(ni) with 4 <p <7, preferably p = 4.

According to a preferred characteristic of the invention, the amounts of D _E and

Dj implemented are such that the molar ratio D _E / Dj is defined as follows:

0, l ≤ D _â / β _& ≤ 8.0 preferably 1.0 ≤ Ds / 2 ^ 5.0 and more preferably still 1.5 <D ₃ / D _E _ <3.5.

In practice, this polymerization is carried out in bulk, at a temperature below 80 ° C (eg 60 ° C), at atmospheric pressure, in a mixture of cyclic siloxanes, and more particularly, in D ₄ used as solvent. By way of example, the reaction scheme for the synthesis can be as follows:

D ₃ + H ₃ PO ₄ } _m (HO) _n P = O

T <80 ° C t = 360 min. with m + n = 3

CH

For these experimental conditions, the mixture of siloxanyl phosphates obtained, results from the polymerization between D ₃ (and not that of D) and phosphoric acid A, without formation of by-products, so that any step of elimination of such by-products by distillation / devolatilization is unnecessary.

The fact of providing in accordance with the invention for the polymerization reaction of D ₃ with H ₃ PO ₄ in a silicone-only medium, for example in a mixture of cyclic siloxane and more particularly in D ₄ inert under the preferred operating conditions, constitutes a significant advantage.

A D ₃ / D ₄ mixture can also be used.

A mixture of solvent (hydrocarbon, for example methyl toluene = cyclohexane, chloroform) making it possible to obtain a liquid and diluted D ₃ . Advantageously, the mixture of silanoxyl phosphates obtained by the process according to the invention and comprising compounds of general formula (I), is free of precursors of siloxy units M: ≡Si-Oι _{/ 2} -, and preferably of disiloxane of formula (IV) below:

(IV) with R ′ independently representing hydrogen or a hydrocarbon group, preferably a Cι-C ₂₀ alkyl (and more preferably linear or branched in C ₆ -C ₆ ), or a C ₂ -C ₂₀ alkenyl (and more preferably still a vinyl or an allyl), at least one of the radicals R ′ corresponding to hydrogen or to an alkenyl as defined above.

One of the benefits induced by the mild temperature / pressure conditions in the process according to the invention is that there is little or no redistribution phenomena, so that the mixture obtained essentially contains polymers. In fact, the polydispersity index (IP) of the compounds of formula (I) is defined as follows in accordance with the invention:

IP <2.5 preferably 0.1 ≤ IP <2.0 and even more preferably 1.0 <IP ≤ 1.6.

Even if this does not correspond to an overriding necessity, provision may be made, according to an implementation variant, for carrying out a purification treatment of the final reaction medium. It may, for example, be a distillation which makes it possible to remove residual water.

According to another of its aspects, the present invention relates to mixtures of silanoxyl phosphates compounds of general formula (I) and capable of being obtained by the process as defined above. Preferably, this mixture is free of precursors of siloxy units M:

≡Si-Oι _{/ 2} -, and preferably hexaalkyledisiloxane of formula (IV) below:

(IN)

with R 'independently representing hydrogen or a hydrocarbon group. preferably a Cι-C ₂₀ alkyl (and more preferably linear or branched Ci-

C ₆ ), or a C ₂ -C ₂ alkenyl (and more preferably still a vinyl or an allyl), at least one of the radicals R 'corresponding to hydrogen or to an alkenyl as defined above .

This mixture of silanoxyl phosphates constitutes a neutralizing agent of choice for the polymerization of linear POS by basic catalysis.

The mixtures according to the invention are all the more advantageous for this application, as they are characterized by a dynamic viscosity η (in mPa.s at 25 ° C) defined as follows: η <15,000 preferably η <10,000 and more preferably still 100 ≤ η <8,000.

The low viscosity of siloxanyl phosphates according to the invention facilitates their incorporation into the siloxane medium during the step of neutralization of the synthesis of POS by basic catalysis.

Their purity (absence of this harmful product) and their low polydispersity index (PI) defined as follows:

IP <2.5 preferably 0, 1 <IP <2.0 and more preferably still 1.0 <IP <1.6 are all other advantages for these new products according to the invention.

According to a preferred arrangement of the invention, the mixture of silanoxyl phosphates comprises:

- from 20 to 40% by weight of a monosiloxanyl phosphate of formula:

- from 50 to 70% by weight of disiloxanyl of formula

from 1 to 10% by weight of a trisiloxanyl phosphate of formula:

It should also be noted that the concentration of free H ₃ PO ₄ in the mixtures of siloxanyl phosphates is between 0 and 5% by weight. This means that H ₃ PO or its derivatives A have reacted completely or practically and therefore are not likely to form troublesome or undesirable by-products.

According to yet another of its aspects, the invention relates to a process for the synthesis of polyorganosiloxanes (POS), this process being of the type of those involving at least one cyclic POS and at least one alkaline catalyst allowing the cracking and polymerization of POS cyclic, this polymerization being stopped by neutralization of the catalyst, to possibly make way for an elimination of volatile POS, characterized in that the neutralization is carried out using the mixture of silanoxyl phosphates comprising compounds of general formula (I) obtained by the method as defined above or by the mixture as defined above. Thus, mixtures of silanoxyl phosphates can be used as neutralizing solution during the synthesis by elongation of chains in basic catalysis, of linear or branched POS oils and POS resins. They may, for example, be α, ω-di-OH polydimethylsiloxane oils or POS resins comprising M (≡SiO ₂ ) units and T (-SiO _{/ 2} ) units and / or Q units: (SiO _4/2 ). By doing this for neutralization, the side reactions are limited, even non-existent, and the reproducibility is significantly improved, even for POSs of high viscosity, of the order of 10 ⁶ mPa.s with hydroxydimethylsiloxy ends. The ratio SiOH / total number of silicon in the chain is not affected. The OH titer is therefore stable. Furthermore, the absence of M ₂ is synonymous with hydroxylated M chain terminations, to the exclusion of only alkylated M units. This presence of OH at the ends generates interactions between the molecules (H bonds) which contribute to the increase in the miscibility of basic catalysts of the potassium salt type. According to an advantageous characteristic of the POS synthesis process according to the invention, the addition of the neutralizing agent is carried out without associated modification of the temperature / pressure conditions of polymerization.

As regards the operating conditions of this process, they are preferably the following: - polymerization at normal atmospheric pressure and at a temperature above room temperature (for example,> 100 ° C.),

- Addition of the neutralizing agent based on the mixture of silanoxyl phosphates, carried out without associated cooling of the polymerization reaction medium. The invention will be better understood in the light of the examples which follow, of the implementation of the process for the preparation of siloxanyl phosphates according to the invention and the use of the latter as neutralizing agents in syntheses by basic polymerization of polydimethylsiloxanes with hydroxyl ends or MQ silicone resins.

EXAMPLES

EXAMPLES 1-4

Examples 1 & 2 relate to reference reactions (D ₃ or D ₄ alone with

H ₃ PO). The next two deal with the synthesis of siloxanyl phosphates from a D ₃ / D mixture. The mass of the reactants, the polymerization temperature and the references of the examples are specified in Table 1 below.

Example 1: Reaction between D and H, PO at 60 ° C

Poured (reference t = 0), with stirring, under a stream of nitrogen, into a dry three-necked flask of 250 ml, 4.80 g (0.049 mole) of phosphoric acid (PROLABO® origin, 99% by mass), into 46 , 2 g (0.155 mol) of D (RHODIA® origin, purity> 99%) previously brought to 60 ° C. The mass percentage of phosphoric acid in the reaction medium is 9.6. The two reagents are not miscible. After 10 hours at 60 ° C, the reaction medium remains biphasic. The assay of the residual acidity of the reaction medium with a 0.01 N ethanolic potassium hydroxide solution shows that the percentage of phosphoric acid is identical to the initial percentage. The ³¹ P phosphorus NMR demonstrates the absence of silylated phosphate compounds. The results are summarized:

No reactions at 60 ° C between D and H ₃ PO

Example 2: Reaction between D, and H, PO at 80 ° C

36.01 g (0.265 mole) of phosphoric acid (99% by mass) are poured into a dry 1000 ml three-necked flask provided with mechanical stirring and a nitrogen inlet. 10 g (0.898 mole) of D ₃ previously brought to 80 ° C. (completely molten medium). The initial mass percentage of phosphoric acid is 11.5. After 360 minutes at 80 ° C, the measured viscosity of the reaction medium is 25,000 mPa.s. The percentage of residual phosphoric acid in the reaction medium, determined by acid-base determination (0.01 N ethanolic potassium hydroxide solution) is 10.95. The results are summarized in Tables 3 & 4 below. D ₃ reacts with H ₃ PO ₄ at 80 ° C Very high viscosity

Examples 3 and 4: Polymerization reaction between D, and H, PO at 60 ° C.

A mixture, previously brought to 60 ° C., consisting of 30 g (0.039 mole) of D ₃ and 20 g (0.067 mole) of D ₄ , is poured (reference t = 0), under an inert atmosphere and with mechanical stirring. , 3.85 g (0.039 mole) 99% phosphoric acid. The medium is left under mechanical stirring for 360 minutes. Samples of the reaction medium, as a function of time, are taken in order to monitor the progress of the reaction. These samples are characterized by acid-base determination, by viscosimetry and by NMR of phosphorus P (Tables 2 & 3) and of silicon Si. The NMR of the silicon of the sample, taken after 60 minutes of reaction, shows that the characteristic signal of D ₃ is absent, the rate of transformation into D ₃ is then 100%. The viscosity and percentage phosphoric acid profiles show that after 240 minutes of reaction, the reaction medium no longer changes. The reaction medium is in thermodynamic equilibrium. A reduced vacuum in order to carry out devolatilization or even partial can be applied at the end of the synthesis.

Comparative example 5

This comparative example corresponds to a preparation of silylated phosphates according to the methodology described in patent application FR-A-2 416 898: D ₄ + MDM + H ₃ PO ₄ + silylated phosphate.

To 8.79 g of a silyl-phosphate solution are added 112.21 g of 85% phosphoric acid. The reaction medium is then brought to 160 ° C. for 3 hours, under an inert atmosphere. Then a partial dehydration of the medium is carried out by applying a reduced vacuum. After cooling to 60 ° C., 19.66 g of polydimethylsiloxane α, tσ-di- (trimethylsilyl) and 59.34 g of tetracyclosiloxane D ₄ are poured in. Table 2:% in H ₃ PO ₄ dosed and kinematic viscosity measured for examples 1 to 4 & 5 comp

a) determined by acid-base determination

Table 3: Determination of the composition of the reaction medium by phosphorus NMR from Examples 1 to 4 & 5 comp (CDC1 ₃ ; T = 25 ° C)

An analysis by NMR ^• 29, Si confirms, for Examples 3 and 4, the absence of D.

The siloxanyl phosphates according to the invention and as described in the examples above, come strictly from the polymerization reaction between D ₃ and H ₃ PO. Indeed, the peak corresponding to the chemical displacement of a silicon atom of the molecule D ₃ is not identified on the NMR spectrum ²⁹ Si of the final solution (examples 3 and 4). No undesirable side reactions are demonstrated. Siloxanyl phosphates have little or no free phosphoric acid. The concentration of monosiloxanyl phosphate is more than twice that of siloxanyl phosphate with M units from Example 5 comp. The synthesized siloxanyl phosphates have low viscosities (<7100 mmfVs ^"1 ) which will thus allow very good homogenization in the siloxane medium during the neutralization step.

Example 6, 7 and 8: stability of neutralizing solutions without M group

The loads and experimental conditions of tests 6 to 8 are summarized in table 4 below. The methodology is that of Examples 2 & 3. A reduced vacuum in order to effect devolatilization of the reaction medium was applied at the end of the synthesis.

Table 4: operating conditions for syntheses of neutralizing solutions

a) determined by acid-base determination

The stability of the various neutralizing solutions was evaluated as a function of time at a temperature of 50 ° C. The parameters used to characterize the solutions were the visual aspect (decantation), the viscosity and the overall concentration of phosphoric acid (acid-base assay).

Table 5 below shows the results obtained.

a) determined by acid-base determination After 365 days of storage at 50 ° C., no change in terms of appearance, viscosity and concentration of phosphoric acid is recorded.

The neutralizing solutions without group M, synthesized from D ₃ and dΗ ₃ PO, in a D ₄ medium, are stable at 50 ° C.

Examples 9 to 11: Application of mixtures of silanoxyl phosphates according to the invention to the neutralization of α.ω-diOH polydimethylsiloxanes

8000 g of a mixture composed of cyclosiloxane and oligodimethylsiloxane α, ω-diOH of low molar mass are added to a 12-liter reactor equipped with an in-line viscometer and mechanical stirring. After bringing the reaction medium to 60 ° C., 110 ppm of the potassium hydroxide-based catalyst solution are added. After setting to temperature at 160 ° C., the medium is left under mechanical stirring for 240 minutes. An increase in viscosity of the reaction medium is observed. Then 430 ppm of the new neutralizing solution prepared in Example 7 are added to the reaction medium. Upon addition, the measured viscosity of the reaction medium no longer increases and stabilizes, there certainly indicating good neutralization of the catalyst. The acid-base character of the reaction medium is controlled by the use of a colored indicator. To 40 ml of a solution composed of ethanol / isopropyl ether (50/50 V / V) and bromocresol purple are added 10 grams of the reaction medium. The color green (neutral) to yellow (acid) indicates that the reaction medium has been perfectly neutralized. The medium is left for another 10 minutes at 160 ° C., with mechanical stirring. Then a reduced vacuum is applied, for 60 minutes, in order to effect devolatilization by distillation of the compounds of low molecular weights.

Measurements by Thermo-Gravimetric Analysis (250 ° C / 16 h / N ₂ ) of the final polydimethylsiloxane, ω-diOH were carried out in order to evaluate their thermal stability. A still basic reaction medium would lead to an increase, under temperature, in the rate of low volatiles.

These polymerization tests were repeated by modifying the nature and the quantity used in neutralizing solution (Table 6). The characteristics of the polydimethylsiloxanes α, ω-diOH synthesized are shown in Table 7. Table 6: experimental conditions of the various polydimethylsiloxane α, ω-diOH oils synthesized (T reaction = 160 ° C)

a) 14.5% by weight of KOH

Table 7: characteristics of the different oils

a) residual percentage at low volatiles

The solution obtained, after homogenization, is either neutral or slightly acid, which shows that the neutralizing solution has perfectly neutralized the reaction medium.

All oils, in accordance with the thermal test, are considered to be thermally stable and therefore perfectly neutralized.

The neutralizing solutions perfectly neutralize the reaction medium during the synthesis of a polydimethylsiloxane α, ω-diOH catalyzed by potassium hydroxide.

The neutrality test indicates that the reaction medium is either neutral or slightly acidic.

By the analyzes carried out by ATG, the rate of volatiles defined is very low, indicating a very good thermal performance of the neutralized oils.

Claims

-1- Process for the preparation of a mixture of silanoxyl phosphates comprising compounds of general formula (I) below:

(I) with m + n = 3, x>3; characterized in that it essentially consists in reacting phosphoric acid or its derivatives A with rhexaorganotricyclo-siloxane D ₃ of formula (II) below:

(II) with R independently representing hydrogen or a hydrocarbon group, preferably a Cι-C ₂₀ alkyl (and more preferably linear or branched Cι-C ₆ ), or a C -C ₂₀ alkenyl (and more preferably another vinyl or allyl).

-2- Method according to claim 1 characterized in that one fixes the temperature T (in ° C) of the reaction A + D ^ as indicated below:

T <80 preferably 40 <T <70 and even more preferably 55 <T <65

-3- The method of claim 1 or 2 characterized in that one carries out the reaction A + PJ, in the presence of at least one polyorgano-cyclosiloxane E ^ of formula (HI) below:

(III) with 4 ≤ p <7, preferably p = 4.

-4- A method according to any one of claims 1 to 3 characterized in that the amounts of Dj and A used are such that the molar ratio D ₃ / A is defined as follows:

0.1 <D ₃ / A <10 preferably 0.5 <D ₃ / A _^ ≤ 7 and more preferably still 1 ≤ D ₃ / A ≤ 5

-5- The method of claim 3 or 4 characterized in that the quantities of D _E and Dj used are such that the molar ratio D _E / D ₃ is defined as follows:

0.1 <D ₃ / D _E _ <8.0 preferably 1, 0 ≤ D ₃ / D ^ ≤ 5.0 and more preferentially still 1.5 ≤ D ₃ / D _E _ <3.5

-6- A method according to any one of claims 1 to 5 characterized in that the mixture of silanoxyl phosphates comprising compounds of general formula (I), is free of precursors of siloxy units M: ≡Si-Oι _{/ 2} - , and preferably hexaalkyledisiloxane of formula (IV) below:

(IV) with R ′ independently representing hydrogen or a hydrocarbon group, preferably a Cι-C ₂₀ alkyl (and more preferably linear or branched in C ₆ -C ₆ ), or a C ₂ -C ₂₀ alkenyl (and more preferably still a vinyl or an allyl), at least one of the radicals R ′ corresponding to hydrogen or to an alkenyl as defined above. -7- A method according to any one of claims 1 to 7 characterized in that the mixture of silanoxyl phosphates comprising compounds of general formula (I), has a polydispersity index (IP) defined as follows:

IP <2.5 preferably 0, 1 <IP ≤ 2.0 and even more preferably 1.0 ≤ IP <1.6

-8- Mixture of silanoxyl phosphates comprising compounds of general formula (I) and capable of being obtained by the process according to any one of claims 1 to 7, characterized in that it is free of precursors of siloxy units M: ≡Si-Oι _{/ 2} -, and preferably hexaalkyledisiloxane of formula (IV) below:

(IV) with R 'independently representing hydrogen or a hydrocarbon group, preferably a Cι-C ₂₀ alkyl (and more preferably linear or branched in d- C ₆ ), or a C ₂ -C ₂ alkenyl ( and more preferably still a vinyl or an allyl), at least one of the radicals R ′ corresponding to hydrogen or to an alkenyl as defined above.

-9- Mixture of silanoxyl phosphates comprising compounds of general formula (I) and capable of being obtained by the process according to any one of claims 1 to 7, characterized by a dynamic viscosity η (in mPa.s to 25 ° C) defined as follows: η <15,000 preferably η <10,000 and more preferably still 100 ≤ η <8,000

-10- Mixture of silanoxyl phosphates comprising compounds of general formula (I) and capable of being obtained by the process according to any one of claims 1 to 7, characterized by a polydispersity index (PI) defined as follows: IP <2.5 preferably 0, 1 <IP <2.0 and more preferably still 1.0, ≤ IP ≤ 1.6

-11- Process for the synthesis of polyorganosiloxanes (POS), this process being of the type involving those involving at least one cyclic POS and at least one alkaline catalyst allowing the cracking and polymerization of cyclic POS, this polymerization being stopped by neutralization of the catalyst , to possibly make room for an elimination of volatile POS, characterized in that the neutralization is carried out using the mixture of silanoxyl phosphates comprising compounds of general formula (I) obtained by the process according to any one of the claims 1 to 7 or the mixture according to any one of claims 8 to 10.

-12- Synthesis process according to claim 11, characterized in that the addition of the neutralizing agent is carried out without associated modification of the temperature / pressure conditions of polymerization.

-13- Synthesis process according to claim 12, characterized in that the polymerization is carried out at normal atmospheric pressure and at a temperature above room temperature, and in that the addition of the neutralizing agent is carried out without cooling related polymerization reaction medium.