GB2468952A - Elevated pressure polysiloxane preparation - Google Patents

Abstract

A method of making a polysiloxane containing polymer comprising the steps of: i) preparing polysiloxane containing polymer by the ring opening of siloxane containing monomers and/or oligomers which comprise at least 2 condensable groups per molecule, in the presence of a) one or more ring opening catalysts and optionally one or both of b) a diluent and/or an end-blocking agent; and ii) where required quenching the polymerisation process. The diluent can be selected from one or more of trialkylsilyl terminated polydimethyl siloxane, polyisobutylene (PIB), and phosphate ester polyalkylbenzenes, linear and/or branched alkyl benzene esters of aliphatic monocarboxylic acids. Wherein, when present, the diluent is substantially retained within the resulting diluted polysiloxane containing polymer; characterised in that the process takes place at a pressure of at least 75 x 105Pa. The polymer can be used in sealant formulations, coating formulations, and high consistency organopolysiloxane gum fomulations.

Description

PREPARATION OF ORGANOSILOXANE POLYMERS

[0001] This invention is concerned with the ring opening polymerisation of cyclic siloxane monomers, optionally in the presence of a diluent, at high pressures.

[0002] It is well known that cyclic siloxane monomers may be polymerised via a ring opening reaction pathway to high molecular weight, high degree of polymerisation (dp) polymers by polymerisation in the presence of a suitable ring opening polymerisation catalyst and, where deemed necessary, heat.

[0003] A new process for the ring opening polymerisation of cyclic siloxane monomers is described in W02006/106361 in which additionally an extender (sometimes referred to as a processing aid) and/or a plasticiser, typically used in compositions containing the polymer end-product, such as silicone based sealants, is/are present during polymerisation. Generally the extender and/or plasticiser is unreactive with the reactants, intermediates and the reaction product(s). This innovative method may result in the preparation of exceptionally long chain polymers whilst avoiding processing problems when subsequently used in compositions. The presence of the plasticiser and/or extender maintains the diluted polymer at a manageable viscosity, whilst the polymer itself would, in the absence of the plasticiser and/or extender, have a viscosity of many millions of mPa.s at 25°C. W02006/1 06361 indicates that ring opening reactions may be carried out at any suitable pressure although in order to facilitate removal of by-products or the like formed or present during the ring opening polymerisation process, the polymerisation process may take place at a pressure below 80 kPa.

[0004] Methods for the production of siloxane polymers using high pressure have been previously described. For example. GB756613 describes ring opening polymerisation at pressures of at least 1 500lbs using an acid catalyst. All examples provided show that very high concentrations (>2%) of acid catalyst are required. GB756614 describes a process for ring opening polymerisation under pressure using a pressure of at least 1500 lbs but no catalyst. It is to be noted that the examples in GB756614 require very long reaction times which effectively renders them of minimal interest commercially. US2759007 and US2759008 describe a ring opening polymerisation process requiring high pressure of least 1500 lbs whilst using a base as the polymerisation catalyst. In the case of both US2759007 and US2759008, it can be seen from the examples that high viscosity polymers are only obtained when using high concentrations of base catalyst and very high temperatures. US4250290 describes a continuous polymerisation process using cyclic polysiloxanes to achieve polymers with viscosities of from 500-500000 centipoise at 25° C. Pressure may be additionally applied to the process.

[0005] EP0221 824 describes a process for the acid or base catalysed polymerisation of cyclic polydiorganosiloxane oligomers or mixtures of cyclic and linear polydiorganosiloxane oligomers having at least one -OH group per molecule. The polymerisation process in EP0221 824 takes place in at least one fluid under supraatmospheric pressure. The physical state of the fluid during polymerisation is chosen from: (I) A gas under supraatmospheric pressure (ii) a liquid state; or (iii) a supercritical state and the resulting polymer is recovered by "expansion" i.e. removal of the fluid by allowing it to change into its normal gaseous state. This results in a substantially undiluted polymer which at high viscosities will be in viscosity of many millions of mPa.s at 25°C. However, the experimental data provided shows that a small but significant amount of low molecular weight volatile siloxanes (>2% by weight) remain in the polymer subsequent to preparation and hence a pure polymer is not obtained. It is further to be appreciated that from the relatively high levels of residual volatile siloxanes located it is apparent that when discharged from the reaction vessel after polymerisation the fluid does not extract the volatile siloxanes out of the polymer.

[0006] None of these cases teaches that reaction rates of the ring opening reaction are increased when high pressures are applied. Furthermore, with the exception of W02006/1 06361 none describe the use of a diluent which is retained after completion of the polymerisation process described.

[0007] The problem of producing high viscosity siloxane polymers with viscosities of above 1000000 mPa at 25° C in an efficient manner is therefore still not completely solved. In order to achieve high conversion rates and high polymer viscosities significant amounts of catalysts and elevated temperatures are currently used. While all catalyst residues are detrimental to polymer stability, high temperatures are not desirable in respect of energy usage.

[00081 Surprisingly the inventors have found that significant reaction rate increases can be obtained during the ring opening polymerisation of cyclic siloxane monomers by undertaking the process at high pressures despite all the ingredients and products being in liquid form and therefore, from typical expectations, unlikely to be significantly affected by such pressure increases.

[0009] In accordance with the present invention there is provided a method of making a polysiloxane containing polymer comprising the steps of: i) Preparing a polysiloxane containing polymer by the ring opening of cyclic siloxane monomers, in the presence of a) one or more ring opening catalysts and optionally one or both of b) a diluent and/or an end-blocking agent; and ii) Where required quenching the polymerisation process; iii) characterised in that the process takes place at a pressure of at least 75 x i05 Pa.

[0010] The concept of "comprising" where used herein is used in its widest sense to mean and to encompass the notions of "include" and "consist of". Unless otherwise indicated all viscosity values given are at a temperature of 25°C.

[0011] A polysiloxane containing polymer is intended to mean a polymer comprising multiple polysiloxane groups per molecule and is intended to include a polymer substantially containing solely polysiloxane groups in the polymer chain or polymers where the backbone contains both polysiloxane groups and organic polymeric groups in the polymer chain.

[0012] The inventors have found that any known suitable cyclic organopolysiloxane monomer/oligomer may be utilised in the polymerisation process in accordance with the present invention. Cyclic siloxanes which are useful are well known and commercially available materials. They have the general formula (R2SO)m, wherein each R may be the same or different and denotes hydrogen or a hydrocarbon group having from 1 to 18 carbon atoms, a substituted hydrocarbon group having from 1 to 18 carbon atoms or a hydrocarbonoxy group having up to 18 carbon atoms. Preferably R is an optionally substituted alkyl, alkenyl, aryl, alkaryl or aralkyl group having up to 8 carbon atoms; m denotes an integer with a value of from 3 to 12. R may contain substituted groups, e.g. by halogen such as fluorine or chlorine. The alkyl group can be, for example, methyl, ethyl, n-propyl, trifluoropropyl, n-butyl, sec-butyl, and tert-butyl. The alkenyl group can be, for example, vinyl, allyl, propenyl, and butenyl. The aryl and aralkyl groups can be, for example, phenyl, tolyl, and benzoyl. The preferred groups are methyl, ethyl, phenyl, vinyl, and trifluoropropyl. Preferably at least 80% of all R groups are methyl or phenyl groups, most preferably methyl. Preferably the average value of m is from 3 to 6. Examples of suitable cyclic siloxanes are octamethylcyclotetrasiloxane, hexamethylcyclotrisiloxane, decamethylcyclopentasiloxane, cyclopenta(methylvinyl)siloxane, cyclotetra(phenylmethyl)siloxane, cyclopentamethylhydrosiloxane and mixtures thereof.

One particularly suitable commercially available material is a mixture of comprising octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane.

[0013] For the purpose of this application "Substituted" means one or more hydrogen atoms in a hydrocarbon group has been replaced with another substituent. Examples of such substituents include, but are not limited to, halogen atoms such as chlorine, fluorine, bromine, and iodine; halogen atom containing groups such as chloromethyl, periluorobutyl, trifluoroethyl, and nonafluorohexyl; oxygen atoms; oxygen atom containing groups such as (meth)acrylic and carboxyl; nitrogen atoms; nitrogen atom containing groups such as amino-functional groups, amido-functional groups, and cyano-functional groups; sulphur atoms; and sulphur atom containing groups such as mercapto groups.

[0014] The starting material for the ring opening polymerisation can be solely cyclic siloxanes as described above but may optionally comprise mixtures of cyclosiloxanes together with polydiorganosiloxane material having units of the general formula RaSO4ai2 wherein each R may be the same or different and is as hereinbefore described. Subscript a is zero or an integer between 1 and 4 inclusive but preferably has an average value of from 1 to 3, more preferably 1.8 to 2.2 per molecule. Preferably the polydiorganosiloxanes are polydialkylsiloxanes, and most preferably polydimethylsiloxanes. They are preferably substantially linear materials, which are end-blocked with a siloxane group of the formula R"3SiO112, wherein R" is R or hydroxyl. In some instances a small proportion of the starting material may comprise a linear polydimethylsiloxane with one terminal group having a formula where each R" is the same and is an alkyl group and a second terminal group at least one R" group is a hydroxy group. Preferably such a polymer has a viscosity of from 1000 to l00000mPa.s at 25°C.

[0015] As previously indicated in the presence of suitable catalysts such monomers will participate in polymerisation processes involving the ring opening of the cyclosiloxanes and an equilibrium stage.

[0016] The ring opening process as hereinbefore described requires a suitable ring opening catalyst for reactions to proceed. Any suitable ring opening catalyst may be utilised. These include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide or caesium hydroxide or complexes of alkali metal hydroxides and an alcohol, alkali metal silanolates such as potassium silanolate caesium silanolate, sodium silanolate and lithium silanolate or trimethylpotassium silanolate. Other catalysts which might be utilised include the catalyst derived by the reaction of a tetra-alkyl ammonium hydroxide and a siloxane tetramer. These various catalyzing agents have different relative reactivities with respect to the present polymerization process, and accordingly, compensation must be made for them. For example, sodium hydroxide will catalyze the reaction more slowly than the others, and therefore the reaction takes longer at any given temperature. On the other hand, caesium hydroxide causes reaction to take place more rapidly. Thus caesium hydroxide may be more effective when a lower reaction temperature is employed or when it is desired to produce a silicone gum having a very high viscosity. Of the above potassium silanolate is particularly preferred as it is an active form of potassium hydroxide and which is also very soluble in a monomer solution such as octamethylcyclotetrasiloxane. The catalyst concentration can be from about 5 ppm to about 500 ppm of Equivalent KOH. The KOH equivalence of potassium silanolate ranges from approximately 0.05% to 6.0% KOH by weight. In the preferred embodiment of the process of the present invention potassium silanolate is employed at a KOH concentration of about 20 ppm by weight.

[0017] Alternatively, phosphonitrile halide catalysts (sometimes referred to as acidic phosphazenes) and phosphazene bases (such as those described in EP 0860461 and EP 1008598 the content of which are included herein by reference) may be used.

[0018] Preferred phosphonitrile chloride, catalysts include those prepared according to U.S. patent specifications 3,839,388 and 4,564,693 or EP application 215 470 and phosphonitrile halide ion based catalysts, as described in GB2252975, having the general formula [X2(PX22=N)SPX23][M2X2(Vt�l)R"tT, wherein X2 denotes a halogen atom, M2 is an element having an electronegativity of from 1.0 to 2.0 according to Pauling's scale, R" is an alkyl group having up to 12 carbon atoms, s has a value of from 1 to 6, v is the valence or oxidation state of M2 and t has a value of from 0 to v-i.

[0019] Further alternative catalysts suitable for use in the present invention may comprise oxygen-containing chlorophosphazenes containing organosilicon radicals having the following general formula: Z1-PCl2=N(-PCl2=N)-PCl2-O in which * Z1 represents an organosilicon radical bonded to phosphorus via oxygen, a chlorine atom or the hydroxyl group and * n represents 0 or an integer from 1 to 8. The catalyst may also comprise condensation products of the above and/or tautomers thereof (the catalyst exists in a tautomeric form when Z1 is a hydroxyl group). All or some of the chlorine atoms can be replaced by radicals Q, in which Q represents the hydroxyl group, monovalent organic radicals, such as alkoxy radicals or aryloxy radicals, halogen atoms other than chlorine, organosilicon radicals and phosphorus-containing radicals. The oxygen-containing chlorophosphazenes of formula (I) are preferably those in which no chlorine atom is replaced by a radical 0. Numerous phosphazene bases and routes for their synthesis have been described in the literature, for example in Schwesinger et al, Liebigs Ann. 1996, 1055-1 081.

[0020] A still further alternative catalyst which might be used as the catalyst in the present invention is any suitable compound providing a source of anions comprising at least one quadri-substituted boron atom and protons capable of interaction with at least one silanol group as defined in WO 0 1/79330. For this type of catalyst, it is important that the boron containing anion does not itself form a covalent bond directly to a silicon atom and that it does not decompose or rearrange to produce an anion which forms a covalent bond directly to a silicon atom. Suitable materials include those incorporating one or more boron atoms disposed within a grouping and several, for example ten or more, halogen atoms connected with each boron atom. The halogen atoms in such compound may be connected to boron atoms by linkages incorporating at least one carbon atom and are selected from fluorine, chlorine and bromine, the most preferred being fluorine.

[0021] Preferred anions incorporate one or more atoms of boron having four organic substituents thereon the most preferred being quadri-substituted borates. The organic substituents are suitably halogenated hydrocarbon groups. Such as pentafluorinated phenyl groups and bis (trifluoromethyl) phenyl groups and preferred materials have four such groups bonded to each boron atom. Examples include tetrakis (pentafluoro phenyl) borate anion (periluorinated aryl borate ion) and the material is preferably employed as the acid of this anion namely H{(C6F5)4B}. Other operative materials include anions having two quadri-substituted boron atoms, for example diperfluoroinatedaryl borate ions, e.g. H{B(C6F5)3CNB (C6F5)3}. Other suitable boron-containing anions for use in the process of the present invention include carboranes, for example of the formula {CB9 H10}, {CB9X25 H5}, {CB11H12} and {CB11X26H6} wherein each X2 is the same or different and is as hereinbefore described. Carboranes may contain boron atoms which are more highly substituted than quadri-substituted, e. g. pentasubstituted and hexa-substituted, and for the sake of clarity "quadri-substituted" where used herein is intended to include those anions containing quadri-substituted and higher substituted boron atoms.

[0022] The temperatures used in the process can be the same as those in the processes known to date for the ring opening polymerisation of cyclic organosilicon compounds. The general method may be carried out in either batch or continuous modes of operation and no heat is required to facilitate the polymerisation (however heat may be applied to influence the chemical equilibrium, if required.

[0023] The activity of the catalyst is preferably quenched by using a neutralizing agent which reacts with the catalyst to render it non-active. Any suitable neutralising agent may be utilised.

For acidic catalysts suitable base neutralising agents include primary, secondary and tertiary amines, such as diethylamine, propylamine, a mono/di and trialkanolamines for example monoethanolamine (MEA) and triethanolamine (TEA), trimethylchlorosilane, trichloroethyl phosphite, primary, secondary and tertiary amines, ammonia, amides, imides and cyclic diamines, hexamethyldisilazane, piperazine, methylmorpholine and succinamide or P2O5.

Of course, it is also possible to employ acid catalysts, e.g. CF3SO3H, which have to be neutralised with usual alkaline substances. The preferred neutralizing agents for alkaline ring-opening catalysts which can be utilized in practicing the preferred process of the present invention may be any of the mild acids effective for neutralizing the basic catalyst.

Such neutralizing agent can be selected from, for example, phosphoric acid, tris(chloroethyl)phosphite and silyl phosphate. One particularly preferred neutralising agent is silyl phosphate because it is quite soluble in siloxane polymers and allows for rapid neutralization.

[0024] In the case of phosphazene based catalysts when the desired viscosity has been reached, the viscosity of the organosilicon compound obtained in the process can be kept constant by a procedure in which the catalyst used, or a reaction product which has been formed from this catalyst by reaction with organosilicon compound to be subjected to equilibration and likewise promotes the equilibration of organosilicon compounds, is inhibited or deactivated by addition of inhibitors or deactivators which have been employed to date in connection with phosphazenes, for example, triisononylamine, n-butyllithium, lithium siloxanolate, hexamethyldisilazane and magnesium oxide. For phosphazene base catalysts suitable neutralising agents are acids such as acetic acid, silyl phosphate, polyacrylic acid chlorine substituted silanes, silyl phosphonate or carbon dioxide.

[0025] Preferably the ring opening catalyst, will be present in an amount of from 0.01 to 6, preferably 0.1 to 3 parts by weight per 100 parts by weight of the monomers.

[0026] The optional diluent which may be utilised in the process in accordance with the present invention is one or more extenders and/or one or more plasticisers. The extenders and/or plasticisers are selected so as to be unreactive with the reactants, intermediates and the reaction product(s) of the process in accordance with the present invention.

[0027] Any suitable plasticiser or extender or combination thereof may be utilised in the process in accordance with the present invention.

[0028] A plasticiser (otherwise referred to as a primary plasticiser) is added to a polymer composition to improve properties such as increasing the flexibility and toughness of the resulting cured product. This is generally achieved by reduction of the glass transition temperature (Tg) of the cured polymer composition thereby, in the case of sealants, enhancing the elasticity of the sealant. Plasticisers are also used to reduce the modulus of e.g. sealant formulations. Whilst plasticisers may reduce the overall unit cost of a sealant that is not their main intended use. Some plasticisers can be expensive and could increase the unit cost of a sealant formulation in which they are used but are utilised because of the properties they provide to the finished product. Plasticisers tend to be generally less volatile than extenders and are typically introduced into the polymer composition in the form of liquids or low melting point solids (which become miscible liquids during processing.

Typically, for silicone based compositions plasticisers are organopolysiloxanes which are unreactive with the siloxane polymer of the composition, such as polydimethylsiloxane having terminal triorganosiloxy groups wherein the organic substituents are, for example, methyl, vinyl or phenyl or combinations of these groups. Such polydimethylsiloxanes normally have a viscosity of from about 5 to about 100,000 mPa.s at 25°C.

[0029] Compatible organic plasticisers may additionally be used, examples include suitable dialkyl phthalates wherein the alkyl group may be linear and/or branched and contains from six to 20 carbon atoms; adipate, azelate, oleate and sebacate esters, polyols such as ethylene glycol and its derivatives, organic phosphates such as tricresyl phosphate and/or triphenyl phosphates, castor oil, tung oil, fatty acids and/or esters of fatty acids.

Details of a wide variety of both plasticisers and extenders which have been used in sealant formulations are discussed in GB 2424898 which is incorporated herein by reference.

[0030] Historically, unreactive siloxanes such as trialkylsilyl terminated polydiorganosiloxanes (for example trimethylsilyl terminated polydimethyl siloxane (PDMS)) were originally used as extenders and/or plasticisers in silicone based sealants because they were chemically similar and had excellent compatibility.

[0031] An extender (sometimes also referred to as a process aid or secondary plasticiser) is used to dilute the sealant composition and basically make the sealant more economically competitive without substantially negatively affecting the properties of the sealant formulation. The introduction of one or more extenders into a silicone sealant composition not only reduces the overall cost of the product but can also affect the properties of resulting uncured and/or cured silicone sealants. The addition of extenders can, to a degree, positively effect the rheology, adhesion and clarity properties of a silicone sealant and can cause an increase in elongation at break and a reduction in hardness of the cured product both of which can significantly enhance the lifetime of the cured sealant provided the extender is not lost from the cured sealant by, for example, evaporation or exudation.

[0032] Particularly preferred extenders are mineral oil based (typically petroleum based) paraffinic hydrocarbons. Any suitable mixture of mineral oil fractions may be utilised as the extender in the present invention but high molecular weight extenders (e.g. >220) are particularly preferred. Examples include linear or branched mono unsaturated hydrocarbons such as linear or branched alkenes or mixtures thereof containing at least 12, e.g. from 12 to 25 carbon atoms; and/or mineral oil fractions comprising linear (e.g. n-paraffinic) mineral oils, branched (iso-paraffinic) mineral oils, cyclic (referred in some prior art as naphthenic) mineral oils and mixtures thereof. Preferably the hydrocarbons utilised comprise at least 10, preferably at least 12 and most preferably greater than 20 carbon atoms per molecule. Other examples include: * alkylcyclohexanes (molecular weight >220); * paraffinic hydrocarbons and mixtures thereof containing from 1 to 99%, preferably from 15 to 80% n-paraffinic and/or isoparaffinic hydrocarbons (linear branched paraffinic) and 1 to 99%, preferably 85 to 20% cyclic hydrocarbons (naphthenic) and a maximum of 3%, preferably a maximum of 1% aromatic carbon atoms. The cyclic paraffinic hydrocarbons (naphthenics) may contain cyclic and/or polycyclic hydrocarbons. Any suitable mixture of mineral oil fractions may be used, e.g. mixtures containing (i) 60 to 80% paraffinic and 20 to 40% naphthenic and a maximum of 1% aromatic carbon atoms; (ii) 30-50 %, preferably 35 to 45% naphthenic and 70 to 50% paraffinic and or isoparaffinic oils; (iii) hydrocarbon fluids containing more than 60 wt.% naphthenics, at least 20 wt.% polycyclic naphthenics and an ASTM 0-86 boiling point of greater than 235°C; (iv) hydrocarbon fluid having greater than 40 parts by weight naphthenic hydrocarbons and less than 60 parts by weight paraffinic and/or ispoaraffinic hydrocarbons based on 100 parts by weight of hydrocarbons.

[00331 Preferably the mineral oil based extender or mixture thereof comprises at least one of the following parameters: (i) a molecular weight of greater than 150, most preferably greater than 200; (ii) an initial boiling point equal to or greater than 230°C (according to ASTM D 86).

(iii) a viscosity density constant value of less than or equal to 0.9; (according to ASTM 2501) (iv) an average of at least 12 carbon atoms per molecule, most preferably 12 to 30 carbon atoms per molecule; (v) an aniline point equal to or greater than 70°C, most preferably the aniline point is from 80 to 110°C (according to ASTM 0 611); (vi) a naphthenic content of from 20 to 70% by weight of the extender and a mineral oil based extender has a paraffinic content of from 30 to 80% by weight of the extender according to ASTM D 3238); (vii) a pour point of from -50 to 60°C (according to ASTM D 97); (viii) a kinematic viscosity of from 1 to 20 cSt at 40°C (according to ASTM D 445) (ix) a specific gravity of from 0.7 to 1.1 (according to ASTM D1298); (x) a refractive index of from 1.1 to 1.8 at 20°C (according to ASTM D 1218) (xi) a density at 15°C of greater than 700kg/m3 (according to ASTM D4052) and/or (xii) a flash point of greater than 100°C, more preferably greater than 110°C (according to ASTM 0 93) (xiii) a saybolt colour of at least +30 (according to ASTM 0 156) (xiv) a water content of less than or equal to 25Oppm (according to ASTM D6304) (xv) a Sulphur content of less than 2.Sppm (according to ASTM D 4927) [0034] In the present invention the diluent may, when required, be only partially miscible or immiscible with polysiloxanes meaning that the polymerisation mixture may be in some circumstances a two phase system (dispersion). The inert fluid may comprise a suitable non-mineral based natural oil or a mixture thereof, i.e. those derived from animals, seeds and nuts and not from mineral oils (i.e. not from petroleum or petroleum based oils) such as for example almond oil, avocado oil, beef tallow, borrage oil, butterfat, canola oil, cardanol, cashew nut oil, cashew nutshell liquid, castor oil, citrus seed oil, cocoa butter, coconut oil, cod liver oil, corn oil, cottonseed oil, cuphea oil, evening primrose oil, hemp oil, jojoba oil, lard, linseed oil, macadamia oil, menhaden oil, oat oil, olive oil, palm kernel oil, palm oil peanut oil, poppy seed oil, rapeseed oil, rice bran oil, safflower oil, safflower oil (high oleic), sesame oil, soybean oil, sunflower oil, sunflower oil (high oleic), tall oil, tea tree oil, turkey red oil, walnut oil perilla oil, dehydrated castor oils, apricot oil, pine nut oil, kukui nut oil, amazon nut oil almond oil, babasu oil, argan oil, black cumin oil, bearberry oil, calophyllum oil, camelina oil, carrot oil, carthamus oil, cucurbita oil, daisy oil, grape seed oil, foraha oil, jojoba oil, queensland oil, onoethera oil, ricinus oil, tamanu oil, tucuma oil, fish oils such as pilchard, sardine and herring oils. The extender may alternatively comprise mixtures of the above and/or derivatives of one or more of the above.

[0035] A wide variety of natural oil derivates are available. These include transesterified natural vegetable oils, boiled natural oils such as boiled linseed oil, blown natural oils and stand natural oils. An example of a suitable transesterified natural vegetable oil is known as biodiesel oil, the transesterification product produced by reacting mechanically extracted natural vegetable oils from seeds, such as rape, with methanol in the presence of a sodium hydroxide or potassium hydroxide catalyst to produce a range of esters dependent on the feed utilised. Examples might include for example methyloleate (CH3(CH2)7CH=CH(CH2)7002CH3).

[0036] Stand natural oils which are also known as thermally polymerised or heat polymerised oils and are produced at elevated temperatures in the absence of air. The oil polymerises by cross-linking across the double bonds which are naturally present in the oil.

The bonds are of the carbon-carbon type. Stand oils are pale coloured and low in acidity.

They can be produced with a wider range of viscosities than blown oils and are more stable in viscosity. In general, stand oils are produced from linseed oil and soya bean oil but can also be manufactured based on other oils. Stand oils are widely used in the surface coatings industry.

[0037] Blown oils which are also known as oxidised, thickened and oxidatively polymerised oils and are produced at elevated temperatures by blowing air through the oil.

Again the oil polymerises by cross-linking across the double bonds but in this case there are oxygen molecules incorporated into the cross-linking bond. Peroxide, hydroperoxide and hydroxyl groups are also present. Blown oils may be produced from a wider range of oils than stand oils. In general, blown oils are darker in colour and have a higher acidity when compared to stand oils. Because of the wide range of raw materials used, blown oils find uses in many diverse industries, for example blown linseed oils are used in the surface coatings industry and blown rapeseed oils are often used in lubricants.

[0038] When the diluent is present during polymerisation of the polymer prepared in accordance with the present invention, it will be appreciated that the resulting polymer/extender/plasticiser mix has a significantly lower viscosity than would normally be expected during polymerisation and in the final product. This is because the viscosity reducing diluent(s) is/are present in the polymer mixture as it polymerises and does not participate in the polymerisation reaction process. This inclusion during polymerisation furthermore avoids the need for expensive and time consuming blending processes typically used in the industry for introducing extenders and plasticisers into a polymer composition, usually at the same time as some or all other constituents. Products of the process in accordance with the present invention may contain polymers of significantly greater chain length/molecular weight than could be practically used in combination with such blending processes. This is because the viscosity of such polymers would be too high to enable the sufficiently thorough blending of the diluent(s) into the polymer.

[0039] The ratio between the diluent(s) and the organopolysiloxane constituent in the product produced by the process of the present invention that can be achieved is dependent on the miscibility of the diluent(s) in the polydimethylsiloxanes and vice versa.

The miscibility was found to depend at least in part, on the molecular weight of the organopolysiloxanes.

[0040] The optional end-blocking agent may be used to regulate the molecular weight of the polymer and/or add functionality. End-blocking agents are a means of controlling the reactivity /polymer chain length of the polymer by introducing compounds which will react with only one hydrolysable end group, subsequently preventing further ring opening. It is also a means of introducing alternative end groups on the polymer, e.g. silicon bonded hydrogen groups, alkenyl groups which may then be utilised to produce alternative reactive end groups or provide a non-reactive end group. Suitable endblockers are, for example, polysiloxanes in the viscosity range of Ito 150,000 mPa.s at 25° C., in particular polydimethylsiloxanes of the general formula MDXM where M is a trimethylsilyl, D is -Si(CH3)20-and x has a value of from 0 to 20. The endblocker may have one or more functional groups such as hydroxy, vinyl, hydrogen or amino. Water also acts as an endblocker, with the introduction of hydroxy functional groups. Particularly preferred end groups for the polymer are SiOH or SiMe, where Me denotes a methyl group. In the presence of added water, SiOH ended gum can be obtained as a blend in cyclics. The concentration of water determines the molecular weight of the gum. SiOH functional polymer of any chain length can thus be obtained. The use of water as an endblocker has the additional advantage of slowing down the reaction for better control.

[0041] The inventors found that undertaking the above discussed process at high pressures i.e. in a range of from about 75 xl 5 Pa to 1 OOMPa, preferably a range 75 xl 5 Pa to 5OMPa (typically> 75 x i05 Pa, preferably> 100 x i05 Pa, most preferably> 150 x Pa) resulted in a significant but unexpected improvement in the reaction rate. In the view of the inventors this is completely unexpected because the reaction takes places solely in the liquid phase and as such the effect of pressure on such a process would have been expected to be negligible because both the reactants and the products are liquids and the change in volume is not so significant as to lead to an expectation of a significant decrease in volume of the products compared to the reactants.

[0042] Thus the process according to the invention is useful for making organopolysiloxanes having units of the general formula RaSO4ai2 wherein R and a are as described above. Preferably at least 80% of all R groups are alkyl or aryl groups, more preferably methyl groups. Most preferably substantially all R groups are alkyl or aryl groups, especially methyl groups. The organopolysiloxanes are preferably those in which the value of a is 2 for practically all units, except for the terminal groups units, and the siloxanes are substantially linear polymers of the general formula R"(R2SiO)SiR2R" wherein R and R" are as defined above and p is an integer. It is, however, also possible that small amounts of units wherein the value of a denotes 0 or 1 are present. Polymers with such units in the chain would have a small amount of branching present. The viscosity of the organopolysiloxanes which may be produced by the process using a catalyst according to the present invention may be in the range of from 1000 to many millions mPa.s at 25°C, depending on the reaction conditions and raw materials used in the method of the invention.

[0043] The process according to the invention can be used to make a whole range of siloxane polymers, including liquid siloxane polymers and gums of high molecular weight, for example from 1 OOxl 5 to 1 OOxl 9 mPa.s. The catalyst used in the present invention has sufficient activity to enable the formation of polymers in a reasonable time at a low catalyst concentration.

[00441 Molecular weight changes during polymerisation can be monitored by sampling the reaction during polymerisation, and analysing each sample by gel permeation chromatography to determine the molecular weight (ASTM D 5296-05). Polymers of very high molecular weights can be obtained because of the very low catalyst concentrations needed for the polymerisation, with the result that the molecular weight of the polymer produced is dependent on the end group concentration as potentially there will be a very low concentration of end groups (especially in the absence of added end-blockers).

However, we have found that at very low catalyst concentrations, such as 2ppm, the molecular weight obtained increases with reaction time. The process may be limited by diffusion of the catalyst, which is very slow in these high molecular weight polymers.

[0045] Preferably the diluted polymer of the present invention comprises a polymer component which in accordance with the present invention is a silicon containing polymer having a number average molecular weight (Mw) of at least 100000 g/mol as determined following ASTM D5296-05 and calculated as polystyrene molecular weight equivalents.

[0046] The ring opening reaction in accordance with the present invention may be carried out at any appropriate temperature i.e. where appropriate catalysts are used the general method may be carried out in either batch or continuous modes of operation and no heat or vacuum is required to facilitate the polymerisation (however heat and/or vacuum may be applied to influence the chemical equilibrium, if required).

[0047] The polymerisation process in accordance with the invention may be carried out either batchwise or continuously using any suitable mixers.

[0048] In one embodiment of the invention the diluted polymer product may be emulsified in the presence of the diluent which has the advantage of providing a silicone emulsion containing very low amounts of cyclics volatile siloxane impurities.

[0049] This product of the process in accordance with the present invention also provides the user with formulations comprising the diluted polymer of the present invention with a variety of improved physical characteristics, not least the elasticity of resulting products, because of the use of polymers having polymer chain length/viscosities which hitherto would not have been possible to use. Applications include, sealants formulations, coating formulations, high consistency organopolysiloxane gum formulations for high consistency rubber applications, and for dispersions thereof in volatile and non-volatile alkylsilicone fluids for use in personal care products.

Claims (10)

1. CLAIMSA method of making a polysiloxane containing polymer comprising the steps of:-i) Preparing a polysiloxane containing polymer by the ring opening of siloxane containing monomers and/or oligomers which comprise at least 2 condensable groups per molecule, in the presence of a) one or more ring opening catalysts and optionally one or both of b) a diluent and/or an end-blocking agent; and ii) Where required quenching the polymerisation process; wherein, when present, the diluent is substantially retained within the resulting diluted polysiloxane containing polymer; characterised in that the process takes place at a pressure of at least 75 x 105 Pa.
2. 2. A method in accordance with claim 1 wherein the polymer has a Mw of greater than l00000g/mol.
3. 3. A method in accordance with claim 1 or 2 wherein the/or each diluent is an extender or plasticiser.
4. 4. A method in accordance with any preceding claim wherein the diluent is selected from one or more of the group * trialkylsilyl terminated polydimethyl siloxane * polyisobutylenes (PIB), * phosphate esters polyalkylbenzenes, * linear and/or branched alkylbenzenes esters of aliphatic monocarboxylic acids.
5. 5. A method in accordance with any one of claims 1 to 4 wherein the diluent is selected from one or more of the group comprising linear or branched mono unsaturated hydrocarbons such as linear or branched alkenes or mixtures thereof containing from 12 to 25 carbon atoms; and/or mineral oil fractions comprising linear (n-paraffinic) mineral oils, branched (iso-paraffinic) mineral oils and/or cyclic (naphthenic) mineral oils and mixtures thereof.
6. 6. A method in accordance with any preceding claim wherein the diluent is at least substantially miscible with monomer/oligomer and the polymer.
7. 7. A method in accordance with any preceding claim wherein the process takes place at a pressure of 150 x 105 Pa or more
8. 8. A method in accordance with any preceding claim wherein subsequent to polymerisation the product of is emulsified.
9. 9. A polymer obtainable by the process in accordance with any preceding claim.
10. 10. Use of a polymer in accordance with claim 11, in sealants formulations, coating formulations, high consistency organopolysiloxane gum formulations for high consistency rubber applications, and for dispersions thereof in volatile and non-volatile alkylsilicone fluids for use in personal care products.