Functional polyorganosiloxane emulsions from silanes having two hydrolysable functional groups and photocurable compositions therefrom

Abstract: A non-crosslinked polymer, comprising a preformed aqueous emulsion having a plurality of silanol-terminated polydiorganosiloxane particles, a functionalizing silane having the formula RQSi(X) 2 where X is a hydrolyzable group, Q is an organic functional group which does not prevent a condensation reaction between X and a silanol-terminated polydiorganosiloxane molecule, R is Q or a saturated monovalent hydrocarbon group of from one to six carbon atoms and an organotin catalyst. The composition results in a non-crosslinked polymer, unlike the polymers described in the prior art. We have found that adding a functionalizing silane having only two hydrolyzable groups to a preformed polydiorganosiloxane emulsion results in functionalized polydiorganosiloxane molecules which are free of crosslinks between the polydiorganosiloxane chains.

Description: The invention relates to a method of end-capping a polydiorganosiloxane molecule with a functional silane and to the compositions resulting therefrom. U.S. Patent 4,273,634 teaches an aqueous silicone emulsion which provides an elastomeric product upon removal of water under ambient conditions. The emulsion comprises a continuous water phase and a dispersed phase of crosslinked silicone. The silicone phase is the product produced by crosslinking of hydroxyl-endblocked polydiorganosiloxane. This polydiorganosiloxane is crosslinked after it has been dispersed in water. Preferred polydiorganosiloxanes contain vinyl-substituted siloxane units and are crosslinked by high energy radiation or the combined action of heat and an organic peroxide. U.S. Patent 4,618,642 describes an aqueous silicone elastomeric emulsion that is obtained by mixing an anionic emulsion containing dispersed particles of hydroxyl-endblocked polydiorganosiloxane, a dialkyltindicarboxylate, a silane of the formula RSi(OR') 3 , where R is a monovalent hydrocarbon radical of 1 to 4 carbon atoms inclusive and R' is a lower alkyl radical of from 1 to 4 carbon atoms inclusive or a radical of the formula -N=CR 2 and inert, non-siliceous filler. U.S. Patent 4,782,112 discloses a mixture of (A) a silicone water-based emulsion composed of water, emulsifying agent and diorganopolysiloxane having at least 2 silicone-bonded hydroxyl groups in each molecule, (B) a silicone water-based emulsion composed of water, emulsifying agent and organohydrogenpolysiloxane having at least 2 silicon-bonded hydrogen atoms in each molecule, and (C) curing catalyst. It is characterized by an excellent storage stability and by the formation on curing of a rubbery elastomeric coating film which has an excellent alkali resistance, water repellency, water-repellant sealability and durability of adhesion. U.S. Patent 4,954,565 claims a shelf-stable aqueous silicone emulsion which yields an elastomer upon removal of water, that is produced by combining a hydroxyl-endblocked polydiorganosiloxane present as an emulsion of dispersed particles in water, a crosslinker and a tin catalyst, the tin catalyst being in the form of a divalent tin atom combined with organic radicals. The emulsion, after crosslinking of the polydiorganosiloxane, can be reinforced with colloidal silica without affecting the shelf life of the reinforced emulsion. U.S. Patent 5,084,849 reveals a silicone emulsion prepared by emulsion polymerization of a hydroxyl-endblocked polydiorganosiloxane with a combination of a siloxane or a siloxane precursor containing unsaturated hydrocarbon groups and a functional silicone selected from organosilicon hydrides, mercapto alkylsilanes or siloxanes, with an acryl or methacryl functional siloxane. U.S. Patent 5,089,537 shows a similar silicone emulsion. When this emulsion is combined with a photoinitiator, the copolymer is crosslinked by exposure to ultraviolet radiation. When water is removed, an elastomer also results which can be used, to produce coatings and sealants. Contrastingly, the present invention provides a process for preparing a curable functionalized silicone polymer composition by combining and reacting : (A) a preformed aqueous polydiorganosiloxane emulsion comprising a surfactant and a plurality of silanol-terminated polydiorganosiloxane molecules; (B) a functionalizing silane having the formula RQSi(X) 2 where X is a hydrolyzable group, Q is an organic functional group which does not prevent a condensation reaction between X and a silanol-terminated polydiorganosiloxane molecule, R is Q or a saturated monovalent hydrocarbon group of from one to six carbon atoms; and (C) an organotin catalyst. Furthermore, the present invention provides a curable silicone polymer composition obtainable by the above mentioned process, which differs from the emulsion polymers described in the prior art. We have surprisingly found that adding a functionalizing silane having only two hydrolyzable groups to a preformed aqueous polydiorganosiloxane emulsion results in functionalized polydiorganosiloxane molecules free of crosslinks between the polydiorganosiloxane terminals. When our functionalizing silane is added to the polydiorganosiloxane emulsion in the presence of an organotin catalyst, an end-capped polymer results which consists of a polydiorganosiloxane molecular chain having a functional group on each end. "Functional group" means a reactive group that may be used in further chemical reactions. Unlike other functionalized polydiorganosiloxane emulsions, wherein the functional alkoxysilane is incorporated randomly during copolymerization, the method of this invention allows for specific placement of the functionalizing silane at the chain end. This result is achieved by specifically selecting a functionalizing silane having two hydrolyzable groups and by adding this silane after polymerization with a tin catalyst. Unexpectedly, once one of the hydrolyzable groups of the functionalizing silane condenses with the hydroxyl group of the polydiorganosiloxane molecule, the remaining hydrolyzable group on the silane is non-reactive in the system. Since the second group on the functionalizing silane is non-reactive, no chain extension or further reaction occurs between the polydiorganosiloxane chains, while the functional groups thereon remain reactive. The functionalized polydiorganosiloxane emulsions of our invention have the physical characteristics of a gum, once the water is removed. The resulting functionalized polydiorganosiloxane of this invention is useable as an intermediate. For example, if the polydiorganosiloxane is end-capped with a photosensitive organic end-group and mixed with a photoinitiator, then the emulsion of this invention will form a clear, waterproof coating which cures to a tack-free elastomer upon exposure to ultraviolet radiation or sunlight. The functionalized polydiorganosiloxane emulsion of our invention can also be used as an intermediate for improving the impact properties of engineering materials, such as epoxy resins or polystyrene. The functionalized polydiorganosiloxane emulsions of this invention are in contrast to systems known in the prior art, which usually employ trialkoxysilanes. If a trialkoxysilane is used, the prior art compositions consist of elastomeric polydiorganosiloxanes which upon removal of water produce elastomeric films that are in insoluble in solvent. In the present invention, the resulting composition consists of non-crosslinked, functionalized polydiorganosiloxane emulsions which form tacky, gum-like films which are soluble in solvent when water is removed. Our aqueous emulsion having a plurality of particles of silanol-terminated polydiorganosiloxane is prepared by conventional methods known in the art. In addition to polydiorganosiloxane and water, this emulsion also contains at least one surfactant which stabilizes the dispersed polydiorganosiloxane particles in the emulsion. These polydiorganosiloxane particles have an average size of 0.1 to 10 micrometers, preferably from 0.5 to 1 micrometer. These polydiorganosiloxanes are characterized by a weight average molecular weight (Mw) of greater than 1,000. It is preferred that the above described emulsion have a solids content ranging from 20 to 70 weight percent, most preferably about 65 weight percent. These emulsions are well known in the art and may be prepared, for example, by methods wherein cyclic or linear diorganosiloxanes are dispersed in an aqueous, continuous phase with the aid of a surfactant. Thereafter, they are emulsion polymerized by the introduction of an acid or base catalyst. These methods are more fully described in US-A(s) 3,294,725 and 2,891,920. In preferred embodiments, the surfactant employed is an anionic type, such as sodium lauryl sulfate or ammonium lauryl sulfate; and the catalyst is dodecylbenzene sulfonic acid, the latter also acting as a system surfactant. The emulsions taught in US-A(s) 4,618,642 and 4,954,565 may also be used in the present invention. Our hydroxyl-terminated, polydiorganosiloxane emulsion can also be prepared by direct emulsification. In this latter process, a mixture of water, polydiorganosiloxane and one or more surfactants is processed under high shear conditions using either conventional mixing equipment or high shear devices such as a homogenizer. Methods for preparing such emulsions are given in US-A 4,177,177. The organic groups pendant from the backbone of the polydiorganosiloxane emulsion molecules are independently selected from hydrocarbon or halogenated hydrocarbon radicals, such as alkyl and substituted alkyl radicals containing from 1 to 20 carbon atoms; cycloalkyl radicals, such as cyclohexyl; and aromatic hydrocarbon radicals, such as phenyl, benzyl and tolyl. Preferred organic groups are lower alkyl radicals containing from 1 to 4 carbon atoms, phenyl and halogen-substituted alkyl such as 3,3,3-trifluoropropyl. Thus, our polydiorganosiloxane can be a homopolymer, a copolymer or a terpolymer containing such organic groups. Examples include systems comprising dimethylsiloxy units and phenylmethylsiloxy units; dimethylsiloxy units and diphenylsiloxy units; and dimethylsiloxy units, diphenylsiloxy units and phenylmethylsiloxy units, among others. Most preferably, our polydiorganosiloxane is a polydimethylsiloxane (PDMS) which is terminated with a hydroxyl group at each end of its molecule. Our functionalizing silane is a silane having the following formula RQSi(X) 2 and partial hydrolysis condensation products thereof. The group Q of our functionalizing silane is an organic functional group which does not prevent a condensation reaction between X and the silanol-terminated polydiorganosiloxane molecule. By "functional group", we mean a reactive group that may be used in further chemical reactions. The term "condensation reaction" means a type of chemical reaction in which two or more molecules combine with the separation of water, alcohol or other simple substances. It is anticipated that there may be certain groups Q which, because of stearic factors, would prevent a condensation reaction between the hydrolyzable group X and our silanol-terminated, polydiorganosiloxane molecules. Molecules having groups which would prevent the aforesaid condensation reaction are excluded from the scope of this invention. R is Q or a saturated monovalent hydrocarbon group of one to six carbon atoms. X can be any hydrolyzable group. "Hydrolyzable group" means any group attached to silicon which is hydrolyzed by water at room temperature. The hydrolyzable group X includes hydrogen atoms, halogen atoms such as F, Cl, Br or I; groups of the formula -OY where Y is any hydrocarbon or halogenated hydrocarbon group such as methyl, ethyl, isopropyl, octadecyl, allyl, hexenyl, cyclohexyl, phenyl or benzyl; beta-phenylethyl; any hydrocarbon ether radical, such as 2-methoxyethyl, 2-ethoxyisopropyl, 2-butoxyisobutyl, p-methoxyphenyl or -(CH 2 CH 2 O) 2 CH 3 ; or any N,N-amino radical such as dimethylamino, diethylamino, ethylmethylamino, diphenylamino or dicyclohexylamino. X can also be any amino radical such as NH 2 , dimethylamino, diethylamino, methylphenylamino or dicyclohexylamino; any ketoxime radical of the formula -ON=CM 2 or -ON=CM', in which M is any monovalent hydrocarbon or halogenated hydrocarbon radical such as those for Y; and M' is any divalent hydrocarbon radical both valences of which are attached to carbon, such as hexylene, pentylene or octylene; ureido groups of the formula -N(M)CONM" 2 in which M is as defined above, hydrocarbon radical such as those shown for Y above and M" is H or any of the M radicals; carboxyl groups of the formula -OOCMM" in which M and M" are as defined above or halogenated hydrocarbon radical as illustrated for Y above or carboxylic amide radicals of the formula -NMC=O(M") in which M and M" are as defined above. X can also be the sulfate group or sulfate ester groups of the formula -OSO 2 (OM) where M is as defined above; hydrocarbon or halogenated hydrocarbon radicals illustrated by Y; the cyano group; the isocyanate group; and the phosphate group or phosphate ester groups of the formula -OPO(OM) 2 in which M is as defined above. The most preferred hydrolyzable groups of the invention are alkoxy groups. Illustrative examples are methoxy, ethoxy, propoxy, butoxy, isobutoxy, pentoxy, hexoxy and 2-ethylhexoxy; alkoxy radicals such as methoxymethoxy or ethoxymethoxy; and alkoxyaryloxy such as ethoxyphenoxy. The most preferred alkoxy groups are methoxy or ethoxy. In a more preferred embodiment, our functionalizing silane is R"Q'Si(OR') 2 , where R' is an alkyl radical having 1 to 4 carbon atoms. Q' is selected from the group consisting of an acryloxypropyl, methacryloxypropyl, vinyl, allyl, chloroalkyl, hexenyl, acrylamidopropyl, trifluoropropyl, glycidoxypropyl, cyanoalkyl, mercaptoalkyl, a group represented by the formula and a group of the formula HCl·ZN(H)-CH 2 CH 2 -N(H)-CH 2 CH 2 CH 2 -, wherein Z is Specific examples of suitable silanes include gamma-acryloxypropylmethyldimethoxysilane, gamma-methacryloxypropyl methyldimethoxysilane, vinylmethyldimethoxysilane, 5-hexenylmethyldimethoxysilane, allylmethyl-dimethoxysilane, 3-acrylamidopropyldimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, (3-glycidoxypropyl)-methyldiethoxysilane, 2-(3,4)-epoxycyclohexylmethyldiethoxysilane, 4-(aminophenyl)-2-ethylmethyldimethoxysilane, 3,3,3-trifluoropropylmethyldimethoxysilane, 3-chloropropylmethyldimethoxysilane, 3-cyanopropylmethyldimethoxysilane, phenylmethyldimethoxysilane and silanes represented by the formulas HCl·ZHN-CH 2 CH 2 -NZ-CH 2 CH 2 CH 2 -SiCH 3 (OMe) 2 and HCl·ZN(H)-CH 2 CH 2 -N(H)-CH 2 CH 2 CH 2 -SiCH 3 (OMe) 2 , wherein Me hereinafter denotes a methyl radical and Z is a vinylbenzyl group having the formula Finally, R" is Q' or an alkyl radical having 1 to 4 carbon atoms. The organotin curing catalyst (C) is an organic salt of tin and may be illustrated by tin (II) carboxylates, such as stannous oleate and stannous naphthenate; dialkyl tin (IV) carboxylates, such as dibutyltin diacetate and dibutyltin dilaurate; and tin (IV) stannoxanes, as exemplified by the structure (Bu) 2 SnCl-O-(Bu) 2 OH, in which Bu denotes a butyl radical, as taught by US-A 5,034,455. In preferred embodiments, the catalyst is stannous octoate. To prepare the composition of the present invention, an organotin curing catalyst and a functionalizing silane are added to the above described preformed aqueous polydiorganosiloxane emulsion. The functionalizing silane migrates into the particles of the polydiorganosiloxane where it condenses with the hydroxyl groups on the ends of the PDMS molecules in the presence of the organotin catalyst. Unlike the prior art, no crosslinking occurs between the polydiorganosiloxane molecules in the present invention because the functionalizing silane contains only 2 hydrolyzable groups and, therefore, it is incapable of crosslinking. This contrasts with the silanes taught in the prior art in which 3 or more hydrolyzable groups at the silicon atom of the silanes lead to a crosslinked polyorganosiloxane emulsion that has the physical characteristics of a crosslinked elastomer upon removal of water. The non-crosslinked polydiorganosiloxane emulsions of this invention therefore have the physical characteristics of gum upon removal of water. Although the order of addition is not considered critical, it is preferred to first add from 0.05 to 2 parts by weight, preferably from 0.3 to 0.6 parts, of the catalyst to 100 parts by weight of the hydroxyl-terminated, polydiorganosiloxane in emulsion. From 0.1 to 10 parts by weight, preferably 1 part, of the functionalizing silane is then added to this mixture for each 100 parts by weight of the polydiorganosiloxane. The resultant emulison is then allowed to age for one-half hour to four hours at room temperature. When the functionalizing silane content is less than 0.1 part, incomplete grafting is observed. When this component exceeds 10 parts, the by-products, formed when the hydrolyzable group X is reacted, can destabilize the emulsion. During the aging process, which can take place at room temperature as well as at elevated temperatures, the pH of the emulsion should be maintained between 4 and 10.5. As indicated, the functionalized silicone emulsion polymer of this invention can function as an intermediate for a variety of end-uses, such as impact modifiers or coatings. For example, our functionalized silicone emulsion polymer can be used as an intermediate to prepare a photocurable composition. A photocurable coating of the type contemplated by this invention would comprise the combination of a functionalized silicone emulsion polymer, prepared with selected functionalizing silanes and of a photoinitiator. The functionalized silicone emulsion polymer used for our photocurable coating can be prepared using the preformed, aqueous polydiorganosiloxane emulsion described above. The functionalizing silane, however, is a silane selected from acryl, methacryl, mercaptoalkyl or alkyl vinylether groups. The functionalizing silane should be a silane or siloxane which is compatible with our hydroxyl-endblocked polydiorganosiloxane. These include methylvinyldialkoxysilanes, such as methyvinyldiethoxysilane. Also included are allyl- or hexenyl-functional siloxanes and siloxane precursors, such as allylmethyldiethoxysilane. Preferably, there is from 0.1 to 10 parts by weight of functionalizing silane containing unsaturated hydrocarbon groups per 100 parts by weight of polydiorganosiloxane. A preferred embodiment uses methylvinyldiethoxysilane at a level of 1.0 part by weight per 100 parts by weight of hydroxyl-endblocked polydiorganosiloxane. Another functionalizing silane is mercaptoalkylsilane which is compatible with the hydroxyl-endblocked polydiorgano-siloxane. A suitable mercaptoalkylsilane is mercaptopropyl(methyl)diethoxysilane. A preferred embodiment uses mercaptopropyl(methyl)dimethoxysilane at a level of 0.5 to 1.0 part by weight per 100 parts by weight of polydiorganosiloxane. Preferably, there is 1 mole of mercaptoalkylsiloxane units per mole of unsaturated hydrocarbon units. The acryl- or methacryl-functional silanes are preferably dialkoxyfunctional, all containing 1 or more acryl- or methacryl-functional radicals. Preferred acryl- or methacryl-functional silanes include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane and 3-acryloxypropylmethyldimethoxysilane at a level of from 0.5 to 1.0 part by weight per 100 parts by weight of polydiorganosiloxane. The photoinitiator can be one or a combination of photoinitiators, which will form radical species when irradiated with ultraviolet light. The photoinitiator should be compatible with the silicone phase of our emulsion. Preferred photoinitiators are benzophenone and Darocure™ 1173, which has the formula C 6 H 5 =C(O)-C(CH 3 ) 2 OH. The photoinitiator is used in amounts sufficient to provide the desired cure rate. If too little is used, the cure takes longer than desired. If too much is used, the physical and mechanical properties of the emulsion or cured elastomer may be degraded. The preferred amount is from 0.25 to 0.5 part of photoinitiator per 100 parts by weight of polydiorganosiloxane. The photoinitiator may be added at any time to the reaction mixture. For example, the photointiator may be added to the preformed aqueous polydiorganosiloxane emulsion before the functionalizing silane is reacted therewith. The photoinitiator could also be added to the reaction mixture after the functionalized silicone emulsion polymer is formed. The photoinitiator in the emulsion reacts in the presence of ultraviolet light to form radicals which cause reactions between the functional groups at the polymer chain ends. For example, the radicals formed by the ultraviolet light and the photoinitiator cause the acryl groups to react with each other, causing crosslinks to form and thereby changing the copolymer into an elastomer. When the crosslinked emulsion is dried, the elastomeric particles coalesce to form an elastomeric film. It is also possible to first remove the water from the emulsion and then to expose the composition to ultraviolet light to cause the crosslinking. The emulsions containing the mercaptoalkyl group, as well as those containing the acryloxy propyl group, as the reactive crosslinker can be crosslinked by exposure to ambient sunlight, since these groups are very reactive. Additional ingredients can be added to our emulsion to change the properties of the emulsion or of the elastomer formed by drying the emulsion. The physical strength of the elastomer can also be increased by addition of reinforcing filler. Any of the well known reinforcing fillers for silicone polymers can be used, such as fumed silica, precipitated silica, aqueous, dispersed colloidal silica and aqueous, dispersed fumed silica. The aqueous, dispersed fumed silica is a preferred reinforcing filler. Extending filler, such as clay or calcium carbonate; pigments; dyes; thickening agents and such can be added as long as they do not adversely affect the properties or storage stability of our emulsion or the product elastomer. The amount of ultraviolet radiation necessary to crosslink the emulsion copolymer into an elastomer will depend on a number of variables and can be determined by routine experiment. Factors such as wavelength of UV light, amount and type of photoreactive functional groups in the copolymer, quantity and type of photoinitiator and reactor design will all influence the amount of ultraviolet radiation required. For example, the energy required to dissociate SiH bonds into radicals is far less than that required to dissociate SiOH bonds. Thus, emulsion copolymers containing the former require significantly less ultraviolet radiation to complete crosslinking processes than do emulsion copolymers containing the latter. However, the most preferred parameters are those which cause the composition to be cured by ambient sunlight or lower doses of ultraviolet radiation. The emulsion of this invention is useful as a coating material which gives an elastomeric coating. It can be used as a protective coating or as a release coating. When reinforced, the elastomeric coating can be used as a coating material, an adhesive or as a sealant material. The following examples are presented to further illustrate the compositions of this invention, but are not to be construed as limiting the invention of the appended claims. All parts and percentages in the examples are on a weight basis and all measurements were obtained at 25°C., unless indicated to the contrary. Example 1 A silanol-functional PDMS latex was prepared by adding 34 g of dodecylbenzene sulfonic acid to 1200 g of water followed by 2,275 g of an 80 cp (mPa·s) (25°C.) hydroxyl end-blocked PDMS fluid. The mixture was stirred for 15 minutes and the resulting dispersion was homogenized by passing it twice through a Microfluidics Microfluidizer™ at 8000 psi (55.2 MPa). One hundred twenty grams of Dowex® HClW2H Cationic Exchange resin (Dow Chemical Co., Midland, Mi.) were mixed into the emulsion to initiate polymerization. After standing at room temperature for 20 hours, the emulsion was filtered to remove the ion-exchange resin and neutralized to pH 7 using a 14% aqueous ammonium hydroxide solution. The resulting latex contained 62 wt% of PDMS having a average particle size of 350 nm. The polymer molecular weight was analyzed by size exclusion chromatography (SEC) using a Waters™ model 590 programmable pump system equipped with two 30 cm Polymer Labs™ Series C crosslinked polystyrene columns and a Model 410 refractive index detector. The molecular weights were determined in toluene by comparing the chromatogram to PDMS standards in toluene. A number average molecular weight (Mn) of 29,600 g/mole and a Mw of 269,000 g/mole were recorded. To 400 g of the above PDMS emulsion, 1.3 g of stannous octoate were added. The latex was stirred and 2.7 g of 3-methacryloxypropylmethyldiethoxysilane were added dropwise. After 24 hours, the emulsion pH was increased to 10 using a 14 wt% ammonium hydroxide solution. The resulting methacryloxypropyl end-capped emulsion had a Mn of 34,600 and a Mw of 277,000 g/mole indicating little or no chain extension. Example 2 In a 1 liter flask, 200 g of a 65 wt% solids methacryloxypropyl end-capped PDMS latex, prepared in similar fashion to Example 1, were diluted to 30% solids by adding 235 g of deionized water. The reaction flask was then heated to 70°C. under a nitrogen blanket. 35 ml of methylmethacrylate containing 0.125 g of AIBN (azobisisobutyronitrile) were dripped into the emulsion at rate of 0.6 ml/min. After all monomer was added, the reaction was allowed to continue for 8 hours at 70°C. with constant stirring. After room temperature cooling, the latex was coagulated in isopropanol, filtered and vacuum dried. The resulting polymer was then analyzed for percent Si by a bomb digestion technique. This test demonstrated that the polymer contained 80 wt% PDMS. Films cast from this latex were translucent indicating an inter-penetrating morphology. The films of this latex exhibited superior adhesion to plastic in comparison to a pure PDMS material. Example 3 In a 1 liter flask, 200 g of a 65% solids methacryloxypropyl end-capped PDMS latex, prepared in the manner of Example 1, were diluted to 30% solids by adding 235 g of deionized water. The reaction flask was then heated to 70°C. under a nitrogen blanket. 35 ml of butylacrylate containing 0.125 g of AIBN were then dripped into the emulsion at rate of 0.6 ml/min. After all monomer was added, the reaction was allowed to continue for 8 hours at 70°C. with constant stirring. After cooling to room temperature, the latex was then coagulated into isopropanol, filtered and vacuum dried. The resulting polymer was then analyzed for percent Si by a bomb digestion technique. This test demonstrated that the polymer contained 80 wt% PDMS. Films cast from the resulting composition were translucent also indicating an inter-penetrating morphology. The films produced from this core shell latex exhibited superior adhesion to plastic in comparison to their pure silicone counterparts. Example 4 One hundred fifty five grams of 65 wt% solids hydroxyl-endblocked PDMS emulsion were weighed into a 500 ml jar equipped with a stirrer. 1.2 g of an aqueous emulsion of 50 wt% of dioctyltin dilaurate were added dropwise to the emulsion and the emulsion was stirred for 3 minutes. Next, 1.0 g of 3-acryloxypropylmethyldimethoxysilane was added dropwise to the emulsion with continued stirring. To this emulsion was added 1.0 g of α,α-hydroxymethylacetophenone (a photoinitiator), by dropwise addition with stirring. The stirring was continued for an additional 30 minutes. This composition consisted of an approximately 60-62% solids emulsion of PDMS containing 0.5 pph dioctyltindiluarate, 1 pph 3-acryloxypropylmethyldimethoxy silane and 1 pph photoinitiator (Darocure™ 1173), all based on total composition weight. A film of the functional emulsion was cast into a polystyrene petri dish and allowed to dry at room temperature for 2 days. The resulting film was a sticky, gummy polymer that was soluble in heptane. The film was then exposed to 950 mJ/cm 2 of UV radiation by using a photocure apparatus which consisted of a UV light mounted above a moving belt. The film was transformed into an elastomer. A tensile strength of 50 psi (344.7 kPa), elongation at break of 875% and a modulus at 100% elongation of 12 psi (82.7 kPa) were recorded. Example 5 A silanol functional PDMS latex was prepared by the method of Example 1. To 400 g of the PDMS emulsion were added 1.3 g of stannous octoate. The latex was stirred and 1.5 g of 3-mercapto propylmethyldimethoxysilane were added dropwise. After 24 hours, the above emulsion was taken to pH 10 using a 14 wt% ammonium hydroxide solution. To 55 g of the mercapto end-capped PDMS emulsion were added 0.28 g of tetramethyltetravinylcyclosiloxane and 0.14 g of Darocure™ 1173. Films of the above latex were cast and allowed to dry for 16 hours. The films cured to an elastomer (insoluble in heptane) after exposing the film to UV light. Example 6 (Comparative Example) A similar composition to Example 4 was prepared without a tin compound. To 20 g of the hydroxyl-endblocked PDMS latex were added 0.13 g of tetramethyltetravinylcyclosiloxane, 0.08 g of Darocure™ 1173 and 0.13 g of mercaptopropylmethyldimethoxysilane. After casting a film, allowing the latex to dry and exposing to UV light under the same conditions as Example 4, the film was still an uncrosslinked elastomer that was soluble in heptane. Example 7 A silanol functional PDMS latex was prepared in accordance with Example 1. To 300 g of the hydroxyl-endblocked PDMS emulsion were added 0.90 g of stannous octoate. The latex was stirred and 1.8 g of 3-glycidoxypropylmethyldiethoxysilane were added dropwise. After 24 hours, 10 g of the latex were poured into a 10 cm diameter polystyrene petri dish. Four drops of diethylenetriamine were stirred into the latex. Upon drying, an elastomer was produced that was insoluble in heptane. Example 8 One hundred fifty five grams of an anionically stabilized, non-crosslinked, aqueous emulsion of hydroxyl-endblocked PDMS having a Mw of 250,000 and a solids content of 60-62 wt% was prepared by the method of Example 1 of US-A 4,618,642. The product emulsion was weighed into a 500 ml jar equipped with a stirrer. Next, 0.6 g of stannous octoate was added to the emulsion and stirred for 3 minutes. This was followed by 1.0 g of 3-acryloxypropylmethyldimethoxysilane which was added dropwise to the emulsion with continued stirring. After 10 minutes, the stirring was discontinued and the emulsion was allowed to remain undisturbed for an additional hour. An aqueous 35 percent aminomethylpropanol solution was added to the emulsion to adjust the pH to 10.0. To this emulsion was added 2.0 g of Darocure™ 1173 (a photoinitiator) by dropwise addition with stirring. Therefore, the composition consisted of an approximately 60-62 wt% solids emulsion of PDMS containing 0.5 pph stannous octoate, 1 pph 3-acryloxypropylmethyldimethoxysilane and 2 pph photoinitiator (Darocure™ 1173), all based on total composition weight. A film of this emulsion was cast into a polystyrene petri dish and allowed to dry at ambient conditions for 2 days. The resulting film was a sticky, gummy polymer that was soluble in heptane. The film was then placed in the outdoor sunlight (temperature < 45°C.) for 8 days. The film was transformed into an elastomer that was insoluble in heptane. Samples of the film were tested and had a tensile strength of 24 psi (165.5 kPa), an elongation at break of 450% and a modulus at 100% elongation of 15 psi (103.4 kPa). Example 9 Two hundred grams of an anionically stabilized, non-crosslinked aqueous emulsion of hydroxyl-endblocked PDMS as in Example 8 were weighed into a 500 ml jar equipped with a stirrer. 0.6 g of stannous octoate was added to the emulsion, the stirrer was started and the mixture was stirred for three minutes. Next 1.2 g of 3-acryloxypropylmethyldimethoxysilane was added dropwise to the emulsion with stirring. The mixture was stirred for an additional five minutes after addition of all of the silane endcapper. The jar was capped and the emulsion was allowed to remain undisturbed for 24 hours. The pH of the emulsion was adjusted to between 9-10 by dropwise addition of 14 percent aqueous ammonia with stirring. Darocure™ 1173, (0.6 g), was added to the emulsion dropwise with stirring and the composition was stirred for an additional 45 minutes. This composition consisted of an approximately 60-62% solids emulsion of PDMS containing 0.5 pph stannous octoate, 1 pph 3-acryloxypropylmethyldimethoxysilane and 0.5 pph photoinitiator (Darocure™ 1173), all based on total composition weight. A film cast from this emulsion (by removal of water) produced a sticky, gummy polymer that was soluble in heptane. An aqueous colloidal suspension of CH 3 SiO 3/2 was prepared by a similar method to US-A 3,433,780. Eight hundred fifty six grams of distilled water were charged to a 2 liter, 3-neck flask equipped with a dropping funnel and a stirrer. 2.77 g of dodecylbenzenesulfonic acid (DBSA) were added to the flask and the contents were stirred for 5 minutes to allow the DBSA to dissolve. Six grams of 2N sodium hydroxide solution were added and pH of the solution was measured and found to be between 10 and 11.5. Two hundred twenty five grams of MeSi(OMe) 3 were added dropwise at a rate of 1 drop ever 3.8 seconds. After 8 hours, all of the silane had been added and the mixture was stirred for 16 hours more. The contents of the flask were charged to a single necked flask and methanol was removed under vacuum with gentle heating using a rotary evaporator. The resulting emulsion was transparent and had a bluish hue. It also had a solids content of 10.6 wt% and a mean particle size of 63 nm. One hundred twenty grams of the colloidal suspension of CH 3 SiO 3/2 were added to the above described emulsion and the mixture was stirred for 5 minutes. The emulsion now contained approximately 10 pph colloidal CH 3 SiO 3/2 based on the total composition. Five films were cast from this emulsion by weighing 8 g into a 100 mm (diameter) polystyrene petri dish for each film and by allowing them to dry uncovered for 3 days. The films were exposed to various intensities of UV radiation by using a photocurable apparatus which consisted of a UV light mounted above a moving belt. Intensity of the UV radiation was measured by a meter and recorded for each film. Each film became tack free and elastomeric after exposure to UV light. Tensile properties of the cured films were measured (Instron™) and are given in Table I. UV Intens. Tensile Elongation Modulus @ 100% strain mJ/cm 2 psi MPa % psi MPa 260 101 0.70 149 66 0.45 520 136 0.94 600 65 0.45 1040 152 1.05 690 66 0.45 2080 157 1.08 665 68 0.47 4160 172 1.19 650 70 0.48 8320 178 1.23 633 74 0.51 Example 10 (Comparative example) An acryloxy-functional emulsion was prepared by a similar method of Example 4 in US 5,084,489 as follows. To 744 g of a 80 cp (mPa·s) hydroxyl-endblocked PDMS were added 7.44 g of 3-acryloxypropylmethyldimethoxysilane. This mixture was then stirred into 374.2 g of deionized water containing 74.4 g of a 10 wt% sodium lauryl sulfate solution in water. After mixing for 30 minutes, the suspension was then homogenized by passing it twice through a Microfluidics Microfluidizer™ at 8000 psi (55.2 MPa). 6.9 g of DBSA were added to the emulsion to effect polymerization. After standing for 24 hours, the emulsion was neutralized to pH 8-10 with 2N aqueous sodium hydroxide. To 100 g of the above emulsion was added 0.6 g of Darocure™ 1173. This emulsion contained approximately 60-62 wt% of poly(dimethyl-co-acryloxypropylmethylsiloxane) and 1 pph photoinitiator (Darocure™ 1173), all based on total composition weight. Films were cast from this emulsion by weighing 8 g into a 100 mm (diameter) polystyrene petri dish for each film and by allowing them to dry uncovered for 3 days. Films of the above emulsion containing 10 pph 4 nm colloidal silica as Nalco™ 1115 silica were also cast at the same time into 100 mm (diameter) polystyrene petri dishes. Films were also prepared at the same time of an end-capped acryloxy emulsion prepared in similar fashion to Example 1 except only 1 pph Darocure™ was added to these films. The films from the end-capped and randomly copolymerized acrylate functional latices were then exposed to 1020 mJ/cm 2 UV radiation and their strengths were compared. Table 2 shows the result of the comparison and demonstrates that the end-capped polymer of this invention has superior elongation and lower modulus due to the fact that the molecular weight between crosslinks is greater in our end-capped films than the randomly copolymerized samples of the prior art. Comparison of Tensile Properties of Copolymerized and End-Capped Latexes. Method of Acrylate Incorporation Colloidal Silica Tensile Elongation Modulus @ 100% strain psi MPA % psi MPa random none 57 0.39 405 16 0.11 end-capping none 44 0.30 597 14 0.10 random yes 222 1.53 236 117 0.81 end-capping yes 158 1.09 410 70 0.48

Claims: A process for preparing a curable silicone polymer composition by combining and reacting: (A) a preformed aqueous polydiorganosiloxane emulsion comprising a surfactant and a plurality of silanol-terminated polydimethylsiloxane molecules; (B) a functionalizing silane having the formula: RQSi(X) 2 , where X is a hydrolyzable group, Q is selected from the group consisting of an acryloxypropyl, methacryloxypropyl, vinyl, allyl, chloroalkyl, hexenyl, acrylamidopropyl, trifluoropropyl, glycidoxypropyl, cyanoalkyl, mercaptoalkyl, a group represented by the formula or a group of the formula HCl·ZN(H)-CH 2 CH 2 -N(H)-CH 2 CH 2 CH 2 - wherein Z is R is Q or a saturated monovalent hydrocarbon group of one to six carbon atoms; and (C) an organotin catalyst selected from a tin (II) carboxylate or a dialkyl tin (IV) carboxylate. The process according to claim 1 wherein said organotin catalyst is stannous octoate. The process according to claim 1 wherein said functionalizing silane is 3-acryloxypropylmethyldimethoxysilane. The process according to claim 1 wherein the composition further contains a filler. The process according to claim 1 wherein in an additional step a photoinitiator is incorporated into the composition. Curable silicone polymer composition obtainable by a process according to any of claims 1-5. A method of preparing a coating characterized in that the non-crosslinked polymer composition of claim 6 which contains a photoinitiator is coated onto a substrate and treated with ultraviolet light.

Inventors: LILES DONALD TAYLOR, MURRAY DAVID LOGAN, LILES, DONALD TAYLOR, MURRAY, DAVID LOGAN
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1995
Main classification: C08L83
IPC codes: C09D183, C08F290, C08F299, C08L83, C08G77, C09D4