Stabilized epoxysilicone

Abstract

The present invention is a composition comprising a) an epoxysilicone; b) a platinum catalyst; and d) a stabilizing amount of a stabilizer which is a geminal alkyn-ol or a maleate ester. The composition exhibits improved storage stability and is suitable for UV-catalyzed curing applications.

Description

[0001] Stabilized Epoxysilicone Background of the Invention The present invention relates to an epoxysilicone stabilized with a platinum chelating agent. Silicone polymers and resins functionalized with epoxy groups (epoxysilicones) are key intermediates for many products and formulations used in application related to electronics, construction, and personal care. Epoxysilicones are typically prepared by the hydrosilylation of an ethylenically unsaturated epoxide with an Si-H functionalized organosilane or polyorganosiloxane in the presence of a hydrosilylation catalyst, which is most commonly a platinum-based catalyst, as illustrated: the epoxysilicone. Unfortunately, the presence of platinum causes product degradation, presumably due to polymer formation arising from the reaction of the epoxy groups and unreacted Si-H groups. (See J. Crivello; M. Fam. J. Polym. Sci. Polym. Chem. Ed., 1991, 28, 1852.) Efforts to solve this shelf-stability problem include the use of less reactive catalysts such as rhodium-based catalysts; however, their sluggish catalytic activity when used to promote the reaction of sterically bulky monomers makes them impractical for preparing a broad range of epoxysilicones. Efforts to increase shelf stability of the epoxysilicone include removing the platinum catalyst after hydrosilylation or purifying the product by vacuum distillation. Platinum removal is arduous and costly, generally requiring mixing the product with a solid absorbent (e.g., carbon, silica, or an ion exchange resin) followed by filtration, or passing the product through a solid absorbent packed column; purification by vacuum distillation is limited to a small class of low boiling point epoxysilicones, because most epoxysilicones have high boiling points and degrade when exposed to high temperatures. Accordingly, it would be an advantage in the field of epoxysilicones to find a simple way to improve the storage stability of epoxysilicones prepared by hydrosilylation. Summary of the Invention The present invention addresses a need in the art by providing, in one aspect, a composition comprising a) an epoxysilicone; b) a platinum catalyst; and d) a stabilizing amount of a stabilizer which is a geminal alkyn-ol or a maleate ester. The stabilizer serves two functions by providing shelf-stability for the epoxysilane while not interfering with a subsequent deliberate curing step. Detailed Description of the Invention In one aspect, the present invention is a composition comprising a) an epoxysilicone; b) a platinum catalyst; and d) a stabilizing amount of a stabilizer which is a geminal alkyn-ol or a maleate ester. By definition, an epoxysilicone contains any combination of M units (R2R′SiO1 / 2), D units (RR′SiO2 / 2), and / or T units (R′SiO3 / 2), where each R is independently a C1-C6-alkyl group or a phenyl group; and each R′ is an epoxy functionalized fragment, as defined below. An example of a class of linear epoxysilicones is represented by the compound of Formula 1. where each R1is an epoxy-functionalized fragment; each R2is independently an epoxy- functionalized fragment, a C1-C6-alkyl group, or a phenyl group; x is from 0 to 300; and y is from 0 to 200, with the proviso that when y is 0, each R2is an epoxy-functionalized fragment. As used herein, “epoxy functionalized fragment” refers to a C2-C12hydrocarbyl or hydrocarbyl ether group connecting an oxirane group and a silicon atom. The hydrocarbyl group may be linear, branched, cyclic, or fused cyclic. Examples of suitable epoxy functionalized fragments include 2-(3,4-epoxycyclohexyl) ethyl, 3-glycidoxy propyl, and 3-epoxy propyl fragments, as illustrated: where the dotted lines represent the point of attachment to the silicon atom. In another aspect, each R is methyl, ethyl, or phenyl. In one aspect, the composition comprises at least 90 or at least 95 or at least 99 weight percent of the epoxysilane. The platinum catalyst catalyzes the hydrosilylation reaction of an organosilane or organosiloxane and an epoxide functionalized with an ethylenically unsaturated group to the epoxysilicone. As used herein, the terms “organosilane” and “organosiloxane” refer to Si-H containing organosilanes and organosiloxanes. Karstedt’s catalyst is an example of a suitable platinum catalyst. The platinum is typically present in the composition at a concentration in the range of from 1 to 100 ppm, based on the weight of the composition. This reaction is quite efficient and can be achieved with high conversion of the organosilane or polyorganosiloxane; nevertheless, a residuum of the unreacted organosilane or organosiloxane as low as 10 ppm (i.e., 99.9% conversion) has been found to cause shelf-stability problems. It is believed that instability arises by the reaction of this residuum with the epoxy groups, which catalyzes a polymerization reaction resulting in the formation of unwanted gel. Consequently, a stabilizer has been found to be necessary to prevent unwanted gel formation. The composition of the present invention therefore preferably further comprises, based on the weight of the composition, from 1 ppm or from 10 ppm, to 5 weight percent or to 2 weight percent or to 1 weight percent of an organosilane or organosiloxane. The presence of some residual amount of organosilane or organosiloxane is expected in the preparation of the epoxysilicone, hence the need for a stabilizer. Many compounds have been found to stabilize organosiloxanes against degradation, but some, like triphenylphosphine, have been found to retard the rate reaction when added to the starting materials. On the other hand, only two classes of stabilizers to date have been found to improve shelf-stability, yet not interfere with UV curing of the epoxysilicone UV: geminal alkyn-ols and maleate esters. A geminal alkyn-ol is a compound with an alkyne group and a hydroxy group attached to the same carbon atom. Examples of geminal alkyn-ols include 1-ethynyl-1- cyclohexanol (ETCH), 1-ethynyl-1-cyclopentanol, and 1-alkynyl-1-hydroxyethylbenzene. Examples of maleate esters include dimethyl maleate, diethyl maleate, diphenyl maleate, di-n-propyl maleate, and diallyl maleate (DAM). The concentration of the geminal alkyn-ol or maleate ester stabilizer is preferably in the range of from 0.02 or from 0.05 weight percent, to 2 or to 1 or to 0.5 weight percent, based on the weight of the composition. In another aspect, the present invention is a process comprising the step of contacting a mixture of an epoxysilicone, a catalytic amount of platinum, and from 10 ppm to 5 weight percent of an organosilane or organosiloxane, with a stabilizer, which is a geminal alkyn-ol, a maleate ester, a phosphine, a sulfide, a disulfide, or a tetrasulfide, at a concentration of from 0.02 to 2 weight percent, based on the weight of the epoxysilicone. The addition of a stabilizer prior to or during the hydrosilylation reaction is disfavored because this in situ addition often causes a dramatic reduction in the rate of reaction and / or incomplete hydrosilylation with concomitant undesired byproducts in the product composition. The post- addition of a stabilizer, as disclosed in this invention, does not interfere with the rate and extent of the hydrosilylation reaction, but ensures the desired stability of the epoxysilicones. The composition of the present invention provides a shelf-stable epoxysilicone that can be UV-cured without further purification. Examples In the following examples, pbw refers to parts by weight of the composition. Hydrosilsesquioxane was synthesized via the controlled hydrolysis of trichlorosilane in the presence of concentrated sulfuric acid in toluene as described by Frye, C. L.; Collins, W. T.; J. Am. Chem. Soc.92 (19): 1970, 5586–55889. Molecular Weight Determinations Gel permeation chromatography was carried out using a Waters 600 pump, a Waters 717 autosampler, and a Waters 410 differential refractometer. Weight average molecular weight (Mw) was determined relative to a calibration curve (3rdorder) created with polystyrene standards covering the molecular weight range of 580 -2,300,000. Intermediate Example 1 – Synthesis of an Epoxysilicone 1 1,1,3,3-Tetramethyldisiloxane (MHMH, 134.3 g, 1 mole) and a catalytic amount of Karstedt’s catalyst (20 ppm Pt) were added to a flask, followed by the dropwise addition of 4-vinyl-1- cyclohexene 1,2-epoxide (248.4 g, 2.0 mole) 70 °C. The mixture was stirred for 4 h, at which time the reaction was substantially complete as determined by1H NMR spectroscopy. The flask was cooled to room temperature. When 0.1% pbw of triphenylphosphine (PPh3) was added to the reaction mixture in-situ prior to hydrosilylation, substantial starting material remained unreacted at 24 h, as determined by1H NMR spectroscopy. Intermediate Example 2 – Synthesis of an Epoxysilicone 2 1,1,3,3-Tetramethyl-diphenyl-trisiloxane (MHDPh2MH, 332.7 g, 1 mole) and a catalytic amount of Karstedt’s catalyst (20 ppm Pt) were added to a flask followed by the dropwise addition of 4-vinyl-1-cyclohexene 1,2-epoxide (248.4, 2 mole) at 70 °C. The mixture was stirred for 6 h, at which time the reaction was substantially complete as determined by1H NMR spectroscopy. The flask was cooled to room temperature. When 0.1% pbw of PPh3 was added to the reaction mixture in-situ prior to hydrosilylation, about 30% of the starting epoxide remained unreacted at 64 h at 70 °C, as determined by1H NMR spectroscopy. Intermediate Example 3 – Synthesis of Epoxysilicone 3 Hydrosilsesquioxane (300 g, 20.0% wt in toluene), and vinyl cyclohexene oxide (42.2 g) were added to a 500-mL flask, followed by the addition of Karstedt’s catalyst (20 ppm Pt). The mixture was stirred at room temperature for 3 h, after which time the solution was stripped by a solvent exchange process to yield a 20% resin solution in propylene glycol methyl ether acetate. The solution was filtered through a 0.2-µm PTFE filter and stored in a high-density polyethylene bottle Product was determined to be TH0.7TEp 0.3 by29Si NMR spectroscopy. When 0.1% pbw of PPh3 was added to the reaction mixture in-situ prior to hydrosilylation reaction, less than 97% of the starting epoxide remained unreacted at 64 h at room temperature, as determined by1H NMR spectroscopy. No THEp 0.7T 0.3 was observed in the final product mixure. Examples 1 and 2 – Preparation of Epoxysilicones and ETCH Stabilizer ETCH (0.1 pbw) was added to each of Epoxysilicones 1 and 2. Viscosity of the mixtures were monitored at 25 °C over 10-d intervals using a Brookfield cone & plate Digital Rheometer (cone / plate model# DV-III). Example 3 – Preparation of Epoxysilicone 3 and ETCH Stabilizer ETCH (0.1 pbw) was added to Epoxysilicone 3. Mwwas monitored at 10-d intervals. Examples 4 and 5 – Preparation of Epoxysilicones and DAM Stabilizer DAM (0.1 pbw, 0.5 pbw) was added to Epoxysilicones 1 and 2, respectively. Viscosity of the mixtures were monitored at 25 °C over 10-d intervals. Example 6 – Preparation of Epoxysilicone 3 and DAM Stabilizer DAM (0.1 pbw) was added to Epoxysilicone 3. Mwwas monitored at 10-d intervals. Table 1 illustrates differences in viscosity (γ in cP units) over time between epoxysilicones containing ETCH or DAM and epoxysilicones without any stabilizer. The Pt concentration was 20 ppm for each sample. The viscosities were measured at 25 °C and each sample was stored at 23 °C. Comparative 1 refers to Intermediate Example 1, Comparative 2 refers to Intermediate Example 3, and Comparative 3 refers to Intermediate Example 3.

[0002] Table 1 – Viscosity Profiles for Epoxysilicones with and without Stabilizer at 23 °C Example Stabilizer (pbw) Day γ (cP) Comp.1 0 0 5 The data show an increase in viscosity over 60 d for the epoxysilicones without any stabilizer from 5 to 105 cP (Comparative Example 1) or from 51 to 457 cP (Comparative Example 2). In contrast, the viscosity increased only incrementally for the compositions that included ETCH or DMA, indicating storage stability. Table 2 illustrates the differences in Mwfor Epoxysilicone 3 (epoxysilsesquioxane resin) with and without stabilizer. PDI refers to polymer dispersity index. Table 2 – Mw Profiles Epoxysilsesquioxane Resin with and without Stabilizer at 23 °C Example Stabilizer (pbw) Day MwPDI 2 15 5 2 4 M 5 2 6 8 0 5 6 8 0 2 The data i us ra e e s orage s a y o e epoxys sesqu oxane res n as measured by the constancy of Mwand PDI over 60 d. In contrast, the sample without any stabilizer gelled by the end of the testing period. Many stabilizers were post-added to the epoxysilicone intermediates and found to be suitable for improving shelf stability. Table 3 illustrates the effect of stabilizers on UV-cure inhibition. Epoxysilicone 1 was purified in vacuo to remove residual MHMHand platinum. The purified epoxysilicone was then doped with Karstedt’s catalyst (0.01 pbw, 46 ppm Pt) and MHMH(2.06 pbw, Comparative Example 4). Examples 7 and 8 and Comparative Examples 5, 6, and 7 were prepared by adding a stabilizer (0.2 pbw) to the formulation of Comparative Example 4. Each mixture was tested for shelf-life stability as described above. After the completion of the shelf- stability test, UV 9390C photoinitiator (1 pbw, 30 to 60 wt.% bis(4 dodecylphenyl)iodonium hexafluoroantimonate) was added to mixture. Each formulation was coated on a glass substrate using a draw-down bar (thickness of 25 µm to 50 µm). The coatings were then irradiated under UV radiation (broadband, 0.5 J / cm2 dosage) at room temperature using UV cure unit Model# 31983-E (Fusion Systems Corporation, Decatur, Georgia). Curability was assessed using a Q-tip swab for surface tackiness. Table 3 illustrates the impact of a variety of stabilizers on shelf stability and inhibition of UV-cure of the epoxysilicone 1. Example 7 was prepared by adding ETCH and photoinitiator to Intermediate Example 1. Example 8 was prepared by adding DAM and photoinitiator to Intermediate Example 1. ROP refers to the amount of ring opened product as determined by the integration of the corresponding ROP resonances in the1H NMR spectra. The ROP exhibits two distinct and broad peaks (1:1 ratio) at 1.5-1.7 ppm and 3.2-3.6 ppm in1H-NMR spectrum. TETDS refers to tetraethyl thiuram disulfide, and TBTDS refers to tetra-n-butyl thiuram disulfide.

[0003] Table 3 – Shelf Stability and UV-cure Inhibition Study Example Stabilizer MHMHdope Temp / Time ROP UV-cure (pbw) inhibition? The r bilizers against ring opening and concomitant gelation. On the other hand, TETDS, TBTDS, and PPH3all interfered with UV curing of the resin, while ETCH and DAM did not. Experiments were carried out to determine the shelf stability of purified epoxysilicone 1 (40 pbw) doped with Karstedt’s catalyst (46 ppm Pt) and different amounts of MHMH. Stabilizer was not added in this study. Table 4 illustrates the relationship between mole% of ROP generated based on starting moles of the epoxysilicone 1, as determined by1H NMR spectroscopy. Table 4 – Shelf-stability Study of Epoxysilicone with Varying MHMHAmounts Example MHMHconc. Temp / Time ROP formed ) ) The shelf-stabili ty of the epoxysilicone without any stabilizer results in ROP formation of 2.5% even with as little as 100 ppm of MHMH.

Claims

Claims:

1. A composition comprising a) an epoxysilicone; b) a platinum catalyst; and d) a stabilizing amount of a stabilizer which is a geminal alkyn-ol or a maleate ester.

2. The composition of Claim 1 wherein the epoxysilicone is a compound of Formula 1.where each R is independently, C1-C6-alkyl; each R1is an epoxy-functionalized fragment; each R2is independently an epoxy-functionalized fragment, a C1-C6-alkyl group, or a phenyl group; x is from 0 to 300; and y is from 0 to 200, with the proviso that when y is 0, each R2is an epoxy-functionalized fragment.

3. The composition of Claim 2 wherein the concentration of the geminal alkyn-ol or a maleate ester is in the range of from 0.02 to 2 weight percent, based on the weight of the composition.

4. The composition of any of Claims 1 to 3 which further comprises, based on the weight of the composition, from 10 ppm to 5 weight percent of an organosilane.

5. The composition Claim 4 where the stabilizer is 1-ethynyl-1-cyclohexanol dimethyl maleate, diethyl maleate, diphenyl maleate, di-n-propyl maleate, or diallyl maleate.

6. The composition of Claim 5 wherein each R is independently, methyl, ethyl, or phenyl; and the epoxy-functionalized fragment is a (3,4-epoxycyclohexyl) ethyl, a 3-glycidoxy propyl, or a 3-epoxy propyl fragment.

7. The composition of Claim 6 wherein each R is methyl, x is 0, and y is 0; where the stabilizer is 1-ethynyl-1-cyclohexanol dimethyl maleate or diallyl maleate.

8. A process comprising the step of contacting a mixture of an epoxysilicone, a catalytic amount of platinum, and from 10 ppm to 5 weight percent of an organosilane with a stabilizer, wherein the stabilizer is a geminal alkyn-ol, a maleate ester, a phosphine, a sulfide, a disulfide, or a tetrasulfide at a concentration of from 0.02 to 2 weight percent, based on the weight of the epoxysilicone.

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