Platinum(II) dithiocarbamate complex synthesis and use

Abstract

A process includes combining the following components to form a platinum(II) dithiocarbamate complex in solvent: (i) platinum(O) complex; (ii) tetrahydrocarbylthiuram disulfide; and (iii) a solvent. The process can further include separating the platinum(II) dithiocarbamate complex from solvent to isolate the platinum(II) dithiocarbamate complex. The process can further include preparing a curable silicone composition by combining the platinum(II) dithiocarbamate complex with a vinyl-functional silicone and a silyl hydride functional silicone to form a curable composition.

Description

[0001] PLATINUM(U) D1TH10CARBAMATE COMPLEX SYNTHESIS AND USE

[0002] FIELD

[0003] The present invention relates to a process for preparing a platinum(II) dithiocarbamate complex, optionally isolating the platinum(II) dithiocarbamate complex, and optionally the use of the platinum(II) dithiocarbamate complex in preparing a curable silicone composition.

[0004] INTRODUCTION

[0005] Platinum(II) dithiocarbamate complexes are useful in applications such as cancer treatment (see, US10494394) and dye-sensitized solar cells (see, US2020 / 0381186). These citations teach preparing platinum(II) dithiocarbamate complexes by reacting platinum(II) chloride salts (PtCh) with dithiocarbamate sodium salts. A representative reaction scheme is as follows:

[0006] It would advance the art to identify a way to prepare platinum(II) dithiocarbamate complexes without requiring salts as reactants thereby facilitating compatibility of the reaction in chemical environments having a broader range of polarity, and to avoid having metal ion byproducts. In particular, it is desirable to be able to prepare platinum(II) dithiocarbamate complexes from a platinum(O) reactant.

[0007] A seemingly unrelated challenge is in the field of curable silicone compositions. Curable silicone compositions are useful as secondary insulators for electric motors because they can provide a desirable level of electrical insulation and thermal protection. Curable silicone compositions for such applications typically contain a silicone that has a vinyl (Vi) functionality and a silicone crosslinker that contains multiple silyl hydride (SiH) functionalities. The curable silicone composition also typically comprises a hydrosilylation catalyst. The Vi and SiH groups undergo hydrosilylation to cure the composition. Hydrosilylation occurs more rapidly at elevated temperatures, but it can also occur at lower temperatures and that can result in storage instability for the curable silicone compositions.

[0008] One approach to increasing the storage stability of curable silicone compositions is to add an inhibitor to deter hydrosilylation curing at lower temperatures. US4260726, for instance, describes adding organic compounds containing a [=N-C(-S-)2-] sub-unit to a curable silicone composition in order to reduce the viscosity build of the curable composition when aged at 80 °C (indicative of increasing storage stability) while still achieving rapid cure reactivity at 175 °C. However, the method of US4260726 still results in viscosity build of the composition at temperatures of 80 °C. It is desirable to identify a way to obtain storage stability of curable silicone compositions that results in less viscosity build during storage than is obtainable by the method disclosed in US4260726 and yet still achieves rapid onset of curing at temperatures above 120 °C.

[0009] US provisional application 63 / 535620 discloses a process for preparing a curable silicone composition that achieves these objectives. However, the process requires forming a catalyst / inhibitor master batch that contains platinum hydrosilylation catalyst, tetrahydrocarbylthiuram disulfide and an aromatic silicone carrier fluid and then combining that masterbatch to a vinyl-functional silicone and a silyl hydride functional silicone to form a curable composition. It is desirable to advance that solution in a way that does not require adding a catalyst / inhibitor masterbatch containing an aromatic silicone carrier fluid to form the curable composition in order to avoid the need for the aromatic silicone carrier fluid.

[0010] SUMMARY

[0011] The present invention provides a process for preparing platinum(II) dithiocarbamate complexes from platinum(O) complexes without requiring salt reactants. Surprisingly, the platinum(II) dithiocarbamate complexes have been found useful to solve the challenges identified herein above with curable silicone compositions. In particular, the platinum(II) dithiocarbamate complexes prepared by the process of the present invention are useful as thermally triggered catalysts for curable silicone compositions.

[0012] The present invention provides a curable silicone composition, where the curable silicone composition demonstrates enhanced storage stability as evidenced by less viscosity build during storage than is obtained by simply adding an inhibitor to a composition of catalyst and reactive silicone composition, such as is described in US426076. Yet, the present invention does not require combining a catalyst / inhibitor masterbatch containing aromatic silicone carrier fluid to vinyl -functional silicone and a silyl hydride functional silicone to form a curable composition.

[0013] Testing of silicone compositions prepared according to the method disclosed in US426076 have demonstrated a viscosity increase of 40% or more when stored at 80 °C for 150 hours. Silicone compositions prepared according to the process of the present invention experience a viscosity build of 20% or less, even 10% or less, when stored at 80 °C for 150 hours. Moreover, curable silicone compositions prepared according to the process of the present invention demonstrate rapid curing as indicated by a DSC Exotherm Sharpness of 35 °C or less when using a temperature ramping rate of 20 °C / minute from 25 °C to 300 °C with an onset temperature of exotherm (start of curing) that is above 120 °C. Yet moreover, the process of the present invention can contain less than 5 wt%, even less than 2 wt% , even less than one wt% and can be completely free of organic solvent so that the curable silicone compositions prepared according to the present invention have less than 5 wt%, less than 2 wt% , less than one wt%, or even are free of organic solvent.

[0014] The present invention is a result of surprisingly discovering that combining a platinum(O) complex together with a tetrahydrocarbylthiuram disulfide in a solvent results in formation of a platinum(II) dithiocarbamate complex. The reaction can be represented by the following exemplary reaction scheme: tetrahydrocarbylthiuram disulfide platinum(ll) dithiocarbamate complex

[0015] The reaction is typically spontaneous and can result in phase separation of the platinum(II) dithiocarbamate complex from the solvent. The platinum(II) dithiocarbamate complex can be isolated from the solvent and used as desired. One particularly desirable and surprising application is as a thermally triggered catalyst for curable silicone compositions that cure by hydrosilylation reactions. The platinum(II) dithiocarbamate complex can then be added to a vinyl-functional silicone and a silyl hydride functional silicone to form a curable silicone composition without the need for an aromatic silicone carrier fluid, or any carrier fluid, to achieve a curable silicone with a storage stability that is much better than for a curable silicone composition formed by adding inhibitor to a composition already containing the curable silicone and catalyst.

[0016] In a first aspect, the present invention is a process comprising the following step: (a) combining the following components to form a platinum(II) dithiocarbamate complex in a solvent; (i) platinum(O) complex; (ii) tetrahydrocarbylthiuram disulfide; and (iii) a solvent.

[0017] In a second aspect, the present invention is the process of the first aspect further comprising the following step (b) after step (a): (b) separating the platinum(II) dithiocarbamate complex from the solvent to isolate the platinum(II) dithiocarbamate complex.

[0018] In a third aspect, the present invention is the process of the first or second aspect wherein the process is a process for preparing a curable silicone composition that further comprises a step of combining the platinum(II) dithiocarbamate complex prepared in step (a) with a vinylfunctional silicone and a silyl hydride functional silicone to form a curable composition.

[0019] The present invention is useful for preparing platinum(II) dithiocarbamate complexes. The present invention is also useful for forming curable silicone composition that has enhanced storage stability.

[0020] DETAILED DESCRIPTION

[0021] Test methods refer to the most recent test method as of the priority date of this document when a date is not indicated with the test method number. References to test methods contain both a reference to the testing society and the test method number. The following test method abbreviations and identifiers apply herein: ASTM refers to ASTM International methods; END refers to European Norm; DIN refers to Deutsches Institut fur Normung; ISO refers to International Organization for Standards; and UL refers to Underwriters Laboratory.

[0022] Products identified by their tradename refer to the compositions available under those tradenames on the priority date of this document.

[0023] “Multiple” means two or more. “And / or” means “and, or as an alternative”. All ranges include endpoints unless otherwise indicated.

[0024] “Silicone” refers to a polysiloxane, which is a molecule that comprises multiple siloxane units. Identification of siloxane units often utilize abbreviations M, D, T and Q to refer to siloxane units in a siloxane molecule. M-type siloxane units refer to units having the chemical formula: Ra3SiOi / 2- D-type siloxane units refer to units having the chemical formula: Ra2SiO2 / 2- T-type siloxane units refer to units having the chemical formula: RaSiO3 / 2- Q-type siloxane units refer to units having the chemical formula: SiO.4 / 2. In these general formulae, each Rais independently in each occurrence selected from a hydrogen, hydrocarbyl group (substituted or non- substituted), hydroxyl, alkoxyl, or essentially any other group bound to the silicon atom. The O’s refer to oxygen atoms bound the silicon that are bound to a silicon atom of another siloxane unit. The subscript is a multiple of Vi to reflect that the oxygen is bound to this silicon atom and another silicon atom of another siloxane unit also having a multiple of 14 in the denominator - both siloxane units reflect ownership of 14 of the same oxygen atom. The number in the oxygen subscript reflects how many oxygens are bound to the specified silicon atom that are also bound to another siloxane unit silicon atom. Typically, there are subscripts associated with the siloxane units themselves to indicate the relative amounts of the siloxane unit in the molecule. If the subscripts associated with siloxane units are greater than one, then the subscript refers to the average number of those siloxane units in the molecule. If the subscript associated with siloxane units is less than one, then the subscript refers to the average molar ratio of the siloxane unit associated with the subscript relative to total moles of all siloxane units in the molecule. Subscripts of one are typically left unstated so if a siloxane unit does not include a subscript it is understood to have a subscript of one. A chemical formula for a silicone typically lists the siloxane units in blocks, but that does not necessarily imply block polymerization (that is, that the siloxane units exist in the molecule as blocks) but rather are presented in block for convenience to indicate how much of each siloxane unit is present total in the polymer.

[0025] A “resinous poly siloxane”, or “resin”, contains 30 mole-percent (mol%) or more and can contain 50 mol% or more, 70 mol% or more, 90 mol% or more , even 100 mol% of Q-type, T- type or a sum of Q-type and T-type siloxane units. In contrast, a “non-resinous” silicone, which is often referred to simply as a “polymer”, “polymeric”, or “linear” silicone, siloxane or polysiloxane, contains less than 30 mol% of a combination Q-type and T-type siloxane units and often contains only M-type and D-type siloxane units.

[0026] “Silyl hydride” functionality refers to having a hydrogen atom bonded directly to a silicon atom to form an SiH group.

[0027] “DSC Exotherm Sharpness” refers to the temperature range defined by the onset of exotherm to peak exotherm temperature. Or, put another way, DSC Exotherm Sharpness is the value of (Peak Exotherm Temperature) - (Onset Temperature of Exotherm). DSC Exotherm Sharpness is a measure of how rapidly a composition cures once curing begins with a shorter value corresponding to a faster curing.

[0028] “Solid” refers to a state of matter that does not perceptively flow to the unaided eye.

[0029] “Flowing point” refers to a melting point for crystalline materials and glass transition temperature for amorphous materials. If a material has both a melting point and a glass transition temperature then the flowing point is the higher of the two. Basically, the flowing point refers to the temperature at which a solid (non- flowing) material transitions to a flowable state. Determine flowing point for a material by differential scanning calorimetry (DSC) using ASTM method D3418.

[0030] The present invention is a process that includes preparing a platinum(II) dithiocarbamate complex in a solvent by combining: (i) platinum(O) complex; (ii) tetrahydrocarbylthiuram disulfide; and (iii) solvent. The platinum(O) complex and tetrahydrocarbylthiuram disulfide react to form a platinum(II) dithiocarbamate complex in the solvent. Typically, the platinum(II) dithiocarbamate complex forms spontaneously upon combining the components together in the solvent. It is possible to agitate the combination of components by, for instance, mechanical stirring. In the broadest scope, it is not critical what temperature the combining of components (i)-(iii) occur, but typically they are combined at a temperature of zero °C or higher, preferably 10 °C or higher, and can be 15 °C or higher, 20 °C or higher, 23 °C or higher, 25 °C or higher, or even 30 °C or higher while at the same time is typically 70 °C or lower, 60 °C or lower, 50 °C or lower, 40 °C or lower, or even 30 °C or lower.

[0031] The platinum(O) complex is a complex of platinum(O) with complexing agents to form a compound that is soluble in the solvent. That is, it is desirable for the platinum (0) complex to be soluble in the solvent. Examples of desirable platinum(O) complexes are those useful as hydrosilylation catalysts such as any one or any combination of more than one selected from a group consisting of as platinum (0)-l,3-divinyl-l,l,3,3-tetramethyldisiloxane (Karstedt’s catalyst), platinum-carbonyl complexes, platinum(0)-divinyltetramethyldisiloxane complexes, platinum(O) cyclovinylmethylsiloxane complexes, platinum carbene complexes, platinum(O) complexes with phosphine, olefin, and / or carbonyl ligands.

[0032] The tetrahydrocarbylthiuram disulfide component (ii) is desirably any one or any combination of more than one component selected from a group consisting of tetraalkylthiuram disulfides and tetraarylthiuram disulfides. Preferably, the tetrahydrocarbylthiuram disulfide is any one or any combination of more than one component selected from a group consisting of tetrabenzylthiuram disulfide (flowing point of 124 °C per SigmaAldrich), tetramethylthiuram disulfide (flowing point of 156-158 °C per SigmaAldrich), tetraethylthiuram disulfide (flowing point of 69-71 °C per SigmaAldrich), tetra(iso-propyl)thiuram disulfide (flowing point of 115- 117 °C per SigmaAldrich), tetra(iso-butyl)thiuram disulfide (flowing point of 73.5-74.5 °C per ChemBK), and tetra(n-butyl)thiuram disulfide (flowing point of 33 °C per Fisher Scientific).

[0033] The concentration of tetrahydrocarbylthiuram disulfide is desirably such that the molar ratio of tetrahydrocarbylthiuram disulfide to platinum in the platinum(O) complex is in a range of one to 3, and can be in a range of 1 to 2. Such a ratio is desirable to avoid an excess platinum (0) complex.

[0034] The solvent component (iii) is, in the broadest scope of the invention, any material that can dissolve the platinum(O) complex and tetrahydrocarbylthiuram disulfide in the process. Examples of suitable solvents include any one or any combination or more than one selected from a group consisting of aromatic hydrocarbons, halogenated hydrocarbons, ethers, and aprotic polar solvents. It is generally desirable to use a solvent with as low of a boiling point as possible in the process to facilitate isolation of the platinum(II) dithiocarbamate complex from the solvent by evaporation of residual solvent. Particularly useful solvents include those selected from halogenated hydrocarbons such as chloroform (CHCI3) and / or deuterated chloroform (CDCI3). Preferably the solvent is silicon-free.

[0035] It is desirable to use as little solvent as possible to dissolve the platinum(O) complex and tetrahydrocarbylthiuram disulfide to facilitate ready contact between the two reactants and, if desired, to later remove the solvent. Examples of a suitable concentration range for each of platinum(O) complex and tetrahydrocarbylthiuram disulfide in the solvent is, for each one, 0.01 molar (M) or higher, preferably 0.1 M or higher while at the same time typically 2.5 M or lower, and can be 1.0 M or lower.

[0036] During step (a), the platinum(O) complex and the tetrahydrocarbylthiuram disulfide react to form a platinum(II) dithiocarbamate complex. The platinum(II) dithiocarbamate complex is typically a solid at 25 °C that is either dissolved or dispersed in the solvent. The platinum(H) dithiocarbamate complex can phase separate from the solvent resulting in a precipitate or dispersion.

[0037] The process of the present invention can further comprise the following step (b) after step (a): (b) separating the platinum(II) dithiocarbamate complex from the solvent to isolate the platinum(II) dithiocarbamate complex.

[0038] In the broadest scope of the invention the separation can occur by any means that can isolate the platinum(II) dithiocarbamate complex from the solvent. For example, evaporation of solvent from the platinum(II) dithiocarbamate complex is a suitable method to separate the platinum(Il) dithiocarbamate complex from the solvent. Another possible method for separating the platinum(II) dithiocarbamate complex from the solvent includes decanting solvent off from the platinum(II) dithiocarbamate complex preferably after centrifugation. Y et another possible method is filtering the solvent off from the platinum(II) dithiocarbamate complex preferably followed by washing with platinum(II) dithiocarbamate complex with a low-boiling solvent and evaporation of the solvent(s) from the platinum(II) dithiocarbamate complex. It is also possible to spray dray the mixture of platinum(II) dithiocarbamate complex in solvent to remove solvent and isolate the platinum(II) dithiocarbamate complex.

[0039] The objective of step (b) is to isolate platinum(II) dithiocarbamate complex by removing solvent, and preferably any excess reactants and by-products, from the platinum(II) dithiocarbamate complex. This step (b) reduces the amount of solvent and preferably reactants and by-products introduced by the platinum(II) dithiocarbamate complex when it is used in further applications. In the broadest scope of the invention, some solvent can remain with the platinum(II) dithiocarbamate complex. However, it is desirable to have less than one wt%, preferably less than 0.1 wt% solvent remaining with the platinum(ll) dithiocarbamate complex after step (b). It is most desirable to remove all solvent from the platinum(II) dithiocarbamate complex.

[0040] A particularly desirable form of the process of the present invention is a process for preparing a curable silicone composition that comprises, in addition to step (a), and preferably in addition to and after step (b), a step of combining the platinum(II) dithiocarbamate complex prepared in step (a) with a vinyl-functional silicone and a silyl hydride functional silicone to form a curable composition. “Curable” means that composition has components that can react with one another in an additive way to form a crosslinked material. In the case of the curable silicone composition of the present invention, curable refers to being capable of undergoing a hydrosilylation curing reaction. The platinum(II) dithiocarbamate serves as a hydrosilylation catalyst for the curable silicone composition. The curable silicone composition can be a liquid composition, meaning that it is flowable at 25 °C and 101 kiloPascals pressure.

[0041] The vinyl-functional silicone and the silyl hydride functional silicone can be different silicone molecules or they can be the same molecule having both vinyl and silyl hydride functionalities. Both the vinyl-functional silicone and the silyl hydride functional silicone can be linear silicones, both can be silicone resins, or one can be a linear silicone and the other a silicone resin.

[0042] Examples of suitable vinyl-functional silicones that are linear silicones include any one or any combination of more than one silicone selected from those having chemical structure (I):

[0043] ViR2SiO(R2SiO)dSiR2Vi (I) where:

[0044] “Vi” refers to a vinyl group.

[0045] “R” is independently in each occurrence a hydrocarbyl, preferably a hydrocarbyl having from one to 10 carbon atoms and can have one or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, even 9 or more while at the same time typically has 10 or fewer, 9 or fewer, 8 or fewer, 7 or fewer, 6 or fewer, 5 or fewer, 4 or fewer, 3 or fewer, even 2 or fewer carbon atoms. Typically, each R is a methyl.

[0046] Subscript d is a value that is 10 or higher, preferably 20 or higher, and can be 30 or higher, 40 or higher, 50 or higher, 60 or higher, 70 or higher, 80 or higher, 90 or higher, 100 or higher, 110 or higher, 120 or higher, 130 or higher, 140 or higher, 150 or higher, 160 or higher, 170 or higher, even 175 or higher while at the same time is typically 1000 or lower, and can be 900 or lower, 800 or lower, 700 or lower, 600 or lower, 500 or lower, 400 or lower, 300 or lower, and can be 270 or lower, 250 or lower, 225 or lower, 200 or lower, 190 or lower, even 180 or lower.

[0047] Examples of suitable silyl hydride functional silicones that are linear silicones include any one or any combination of more than one silicone selected from those having chemical structure (II):

[0048] R3SiO(R2SiO)x(HRSiO)ySiR3(II) where:

[0049] “R” is independently in each occurrence a hydrocarbyl, preferably a hydrocarbyl having from one to 10 carbon atoms and can have one or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, even 9 or more while at the same time typically has 10 or fewer, 9 or fewer, 8 or fewer, 7 or fewer, 6 or fewer, 5 or fewer, 4 or fewer, 3 or fewer, even 2 or fewer carbon atoms. Typically, each R is a methyl.

[0050] Subscript x is a value that is one or higher, preferably 2 or higher, 3 or higher, 4 or higher, 5 or higher, 6 or higher, 7 or higher, 8 or higher, 9 or higher, 10 or higher, 15 or higher, 20 or higher, and can be 30 or higher, 40 or higher, 50 or higher, 60 or higher, 70 or higher, 80 or higher, 90 or higher, 100 or higher, 110 or higher, 120 or higher, 130 or higher, 140 or higher, 150 or higher, 160 or higher, 170 or higher, even 175 or higher while at the same time is typically 300 or lower, and can be 270 or lower, 250 or lower, 225 or lower, 200 or lower, 190 or lower, even 180 or lower.

[0051] Subscript y is a value that is 2 or higher, 3 or higher, 4 or higher, 5 or higher, 6 or higher, 7 or higher, 8 or higher, 9 or higher, 10 or higher, 15 or higher, 20 or higher, and can be 30 or higher, 40 or higher, 50 or higher, 60 or higher, 70 or higher, 80 or higher, 90 or higher, 100 or higher, 110 or higher, 120 or higher, 130 or higher, 140 or higher, 150 or higher, 160 or higher, 170 or higher, even 175 or higher while at the same time is typically 300 or lower, and can be 270 or lower, 250 or lower, 225 or lower, 200 or lower, 190 or lower, even 180 or lower.

[0052] The vinyl-functional silicone and the silyl hydride functional silicone can be the same silicone resin having both vinyl and silyl hydride functionalities. When the vinyl-functional silicone and the silyl hydride functional silicone are the same silicone, the composition can still further comprise an additional vinyl-functional silicone and / or silyl hydride functional silicone. Alternatively, when the vinyl-functional silicone and the silyl hydride functional silicone are the same silicone, the composition can be free of additional vinyl-functional silicone and / or silyl hydride functional silicone.

[0053] The vinyl-functional silicone and the silyl hydride functional silicone can be the same silicone resin that has the chemical structure (III):

[0054] (PhSiO3 / 2)a(ViMeSiO2 / 2)b(HMeSiO2 / 2)c[(Me)3SiOi / 2]d (III) where “Ph” refers to a phenyl group, “Vi” refers to a vinyl group, “Me” refers to a methyl group subscripts a, b, c and d refer to molar ratios of the associated siloxane unit relative to moles of all siloxane units in the molecule. Subscript a has a value of 0.3 or more, and can be 0.4 or more, 0.43 or more and at the same time is typically 0.7 or less and can be 0.5 or less, even 0.45 or less. Subscript b has a value of 0.05 or more, and can have a value of 0.10 or more, 0.12 or more, even 0.14 or more while at the same time typically has a value of 0.2 or less, and can be 0. 15 or less. Subscript c typically has a value of 0.05 or more and can be 0. 13 or more, 0. 14 or more, 0.15 or more, even 0.16 or more while at the same time is typically 0.2 or less and can be 0.18 or less, even 0.17 or less. Subscript d generally has a value of 0.15 or more, and can be 0.20 or more, even 0.25 or more while at the same time is typically 0.35 or less, and can be 0.30 or less, even 0.26 or less.

[0055] The molar ratio of SiH functionality to vinyl functionality in the curable silicone composition is desirably 0.8 or more, and can be 1 .0 or more, 1 .1 or more, 1 .2 or more, 1 .3 or more, 1.4 or more, even 1.5 or more while at the same time is desirably 2 or less.

[0056] The process of the present invention can be free of aromatic silicone carrier fluid in combination with the platinum(II) dithiocarbamate complex prior to combining the platinum(II) dithiocarbamate complex with a vinyl-functional silicone and a silyl hydride functional silicone to form a curable silicone composition.

[0057] The curable silicone composition of the present invention demonstrates a rapid cure reactivity as indicated by a DSC Exotherm Sharpness of 35 °C or less when using a temperature ramping rate of 20 “ / minute from 25 °C to 300 °C. Curing can initiate at temperatures of 200 °C or higher, 175 °C or higher, 150 °C or higher, or even 120 °C or higher. Curing typically has a peak temperature that is less than 275 °C as determined in the DSC Exotherm Sharpness evaluation. The curable silicone composition demonstrates stability from curing at temperatures of 80 °C even after aging for 150 hours or more as evidenced by a viscosity increase of less than 20% after aging.

[0058] EXAMPLES

[0059] Prepare the examples using the materials listed in Table 1. Table 1

[0060] DOWSIL is a trademark of The Dow Chemical Company. SYL-OFF is a trademark of the Dow Silicones Corporation.

[0061] Preparation of Platinum(II) Dithiocarbamate Complex

[0062] Complex 1 — Pt(0) Complex with Tetrahydrocarbylthiuram Disulfide 1

[0063] Into a 10 milliliter (mL) vial add 400 milligrams (mg) Pt(O) Complex and 3 mL of

[0064] Solvent 1 to get a clear yellow solution. Add 170 mg of tetrahydrocarbylthiuram disulfide 1 in 3 mL of Solvent 1 to the vial. The molar ratio of Tetrahydrocarbylthiuram Disulfide 1 to Pt from the Pt(O) complex is 1.5. A precipitate rapidly forms. Mix the contents of the vial at 23 °C for 10 minutes then centrifuge the vial to obtain a clear orange supernatant over a solid precipitate. Remove the clear orange supernatant with a pipette. Complete two rinses of the precipitate by adding one mL of Solvent 1 followed by centrifuging and removing solvent with a pipette for each rinse. Allow the remaining yellow solid to dry in air under atmospheric conditions (23 °C and 101 kPa pressure) as the solvent evaporates leaving Complex 1.

[0065] Complex 2 — Pt(0) Complex with Tetrahydrocarbylthiuram Disulfide 2

[0066] Into a 10 milliliter (mL) vial add 400 milligrams (mg) Pt(O) Complex and 3 mL of Solvent 1 to get a clear yellow solution. Add 140 mg of Tetrahydrocarbylthiuram Disulfide 2 in 3 mL of Solvent 1 to the vial. The molar ratio of Tetrahydrocarbylthiuram Disulfide 2 to Pt from the Pt(0) complex is one. The contents of the vial rapidly changes color from yellow to deep red / brown. Mix the contents of the vial at 23 °C for 10 minutes as brown precipitate / crystal formations occurs. Allow the mixture to dry in air under atmospheric conditions (23 °C and 101 kPa pressure) as the solvent evaporates. Wash the remaining solid with hexanes and to obtain a clean brown solid. Allow the clean brown solid to dry as hexanes evaporate in air under atmospheric conditions to obtain Complex 2.

[0067] Complex 3 — Pt(0) Complex with Tetrahydrocarbylthiuram Disulfide 3

[0068] Into a 10 milliliter (mL) vial add 400 milligrams (mg) Pt(0) Complex and 3 mL of Solvent 1 to get a clear yellow solution. Add 193 mg of Tetrahydrocarbylthiuram Disulfide 3 in 3 mL of Solvent 1 to the vial. The molar ratio of Tetrahydrocarbylthiuram Disulfide 3 to Pt from the Pt(0) complex is one. The contents of the vial rapidly changes color from yellow to deep red / brown. Mix the contents of the vial at 23 °C for 10 minutes forming a deep red / brown solution. Allow the mixture to dry in air under atmospheric conditions (23 °C and 101 kPa pressure) as the solvent evaporates. Wash the remaining solid with hexanes and to obtain a clean brown solid. Allow the clean brown solid to dry as hexanes evaporate in air under atmospheric conditions to obtain Complex 3.

[0069] Preparation of Curable Silicone Compositions

[0070] Prepare curable silicone composition Samples 1-4 by combining the components for each sample listed in Table 2 for a given sample (values are in grams) into a 200 gram dental mixer cup and then blend them together using a planetary mixer for 1 minute at 3500 revolutions per minute to obtain the curable silicone composition sample.

[0071] Prepare Sample A by combining in a first 40 g dental mixer cup 0.0978 g Pt(0) Complex and 19.91 g of Carrier fluid, blend with a planetary mixer at 3000 revolutions per minute for 2 minutes. In a second 40 g dental mixer cup add 10.015 g of Difunctional Silicone Resin and 0.207 g of the contents of the first 40 g dental mixer cup, and then blend by planetary mixer at 3000 revolutions per minute for 2 minutes to obtain Sample A. Prepare Sample B by combining in a first 40 g dental mixer cup 4.972 g of Vinyl Functional Linear Siloxane 1 and 0.034 g of Diluted PltO) Complex and then mix with a planetary mixer at 3000 revolutions per minute for 2 minutes. In a second 40 g mixer cup add 4.978 g Vinyl Functional Linear Siloxane 1, 0.0087 g Silyl Hydride Functional Liner Siloxane 1 and 0.005 g Inhibitor 1 and mix with a planetary mixer at 3000 revolutions per minute for 2 minutes. Combine the components of the first and second 40 g dental mixer cups and mix at 3000 revolutions per minute with a planetary mixer for 2 minutes to obtain Sample B.

[0072] Table 2

[0073] * viscosity increased too much to age for target time period.

[0074] Sample Characterization

[0075] Characterize each of the samples of curable silicone compositions for storage stability and for rapid cure. Test methods are below and results are included in Table 2.

[0076] Storage Stability

[0077] Characterize storage stability by measuring the extent of viscosity increase as a sample ages. The objective is to achieve less than a 20% viscosity increase after aging 142-191 hours at 80 °C (50 °C for Sample 3 and Sample B). Measure viscosity of samples with a Brookfield DV3T cone / plate (CP40) viscometer with Haake K20 / DC3 water circulating bath maintaining a sample temperature of 25 °C. Measure an Initial Viscosity immediately after preparing the sample. Then age the sample at a temperature of 50 °C or 80°C for 142-191 hours as indicated in Table 3 and measure the viscosity of the aged sample to get the Aged Viscosity.

[0078] Rapid Cure Testing

[0079] Evaluate the speed of cure of the samples using differential scanning calorimetry (DSC). Use a TA instruments Q2000 DSC with a liquid nitrogen cooling system. Use 10 milligram samples in a perforated DSC pan. Collect a DSC scan using a sampling interval of one second per point. First equilibrate the sample at -100 °C and then ramp the sample to 300 °C at a rate of 20 °C per minute. Note the temperature of initial exotherm (Onset Temperature of Exotherm) and the peak temperature achieved (Peak Exotherm Temperature). If the difference Onset Temperature and Peak Exotherm Temperature, that is, the DSC Exotherm Sharpness, is less than 35 °C, then the sample is considered to undergo “rapid cure”. If the temperature difference (DSC Exotherm Sharpness) is greater than 35 °C then the sample is not considered to undergo a “rapid cure”. Put another way, if curing continues for 35 minutes or longer (the temperature ramp is one degree per minute) then the curing is not considered “rapid cure”.

[0080] Discussion

[0081] Samples 1-4 represent curable liquid silicone compositions prepared by adding a platinum(II) dithiocarbamate complex without solvent or carrier fluid to reactive silicone components. Samples 1-3 utilize a silicone comprising both vinyl and SiH functionality on the same molecule. Sample 4 utilizes separate reactive silicone components, one with vinyl functionality and the other with SiH functionality.

[0082] Samples 1-3 demonstrate a % Viscosity Increase of less than 20% when stored at 80 °C for 150 hours. Similarly, Sample 4 demonstrates a viscosity increase of less than 20% when stored at 50 °C for 142 hours and the data suggests would have a viscosity increase of less than 20% when stored at 80 °C for 150 hours. Moreover, silicone compositions prepared according to the process of the present invention demonstrate rapid curing as indicated by a DSC Exotherm Sharpness of 35 °C or less when using a temperature ramping rate of 20 °C / minute from 25 °C to 300 °C with an onset temperature of exotherm (start of curing) that is above 120 °C.

[0083] Comparing Sample 1 with Sample A reveals a benefit of using a Pt(II) dithiocarbamate complex as a hydrosilylation catalyst to maintain the viscosity stability (storage stability) when the reactive silicone composition contains both SiH and SiVi on the same molecule as compared to formulations using Karsetedt’ s catalyst alone. Comparing Sample 4 with Sample B also reveals a benefit of using a Pt(ll) dithiocarbamate complex as a hydrosilylation catalyst to maintain the viscosity stability (storage stability) when the reactive silicone composition contains both SiH and SiVi, but on different silicone components versus a one-part formulation containing Karstedt’ s catalyst with an inhibitor such as 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane.

Claims

CLAIMS:What is claimed is1. A process comprising the following step:(a) combining the following components to form a platinum(II) dithiocarbamate complex in a solvent:(i) platinum(O) complex;(ii) tetrahydrocarbylthiuram disulfide; and(iii) a solvent.

2. The process of claim 1, wherein the platinum(O) complex is a platinum(O) hydrosilylation catalyst.

3. The process of any one previous claim, wherein the platinum(O) complex is Karstedt’s catalyst.

4. The process of any one previous claim, wherein the tetrahydrocarbylthiuram disulfide is selected from a group consisting of tetrabenzylthiuram disulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetra(iso-propyl)thiuram disulfide, tetra(n- butyl)thiuram disulfide, and tetra(iso-butyl)thiuram disulfide.

5. The process of any one previous claim, wherein the molar ratio of tetrahydrocarbylthiuram disulfide to platinum in the hydrosilylation catalyst is in a range of one to 3.

6. The process of any one previous claim, wherein the solvent is selected from a group consisting of aromatic hydrocarbons, halogenated hydrocarbons, ethers, and aprotic polar solvents.

7. The process of any one previous claim, wherein the process further comprises the following step (b) after step (a):(b) separating the platinum(II) dithiocarbamate complex from the solvent to isolate the platinum(II) dithiocarbamate complex.

8. The process of any on previous claim, wherein the process is a process for preparing a curable silicone composition that further comprises a step of combining the platinum(II) dithiocarbamate complex prepared in step (a) with a vinyl-functional silicone and a silyl hydride functional silicone to form a curable composition.

9. The process of any one previous claim, where in the vinyl-functional silicone and a silyl hydride functional silicone are the same silicone that contains both vinyl functionality and silyl hydride functionality.

10. The process of claim 9, wherein the vinyl-functional silicone has the chemical formula: (PhSiO3 / 2)a(ViMeSiO2 / 2)b(HMeSiO2 / 2)c[(Me)3SiOi / 2]d; wherein Ph refers to a phenyl group, Vi refers to a vinyl group, Me refers to a methyl group, subscripts a, b, c and d refer to molar ratios of the associated siloxane unit relative to moles of all siloxane units in the molecule and subscript a is in a range of 0.3 to 0.7, subscript b is in a range of 0.05 to 0.2, subscript c is in a range of 0.05 to 0.2, and subscript d is in a range of 0. 15 to 0.35.

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