Platinum (II) dithiocarbamate complex synthesis and use

Abstract

Disclosed is a method comprising combining the following components to form a platinum (II) dithiocarbamate complex in a solvent: (i) a platinum (0) complex; (ii) tetrahydrocarbyl thiuram disulfide; and (iii) a solvent. The method may also include separating the platinum (II) dithiocarbamate complex from a solvent to separate the platinum (II) dithiocarbamate complex. The method can also 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

Technical Field

[0001] This invention relates to a method for preparing a platinum(II) dithiocarbamate complex, optionally separating the platinum(II) dithiocarbamate complex, and optionally using the platinum(II) dithiocarbamate complex in the preparation of curable silicone compositions. Background Technology

[0002] Platinum(II) dithiocarbamate complexes can be used in applications such as cancer therapy (see US10494394) and dye-sensitized solar cells (see US2020 / 0381186). These citations propose the preparation of platinum(II) dithiocarbamate complexes by reacting platinum(II) chloride (PtCl2) with sodium dithiocarbamate. A representative reaction scheme is as follows:

[0003]

[0004] Developing a method for preparing platinum(II) dithiocarbamate complexes while avoiding metal ion byproducts would be an advancement in the art, one that does not require salts as reactants, thereby promoting compatibility of the reaction in chemical environments with a wider range of polarities. Specifically, it is desirable to be able to prepare platinum(II) dithiocarbamate complexes from platinum(0) reactants.

[0005] There appears to be an unrelated challenge in the field of curable silicone compositions. Curable silicone compositions can be used as secondary insulators for electric motors because they provide the desired level of electrical insulation and thermal protection. Curable silicone compositions for such applications typically contain a silicone with vinyl (Vi) functionality and a silicone crosslinker containing multiple silyl hydride (SiH) functionalities. Curable silicone compositions also typically contain 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 this can lead to storage instability for curable silicone compositions.

[0006] One method to increase the storage stability of curable silicone compositions is to add inhibitors to prevent hydrosilylation curing at lower temperatures. For example, US4260726 describes adding an organic compound containing the [=NC(-S-)2-] subunit to a curable silicone composition to reduce viscosity buildup when the curable composition ages at 80°C (indicating increased storage stability) while still achieving rapid curing reactivity at 175°C. However, the method in US4260726 still results in viscosity buildup of the composition at 80°C. It is desirable to determine a way to achieve storage stability of curable silicone compositions that results in less viscosity buildup during storage than that achievable by the method disclosed in US4260726, while also achieving rapid initiation of curing at temperatures above 120°C.

[0007] U.S. Provisional Application 63 / 535620 discloses a method for preparing curable silicone compositions that achieve these objectives. However, this method requires forming a catalyst / inhibitor masterbatch containing a platinum hydride silanization catalyst, a tetraalkylthiuram disulfide, and an aromatic silicone carrier fluid, and subsequently combining the masterbatch with vinyl-functionalized silicones and silylhydride-functionalized silicones to form a curable composition. It is desirable to improve this solution in a way that eliminates the need for adding a catalyst / inhibitor masterbatch containing an aromatic silicone carrier fluid to form the curable composition, thereby avoiding the requirement for an aromatic silicone carrier fluid. Summary of the Invention

[0008] This invention provides a method for preparing platinum dithiocarbamate (II) complexes from platinum (O) complexes without the need for salt reactants. Surprisingly, platinum dithiocarbamate (II) complexes have been found to be useful in addressing the challenges identified above with curable silicone compositions. Specifically, the platinum dithiocarbamate (II) complexes prepared by the method of this invention can be used as thermally triggered catalysts for curable silicone compositions.

[0009] This invention provides a curable silicone composition that exhibits enhanced storage stability, as demonstrated by less viscosity buildup during storage compared to compositions obtained by simply adding an inhibitor to a catalyst and a reactive silicone composition, as described in, such as, US426076. However, this invention does not require combining a catalyst / inhibitor masterbatch containing an aromatic silicone carrier fluid with vinyl-functionalized silicones and silylhydride-functionalized silicones to form a curable composition.

[0010] Tests of silicone compositions prepared according to the method disclosed in US426076 have shown that the viscosity increases by more than 40% when stored at 80°C for 150 hours. When stored at 80°C for 150 hours, silicone compositions prepared according to the method of the present invention experience a viscosity buildup of less than 20%, even less than 10%. Furthermore, curable silicone compositions prepared according to the method of the present invention exhibit rapid curing, as indicated by the rapid exothermic DSC below 35°C when using a heating rate of 20°C / min from 25°C to 300°C, and an exothermic onset temperature (curing start) above 120°C. Moreover, the method of the present invention may contain less than 5% by weight, even less than 2% by weight, even less than one% by weight of organic solvent, and may be completely solvent-free, such that the curable silicone compositions prepared according to the present invention have less than 5% by weight, less than 2% by weight, less than one% by weight of organic solvent, or even no organic solvent.

[0011] The present invention is a surprising discovery that combining a platinum(0) complex with tetraalkylthiuram disulfide in a solvent results in the formation of a platinum(II) dithiocarbamate complex. This reaction can be represented by the following exemplary reaction scheme:

[0012]

[0013] The reaction is typically spontaneous and can lead to phase separation of the platinum(II) dithiocarbamate complex from the solvent. The platinum(II) dithiocarbamate complex can be separated from the solvent and used as needed. A particularly desirable and surprising application is as a thermally triggered catalyst for curable silicone compositions cured via a hydrosilylation reaction. The platinum(II) dithiocarbamate complex can then be added to vinyl-functionalized silicones and silylhydride-functionalized silicones to form curable silicone compositions without the need for aromatic silicone carrier fluids or any carrier fluid, to obtain curable silicones with significantly better storage stability than curable silicone compositions formed by adding inhibitors to compositions already containing curable silicones and catalysts.

[0014] In a first aspect, the present invention is a method comprising the steps of: (a) combining the following components to form a platinum(II) dithiocarbamate complex in a solvent; (i) a platinum(O) complex; (ii) a tetrahydrothiuram disulfide; and (iii) a solvent.

[0015] In a second aspect, the present invention is a method of the first aspect, which further includes the step (b) after step (a): (b) separating the platinum (II) dithiocarbamate complex from the solvent to separate the platinum (II) dithiocarbamate complex.

[0016] In a third aspect, the present invention is a method of the first or second aspect, wherein the method is a method for preparing a curable silicone composition, the method further comprising the step of combining the platinum dithiocarbamate (II) complex prepared in step (a) with vinyl-functional silicones and silyl hydride-functional silicones to form a curable composition.

[0017] This invention can be used to prepare platinum(II) dithiocarbamate complexes. This invention can also be used to form curable silicone compositions with enhanced storage stability. Detailed Implementation

[0018] When a date is not indicated by a test method number, the test method refers to the most recent test method as of the priority date of this document. References to test methods include references to both the testing association and the test method number. The following test method abbreviations and designations apply to this document: ASTM refers to ASTM International Society Methods; END refers to European Standards; DIN refers to the German Institute for Standardization; ISO refers to the International Organization for Standardization; and UL refers to Underwriters Laboratories.

[0019] Products identified by their trade names refer to compositions available under those trade names as of the priority date of this document.

[0020] "Multiple" means two or more. "And / or" means "and, or as an alternative." Unless otherwise specified, all ranges include the endpoints.

[0021] "Silicone" refers to polysiloxane, which is a molecule containing multiple siloxane units. Siloxane units are typically identified using the abbreviations M, D, T, and Q to represent the siloxane units in a siloxane molecule. An M-type siloxane unit is a unit with the following chemical formula: R a 3SiO 1 / 2 D-type siloxane units refer to units with the following chemical formula: R a 2SiO 2 / 2 T-type siloxane units refer to units with the following chemical formula: R a SiO 3 / 2 Q-type siloxane units refer to units with the following chemical formula: SiO 4 / 2 In these general formulas, each R aEach occurrence is independently selected from hydrogen, a hydrocarbon group (substituted or unsubstituted), a hydroxyl group, an alkoxy group, or essentially any other group bonded to a silicon atom. O refers to an oxygen atom bonded to silicon, which is also bonded to a silicon atom in another siloxane unit. The subscript is a multiple of ½ to reflect the bonding of oxygen to this silicon atom and to another silicon atom in the other siloxane unit, which also has a multiple of ½ in the denominator, with both siloxane units reflecting ½ ownership of the same oxygen atom. The number in the oxygen subscript reflects how much oxygen is bonded to the specified silicon atom, which is also bonded to a silicon atom in another siloxane unit. Typically, there is a subscript associated with the siloxane unit itself to indicate the relative amount of siloxane units in the molecule. If the subscript associated with the siloxane unit is greater than one, the subscript refers to the average number of those siloxane units in the molecule. If the subscript associated with the siloxane unit is less than one, the subscript refers to the average molar ratio of the siloxane unit associated with the subscript to the total molar number of all siloxane units in the molecule. The subscript 1 is usually not specified, so if a siloxane unit does not include a subscript, it should be understood that it has a subscript 1. The chemical formula of silicones is usually listed in blocks for siloxane units, but this does not necessarily mean block polymerization (i.e., siloxane units exist as blocks in the molecule), but rather it is presented in blocks for convenience to indicate how much of each siloxane unit is present in the polymer in total.

[0022] "Resin-like polysiloxanes" or "resins" contain 30 mol% or more, and may contain 50 mol% or more, 70 mol% or more, 90 mol% or more, or even 100 mol% of Q-type, T-type, or a combination of Q-type and T-type siloxane units. In contrast, "non-resin-like" silicones, which are usually simply referred to as "polymers," "polymeric," or "linear" silicones, siloxanes, or polysiloxanes, contain less than 30 mol% of a combination of Q-type and T-type siloxane units, and typically contain only M-type and D-type siloxane units.

[0023] The functionality of "silyl hydride" refers to the presence of hydrogen atoms that are directly bonded to silicon atoms to form SiH groups.

[0024] "DSC exothermic rate" refers to the temperature range defined from the onset of exothermic reaction to the peak exothermic temperature. In other words, DSC exothermic rate is the value of (peak exothermic temperature) minus (exothermic onset temperature). DSC exothermic rate is a measure of how quickly a composition cures once curing begins, with shorter values ​​corresponding to faster curing.

[0025] "Solid" refers to a state of matter that is imperceptible to the naked eye and flows.

[0026] "Flow point" refers to the melting point of crystalline materials and the glass transition temperature of amorphous materials. If a material has both a melting point and a glass transition temperature, the flow point is the higher of the two. Essentially, the flow point is the temperature at which a solid (non-flowing) material transforms into a flowable state. The flow point of a material is determined using ASTM Method D3418 by differential scanning calorimetry (DSC).

[0027] This invention is a method comprising preparing a platinum(II) dithiocarbamate complex in a solvent by combining the following substances: (i) a platinum(O) complex; (ii) a tetraalkylthiuram disulfide; and (iii) a solvent. The platinum(O) complex and the tetraalkylthiuram disulfide react to form the platinum(II) dithiocarbamate complex in the solvent. Typically, the platinum(II) dithiocarbamate complex forms spontaneously when the components are combined in the solvent. The combination of components can be stirred, for example, by mechanical agitation. The temperature at which the combination of components (i) to (iii) occurs is not critical over a wide range, but they are typically above 0°C, preferably above 10°C, and can be above 15°C, above 20°C, above 23°C, above 25°C, or even above 30°C, while simultaneously typically below 70°C, below 60°C, below 50°C, below 40°C, or even below 30°C.

[0028] A platinum (0) complex is a complex of platinum (0) with a complexing agent to form a compound soluble in a solvent. That is, it is desirable that the platinum (0) complex is soluble in a solvent. Examples of desirable platinum (0) complexes are those that can be used as hydrosilylation catalysts, such as any combination of one or more of the group consisting of platinum (0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane (Karstedt catalyst), platinum-carbonyl complexes, platinum (0)-divinyltetramethyldisiloxane complexes, platinum (0)cyclovinylmethylsiloxane complexes, platinum carbene complexes, and complexes of platinum (0) with phosphine, olefins, and / or carbonyl ligands.

[0029] The tetraalkylthiuram disulfide component (ii) is advantageously any combination of one or more of the group consisting of tetraalkylthiuram disulfide and tetraarylthiuram disulfide. Preferably, the tetraalkylthiuram disulfide is any combination of one or more of the group consisting of tetrabenzylthiuram disulfide (flow point 124°C, Sigma-Aldrich), tetramethylthiuram disulfide (flow point 156°C to 158°C, Sigma-Aldrich), tetraethylthiuram disulfide (flow point 69°C to 71°C, Sigma-Aldrich), tetra(isopropyl)thiuram disulfide (flow point 115°C to 117°C, Sigma-Aldrich), tetra(isobutyl)thiuram disulfide (flow point 73.5°C to 74.5°C, ChemBK), and tetra(n-butyl)thiuram disulfide (flow point 33°C, Fisher Scientific).

[0030] The concentration of tetradisulfide thiuram is advantageously such that the molar ratio of tetradisulfide thiuram to platinum in the platinum(0) complex is in the range of one to three, and may be in the range of one to two. Such a ratio is desirable to avoid an excess of platinum(0) complex.

[0031] Within the broadest scope of the invention, solvent component (iii) is any material capable of dissolving the platinum (0) complex and tetrahydrothiuram disulfide in this method. Examples of suitable solvents include any combination of one or more of the group consisting of aromatic hydrocarbons, halogenated hydrocarbons, ethers, and aprotic polar solvents. It is generally desirable to use a solvent with the lowest possible boiling point in this method to facilitate the separation of the platinum (II) disulfide complex from the solvent by evaporation of the residual solvent. Particularly useful solvents include those selected from halogenated hydrocarbons such as chloroform (CHCl3) and / or deuterated chloroform (CDCl3). Preferably, the solvent is silicon-free.

[0032] It is desirable to use as little solvent as possible to dissolve the platinum(0) complex and tetraalkylthiuram disulfide to facilitate rapid contact between the two reactants, and to subsequently remove the solvent if necessary. Examples of suitable concentration ranges for each of the platinum(0) complex and tetraalkylthiuram disulfide in the solvent are: for each, 0.01 mol (M) or more, preferably 0.1 M or more, while typically below 2.5 M, and possibly below 1.0 M.

[0033] During step (a), the platinum (0) complex reacts with tetrahydrothiuram disulfide to form a platinum (II) dithiocarbamate complex. The platinum (II) dithiocarbamate complex is typically a solid at 25°C and is dissolved or dispersed in a solvent. The platinum (II) dithiocarbamate complex can undergo phase separation from the solvent, resulting in a precipitate or dispersion.

[0034] The method of the present invention may further include the following step (b) after step (a): (b) separating the platinum dithiocarbamate (II) complex from the solvent to separate the platinum dithiocarbamate (II) complex.

[0035] Within the broadest scope of this invention, separation can occur by any means that separates the platinum(II) dithiocarbamate complex from the solvent. For example, evaporating the solvent from the platinum(II) dithiocarbamate complex is a suitable method for separating the platinum(II) dithiocarbamate complex from the solvent. Another possible method for separating the platinum(II) dithiocarbamate complex from the solvent includes, preferably, decanting the solvent from the platinum(II) dithiocarbamate complex after centrifugation. Yet another possible method is to filter the solvent from the platinum(II) dithiocarbamate complex, preferably followed by washing the platinum(II) dithiocarbamate complex with a low-boiling-point solvent, and then evaporating the solvent from the platinum(II) dithiocarbamate complex. It is also possible to spray-dry the mixture of the platinum(II) dithiocarbamate complex in the solvent to remove the solvent and separate the platinum(II) dithiocarbamate complex.

[0036] The purpose of step (b) is to separate the platinum(II) dithiocarbamate complex by removing the solvent from the complex, and preferably removing any excess reactants and byproducts. This step (b) reduces the amount of solvent, and preferably reactants and byproducts, introduced by the platinum(II) dithiocarbamate complex when it is used in other applications. At the widest extent of the invention, some solvent may be retained with the platinum(II) dithiocarbamate complex. However, it is desirable that less than one wt%, preferably less than 0.1 wt%, of solvent is retained with the platinum(II) dithiocarbamate complex after step (b). Ideally, all solvent should be removed from the platinum(II) dithiocarbamate complex.

[0037] A particularly desirable form of the method of the present invention is a method for preparing a curable silicone composition, which, in addition to step (a), and preferably in addition to and after step (b), further comprises combining the platinum dithiocarbamate (II) complex prepared in step (a) with vinyl-functionalized silicones and silylhydride-functionalized silicones to form a curable composition. "Cureable" means that the composition has components that can react with each other in an additive manner to form a crosslinked material. In the case of the curable silicone composition of the present invention, curable means capable of undergoing a hydrosilylation curing reaction. Platinum dithiocarbamate (II) acts 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 kPa.

[0038] Vinyl-functional silicones and silylhydride-functional silicones can be different silicone molecules, or they can be the same molecule having both vinylhydride and silylhydride functionality. Both vinyl-functional silicones and silylhydride-functional silicones can be linear silicones, both can be silicone resins, or one can be a linear silicone and the other can be a silicone resin.

[0039] Examples of suitable vinyl-functional silicones as linear silicones include any one or any combination of more than one silicone selected from those having chemical structure (I):

[0040] ViR2SiO(R2SiO) d SiR2Vi(I)

[0041] in:

[0042] “Vi” refers to the vinyl group.

[0043] Each time “R” appears, it is independently a hydrocarbon group, preferably having one to 10 carbon atoms, and may have one or more, two or more, three or more, four or more, five or more, six or more, seven or more, eight or more, or even nine or more, while typically having 10 or fewer, nine or fewer, eight or fewer, seven or fewer, six or fewer, five or fewer, four or fewer, three or fewer, or even two or fewer carbon atoms. Typically, each R is a methyl group.

[0044] The subscript d 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, or even 175 or higher. At the same time, it is usually below 1000, and can be below 900, below 800, below 700, below 600, below 500, below 400, below 300, and can be below 270, below 250, below 225, below 200, below 190, or even below 180.

[0045] Examples of suitable silylhydride-functionalized silicones as linear silicones include any one or any combination of more than one silicone selected from those having chemical structure (II):

[0046] R3SiO(R2SiO) x (HRSiO) y SiR3(II)

[0047] in:

[0048] Each time “R” appears, it is independently a hydrocarbon group, preferably having one to 10 carbon atoms, and may have one or more, two or more, three or more, four or more, five or more, six or more, seven or more, eight or more, or even nine or more, while typically having 10 or fewer, nine or fewer, eight or fewer, seven or fewer, six or fewer, five or fewer, four or fewer, three or fewer, or even two or fewer carbon atoms. Typically, each R is a methyl group.

[0049] The subscript x is one or more, preferably 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 15 or more, 20 or more, and can also be 30 or more, 40 or more, 50 or more, 60 or more, 70 or more, 80 or more, 90 or more, 100 or more, 110 or more, 120 or more, 130 or more, 140 or more, 150 or more, 160 or more, 170 or more, or even 175 or more, while usually below 300, and can also be below 270, 250, 225, 200, 190 or even 180.

[0050] The subscript y 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 also 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, or even 175 or higher, while it is usually below 300, and can also be below 270, below 250, below 225, below 200, below 190, or even below 180.

[0051] The vinyl-functionalized silicone and the silylhydride-functionalized silicone can be the same silicone resin having both vinylhydride functionality and silylhydride functionality. When the vinyl-functionalized silicone and the silylhydride-functionalized silicone are the same silicone, the composition may also still contain additional vinyl-functionalized silicone and / or silylhydride-functionalized silicone. Alternatively, when the vinyl-functionalized silicone and the silylhydride-functionalized silicone are the same silicone, the composition may not contain additional vinyl-functionalized silicone and / or silylhydride-functionalized silicone.

[0052] Vinyl-functional silicones and silyl hydride-functional silicones can be the same silicone resin having chemical structure (III):

[0053] (PhSiO 3 / 2 ) a (ViMeSiO 2 / 2 ) b (HMeSiO 2 / 2 ) c [(Me)3SiO 1 / 2 ] d (III)

[0054] Where "Ph" refers to a phenyl group, "Vi" refers to a vinyl group, and "Me" refers to a methyl group. Subscripts a, b, c, and d indicate the molar ratio of the associated siloxane unit to the total number of siloxane units in the molecule. Subscript a has a value of 0.3 or higher, and can be 0.4 or higher, 0.43 or higher, and is typically below 0.7, and can be below 0.5, or even below 0.45. Subscript b has a value of 0.05 or higher, and can be 0.10 or higher, 0.12 or higher, or even above 0.14, and is typically below 0.2, and can be below 0.15. Subscript c typically has a value of 0.05 or higher, and can be 0.13 or higher, 0.14 or higher, 0.15 or higher, or even above 0.16, and is typically below 0.2, and can be below 0.18, or even below 0.17. The subscript d typically has a value greater than 0.15, and can be greater than 0.20 or even greater than 0.25, while it is typically less than 0.35 and can be less than 0.30 or even less than 0.26.

[0055] The molar ratio of SiH functionality to vinyl functionality in the curable silicone composition is advantageously 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, or even 1.5 or more, while advantageously being 2 or less.

[0056] Before combining the platinum (II) dithiocarbamate complex with vinyl-functionalized and silyl hydride-functionalized silicones to form a curable silicone composition, the method of the present invention may be free of aromatic silicone carrier fluids combined with the platinum (II) dithiocarbamate complex.

[0057] The curable silicone compositions of the present invention exhibit rapid curing reactivity, as indicated by the exothermic DSC below 35°C when heating from 25°C to 300°C at a rate of 20°C / min. Curing can be initiated at temperatures above 200°C, above 175°C, above 150°C, or even above 120°C. Curing typically has a peak temperature of less than 275°C, as determined in the DSC exothermic assessment. The curable silicone compositions exhibit stability at 80°C even after aging for more than 150 hours, as evidenced by a viscosity increase of less than 20% after aging.

[0058] Example

[0059] Examples of preparation were made using the materials listed in Table 1.

[0060] Table 1

[0061]

[0062] DOWSIL is a trademark of Dow Chemical Company. SYL-OFF is a trademark of Dow Silicones Corporation.

[0063] Preparation of platinum(II) dithiocarbamate complex

[0064] Complex 1-Pt(0) with tetrahydrothiuram 1 disulfide

[0065] Add 400 mg of Pt(0) complex and 3 mL of solvent 1 to a 10 mL vial to obtain a clear yellow solution. Add a solution of 170 mg of tetrahydrothiuram 1 in 3 mL of solvent 1 to the vial. The molar ratio of tetrahydrothiuram 1 to Pt from the Pt(0) complex is 1.5. A precipitate forms rapidly. Mix the contents of the vial at 23 °C for 10 minutes, then centrifuge the vial to obtain a clear orange supernatant above the solid precipitate. Remove the clear orange supernatant with a pipette. Complete two washes of the precipitate by adding one mL of solvent 1, followed by centrifugation and removal of the solvent from each wash with a pipette. As the solvent evaporates, air-dry the remaining yellow solid under atmospheric conditions (23 °C and 101 kPa pressure) to leave complex 1.

[0066] Complex 2-Pt(0) with tetrahydrothiuram 2 disulfide

[0067] Add 400 mg of Pt(0) complex and 3 mL of solvent 1 to a 10 mL vial to obtain a clear yellow solution. Add a solution of 140 mg of tetrahydrothiuram 2 in 3 mL of solvent 1 to the vial. The molar ratio of tetrahydrothiuram 2 to Pt from the Pt(0) complex is one. The contents of the vial rapidly change from yellow to dark red / brown. Mix the contents of the vial at 23 °C for 10 minutes, at which point a brown precipitate / crystals form. As the solvent evaporates, air-dry the mixture under atmospheric conditions (23 °C and 101 kPa pressure). Wash the remaining solid with hexane to obtain a pure brown solid. Dry the clean brown solid under atmospheric conditions as the hexane evaporates in air to obtain complex 2.

[0068] Complex 3-Pt(0) with tetrahydrothiuram 3 disulfide

[0069] Add 400 mg of Pt(0) complex and 3 mL of solvent 1 to a 10 mL vial to obtain a clear yellow solution. Add a solution of 193 mg of tetrahydrothiuram 3 in 3 mL of solvent 1 to the vial. The molar ratio of tetrahydrothiuram 3 to Pt from the Pt(0) complex is one. The contents of the vial rapidly change from yellow to dark red / brown. Mix the contents of the vial at 23 °C for 10 minutes to form a dark red / brown solution. As the solvent evaporates, air-dry the mixture under atmospheric conditions (23 °C and 101 kPa pressure). Wash the remaining solid with hexane to obtain a pure brown solid. Dry the clean brown solid under atmospheric conditions as the hexane evaporates in air to obtain complex 3.

[0070] Preparation of Curable Silicone Compositions

[0071] Curable silicone composition samples 1 to 4 were prepared by combining the components (values ​​in grams) of each of the given samples listed in Table 2 into a 200-gram dental mixer cup and then mixing them together for 1 minute at 3500 rpm using a planetary mixer to obtain a curable silicone composition sample.

[0072] Sample A was prepared by combining 0.0978 g of Pt(0) complex and 19.91 g of carrier fluid in a first 40 g dental mixer cup and mixing with a planetary mixer at 3000 rpm for 2 minutes. Sample A was obtained by adding 10.015 g of bifunctional silicone resin and 0.207 g of the contents of the first 40 g dental mixer cup to a second 40 g dental mixer cup and then mixing with a planetary mixer at 3000 rpm for 2 minutes.

[0073] Sample B was prepared by combining 4.972 g of vinyl-functionalized linear silicone 1 and 0.034 g of diluted Pt(0) complex in a first 40 g dental mixer cup and then mixing with a planetary mixer at 3000 rpm for 2 minutes. In a second 40 g mixer cup, 4.978 g of vinyl-functionalized linear silicone 1, 0.0087 g of silylhydride-functionalized linear silicone 1, and 0.005 g of inhibitor 1 were added and mixed with a planetary mixer at 3000 rpm for 2 minutes. The components from the first and second 40 g dental mixer cups were combined and mixed with a planetary mixer at 3000 rpm for 2 minutes to obtain Sample B.

[0074] Table 2

[0075]

[0076] The viscosity increased too much, causing it to age within the target time period.

[0077] Sample characterization

[0078] The storage stability and rapid curing of each sample in the curable silicone composition were characterized. The test methods are as follows, and the results are included in Table 2.

[0079] Storage stability

[0080] Storage stability was characterized by measuring the increase in viscosity during sample aging. The goal was to achieve a viscosity increase of less than 20% after aging at 80°C (50°C for samples 3 and B) for 142 to 191 hours. The viscosity of the samples was measured using a Brookfield DV3T cone / plate (CP40) viscometer, with a Haake K20 / DC3 water circulating bath maintaining the sample temperature at 25°C. The initial viscosity was measured immediately after sample preparation. Then, as indicated in Table 3, the samples were aged at 50°C or 80°C for 142 to 191 hours, and the viscosity of the aged samples was measured to obtain the aged viscosity.

[0081] Rapid curing test

[0082] The curing rate of the samples was assessed using differential scanning calorimetry (DSC). A TA Q2000 DSC instrument with a liquid nitrogen cooling system was used. A 10 mg sample was used in a perforated DSC disk. DSC scans were collected at sampling intervals of one second per point. The sample was first equilibrated at -100°C and then heated to 300°C at a rate of 20°C / min. The initial exothermic temperature (exothermic onset temperature) and the achieved peak temperature (peak exothermic temperature) were noted. If the difference between the onset temperature and the peak exothermic temperature (i.e., the DSC exothermic rate) was less than 35°C, the sample was considered to have undergone “rapid curing.” If the temperature difference (DSC exothermic rate) was greater than 35°C, the sample was not considered to have undergone “rapid curing.” In other words, if curing lasted 35 minutes or longer (a temperature ramp of one degree per minute), curing was not considered “rapid curing.”

[0083] discuss

[0084] Samples 1 to 4 represent curable liquid silicone compositions prepared by adding a platinum(II) dithiocarbamate complex to a reactive silicone component without the presence of a solvent or carrier fluid. Samples 1 to 3 utilize silicones having 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.

[0085] Samples 1 to 3 showed a viscosity increase of less than 20% when stored at 80°C for 150 hours. Similarly, sample 4 showed a viscosity increase of less than 20% when stored at 50°C for 142 hours, and the data indicated a viscosity increase of less than 20% when stored at 80°C for 150 hours. Furthermore, the silicone compositions prepared according to the method of the present invention exhibit rapid curing, as indicated by the rapid exothermic reaction rate (DSC) below 35°C when heating from 25°C to 300°C at a heating rate of 20°C / min, and the exothermic onset temperature (curing start) is above 120°C.

[0086] A comparison of Sample 1 with Sample A shows that when the reactive silicone composition contains both SiH and SiVi on the same molecule, there is a benefit in using the dithiocarbamate Pt(II) complex as a hydrogen silylation catalyst to maintain viscosity stability (storage stability) compared to the formulation using only Karsetedt.

[0087] Comparison of Sample 4 with Sample B also showed that, when the reactive silicone composition contains both SiH and SiVi but on different silicone components, the use of a dithiocarbamate Pt(II) complex as a hydrogenation silylation catalyst to maintain viscosity stability (storage stability) is beneficial compared to single-component formulations containing a Karstedt catalyst and an inhibitor such as 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane.

Claims

1. A method comprising the steps of: (a) combining to form a platinum (II) dithiocarbamate complex in a solvent: (i) a platinum (0) complex; (ii) a tetraalkyl thiuram disulfide; and (iii) a solvent.

2. The method of claim 1, wherein the platinum (0) complex is a platinum (0) hydrosilylation catalyst.

3. The method of any preceding claim, wherein the platinum (0) complex is Karstedt’s catalyst.

4. The method of any preceding claim, wherein the tetraalkyl thiuram disulfide is selected from the group consisting of tetrabenzyl thiuram disulfide, tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, tetraisopropyl thiuram disulfide, tetra-n-butyl thiuram disulfide, and tetraisobutyl thiuram disulfide.

5. The method of any preceding claim, wherein the molar ratio of tetraalkyl thiuram disulfide to platinum in the hydrosilylation catalyst is in the range of one to three.

6. The method of any preceding claim, wherein the solvent is selected from the group consisting of aromatic hydrocarbons, halogenated hydrocarbons, ethers, and aprotic polar solvents.

7. The method of any preceding claim, wherein the method 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 method of any preceding claim, wherein the method is a method for preparing a curable silicone composition, the method further comprising the 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 method of any preceding claim, wherein the vinyl-functional silicone and silyl hydride-functional silicone is the same silicone containing both vinyl functionality and silyl hydride functionality.

10. The method of claim 9, wherein the vinyl-functional silicone has the chemical formula: (PhSiO 3 / 2 ) a (ViMeSiO 2 / 2 ) b (HMeSiO 2 / 2 ) c [(Me)3SiO 1 / 2 ] d ; wherein Ph refers to a phenyl group, Vi refers to a vinyl group, Me refers to a methyl group, the subscripts a, b, c, and d refer to the molar ratio of the associated siloxane unit relative to the moles of all siloxane units in the molecule, and the subscript a is in the range of 0.3 to 0.7, the subscript b is in the range of 0.05 to 0.2, the subscript c is in the range of 0.05 to 0.2, and the subscript d is in the range of 0.15 to 0.35.

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