Process for preparing clustered epoxy silicones avoiding gelation or undesirable molecular weight build

Abstract

A process for preparing a clustered epoxy silicone with the following steps: (a) conduct a hydrosilylation reaction between the following reactants in the presence of a platinum-based hydrosilylation catalyst to form a SiH-functional siloxane intermediate: (i) an alkenyl functional siloxane with 2 or more silicon-bound alkenyl groups per molecule; and (ii) a cyclic SiH-functional siloxane with 4 or more SiH groups per molecule; (b) add thiuram disulfide at a concentration at least twice that of platinum from step (a); (c) strip unreacted SiH-functional siloxane at a temperature at or below 120 °C to obtain a stripped reaction product of SiH-functional siloxane intermediate and inhibited platinum; (d) optionally, combining the stripped reaction product with a non-platinum hydrosilylation catalyst and an alkenyl-functional epoxide; and (e) heat to 80-120 °C to facilitate a hydrosilylation reaction between the SiH-functional siloxane intermediate and the alkenyl-functional epoxide to produce a clustered epoxy silicone.

Description

[0001] PROCESS FOR PREPARING CLUSTERED EPOXY SILICONES AVOIDING GELATION OR UNDESIRABLE MOLECULAR WEIGHT BUILD

[0002] FIELD

[0003] The present invention relates to a process for making clustered epoxy silicones using a 2-step process that avoids gelation or undesirable molecular weight build during the process by using thiuram disulfide. The present invention also is a composition comprising a product from such a process.

[0004] INTRODUCTION

[0005] Multifunctional end-blocked siloxanes (cluster functional siloxanes) have desirable utility, but can be a challenge to synthesize. Multifunctional end-blocked siloxanes have multiple functional groups on the ends of a siloxane backbone. The functional groups are “terminal” (that is, “terminally-bound” or bound to terminal silicon atoms) on the siloxane. The siloxane backbone can be branched, having multiple ends that have terminal functional groups to form the multifunctional end-blocked siloxane. Alternatively, the siloxane backbone can be linear with two opposing ends that have functional groups bound to them to form the multifunctional end-blocked siloxane.

[0006] US9593209 (‘209) describes multifunctional end-blocked siloxanes, how to make them, and some of the challenges with making them. The synthesis of multifunctional end-blocked siloxanes is typically a 2-step process. The first step is a hydrosilylation reaction between a vinyl-end blocked linear polyorganosiloxane with a cyclic, linear or branched silicone containing silylhydride (SiH) groups to form a “dumb-bell” intermediate. The second step is another hydrosilylation reaction to react the SiH end-groups on the dumb-bell intermediate with vinylfunctional reactants that also have a functional group that is desirable for the end-group functionalization of the multifunctional end-blocked siloxanes.

[0007] A challenge with the first step is that if allowed to sit too long with a platinum (Pt) hydrosilylation catalyst after the reaction is done, or if purified at an elevated temperature by distillation or other stripping step with a Pt hydrosilylation catalyst present, undesirable gelling of the dumb-bell intermediate usually occurs. ‘209 discloses the possibility of adding an inhibitor such as diallyl maleate to deactivate the Pt catalyst after the first step is complete to inhibit the Pt from facilitating a gelling reaction during subsequent stripping or distillation procedures. Despite the challenges with Pt catalysts, it is desirable to use a Pt hydrosilylation catalyst in the first step because Pt catalysts are some of the most effective for efficient hydrosilylation reactions. A challenge with the second step arises when trying to make clustered epoxyfunctionalized siloxanes because Pt hydrosilylation catalyst can cause ring-opening polymerization of the epoxide groups used as a reactant in the second step. US5169962 describes such a ring-opening polymerization. In the 2-step process for making clustered epoxyfunctionalized siloxanes. Epoxy ring-opening polymerization results in undesirable molecular weight building in the resulting product of the second reaction. To avoid ring-opening polymerization of epoxide groups, US5169962 discloses use of rhodium-based catalysts when conducting a hydrosilylation reaction with epoxy-functional reactants. However, US5169962 is silent on how to avoid problems when this hydrosilylation reaction in the second hydrosilylation reaction when using a multistep process where platinum catalyst is used in the first step and carried into the second step.

[0008] It is desirable to identify a process for preparing clustered epoxy-functionalized siloxanes that avoids the problems taught in US9593209 and US5169962 in a 2-step process for preparing clustered epoxy-functionalized siloxanes that use a platinum catalyst in the first step that is carried into the second step.

[0009] SUMMARY

[0010] The present invention provides a solution to the challenge of identifying a process for preparing clustered epoxy-functionalized siloxanes that avoids the problems taught in US9593209 and US5169962 in a 2-step process for preparing clustered epoxy-functionalized siloxanes that use a platinum catalyst in the first step that is carried into the second step.

[0011] The process of the present invention requires simultaneously solving the gelation problems identified in US9593209 and the ring-opening polymerization of epoxide groups identified in US516962. The present work has further discovered that the problem of ringopening polymerization of epoxide groups is especially problematic when using cyclic epoxy reactants. Unfortunately, even when inhibiting Pt catalyst from the first step with excessive amounts of diallyl maleate inhibitor, as taught as a solution to the gelation problem in US9593209, gelling still occurs over time and undesirable molecular weight build occurs during the second step of forming clustered epoxy-functionalized siloxanes.

[0012] The present invention is a result of discovering how to avoid gelling in the first step and undesirable molecular weight build in the second step when synthesizing clustered epoxy- functionalized siloxanes. Moreover, the solution does not require extensive amounts of inhibitor. The present invention is a result of discovering that thiuram disulfide can be used as a Pt inhibitor after the first step, prior to stripping, to avoid gelling of the resulting SiH-functional siloxane intermediate even after aging or storing. At the same time, the second step hydrosilylation reaction can be done in the presence of the inhibited Pt without undesirable molecular weight build in the final product. Surprisingly, even though the second step is done at a temperature of 100 °C or higher, the thiuram disulfide-inhibited Pt does not trigger undesirable molecular weight build during the second hydrosilylation reaction. This is surprising in view of the fact US4260726 indicates that thiuram disulfide-inhibited Pt serves as a latent catalyst that facilitates curing hydrosilylation reactants to a solid at temperatures in excess of 100 °C, which indicates that Pt is released from the thiuram disulfide inhibitor at temperatures above 100 °C where our second reaction is conducted. A catalyst other than a Pt hydrosilylation catalyst can be used in the second step.

[0013] In a first aspect, the present invention is a process for preparing a clustered epoxy silicone, the process comprising the following steps: (a) conduct a hydrosilylation reaction between the following reactants in the presence of a platinum-based hydrosilylation catalyst to form a SiH-functional siloxane intermediate: (i) an alkenyl functional siloxane with an average of 2 or more terminal silicon-bound alkenyl groups per molecule; and (ii) a cyclic SiH-functional siloxane having an average of 4 to 15 silicon atoms per molecule and an average of 4 or more SiH groups per molecule; where the molar ratio of SiH groups to silicone-bound alkenyl groups is in a range of 4 to 40; (b) after all alkenyl-terminal siloxane has reacted, add thiuram disulfide at a concentration of at least twice the molar amount of platinum hydrosilylation catalyst present in step (a) to obtain a reaction product that contains a combination of SiH-functional siloxane intermediate and inhibited residual platinum hydrosilylation catalyst; (c) strip unreacted SiH- functional siloxane from the reaction product at a temperature at a temperature below 120 degrees Celsius to obtain a stripped reaction product that contains a combination of SiH- functional siloxane intermediate and inhibited residual platinum hydrosilylation catalyst; (d) combine the stripped reaction product with a non-platinum hydrosilylation catalyst and an alkenyl-functional epoxide; and (e) heat the combination of step (d) to a temperature in a range of 80 to 120 degrees Celsius to facilitate a hydrosilylation reaction between the SiH-functional siloxane intermediate and the alkenyl-functional epoxide to produce a clustered epoxy silicone, wherein step (d) is required when the thiuram disulfide in step (b) is tetra(methyl)thiuram disulfide and optional when the thiuram disulfide is other than tetramethyl thiuram disulfide.

[0014] In a second aspect, the present invention is a composition comprising a clustered epoxyfunctional silicone and thiuram disulfide.

[0015] The present invention is useful for preparing clustered epoxy-functionalized siloxanes. DETAILED DESCRIPTION

[0016] Materials identified only by a product name or tradename refer to the material sold under that product name or tradename at the priority filing date of this document unless otherwise stated herein.

[0017] “Multiple” means two or more. “And / or” means “and, or as an alternative”. All ranges include endpoints unless otherwise indicated. The sum of components in a composition do not exceed 100 weight-percent or volume-percent based respectively on the weight or volume of the composition.

[0018] Polysiloxanes (“siloxanes”, or “silicones”) comprise multiple siloxane units linked together through siloxane bonds. Siloxane units can be characterized by the designation M, D, T or Q. Unless stated otherwise: “M” correspond to RsSiOi / 2 siloxane units. “D” corresponds to R2SiO2 / 2. “T” corresponds to RSiOa / 2 siloxane units. “Q” corresponds to SiO4 / 2 siloxane units. Notably, an oxygen atom having a multiple of “1 / 2” subscript is an oxygen of a siloxane bond that is shared with a silicon atom of two siloxane units including the one of the subject siloxane unit. The numerator of the subscript indicates how many shared oxygen atoms are attached to the silicon atom. For example, SiOs / 2 has three siloxane bonded oxygen atoms that are shared with other siloxane units. Unless otherwise indicated, each R group is selected from hydrogen (H), hydrocarbyl groups and substituted hydrocarbyl groups. Silicon-bound hydroxyl (Si-OH) and alkoxy (Si-OR) groups are collectively called “OZ” groups and are identified in siloxane formulations herein as (HO1 / 2) or (RO1 / 2) units (or collectively as (ZO1 / 2) units), where the O1 / 2 is a shared oxygen with a O1 / 2 of a siloxane unit. Siloxane unit compositions of polysiloxanes is discernable using “ Si NMR methods.

[0019] In a first aspect, the present invention is a process for making a clustered epoxy silicone. A clustered epoxy silicone is a silicone having multiple epoxy functional groups at terminal ends of the silicone. The clustered epoxy silicone can be linear, in which case it has multiple epoxy functional groups at either end of the linear silicone. The clustered epoxy silicone can be a branched silicone with multiple branches of silicone segments, in which case it has multiple epoxy functional groups at the end of multiple silicone branch segments of the silicone. The process of the present invention comprises five steps: (a)-(e).

[0020] Step (a)

[0021] Step (a) is a hydrosilylation reaction to produce a SiH-functional siloxane intermediate. The hydrosilylation reaction of step (a) comprises combining and reacting the following reactants in the presence of a platinum-based hydrosilylation catalyst: (i) an alkenyl-functional siloxane; and (ii) a cyclic SiH-functional siloxane. The relative concentration of alkenyl- function siloxane and cyclic SiH-functional siloxane is such that the molar ratio of SiH groups to silicon-bound alkenyl groups is in a range of 4 to 40. The reaction can be run in an organic solvent.

[0022] (i) Alkenyl-functional siloxane

[0023] The alkenyl-functional siloxane has an average of 2 or more terminal silicon-bound alkenyl groups per molecule. Terminal silicon-bound alkenyl groups are alkenyl groups bound to a terminal silicon atom in the alkenyl-functional siloxane. The alkenyl group can have 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, even 7 or more carbon atoms 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, even 3 or fewer carbon atoms. The alkenyl group is itself desirably a terminal alkenyl group, which means the alkenyl group is between carbon atoms most remote from the carbon bound to the silicon atom of the siloxane. One typical and desirable alkenyl group is a vinyl group.

[0024] The alkenyl-functional siloxane can be branched, with multiple siloxane segments each having a terminal silicon atom, in which case there are at least 2 alkenyl groups in the molecule that are bound to terminal silicon atoms. Typically, the alkenyl-functional siloxane is linear having two terminal silicon atoms, preferably with at least one alkenyl group on each terminal silicon atom.

[0025] An example of a suitable alkenyl-functional siloxane has an average structure (I):

[0026] (R’R2SiO)-(R2SiO)n-(SiR2R’) (I) where: each R’ is independently selected from terminal alkenyl groups having from two to 8 carbon atoms, and is desirably a vinyl group; each R is independently selected from hydrocarbyl groups having from one to 16 carbon atoms, and typically has one or more, 2 or more, 3 or more, 4 or more, 5 or more, even 6 or more carbon atoms, while at the same time typically has 16 or fewer, 15 or fewer, 14 or fewer, 13 or fewer, 12 or fewer, 11 or fewer, 10 of fewer, 9 or fewer, 8 or fewer, 7 or fewer, even 6 or fewer carbon atoms; and is desirably selected from methyl and phenyl groups; and subscript n is the average number of R2SiO groups per molecule and has a value in a range of one to 1000, and can be one or more, 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, 12 or more, 14 or more, 16 or more, 18 or more, 20 or more, 25 or more, 50 or more, 75 or more, 100 or more, 125 or more, even 150 or more, while at the same time is typically 1000 or lower, 900 or lower, 800 or lower, 700 or lower, 600 or lower, 500 or lower, 400 or lower, 300 or lower, 200 or lower, 100 or lower, 80 or lower, 60 or lower, 40 or lower 30 or lower, 25 or lower, or even 20 or lower.

[0027] One desirably alkenyl-functional siloxane has an average structure (I) where the terminal R groups are methyl and one of the R group on each D-type siloxane unit is a phenyl while the other is methyl. Even more desirable is such an alkenyl-functional siloxane where subscript n has a value of 15 or higher, 18 or higher, even 20 or higher, while at the same time 30 or lower, 25 or lower, even 20 or lower.

[0028] (ii) Cyclic SiH-functional siloxane

[0029] A cyclic siloxane is a siloxane that comprises, preferably consists of, a ring of D-type siloxane units. The cyclic SiH-functional siloxane is a cyclic siloxane that has hydrogen bound to multiple silicon atoms in the ring of D-type siloxane units. The cyclic SiH-functional siloxane of the present invention typically has 4 or more and can have 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more silicon atoms, while at the same time typically has 15 or fewer, even 14 or fewer, 13 or fewer, 12 or fewer, 11 or fewer, 10 or fewer, 9 or fewer, 8 or fewer, 7 or fewer, even 6 or fewer silicon atoms. At the same time, the cyclic SiH-functional siloxane typically has 4 or more, and can have 5 or more, even 6 or more silicon-bound hydrogen atoms, while at the same time typically has 20 or fewer, 18 or fewer, 16 or fewer, 14 or fewer, 12 or fewer, 10 or fewer, 8 or fewer, even 6 or fewer silicon- bound hydrogen atoms.

[0030] The cyclic SiH-functional siloxane can have an average structure: (RHSiO)x, where: each R is independently selected from hydrocarbyl groups that have from one to 8 carbon atoms, and that can have one or more, 2 or more, 3 or more, 4 or more, 5 or more, even 6 or more, while at the same time typically has 8 or fewer, 7 or fewer, 6 or fewer, 5 or fewer, 4 or fewer, 3 or fewer, even 2 or fewer carbon atoms; each R can be methyl; and subscript x is the average number of (RHSiO) group in the molecule and has a value in a range of 4 to 15, and can be 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, even 13 or more, while at the same time is typically 15 or lower, 14 or lower, 13 or lower, 12 or lower, 11 or lower, 10 or lower, 9 or lower, 8 or lower, 7 or lower, even 6 or lower. The platinum hydrosilylation catalyst can be any one or any combination of more than one catalyst containing platinum that is useful in catalyzing hydrosilylation reactions. Platinum hydrosilylation catalysts include compounds and complexes such as platinum (0)- 1 ,3-di vinyl - 1,1,3,3-tetramethyldisiloxane (Karstedt’s catalyst), platinum-carbonyl complexes, platinum- divinyltetramethyldisiloxane complexes, [ 1 ,3-Bis(2,6-diisopropylphenyl)imidazol-2- ylidene][ 1 ,3-divinyl- 1 , 1 ,3,3-tetramethyldisiloxane]platinum(0), platinum cyclovinylmethylsiloxane complexes, platinum acetylacetonate (acac), platinum black, platinum compounds such as chloroplatinic acid (I PPtCle), chloroplatinic acid hexahydrate, a reaction product of chloroplatinic acid and a monohydric alcohol, platinum bis(ethylacetoacetate), platinum bis(acetylacetonate), platinum dichloride, and complexes of the platinum compounds with olefins or low molecular weight polyorganosiloxanes or platinum compounds microencapsulated in a matrix or core-shell type structure

[0031] The platinum concentration of platinum hydrosilylation catalyst is typically sufficient to provide 0.05 weight-parts per million (ppm) or more platinum while at the same time 10 ppm or less, preferably 9 ppm or less, 8 ppm or less, 7 ppm or less, 6 ppm or less, or even 5 ppm or less platinum based on the combined weight of alkenyl-functional siloxane and cyclic SiH-functional siloxane.

[0032] Step (b)

[0033] Step (b) comprises adding thiuram disulfide to the reaction product of step (a) after all of the alkenyl-terminal siloxane has reacted. Monitor the reaction of step (a) using proton nuclear magnetic resonance NMR) spectroscopy to track consumption of the alkenyl group. When the terminal alkenyl group of the alkenyl-terminal siloxane is no longer apparent by NMR spectrum then all of the alkenyl-terminal siloxane has reacted.

[0034] Thiuram disulfide is a class of organosulfur compounds having the formula (RsNCSSh and the general structure (II): where each R is a hydrocarbyl group. Thiuram disulfide is also referred to as tetrahydrocarbylthiuram disulfide. The thiuram disulfides desirably have R groups selected from alkyl groups having one or more, 2 or more, 3 or more, 4 or more, 4 or more, 6 or more, 7 or more, even 8 or more carbon atoms, while at the same time typically having 10 or fewer, 9 or fewer, 8 or fewer, 7 or fewer, 6 or fewer, 5 or fewer, even 4 or fewer carbon atoms. Examples of common suitable thiuram disulfides include any one or any combination of more than one selected from a group consisting of tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetra(iso-propyl)thiuram disulfide, tetra(iso-butyl)thiuram disulfide, and tetra(n-butyl)thiuram disulfide. As taught in US4260726, thiuram disulfide complexes with platinum (Pt) to form an inhibited Pt at temperatures, according to US4260726, of 100 °C and lower. Inhibited Pt does not catalyze hydrosilylation reactions and so it is a way to block Pt in a composition from acting as a hydrosilylation catalyst. In step (b) of the present process, add thiuram disulfide at a concentration of at least twice the molar amount of platinum hydrosilylation catalyst present in step (a) to obtain a reaction product that contains a combination of SiH-functional siloxane intermediate and inhibited residual platinum hydrosilylation catalyst. The molar ratio of thiuram disulfide to Pt from the platinum hydrosilylation catalyst is 2 or more, and can be 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 is typically 100 or less, 75 or less, 50 or less, 40 or less, 30 or less, 20 or less, even 10 or less, and can be 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, even 3.5 or less. Step (c) After adding the thiuram disulfide in step (b), strip unreacted SiH-functional siloxane from the reaction product at a temperature below 120 °C, typically in a range of 100 to120 °C to obtain a stripped reaction product that contains a combination of SiH-functional siloxane intermediate and inhibited residual platinum hydrosilylation catalyst. The stripping temperature is typically at a temperature of 100 °C or higher, even 105 °C or higher, 110 °C or higher, or 115 °C or higher, while at the same time is typically 150 °C or lower, and can be 140 °C or lower, 130 °C or lower, 120 °C or lower, 115°C or lower, even 110 °C or lower. Stripping can be done by distillation to remove unreacted SiH-functional siloxane, including distillation under vacuum. Desirably, continue stripping until all of the unreacted SiH-functional siloxane has been removed from the composition of step (b), which can be evident when no more distillate is removed. Surprisingly, even when stripping at these high of temperatures, gelling does not occur even with the Pt hydrosilylation catalyst present. The thiuram disulfide seems to inhibit the Pt even at these higher temperatures than expected from US4260726. Step (d) To the stripped reaction product resulting from step (c), it can be desirable, but is not always required, to add a non-platinum hydrosilylation catalyst, alkenyl-functional epoxide, and optionally organic solvent to form a reactive mixture. Work on the present invention reveals that when using tetra(methyl)thiuram disulfide then additional non-platinum hydrosilylation catalyst is required in step (d). However, when using a thiuram disulfide with longer alkyl groups on the thiuram then this step of introducing a non-platinum hydrosilylation catalyst is surprisingly optional and the subsequent hydrosilylation reaction in step (e) actually can proceed with or without step (d) of adding hydrosilylation catalyst. Examples of suitable non-platinum hydrosilylation catalyst include those selected from rhodium-based catalyst such as Wilkinson’s catalyst (RhCl(PPh3)3. When adding non-platinum hydrosilylation catalyst in step (d), it is typical to add the non-platinum hydrosilylation at a concentration of one ppm or more, 10 ppm or more 20 ppm or more 30, ppm or more, 40 ppm or more, 50 ppm or more, 60 ppm or more, 70 ppm or more, 80 ppm or more, 90 ppm or more, 100 ppm or more, 120 ppm or more, 140 ppm or more, 160 ppm or more, even 180 ppm or more, while at the same time is typically 200 ppm or less, and can be 180 ppm or less, 160 ppm or less, 140 ppm or less, 120 ppm or less, 110 ppm or less, 100 ppm or less, even 80 ppm or less, with ppm relative to the combined weight used in step (d) of stripped reaction product from step (c) and alkenyl-functional epoxide. The alkenyl-functional epoxide has an average of at least one alkenyl group and at least one epoxy group per molecule. The alkenyl-functional epoxide can be a cyclic epoxide, which is an epoxide having an epoxy group formed by an oxygen bound to adjacent carbon atoms that are part of a carbon ring structure. The present work has discovered that cyclic epoxides are particularly challenging to incorporate into a clustered epoxy silicone without experiencing undesirable molecular weight build while reacting the cyclic epoxide to a SiH-functional siloxane intermediate. Nonetheless, the present process can use a cyclic epoxide without experiencing undesirably molecular weight build. For instance, the alkenyl-functional epoxide of the present invention can be a cyclic epoxide having an average structure (III): O (III) The concentration of alkenyl- ratio of alkenyl-functional epoxide to SiH groups on the siloxane intermediate from step (a) that is in a range of 1:1 to 2:1. Step (e) Heat the reactive mixture of step (d) to a temperature in a range of 80 to 120 °C, preferably 100-120 °C, to facilitate a hydrosilylation reaction between the siloxane intermediate and the alkenyl-functional epoxide to produce a clustered epoxy-functional silicone. The temperature during step (e) can be 100 °C or higher, even 105 °C or higher, 110 °C or higher, or 115 °C or higher, while at the same time is typically 120 °C or lower, and can be 115 °C or lower, or even 110 °C or lower. Maintain heating until all of the SiH functionality has been consumed as determined by Fourier transform infrared spectroscopy (FTIR). The resulting product of step (e) is a clustered epoxy-functional silicone in the presence of thiuram disulfide. The thiuram disulfide is typically complexed with Pt catalyst to form an inhibited Pt catalyst. Optional Steps One of ordinary skill understands that while the process of the present invention comprises the five steps (a)-(e), the process can further include additional steps as well. For instance, after step (e) the process can include a step (f) of stripping unreacted reactants and solvent (if present) from the clustered epoxy-functional silicone or otherwise purifying the clustered epoxy-functional silicone. Stripping can occur by distillation, typically at temperature up to 130 °C under vacuum. In a second aspect, the present invention is a composition comprising a clustered epoxy- functional silicone and thiuram disulfide, where the thiuram disulfide is typically complexed with a Pt catalyst. A composition comprising a clustered epoxy-functional silicone and thiuram disulfide is a fingerprint product of the process of the present invention. Such a composition is the reaction product of step (e) of the first aspect of the present invention and has a fingerprint of having the thiuram disulfide present along with the clustered epoxy-functional silicone. The thiuram disulfide can be in a complex with Pt. The clustered epoxy-functional silicone can have cyclic siloxane groups on its terminal ends to which epoxy groups are bound. At the same time, the epoxy groups can be cyclic epoxy groups on the terminal ends of the clustered epoxy- functional silicone. EXAMPLES Table 1 lists the components for use in preparing the following examples. “Me” refers to methyl. “Ph” refers to phenyl. TDCC refers to The Dow Chemical Company. DOWSIL is a trademark of TDCC.

[0035] Table 1 Component Description Source AlkenylCH2=CH(Me)2SiO[(Ph)(Me)SiO]20Si(Me)2CH=CH2DOWSIL™ MP 153SP fromSiloxane 1 TDCC p p To facilitate usage, prepare solvent solutions of several of the components. Pt Catalyst Sol’n. Prepare a solution of the Pt Catalyst in Solvent 2 that contains 1.0 wt% platinum in the solution. Rh Catalyst Sol’n. Prepare a solution of the Rh Catalyst in Solvent 3 that is 0.025 molar. Inhibitor 2 Sol’n through Inhibitor Sol’n 6. Prepare a solution of the indicated inhibitor (Inhibitor 2, 3, 4, 5 or 6) in Solvent 1 that contains 1.0 wt% of the indicated inhibitor. Synthesis of SiH-Functional Siloxane Intermediate Prepare three SiH-functional siloxane intermediates using the procedure below and the formulations as set forth in Table 2. Amounts of each component in Table 2 are in grams (g). The molar ratio of inhibitor / Pt is a ratio of moles of inhibitor active to moles of platinum in the formulation. Combine Alkenyl Siloxane 1, Cyclic SiH Siloxane 1 and toluene components together in a 4-neck round bottom flask and then heat to 60 °C. Add the Pt Catalyst Sol’n component to initiate a hydrosilylation reaction and accompanying exotherm. Maintain a temperature below 95 °C while stirring under a nitrogen gas sweep for at least 30 minutes. Upon initiation of an exothermic reaction monitor the reaction components by proton NMR every 10-15 minutes to monitor consumption of vinyl groups. When all the vinyl groups have been consumed, then the temperature to cool to 60 °C and add the appropriate inhibitor if one is included. Continue stirring for at least 3 hours as the temperature drops to 24 °C. Transfer the contents of the 4- neck round bottom flask to a receiving flask and remove volatiles by rotovapping at 100-120 °C at 0.27-0.53 kiloPascals (2-4 Torr) pressure for 2 hours. The resulting product is a combination of Pt (for Int-A) or inhibited Pt (for remaining samples) and SiH-functional intermediate. Analyze the resulting clear, colorless-to-light-yellow solution by1H NMR and29Si NMR to confirm SiH-functional intermediate structure. The resulting product has the following average structure, where n=20: Table 2 Component Int-A Int-B Int-C Int-1 Int-2 Int-3 Int-4 Int-5 Alkenyl 5 1000 5 1000 10 10 10 10 Stability to Gelling One of the challenges in the process is achieving a SiH-functional siloxane intermediate that is stable to gelling, particularly due to the presence of Pt catalyst. Int-A has no inhibitor to block the Pt. Int-B has 438-times as many moles diallyl maleate to inhibit Pt. Int-1 has 3.3 times as many moles tetra(n-butyl)thiuram disulfide to inhibit Pt. Int-A gels within one hour of stripping off volatiles. Therefore, this intermediate was not carried on to try to prepare a clustered epoxy silicone. Int-B gels after storing at 23-25 °C for more than 6 months even with the massive excess of diallyl maleate, indicating diallyl maleate is not a sufficient inhibitor for long term gel stability. Int-C gels after storing at 23-25 C for more than 3 weeks, indicating dodecyl disulfide is not a sufficient inhibitor for long term gel stability. Int-1 through Int-5 all remain without visible indication of gelling even after storing for longer than 6 months, even when using fewer inhibitor mols per platinum than Int-B and equivalent amounts of inhibitor as Int-C. These results indicate that thiuram disulfide is a sufficient inhibitor for long term gel stability. Synthesis of Clustered Epoxy Silicone Prepare clustered epoxy silicone from Int-B, Int-C, Int 1, Int-2, Int-3, Int-4, and Int-5 using the procedure below and the formulations in Table 3 within 24 hours of preparing the corresponding SiH-Functional Siloxane Intermediate. Amounts of materials in Table 3 are in grams (g). Table 3 also contains molecular weight characteristics for the resulting clustered epoxy silicone as measured by gel permeation chromatography (described below). Combine in a 4-neck round bottom flask the Int-B or Int-1 and the Solvent 1 components and mix while heating to 80 °C. Add a few drops of Alkenyl Epoxide 1 and then add the Rh Catalyst Sol’n. Dropwise add the remaining Alkenyl Epoxide 1 over 20-30 minutes and then heat to 100-120 °C while stirring. Continue stirring for 2 hours under a nitrogen gas sweep. Allow the temperature to drop to 24 °C over at least 3 hours while stirring. Transfer the reaction mixture to a receiving flask and remove volatiles by rotovapping at 120-130 °C at 0.27-0.53 kiloPascals (2-4 Torr) pressure for 4 hours. Analyze the resulting brown liquid by1H NMR and29Si NMR to confirm product structure. The resulting brown liquid is a of clustered epoxy silicone and inhibited Pt catalyst. The clustered epoxy silicone product has the following average structure, where n=20:

[0036] Also evaluate the resulting product by gel permeation chromatography to determine molecular weight characteristics including number average molecular weight (Mn), weight average molecular weight (Mw), and z-average molecular eight (Mz), as well as molecular weight dispersity. Conduct the gel permeation evaluation in toluene using a Waters 2695 LC pump and autosampler equipped with two Agilent PLgel Mixed C columns calibrated with polystyrene standards. Molecular weight characteristics are included in Table 3. CE A, CE B, and CE C show undesirable molecular weight build relative to Ex 1-8, which is evident in the significantly higher Mw, Mz and Dispersity values. CE A and CE B use inhibitors other than thiuram disulfide. CE C uses tetra(n0butyl)thiuram disulfide, but also uses a Pt catalyst in the second part of the process where a non-Pt catalyst is needed in the present invention. CE D failed to successfully proceed in the second hydrosilylation reaction. CE D uses tetra(methyl)thiuram disulfide inhibitor but no additional catalyst in the second reaction (that is, no additional catalyst for step (d) of the process of the present invention). In contrast, Ex 8 also uses tetra(methyl)thiuram disulfide inhibitor in combination with addition non-platinum catalyst in step (d) and results in desirable product. Ex 2, Ex 3, Ex 5 and Ex 7 each illustrate that the non-platinum catalyst of step (d) is optional when using a thiuram disulfide other than tetra(methyl)thiuram disulfide.

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Claims

CLAIMS: What is claimed is:

1. A process for preparing a clustered epoxy silicone, the process comprising the following steps: (a) conduct a hydrosilylation reaction between the following reactants in the presence of a platinum-based hydrosilylation catalyst to form a SiH-functional siloxane intermediate: (i) an alkenyl functional siloxane with an average of 2 or more terminal silicon-bound alkenyl groups per molecule; and (ii) a cyclic SiH-functional siloxane having an average of 4 to 15 silicon atoms per molecule and an average of 4 or more SiH groups per molecule; where, the molar ratio of SiH groups to silicone-bound alkenyl groups is in a range of 4 to 40; (b) after all alkenyl-terminal siloxane has reacted, add thiuram disulfide at a concentration of at least twice the molar amount of platinum hydrosilylation catalyst present in step (a) to obtain a reaction product that contains a combination of SiH-functional siloxane intermediate and inhibited residual platinum hydrosilylation catalyst; (c) strip unreacted SiH-functional siloxane from the reaction product at a temperature at a temperature at or below 150 degrees Celsius to obtain a stripped reaction product that contains a combination of SiH-functional siloxane intermediate and inhibited residual platinum hydrosilylation catalyst; (d) combine the stripped reaction product with a non-platinum hydrosilylation catalyst and an alkenyl-functional epoxide; and (e) heat the combination of step (d) to a temperature in a range of 80 to 120 degrees Celsius to facilitate a hydrosilylation reaction between the SiH-functional siloxane intermediate and the alkenyl-functional epoxide to produce a clustered epoxy silicone; wherein step (d) is required when the thiuram disulfide in step (b) is tetra(methyl)thiuram disulfide and optional when the thiuram disulfide is other than tetramethyl thiuram disulfide.

2. The process of claim 1, wherein the alkenyl-functional epoxide is a cyclic epoxide.

3. The process of any one previous claim, wherein the alkenyl-functional siloxane has an average structure: (R’R2SiO)-(R2SiO)n-(SiR2R’), where each R’ is independently selected from terminal alkenyl group having from two to 8 carbon atoms, each R is independently selected from hydrocarbyl groups having from one to 16 carbon atoms, and subscript n is the average number of R2SiO groups per molecule and has a value in a range of 1 to 1000.

4. The process of any one previous claim, wherein the cyclic SiH-functional siloxane has an average structure: (RHSiO)x, where each R is independently selected from hydrocarbyl groups that have from one to 8 carbon atoms and x has a value in a range of 4 to 15.

5. The process of any one previous claim, wherein the molar ratio of thiuram disulfide in step (b) to platinum hydrosilylation catalyst in step (a) is in a range of 2 to 10.

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

7. The process of any one previous claim, wherein the non-platinum hydrosilylation catalyst is a rhodium-based catalyst.

8. A composition comprising a clustered epoxy-functional silicone and thiuram disulfide.

9. The composition of claim 8, wherein the clustered epoxy-functional silicone has cyclic siloxane groups on its terminal ends.

10. The composition of claim 8 or claim 9, wherein the clustered epoxy-functional silicone has cyclic epoxy groups on the terminal ends of the clustered epoxy-functional silicone.

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