WO2025129486A1

WO2025129486A1 - Silicone composition

Info

Publication number: WO2025129486A1
Application number: PCT/CN2023/140143
Authority: WO
Inventors: Yan Huang; Yifan Xu; Bin Fan; Joseph R. Sootsman; Hua Ren; Zhongwei Cao; Yanbin FAN
Original assignee: Dow Global Technologies LLC; Dow Silicones Corp
Current assignee: Dow Global Technologies LLC; Dow Silicones Corp
Priority date: 2023-12-20
Filing date: 2023-12-20
Publication date: 2025-06-26
Anticipated expiration: 2026-06-20
Also published as: TW202525925A

Abstract

A silicone composition contains (A) from 29 to 49 volume percent, based on the volume of the silicone composition, of an electrically conductive filler; (B) from 50 to 70 volume percent, based on the volume of the silicone composition, of an alkenyl-functional polyorganosiloxane having an average of at least two alkenyl groups per molecule; (C) a silyl-hydride functional polyorganosiloxane having an average of at least two silicon atom-bonded hydrogen atoms per molecule and free of an alkenyl group; wherein the silyl-hydride functional polyorganosiloxane is present in an amount sufficient to provide a molar ratio of silicon-bonded hydrogen atoms to alkenyl groups for the composition of 0.5 to 3.0; (D) a platinum-based hydrosilylation reaction catalyst; and (E) from 0.025 to 2 weight percent, based on the weight of the silicone composition, of a polymer additive having a number average molecular weight in a range of greater than 1000 to 5000 grams per mole; wherein the polymer additive is selected from the group consisting of a poly (tetramethylene ether glycol) homopolymer, a poly (tetramethylene ether glycol) copolymer, and mixtures thereof.

Description

SILICONE COMPOSITION

FIELD

The present invention is a silicone composition, particularly, a one-part curable electrically conductive silicone composition, and an electrically conductive silicone adhesive produced from such composition.

INTRODUCTION

Silicone adhesives are useful in a variety of applications such as in automotive, electronic, construction, appliance, and aerospace industries. Due to inherent insulation properties of silicone resins, silicone compositions need to incorporate electrically conductive fillers to improve electrical performance of cured products made therefrom for electrically conductive applications such as electrically conductive adhesives and electromagnetic interference (EMI) shielding materials.

Increasing the amount of electrically conductive fillers can improve electrical conductivity of silicone adhesives, but may result in increased cost, viscosity, and density, or even reduced mechanical properties. Therefore, there is a continued need for silicone compositions affording silicone adhesives with improved electrical performance without increasing the density.

Moreover, electrically conductive metal fillers tend to oxidize over time and can eventually become non-conductive. Silicone adhesives comprising such fillers generally show poor electrical stability after heat aging at high temperatures such as 120 degrees Celsius (℃) or higher. Thus, it is also challenging to provide silicone adhesives with good thermal stability as indicated by reduced variation of volume resistance after heat aging for an extended period of time.

It is desirable to discover a silicone composition suitable for preparing electrically conductive adhesives with improved electrical conductivity and good thermal stability without increasing filler loadings.

SUMMARY

The present invention solves the problem of discovering a silicone composition without the aforementioned problems. The present invention provides a novel silicone composition comprising an electrically conductive filler (A) , an alkenyl-functional polyorganosiloxane (B) , a silyl-hydride functional polyorganosiloxane (C) , a platinum-based hydrosilylation reaction catalyst (D) , and a specific polymer additive (E) , and optionally a hydrosilylation reaction inhibitor (F) . The silicone composition, upon curing, provides a cured product such as a silicone adhesive having improved electrical conductivity as indicated by a volume resistance of less than 0.005 Ohm-centimeter (Ohm·cm) according to GB/T 1551-2009, and a density that is lower than 4.8 grams per cubic meter (g/cm³) . At the same time, the silicone composition also affords good retention of electrical conductivity after heat aging, for example, the cured product of the silicone composition shows a volume resistance of less than 0.01 Ohm·cm after heat aging at 120 ℃ for 1000 hours or 125 ℃ for 720 hours. These properties above are measured according to the test methods described in the Examples section below. The silicone composition of the present invention also provides the cured product with lower volume resistance than cured products made from a similar silicone composition lacking only the polymer additive (E) (hereinafter “Incumbent Silicone Composition” ) . The silicone composition of the present invention even at lower filler loadings can still achieve comparable or better electrical conductivity than Incumbent Silicone Composition.

In a first aspect, the present invention provides a silicone composition comprising,

(A) from 29 to 49 volume percent, based on the volume of the silicone composition, of an electrically conductive filler;

(B) from 50 to 70 volume percent, based on the volume of the silicone composition, of an alkenyl-functional polyorganosiloxane having an average of at least two alkenyl groups per molecule;

(C) a silyl-hydride functional polyorganosiloxane having an average of at least two silicon atom-bonded hydrogen atoms per molecule and free of an alkenyl group; wherein the silyl-hydride functional polyorganosiloxane is present in an amount sufficient to provide a molar ratio of silicon-bonded hydrogen atoms to alkenyl groups for the composition of 0.5 to 3.0;

(D) a platinum-based hydrosilylation reaction catalyst; and

(E) from 0.025 to 2 weight percent, based on the weight of the silicone composition, of a polymer additive having a number average molecular weight in a range of greater than 1000 to 5000 grams per mole; wherein the polymer additive is selected from the group consisting of a poly (tetramethylene ether glycol) homopolymer, a poly (tetramethylene ether glycol) copolymer, and mixtures thereof.

In a second aspect, the present invention provides a process for preparing the silicone composition of the first aspect. The process comprises: admixing the electrically conductive filler (A) , the alkenyl-functional polydiorganosiloxane (B) , the silyl-hydride functional polyorganosiloxane (C) , the platinum-based hydrosilylation reaction catalyst (D) , and the polymer additive (E) .

In a third aspect, the present invention provides a silicone adhesive comprising a cured product of the silicone composition of the first aspect.

DETAILED DESCRIPTION

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 and ISO refers to International Organization for Standards. GB/T refers to China recommended national standard.

Products identified by their tradename refer to the compositions available under those tradenames on the priority date of this document. “And/or” means “and, or as an alternative” . All ranges include endpoints unless otherwise indicated. Unless otherwise stated, all weight percent (wt%) values are relative to composition weight and all volume percent (vol%) values are relative to composition volume.

Viscosities of polyorganosiloxanes can be determined according to ASTM-D1084 at 25 degrees Celsius (℃) , for example, using a rotational viscometry with a Brookfield viscometer DV-II, unless otherwise stated.

Characterization of a polyorganosiloxane can be conducted using ²⁹Si and ¹³C nuclear magnetic resonance (NMR) technique, such as, described in US Patent 9, 593, 209, Reference Example 2 at col. 32, which can be used to measure the mole percentage of methyl, weight content of silicon-bonded hydrogen atoms, silicon-bonded hydroxyl content, and molar percentage and weight percentage of alkenyl (e.g., vinyl) groups described below.

The silicone composition of the present invention comprises one or more electrically conductive filler as component (A) . “Electrically conductive filler” here refers to any filler that exhibits an intrinsic resistivity of less than 10 Ohm-centimeter (Ohm·cm) at 20 ℃ as determined by GB/T 351-2019 (China national standard for metallic materials-resistivity measurement method) . The electrically conductive filler typically comprises graphene, graphite, carbon fibers, and particles having at least an outer surface of a metal selected from the group consisting of silver, gold, platinum, palladium, nickel, copper, or alloys thereof. The electrically conductive filler may comprise particles consisting of silver, gold, platinum, palladium, nickel, copper, or alloys thereof; desirably silver. Alternatively, the electrically conductive filler may comprise particles having only an outer surface consisting of silver, gold, platinum, palladium, or alloys thereof; and a core that is different from the outer surface (also referred to as “metal-coated particles” ) . The core of such particles can be any material, electrical conductor or insulator, that supports the outer surface and does not adversely affect electrical properties of silicone adhesives made from the silicone composition (i.e., cured products of the silicone composition) . Examples of such materials for the core include copper, graphite, aluminum, glass such as solid glass or hollow glass, mica, nickel, carbon fiber, or ceramic particles. Desirably, the electrically conductive filler comprises silver coated particles. The electrically conductive filler may include, for example, silver coated nickel particles, silver coated aluminum particles, silver coated copper particles, silver coated glass particles, or mixtures thereof. Desirably, the electrically conductive filler comprises silver coated nickel particles, silver coated aluminum particles, or combinations thereof. The silver coated particles typically have a silver content of from 1 to 60 wt%, and can be 2 wt%or more, 3 wt%or more, 4 wt%or more, 5 wt%or more, 6 wt%or more, 7 wt%or more, 8 wt%or more, 9 wt%or more, 10 wt%or more, 11 wt%or more, even 12 wt%or more while at the same time is generally 60 wt%or less, 55 wt%or less, 50 wt%or less, 45 wt%or less, or even 40 wt%or less, based on the weight of the silver-coated particles, as determined by inductively coupled plasma mass spectrometry (ICP-MS) .

The electrically conductive filler useful in the present invention typically have the form of a powder with the shape of flakes, rods, fibers, or spherical or other irregular shape. The electrically conductive filler useful in the present invention may include fillers prepared by treating the surfaces of the aforementioned particles with at least one organosilicon compound. Suitable organosilicon compounds include those typically used to treat silica fillers, such as organochlorosilanes, organosiloxanes, organodisilazanes, organoalkoxysilanes, or mixtures thereof. The electrically conductive filler can be a single electrically conductive filler as described above or a mixture of two or more such fillers that differ in at least one of the following properties: composition, surface area, surface treatment, particle size, and particle shape.

Methods of preparing electrically conductive fillers suitable for use in the silicone composition of the present invention are well known in the art. For example, powders of silver, gold, platinum, or palladium, or alloys thereof are typically produced by chemical precipitation, electrolytic deposition, or cementation. Flakes of the aforementioned metals are typically produced by grinding or milling the metal powder. Particles having only an outer surface of at least one of the metals described above are typically produced by metallizing an appropriate core material using a method such as electrolytic deposition, electroless deposition, or vacuum deposition. When the electrically conductive filler is a filler prepared by treating the surfaces of the particles with the organosilicon compound, the particles can be treated prior to admixture with the other components of the silicone composition or the particles can be treated in situ during the preparation of the silicone composition.

The electrically conductive filler useful in the present invention may have a median particle size of from 0.5 micrometer (μm) to 100 μm, and can be 1 μm or more, 5 μm or more, 8 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, even 40 μm or more while at the same time is 100 μm or less, and can be 90 μm or less, 80 μm or less, 75 μm or less, 70 μm or less, 65 μm or less, 60 μm or less, 50 μm or less, or even 40 μm or less. “Median particle size” in the present invention refers to a D50 particle size as measured according to the test method described in the Examples section below. Desirably, the silicone composition comprises electrically conductive fillers having two or more, even three or more different median particle sizes. For example, the electrically conductive fillers comprise (a1) a first electrically conductive filler (also referred to as “first filler” ) having a median particle size in a range of from 30 to 100 μm, and (a2) a second electrically conductive filler (also referred to as “second filler” ) having a median particle size in a range of from 5 to 25 μm, and optionally (a3) a third electrically conductive filler (also referred to as “third filler” ) having a median particle size in a range of from 0.1 to 3 μm. The weight ratio of the first filler to the second filler may be in a range of from 9: 1 to 1: 9, from 8: 2 to 2: 8, alternatively from 9: 1 to 3: 7.

The electrically conductive filler in the silicone composition of the present invention may be present in an amount to impart electrical conductivity to the cured products (e.g., silicone adhesives) produced from the silicone composition. The concentration of the electrically conductive filler depends on the desired electrical properties, surface area of the filler, density of the filler, shape of the filler particles, surface treatment of the filler, and nature of the other components in the silicone composition. For example, the electrically conductive filler is present in an amount such that the silicone composition, upon curing, has a volume resistance of less than 0.005 Ohm·cm as measured according to GB/T 1551-2009. Alternatively, the electrically conductive filler may be present in a combined amount of from 29 to 49 vol%, and can be 29.5 vol%or more, 30 vol%or more, 31 vol%or more, 32 vol%or more, 32.5 vol%or more, 33 vol%or more, 34 vol%or more, 35 vol%or more, even 36 vol%or more while at the same time is 49 vol%or less, and can be 48 vol%or less, 46 vol%or less, 45 vol%or less, 44 vol%or less, 43 vol%or less, 42 vol%or less, or even 40 vol%or less, desirably, from 30 to 48 vol%, more desirably, from 32 to 45 vol%, most desirably, from 32 to 44 vol%, based on the volume of the silicone composition.

The silicone composition of the present invention also comprises component (B) an alkenyl-functional polyorganosiloxane having an average of two or more alkenyl groups per molecule. “Polyorganosiloxane” is a silicone polymer with repeating Si-O-Si units. “Alkenyl” means a branched or unbranched, monovalent hydrocarbon group having one or more carbon-carbon double bonds. The alkenyl groups can be terminal, pendant, or a combination of both terminal and pendant. “Terminal” groups are on end siloxane groups of a molecule. “End” siloxane groups are attached to only one other siloxane group. “Pendant” groups are on interior siloxane group -siloxane groups bound to at least two other siloxane groups -of the molecule. “Siloxane group” is a group containing SiO that is bound to another Si through the oxygen of the SiO. Desirably, the alkenyl-functional polyorganosiloxane has an average of one or more terminally alkenyl groups per molecule. The alkenyl-functional polyorganosiloxane is typically free of a silicon atom-bonded alkoxy group. The alkenyl-functional polyorganosiloxane can be a linear structure, partially branched linear structure, branched structure, cyclic structure, network structure, or dendritic structure.

The alkenyl-functional polyorganosiloxane may have an average chemical structure of formula (I) :
R _(3-c) R'_cSiO- (R'RSiO) _a- (R₂SiO) _b-SiR'_dR _(3-d) (I)

where each R is independently an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms, each R'is independently an alkenyl group, a ≥ 0, b ＞ 0, c is from 0 to 2, d is 0 or 1, (a+b) is 10 to 1000, and (a+c+d) ≥ 2.

“Alkyl” means a cyclic, branched, or unbranched, saturated monovalent hydrocarbon group. The alkyl groups represented by R have from 1 to 6 carbon atoms, and can have from 1 to 3 carbon atoms or from 1 to 2 carbon atoms. Examples of suitable alkyl groups for R include methyl, ethyl, propyl (e.g., iso-propyl and/or n-propyl) , butyl (e.g., isobutyl, n-butyl, tert-butyl, and/or sec-butyl) , pentyl (e.g., isopentyl, neopentyl, and/or tert-pentyl) , hexyl, and branched alkyl groups of 6 carbon atoms; and cyclic alkyl groups such as cyclopentyl and cyclohexyl. Suitable aryl groups for R are exemplified by phenyl, tolyl, xylyl, naphthyl, benzyl, and dimethyl phenyl. Each R may be the same or different. Desirably, each R is independently an alkyl group having from 1 to 6 carbon atoms. More desirably, each R is methyl.

The alkenyl groups represented by R'typically have from 2 to 10 carbon atoms, from 2 to 8 carbon atoms, or from 2 to 6 carbon atoms. Examples of suitable alkenyl groups include vinyl (-CH=CH₂) , allyl, propenyl (e.g., isopropenyl, and/or n-propenyl) ; and butenyl, pentenyl, hexenyl, and heptenyl, (including branched and linear isomers of 4 to 7 carbon atoms) ; and cyclohexenyl. Desirably, the alkenyl group is vinyl.

The value of a is the average number of (R'RSiO) groups per molecule. Desirably, a is 0.

The value of b is the average number of (R₂SiO) groups per molecule. The value of b may be in a range of 10 to 1000, and can be 15 or higher, 35 or higher, 50 or higher, 100 or higher, 150 or higher, 200 or higher, 250 or higher, even 300 or higher while at the same time is 1, 000 or lower, and can be 900 or lower, 800 or lower, 700 or lower, 650 or lower, 600 or lower, or even 500 or lower. A quantity (a+b) can be the same as the ranges defined above for the value of b.

Desirably, c can be 0 or 1. The quantity (a+c+d) refers to the average number of alkenyl groups per molecule. The quantity (a+c+d) is 2 or more, even 3 or more while at the same time is typically 30 or less, and can be 20 or less, 10 or less, or even 3 or less.

Desirably, a is 0, c is 1, d is 1, and each Ris methyl; and more desirably, each R'is vinyl.

Examples of suitable alkenyl-functional polyorganosiloxanes include b1) dimethylvinylsiloxy-terminated polydimethylsiloxane, b2) dimethylvinylsiloxy-terminated poly (dimethylsiloxane/methylvinylsiloxane) , b3) dimethylvinylsiloxy-terminated polymethylvinylsiloxane, b4) trimethylsiloxy-terminated poly (dimethylsiloxane/methylvinylsiloxane) , b5) trimethylsiloxy-terminated polymethylvinylsiloxane, b6) dimethylvinylsiloxy-terminated poly (dimethylsiloxane/methylvinylsiloxane) , b7) dimethylvinylsiloxy-terminated poly (dimethylsiloxane/methylphenylsiloxane) , b8) dimethylvinylsiloxy-terminated poly (dimethylsiloxane/diphenylsiloxane) , b9) phenyl, methyl, vinyl-siloxy-terminated polydimethylsiloxane, b10) dimethylhexenylsiloxy-terminated polydimethylsiloxane, b11) dimethylhexenylsiloxy-terminated poly (dimethylsiloxane/methylhexenylsiloxane) , b12) dimethylhexenylsiloxy-terminated polymethylhexenylsiloxane, b13) trimethylsiloxy-terminated poly (dimethylsiloxane/methylhexenylsiloxane) , b14) trimethylsiloxy-terminated polymethylhexenylsiloxane, b15) dimethylhexenylsiloxy-terminated poly (dimethylsiloxane/methylhexenylsiloxane) , b16) dimethylvinylsiloxy-terminated poly (dimethylsiloxane/methylhexenylsiloxane) , or combinations thereof. Desirably, the polydiorganosiloxane polymer is selected from the group consisting of b1) dimethylvinylsiloxy-terminated polydimethylsiloxane, b2) dimethylvinylsiloxy-terminated poly (dimethylsiloxane/methylvinylsiloxane) , or a combination of b1) and b2) .

The alkenyl-functional polyorganosiloxane can be a single polyorganosiloxane or a mixture comprising two or more polyorganosiloxanes that differ in at least one of the following properties: structure, average molecular weight, siloxane units, and sequence. The alkenyl-functional polyorganosiloxanes are known in the art and may be prepared by methods such as hydrolysis and condensation of the corresponding organohalosilanes or equilibration of cyclic polydiorganosiloxanes.

Desirably, the alkenyl-functional polyorganosiloxane is a linear polyorganosiloxane of formula (II) :
R _(3-x) Vi_xSiO- (R₂SiO) _bSiR _(3-y) Vi_y (II)

where R is as described in formula (I) above, desirably an alkyl group having 1 to 6 carbon atoms, more desirably methyl; b is as described in formula (I) above, such as from 10 to 1000; Vi is a vinyl group; x and y indicate the average number of terminal Vi groups on each end of the linear polyorganosiloxane and are each independently 1 or 2, and desirably x=y; (3-x) and (3-y) indicate the average number of terminal R groups on each end of the linear polyorganosiloxane. Desirably, each R is methyl. At the same time, it is desirable for x and y to each be 1.

The alkenyl-functional polyorganosiloxane useful in the present invention may be present in an amount of from 50 to 70 vol%, and can be 52 vol%or more, 55 vol%or more, 60 vol%or more, 63 vol%or more, 65 vol%or more, even 68 vol%or more while at the same time is 70 vol%or less, and can be 65 vol%or less, 62 vol%or less, 60 vol. %or less, 58 vol%or less, 55 vol%or less, 53 vol%or less, or even 51 vol%or less, desirably, from 60 to 67 vol%, based on the volume of the silicone composition.

The silicone composition of the present invention comprises component (C) a silyl-hydride functional polyorganosiloxane. A “silyl-hydride functional” polyorganosiloxane means a polyorganosiloxane containing a silicon atom-bonded hydrogen atom. The silyl-hydride functional polyorganosiloxane useful in the present invention has an average of at least two silicon-bonded hydrogen atoms (i.e., silyl hydride (SiH) groups) per molecule and is free of an alkenyl group, which is useful as a crosslinker.

The silyl-hydride functional polyorganosiloxane may have an average chemical structure of formula (III) :
R_3-hH_hSiO- (HRSiO) _e- (R₂SiO) _f-SiH_h'R_3-h' (III)

where R is as described above in formula (I) ; H is a hydrogen atom, h and h'refer to the average number of terminal hydrogens on the respective ends of the molecule and each independently have a value of 0, 1, 2 or 3, desirably 0, 1 or 2, more desirably 0 or 1, most desirably 0; e is the average number of (HRSiO) groups per molecule and is generally in a range of from 0 to 50; provided that the combination of e, h, and h′ (i.e., a quantity (e+h+h') ) is at least 2; if h and h′are both 0 then e is in a range of 2 to 30. If h and h′are both non-0 then e can be 0 to 30 provided the combination of e, h and h′is 2 or more; f is the average number of (R₂SiO) groups per molecule and generally in a range of from 0 to 200, provided that a quantity (e+f) ＞0.

The value of e may be from 0 to 50, and can be 1 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 is 50 or less, and can be 40 or less, 30 or less, 25 or less, 20 or less, 15 or less, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, 3 or less, even 2 or less, desirably, from 2 to 8.

The value of f may be from 0 to 200, and can be 1 or more, 10 or more, 14 or more, 20 or more, 25 or more, 30 or more, 40 or more, 50 or more, and can be 75 or more, 100 or more, 125 or more, 150 or more, 175 or more, even 190 or more while at the same time is typically 200 or less, and can be 175 or less, 150 or less, 125 or less, 100 or less, 75 or less, 50 or less, 40 or less, 30 or less, 25 or less, 22 or less, or even 20 or less, desirably, from 5 to 30.

Desirably, the R group for formula (III) is each independently selected from methyl, ethyl, propyl, and butyl; more desirably, R is methyl.

The silyl-hydride functional polyorganosiloxane may comprise the silicon-bonded hydrogen atoms in an amount of from 0.01 to 2 wt%, and can be 0.1 wt%or more, 0.2 wt%or more, 0.3 wt%or more, 0.4 wt%or more, 0.5 wt%or more, even 0.75 wt%or more while at the same time is 2 wt%or less, and can be 1.9 wt%or less, 1.8 wt%or less, 1.75 wt%or less, 1.7 wt%or less, 1.6 wt%or less, 1.5 wt%or less, 1.0 wt%or less, 0.8 wt%or less, or even 0.5 wt%or less, based on weight of the silyl-hydride functional polyorganosiloxane. The content of silicon-bonded hydrogen atoms can be determined by NMR analysis.

Methods of preparing silyl-hydride functional polyorganosiloxanes, such as hydrolysis and condensation of organohydridihalosilanes, are well known in the art. The silyl-hydride functional polyorganosiloxane (C) may be a combination of silyl-hydride functional polyorganosiloxanes that may differ in one or more properties selected from molecular weight, structure, siloxane units, and sequence, such as a mixture of trimethyl terminated dimethyl-co-hydrogen methyl polysiloxane and a hydride terminated polydimethylsiloxane. Examples of suitable silyl-hydride functional polyorganosiloxanes include c1) trimethylsiloxy-terminated poly (dimethyl/methylhydrogen) siloxane, c2) trimethylsiloxy-terminated polymethylhydrogensiloxane, c3) dimethylhydrogensiloxy-terminated polydimethylsiloxane, c4) dimethylhydrogensiloxy-terminated poly (dimethylsiloxane/methylhydrogensiloxane, c5) dimethylhydrogensiloxy-terminated polymethylhydrogensiloxane, or combinations thereof. Suitable commercially available silyl-hydride functional polyorganosiloxanes include those available under the names DOWSIL^TM 1-3510, DOWSIL^TM Q2-5057S, and DOWSIL^TM 6-3570 polymers all available from The Dow Chemical Company (DOWSIL is a trademark of The Dow Chemical Company or its affiliates) .

The silyl-hydride functional polyorganosiloxane is present in an amount sufficient to provide a molar ratio of silicon atom-bonded hydrogen atoms in the silyl-hydride functional polyorganosiloxane to alkenyl groups for the silicone composition, referred to as the SiH/Vi ratio, of from 0.5 to 3.0, and can be 0.6 or higher, 0.7 or higher, 0.8 or higher, 0.9 or higher, even 1.0 or higher while at the same time is 3.0 or lower, and can be 2.8 or lower, 2.6 or lower, 2.0 or lower, 1.8 or lower, 1.5 or lower, 1.2 or lower, or even 1.0 or lower, desirably from 0.7 to 2.6. The silicone composition typically comprises the silyl-hydride functional polyorganosiloxane in an amount of from 0.1 to 5 wt%, and can be 0.15%or more, 0.2 wt%or more, 0.25 wt%or more, 0.3 wt%or more, 0.35 wt%or more, even 0.4 wt%or more while at the same time is 5 wt%or less, and can be 4 wt%or less, 3 wt%or less, 2 wt%or less, 1 wt%or less, 0.8 wt%or less, or even 0.7 wt%or less, based on the weight of the silicone composition (e.g., total weight of components (A) to (E) and optionally components (F) to (G) if used) .

The silicone composition of the present invention comprises one or more (Pt) -based hydrosilylation reaction catalyst as component (D) . Such hydrosilylation reaction catalyst may include compounds and complexes such as platinum (0) -1, 3-divinyl-1, 1, 3, 3-tetramethyldisiloxane (Karstedt's catalyst) , H₂PtCl₆, di-μ. -carbonyl di-. π. -cyclopentadienyldinickel, platinum-carbonyl complexes, platinum-divinyltetramethyldisiloxane complexes, platinum cyclovinylmethylsiloxane complexes, platinum acetylacetonate (acac) , platinum black, platinum compounds such as chloroplatinic acid, 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 organopolysiloxanes or platinum compounds microencapsulated in a resin matrix or core-shell type structure. Complexes of platinum with low molecular weight organopolysiloxanes may include 1, 3-diethenyl-1, 1, 3, 3-tetramethyldisiloxane complexes with platinum. The hydrosilylation reaction catalyst including the complexes can be microencapsulated in a resin matrix or non-encapsulated. The resin matrix used for microencapsulating the hydrosilylation reaction catalyst can be a thermoplastic resin having a glass transition temperature (Tg) of greater than 45 ℃ as measured by differential scanning calorimetry (DSC) , so that it can be stored under room temperature (20-25 ℃) or temperatures no greater than 35 ℃, and release Pt during heat curing (e.g., at temperatures of 60 ℃ or higher) . Desirably, the resin matrix is an acrylate polymer such as a thermoplastic polymethyl methylmethacrylate-co-butyl acrylate copolymer. Exemplary hydrosilylation reaction catalysts are described in U. S. Patents 3, 159, 601 and 3, 220, 972, and encapsulated platinum catalysts are described in WO2014017671A1. Platinum-based hydrosilylation reaction catalysts are commercially available, for example, SYL-OFF^TM 4000 Catalyst, SYL-OFF^TM 4500 Catalyst, and SYL-OFF^TM 2700 Catalyst are available from The Dow Chemical Company (SYL-OFF is a trademark of The Dow Chemical Company or its affiliates) . Two different catalysts that activate at different temperatures can be used.

The hydrosilylation reaction catalyst can be in an amount sufficient to catalyze hydrosilylation reaction of silicon-bonded hydrogen atoms and alkenyl groups. Typically, the amount of the hydrosilylation reaction catalyst is sufficient to provide 0.5 part per million (ppm) to 30 ppm, and can be 1 ppm or more, 5 ppm or more, 10 ppm or more, 20 ppm or more, even 30 ppm or more while at the same time is generally even 30 ppm or less, of the platinum, by weight based on the weight of the silicone composition. Alternatively, the amount of the platinum-based hydrosilylation reaction catalyst may be 0.005 to 0.5 wt%, and can be 0.01 wt%or more, 0.03 wt%or more, 0.04 wt%or more, 0.05 wt%or more, even 0.06 wt%or more while at the same time is typically 0.5 wt%or less, and can be 0.4 wt%or less, 0.3 wt%or less, 0.2 wt%or less, 0.1 wt%or less, 0.09 wt%or less, 0.08 wt%or less, 0.07 wt%or less, or even 0.06 wt%or less, based on the weight of the silicone composition.

The silicone composition of the present invention comprises one or more polymer additive as component (E) . The polymer additive has a number average molecular weight (M_n) in a range of greater than 1, 000 grams per mole (g/mol) to 5000 g/mol, and can be 1050 g/mol or more, 1100 g/mol or more, 1200 g/mol or more, 1300 g/more or more, 1400 g/mol or more, 1500 g/mol or more, 1600 g/mol or more, 1800 g/mol or more, 1900 g/mol or more, even 2000 g/mol or more while at the same time is 5000 g/mol or less, and can be 4800 g/mol or less, 4500 g/mol or less, 4200 g/mol or less, 4000 g/mol or less, 3500 g/mol or less, 3200 g/mol or less, 3000 g/mol or less, 2800 g/mol or less, 2600 g/mol or less, 2500 g/mol or less, 2400 g/mol or less, 2200 g/mol or less, or even 2100 g/mol or less, desirably from 1050 to 3000 g/mol, alternatively, 1050 to 2500 g/mol, alternatively, 1200 to 2500 g/mol. M_n is determined by NMR, such as ¹³C NMR and ¹H NMR. Further details may be provided under Molecular Weight Measurement in the Examples section below.

The polymer additive (E) useful in the present invention is selected from the group consisting of a poly (tetramethylene ether glycol) homopolymer, a poly (tetramethylene ether glycol) copolymer, or mixtures thereof. A “poly (tetramethylene ether glycol) homopolymer” (also referred to as “PTMEG homopolymer” ) refers to a polymer whose structural units consisting of - (OCH₂CH₂CH₂CH) - (also as “- (CH₂) ₄O-” or “1, 4-oxybutylene” units) . A “poly (tetramethylene ether glycol) copolymer” (also referred to as “PTMEG copolymer” ) refers to a copolymer that contains structural units of - (OCH₂CH₂CH₂CH) -and additional structural units that are different from 1, 4-oxybutylene units. Desirably, the PTMEG copolymer comprises one or more than one segment A consisting of at least one - (CH₂) ₄O-unit, and one or more than one segment L consisting of at least one - (CH₂) _pCOO-unit described herein below. The PTMEG homopolymer and PTMEG copolymer may each independently also contain pendant, terminal, or end functional groups including, for example, hydroxyl; an alkyl group having 1 to 12 carbon atoms, 1 to 6 carbon atoms, or 1 to 3 carbon atoms; an acetyl groupan epoxy groupor combinations thereof. Desirably, the PTMEG homopolymer and PTMEG copolymer each independently comprises terminal groups selected from the group consisting of hydroxyl, methyl, an acetyl group, an epoxy group, and combinations thereof. Alternatively, the polymer additive may have an average number of hydroxyl groups per molecule of 2 or more, 2.1 or more, 2.5 or more, or even 3 or more while at the same times is 12 or less, and can be 10 or less, 8 or less, or even 6 or less. Desirably, the polymer additive comprises a poly (tetramethylene ether glycol) homopolymer having a M_n of from 1050 to 2500 g/mol and having terminal groups selected from the group consisting of hydroxyl, methyl, an acetyl group, an epoxy group, and combinations thereof. For example, the polymer additive may comprise a poly (tetramethylene ether glycol) homopolymer having terminal groups selected from the group consisting of an acetyl group, an epoxy group, and combinations thereof and a M_n of from 1050 to 2500 g/mol. Alternatively, the polymer additive may comprise a poly (tetramethylene ether glycol) homopolymer having hydroxyl terminal groups and a M_n of from 1200 to 2500 g/mol or from 1400 to 2500 g/mol. Alternatively, the polymer additive may comprise a poly (tetramethylene ether glycol) copolymer such as poly (tetramethylene ether glycol) -polycaprolactone copolymer, and having a M_n of from 1200 to 3000 g/mol, desirably, from 1400 to 3000 g/mol, and typically having hydroxyl terminal groups.

Suitable PTMEG homopolymers may include, for example, poly (tetramethylene ether glycol) (PTMEG) , poly (tetramethylene ether glycol) glycidyl ethers (collectively referred to as “epoxy-capped PTMEG” ) such as poly (tetramethylene ether glycol) monoglycidyl ether, poly (tetramethylene ether glycol) diglycidyl ether, or mixtures thereof, poly (tetramethylene ether glycol) acetates (collectively referred to as “acetyl-capped PTMEG” ) such as poly (tetramethylene ether glycol) monoacetate, poly (tetramethylene ether glycol) diacetates, or mixtures thereof. Desirably, the PTMEG copolymer is a reaction product of a C₄-C₂₀lactone with a PTMEG starting material of HO ( (CH₂) ₄O) _n (CH₂) ₄OH, where n is described as formula (IV) . Thus, such PTMEG copolymer comprises one or more than one - (CH₂) ₄O-unit (in segment A) and one or more than one - (CH₂) _pCOO-unit (in segment L) as described below.

The polymer additive useful in the present invention may include polymers having an average chemical structure of formula (IV) :
(R¹O) -L-A-L- (OR¹) (IV)

wherein A is - [ (CH₂) ₄-O] _n (CH₂) ₄-, where n is in a range of from 13 to 50; L is - [ (CH₂) _pCOO] _m-where m is in a range of from 0 to 10, and p is in a range of from 3 to 19; and each R¹ is independently a hydrogen atom (H) , an alkyl group having 1 to 12 carbon atoms, an acetyl group, or an epoxy group.

“n” is the average number of - (CH₂) ₄O-unit for segment A and can be in a range of from 13 to 50, and can be 14 or more, 17 or more, 20 or more, even 24 or more while at the same time is 50 or less, and can be 40 or less, 35 or less, 30 or less, or even 28 or less, desirably from 13 to 35, more desirably from 14 to 28.

R¹ is a capping group. Desirably, each R₁ is independently H, an alkyl group such as methyl and ethyl, an acetyl group, or an epoxy group. Each R¹ can be same or different.

“m” is the average number of - (CH₂) _pCOO-unit for segment L and can be in a range of from 0 to 10, and can be greater than 0, 1 or more, even 3 or more while at the same time is 10 or less, and can be 9 or less, 8 or less, 6 or less, or even 5 or less, alternatively from 0 to 7, alternatively from 1 to 7, alternatively from 0 to 5, alternatively from 1 to 5. p is in a range of from 3 to 19, and can be 4 or more, even 5 or more while at the same time is 19 or less, 18 or less, 15 or less, 12 or less, or even 10 or less, desirably from 3 to 15, more desirably from 4 to 10. When m is 0 in formula (IV) , the polymer additive is a PTMEG homopolymer. Desirably, m is 0, and each R¹ is independently H, an acetyl group, or an epoxy group. Alternatively, when m is greater than 0, the polymer additive is a PTMEG copolymer. Desirably, m is in a range of from 1 to 7, p is in a range of from 3 to 5, and each R¹ is H.

The PTMEG homopolymers are known in the art, including commercially available polytetramethylene ether glycols with different molecular weights, and PTMEG homopolymers with an end group that is different from hydroxy can be prepared from a poly (tetramethylene ether glycol) as a starting material (also referred to “PTMEG starting material” ) having the structure of HO ( (CH₂) ₄O) _n (CH₂) ₄OH, where n is described in formula (IV) above. For example, the epoxy-capped PTMEG can be prepared by first reacting the PTMEG starting material with epichlorohydrin (e.g., via a ring-opening reaction) in the presence of a catalyst such as boron trifluoride (BF₃) , and then the obtained modified PTMEG (also referred to as “intermediate” ) , typically with two terminal groups each with a chlorine active, is further subject to an intramolecular condensation reaction in the presence of a condensation catalyst such as a base (e.g., NaOH) , thereby forming the epoxy-capped PTMEG. A typical intermediate may have the structure represented by where n is described in formula (IV) above. A typical epoxy-capped PTMEG has the structure shown below (where i = n+1, and n is described in formula (IV) above) :

Acetyl-capped PTMEGs can be prepared using the PTMEG starting material via a condensation reaction with acetic anhydride, for example, by reacting the PTMEG starting material with acetic anhydride in the presence of a condensation catalyst such as p-toluenesulfonic acid monohydrate. A typical acetyl-capped PTMEG may have the structure given below (where i = n+1, and n is described in formula (IV) above) :

The PTMEG copolymer can be prepared by reacting (this is, a reaction product of) the PTMEG starting material with a C₄-C₂₀lactone. “C₄-C₂₀lactone” refers to a lactone having 4 to 20 carbon atoms. The lactone can be unsubstituted or substituted with one or more substituents selected from the group consisting of a C₁-C₁₂ alkyl. Examples of suitable lactones include ε-caprolactone, 4-hydroxybutanoic acid lactone, δ-valerolactone, or mixtures thereof. The PTMEG starting material and the C₄-C₂₀lactone can be used in amounts to provide desired length for - (CH₂) ₄O-units and - (CH₂) _pCOO-units described above. For example, the weight ratio of the PTMEG starting material to the C₄-C₂₀ lactone can be in a range of from 99: 1 to 20: 80, 95: 5 to 30: 70, 90: 10 to 40: 60, 85: 15 to 45: 55, or 80: 20 to 50: 50. Such PTMEG copolymer can be synthesized via ring-opening polymerization of the C₄-C₂₀ lactone (e.g., ε-caprolactone) using the PTMEG starting material as a macromolecular initiator. The polymerization is typically conducted in the presence of a metal organic catalyst such as n-butyl titanate, isobutyl titanate, Tin (II) 2-ethylhexanoate, or mixtures thereof. Methods and conditions used for the ring-opening polymerization are known to those skilled in the art, for example, at temperatures ranging from 100 to 150 ℃ or from 120 to 140 ℃. Preparation of the PTMEG copolymers can be found in references such as US20220306858A1.

The silicone composition of the present invention may comprise the polymer additive in an amount of from 0.025 to 2 wt%, and can be 0.04 wt%or more, 0.06 wt%or more, 0.08 wt%or more, 0.10 wt%or more, 0.15 wt%or more, 0.20 wt%or more, 0.25 wt%or more, 0.30 wt%or more, 0.35 wt%or more, 0.4 wt%or more, 0.5 wt%or more, 0.6 wt%or more, even 0.7 wt%or more while at the same time is 2 wt%or less, and can be 1.8 wt%or less, 1.6 wt%or less, 1.5 wt%or less, 1.2 wt%or less, 1.1 wt%or less, 1.0 wt%or less, 0.9 wt%or less, 0.8 wt%or less, 0.7 wt%or less, 0.6 wt%or less, 0.5 wt%or less, 0.4 wt%or less, 0.3 wt%or less, 0.2 wt%or less, or even 0.1 wt%or less; desirably from 0.05 to 0.8 wt%, more desirably from 0.2 to 0.5 wt%, by weight based on the total weight of the silicone composition.

The silicone composition of the present invention may comprise or be free of one or more hydrosilylation reaction inhibitor ( “inhibitor” ) as component (F) that may optionally be used for altering rate of reaction of the silicon-bonded hydrogen atoms and the alkenyl groups in the silicone composition, as compared to reaction rate of the same starting materials but with the inhibitor omitted. Examples of suitable inhibitors include acetylenic alcohols such as methyl butynol, ethynyl cyclohexanol, dimethyl hexynol, and 3, 5-dimethyl-1-hexyn-3-ol, 1-butyn-3-ol, 1-propyn-3-ol, 2-methyl-3-butyn-2-ol, 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol, 3-phenyl-1-butyn-3-ol, 4-ethyl-1-octyn-3-ol, 3, 5-dimethyl-1-hexyn-3-ol, and 1-ethynyl-1-cyclohexanol, and a combination thereof; cycloalkenylsiloxanes such as methylvinylcyclosiloxanes exemplified by 1, 3, 5, 7-tetramethyl-1, 3, 5, 7-tetravinylcyclotetrasiloxane, 1, 3, 5, 7-tetramethyl-1, 3, 5, 7-tetrahexenylcyclotetrasiloxane, and a combination thereof; ene-yne compounds such as 3-methyl-3-penten-1-yne, 3, 5-dimethyl-3-hexen-1-yne, and a combination thereof; triazoles such as benzotriazole; phosphines; mercaptans; hydrazines; amines, such as tetramethyl ethylenediamine, 3-dimethylamino-1-propyne, n-methylpropargylamine, propargylamine, and 1-ethynylcyclohexylamine; dialkyl fumarates such as diethyl fumarate, dialkenyl fumarates such as diallyl fumarate, dialkoxyalkyl fumarates, maleates such as diallyl maleate and diethyl maleate; nitriles; ethers; carbon monoxide; alkenes such as cyclo-octadiene, divinyltetramethyldisiloxane; alcohols such as benzyl alcohol; or combinations thereof.

The hydrosilylation reaction inhibitor may be present in the silicone composition in an amount of from 0 to 0.5 wt%, and can be 0.01 wt%or more, 0.02 wt%or more, 0.03 wt%or more, 0.05 wt%or more, even 0.1 wt%or more while at the same time is 0.5 wt%or less, and can be 0.4 wt%or less, 0.3 wt%or less, 0.25 wt%or less, 0.2 wt%or less, or even 0.15 wt%or less, based on the weight of the silicone composition.

The silicone composition of the present invention may comprise or be free of one or more adhesion promoter as component (G) . The adhesion promoter may comprise an alkoxysilane including an unsaturated or epoxy-functional alkoxysilane, a combination (i.e., physical blend and/or a reaction product) of an alkoxysilane and a hydroxy-functional polyorganosiloxane, or mixtures thereof. Examples of suitable epoxy-functional alkoxysilanes include 3- glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, (epoxycyclohexyl) ethyldimethoxysilane, (epoxycyclohexyl) ethyldiethoxysilane, or mixtures thereof. Examples of suitable unsaturated alkoxysilanes include vinyltrimethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, hexenyltrimethoxysilane, undecylenyltrimethoxysilane, 3-methacryloyloxypropyl trimethoxysilane, 3-methacryloyloxypropyl triethoxysilane, 3-acryloyloxypropyl trimethoxysilane, 3-acryloyloxypropyl triethoxysilane, or mixtures thereof. The adhesion promoter may be a reaction product and/or a blend of the epoxy-functional alkoxysilane with a hydroxy-terminated polyorganosiloxane such as a hydroxy- terminated vinyl polyorganosiloxane. The adhesion promoter may include a combination (i.e., a physical blend and/or a reaction product) of 3-glycidoxypropyltrimethoxysilane and a hydroxy-terminated vinyl polydimethylsiloxane. Desirably, the adhesion promoter is selected from 3-glycidoxypropyltrimethoxysilane, dimethyl, methylvinyl siloxane with epoxide, a blend and/or a reaction product of 3-glycidoxypropyltrimethoxysilane and a hydroxy-terminated methylvinyl/dimethylsiloxane copolymer, or combinations thereof. Suitable commercially available adhesion promoters may include, for example, SYL-OFF^TM 297, SYL-OFF^TM 397, and SYL-OFF^TM SL 9250 Anchorage Additives all available from The Dow Chemical Company.

The adhesion promoter (G) may be present in the silicone composition in an amount of from 0 to 5 wt%, and can be 0.01 wt%or more, 0.05 wt%or more, 0.1 wt%or more, even 0.3 wt%or more while at the same time is 5 wt%or less, and can be 3 wt%or less, 2 wt%or less, or even 1 wt%or less, based on the weight of the silicone composition.

The silicone composition of the present invention may comprise or be free of one or more filler treating agent as component (H) . The filler treating agent may be selected from an alkyl trialkoxysilane. Suitable alkyl trialkoxysilanes include those having the chemical formula (V) :
R^fSi (OR^g) ₃ (V)

where R^f is independently in each occurrence an alkyl group having 1 to 20 carbon atoms, and can be 6 or more, 7 or more, 8 or more, 9 or more, or even 10 or more carbon atoms, while at the same time having 20 or less, and can be 18 or less, 16 or less, 14 or less, 12 or less, or even 10 or less carbon atoms; and each R^g is independently an alkyl having 1 to 6 carbon atoms, and can be 2 or more, 3 or more, 4 or more, even 5 or more carbon atoms while at the same time generally having 6 or less, 5 or less, 4 or less, 3 or less, or even 2 or less carbon atoms. Desirably, each R^fis independently an alkyl group having 6 to 12 carbon atoms. R^g is desirably methyl so as to form methoxy groups attached to the silicon atom. A particularly desirable alkyl trialkoxysilane is n-decyltrimethoxysilane, n-octyltrimethoxysilane, or a mixture thereof. Suitable alkyl trialkoxysilanes may include n-decyltrimethoxysilane available from The Dow Chemical Company as DOWSIL^TM Z-6210 Silane or under the name SID2670.0 from Gelest.

The filler treating agent (H) may be present at a concentration of from 0 to 2.0 wt%, and can be 0.01 wt%or more, 0.05 wt%or more, even 0.1 wt%or more while at the same time is 2.0 wt%or less, and can be 1.5 wt%or less, 1.0 wt%or less, 0.5 wt%or less, or even 0.1 wt%or less, based on the weight of the silicone composition.

In addition to the components described above, the silicone composition of the present invention may further comprise one or more of the following additives: fillers other than electrically conductive fillers, pigments, and antioxidants. These additives may be present in the silicone composition in a total amount of from 0 to 2 wt%, from 0.01 to 1 wt%, or from 0.05 to 0.5 wt%, based on the total weight of the silicone composition.

The silicone composition of the present invention can be prepared by admixing components (A) through (E) , and optionally components (F) to (G) if used, and any optional components described above, typically at room temperature. The silicone composition can be a one-part composition or a multi-part composition. Mixing of the components in the silicone composition can be accomplished by any of the techniques known in the art such as milling, blending, and stirring, either in a batch or continuous process. The silicone composition can be prepared without the aid of a solvent while it still can be coated using a draw down bar. Thus, the silicone composition of the present invention can be solventless (i.e., containing no solvent or trace amounts of residual solvent from delivery of components in the silicone composition) . The silicone composition is typically stored in a sealed container to prevent exposure to air and moisture. The silicone composition can be stored at room temperature for several weeks without any change in the properties of a cured product made from the silicone composition (e.g., a silicone adhesive) , or at a temperature below 0 ℃, desirably, from -30 to -20 ℃ for 12 months.

The silicone composition of the present invention is useful for a range of applications, for example, the silicone composition cures to form electrically conductive adhesives, electrically conductive coatings, electromagnetic interference (EMI) shielding materials, release coatings, moldmaking compounds; protective coatings for electronic circuitry, planar surfaces, fibers or small particles, or gasketing materials. The silicone composition is a curable composition. Curing the silicone composition may be conducted at room temperature or at elevated temperatures up to 200 ℃, for example, from 70 to 200 ℃, from 125 to 175 ℃, for a time sufficient to cure the silicone composition (e.g., 1 to 3 hours) . Upon curing, the silicone composition forms a cured product with a high electrical conductivity, while at the same time, showing excellent thermal stability. “High electrical conductivity” herein means a volume resistance of less than 0.005 Ohm·cm (＜ 0.005 Ohm·cm) (denoted as “VR_Initial” ) . “Excellent thermal stability” herein means a volume resistance of less than 0.01 Ohm·cm (＜ 0.01 Ohm·cm) after aging the cured product at 120 ℃ for 1000 hours or at 125 ℃ for 720 hours (denoted as “VR_Aging” ) . Volume resistance can be measured according to GB/T 1551-2009. The cured product can achieve the above properties even at lower filler loadings than Incumbent Silicone Composition described above. The use of less amounts of fillers in the silicone composition of the present invention also contributes to a lower density and easier processing than Incumbent Silicone Composition, for example, the cured product of the silicone composition of the present invention has a density of less than 4.8 g/cm³(＜4.8 g/cm³) , as measured according to ASTM D792. Desirably, the silicone composition of the present invention can provide the cured product made therefrom with good retention of electrical conductivity (i.e., good thermal stability) , as indicated by a variation of VR before and after heat aging at 120 ℃ for 1000 hours or at 125 ℃ for 720 hours (i.e., VR_Aging/VR_Initial) of less than 10.0, less than 9.0, less than 8.0, less than 5, less than 4.0, less than 3.5, less than 3.2, or even less than 3.0.

The silicone composition of the present invention is particularly useful for preparing an electrically conductive silicone adhesive. The present invention also relates to a silicone adhesive comprising the cured product of the silicone composition, i.e., a silicone adhesive formed by curing the silicone composition via hydrosilylation reaction. The silicone adhesive may be used to form an adhesive article on a substrate by applying the silicone composition to the substrate. Applying the silicone composition to the substrate can be performed by various means including, for example, dispensing, spinning, a thin film coating, jetting, spraying, dipping, pouring, screen printing, extrusion or by the use of a brush, roller or coating bar. The substrate can be any material that can withstand the curing conditions described below used to cure the silicone composition to form the silicone adhesive on the substrate. Suitable substrates may include, for example, epoxies, polycarbonates, poly (butylene terephthalate) resins, polyamide resins and blends thereof, such as blends of polyamide resins with syndiotactic polystyrene, acrylonitrile-butadiene-styrenes, styrene-modified poly (phenylene oxides) , poly (phenylene sulfides) , vinyl esters, polyphthalamides, polyimides, silicon, aluminum, stainless steel alloys, titanium, copper, nickel, silver, gold, or combinations thereof. Desirably, the substrate that can be used in electronic applications. For example, the present invention can provide an electronic device comprising the substrate and the silicone composition or the silicone adhesive, disposed on the substrate. The silicone composition of the present invention cures to form the silicone adhesive having the high electrical conductivity and excellent thermal stability as described above for the cured products.

The present invention also provides a method of bonding a first substrate to a second substrate. The method comprises the steps of (a) applying the silicone composition to the surface of at least one of the substrates, (b) contacting the two substrates with the silicone composition residing therebetween, and (c) curing the silicone composition. The two substrates are those as described above and can be the same or different. Curing the silicone composition can be conducted as described above.

EXAMPLES

Some embodiments of the invention will now be described in the following Examples, wherein all particle sizes of fillers are median particle size (D50) particle sizes, unless otherwise specified. Table 1 lists the materials for use in the electronically conductive composition of the samples described herein below.

Table 1

*The Pt-1 catalyst having a platinum content of 0.16 wt%relative to the catalyst weight is a mixture containing 40 wt%of a complex of platinum with l, 3-divinyl-l, l, 3, 3 tetramethyldisiloxane dispersed in a thermoplastic polymethyl methylmethacrylate-co-butyl acrylate having a Tg of 64 ℃ as measured by DSC; 55 wt%of a dimethylvinylsiloxy-terminated polydimethylsiloxane having a viscosity of 2 Pa*s at 25 ℃ and 0.2 wt% of vinyl; and 5 wt%of a hexamethyldisilazane-treated fumed silica.

Viscosities of polyorganosiloxanes (e.g., V-P1, V-P2, V-P3, V-P4 and crosslinkers) were determined using a rotary viscometer such as a Brookfield viscometer DV-II at 25 ℃, according to ASTM-D1084.

“wt%vinyl” refers to weight percentage of vinyl groups relative to the vinyl polymer weight.

“mol%SiH” is the molar percentage of silicon-bonded atoms per mole of crosslinker.

Mn of polymer additives and poly (tetramethylene ether glycol) starting materials used for preparing the polymer additives was determined by NMR (further information provided under the Molecular teight Measurement described below) .

Synthesis of Additive-2 PTMEG-PCL copolymer

A poly (tetramethylene ether glycol) with a Mn of 1050 g/mol (herein referred to as “PTMEG-A” , available from Shanghai Aladdin Biochemical Technology Co., Ltd. of China) was used as a macromolecular initiator for the synthesis. Additive-2, a PTMEG-PCL copolymer, was synthesized via ring-opening polymerization of ε-caprolactone using PTMEG-A. Specifically, 50 wt%of PTMEG-Aand 50 wt%of ε-caprolactone, and additional n-butyl titanate (TBT, 25 parts per million by weight (ppm) ) , based on the total weight of PTMEG-Aand ε-caprolactone, were fed into a glass reactor equipped with a vacuum pump and oil bath under nitrogen atmosphere at room temperature. With stirring, the contents of the reactor were allowed to react at 120 ℃ for 17 hours, followed by application of vacuum under 150 mbar (15, 000 Pascals) and 135 ℃ for 3 hours. The final product was cooled down to 80 ℃ and filtered to give Additive-2. The structure of the obtained Additive-2 was characterized by ¹³C-NMR and given below:

where j= 4.3 and k= 13.9

Synthesis of Additive-5 Acetyl-capped PTMEG

A mixture of PTMEG-A (200 g, 0.2 mol) , acetic anhydride (24.5 g, 0.24 mol) , toluene (200 ml) , and p-Toluenesulfonic acid monohydrate (p-TSA, Sigma-Aldrich) (0.76 g, 0.004 mol) was stirred in a 500 ml flask and refluxed with Dean-Stark to remove 3.6 g water from the flask at 130 ℃ overnight. After completion, the resulting yellow solution was concentrated under vacuum, then KOH (44.9 g, 0.8 mol with respect to 0.4 mol of acetic acid residue) was added, and the obtained mixture was stirred at 60 ℃ for 4 hours to neutralize the unreacted acid. After filtration, FLORISIL^TM adsorbent (30 g) and Na₂SO₄ (30 g) were added to absorb water and salt residues at 60 ℃ for 1 hour. The obtained mixture was filtered to give a yellow clear liquid (173 g, yield = 79.8%) . The structure of the obtained Additive-5 was characterized by ¹³C-NMR, indicating both sides of Additive-5 were capped with acetyl groups. The chemical equation is shown below:

Synthesis of Additive-6 Epoxy-capped PTMEG

A mixture of Additive-1 PTMEG (200 g) and boron trifluoride etherate (BF3-etherate, 6000 ppm, based on Additive-1 weight) was placed in a nitrogen (N₂) -charged 3-Liter flask. While maintaining a slow steady N₂ flow, the mixture was stirred at 250 revolutions per minute (rpm) and heated to 70 ℃. After that, epichlorohydrin (48 g) was added to the mixture at a feed rate of 2 g/min. Once completion of feeding epichlorohydrin, the contents in the flask were hold for reaction at 70 ℃ for 30 minutes (min) to ensure complete epichlorohydrin consumption. Then, unreacted epichlorohydrin was removed by rotary evaporation to obtain an intermediate having two terminal groups each with an active chlorine (yield = 80%) . The intermediate has the following structure:

The above intermediate was dropwise added to a mixture solution of 50 mL 45.6 wt%NaOH aqueous solution and 100 mL toluene, then the reaction was heated at 70 ℃ for 2 hours. The toluene portion was collected and dried over MgSO₄ (30 g) overnight. Finally, the resulting mixture was filtered, and toluene was removed by rotary evaporation, thereby obtaining a transparent liquid with a yield ratio of 80 wt%. The structure of the obtained product was characterized by ¹H-NMR and both sides were capped with epoxy groups. The chemical equation is shown below:

The following standard analytical equipment and methods are used in the Examples and in determining the properties and characteristics stated herein:

Characterization of Polymer Additives

Polymer additives were characterized for structure using NMR analysis with conditions given below:

¹³C-NMR Analysis: An additive sample (such as a PTMEG homopolymer or copolymer) was dissolved in THF (tetrahydrofuran) -d8 (0.025M Cr (acac) 3) at room temperature to get a homogenous solution. All ¹³C-NMR data were acquired at room temperature on a Bruker AVANCE II 400 MHz spectrometer operating at a ¹³C resonance frequency of 100 MHz. A 10 mm probe was employed. Chemical shifts were given in ppm (parts per million) relative to THF-d8. Zgig was used as the pulse program of ¹³C-NMR with an observe pulse of 90 degree. Recycle delay was set to 6 seconds. The sample was scanned for 4096 times.

¹H-NMR Analysis: A sample was dissolved in THF-d8 at room temperature to get a homogenous solution. All ¹H-NMR data were acquired at room temperature on a Bruker AVANCE II 400 MHz spectrometer. A 10 mm probe was employed. Chemical shifts were given in ppm relative to THF-d8. Zg30 was used as the pulse program of ¹H-NMR. Recycle delay was set to 10 seconds. The sample was scanned for 32 times.

Molecular Weight Measurement

A polymer additive sample was dissolved in acetone-d6 (0.025M Cr (acac) ₃) at room temperature to get a homogenous solution. All NMR spectra were acquired at room temperature on a Bruker AVANCE II 600 MHz spectrometer operating at a ¹³C resonance frequency of 150 MHz. A 10 mm cryo-probe was employed. Chemical shifts were given in ppm relative to acetone-d6. Zgig was used as the pulse program of ¹³C NMR with an observe pulse of 90 degree. Recycle delay was set to 6 seconds. The sample was scanned for 256 times. Polymerization degree of the polymer additive and the average molecular weight of polymer segments in the polymer additive can be determined.

Mn of some typical examples of polymer additives can be determined as below:

1) For PTMEG homopolymers (e.g., PTMEGs or capped-PTMEGs) , the average molecular weight of segments consisting of repeating units of - (OCH₂CH₂CH₂CH) - (hereinafter referred to “PTMEG segments” ) was calculated based on quantitative ¹³C NMR spectrum. The integral CH₂OH end peak (61-62 ppm) was set to 2, thus the integral of C-O ether (68-72 ppm) was obtained (X) . The number of repeating units in PTMEG segments was calculated by equation n= (X+2) /2. The average molecular weight of PTMEG segments was M= 72* (X+2) /2.

2) For PTMEG-PCL copolymers, the average molecular weights of a) PTMEG segments, and b) segments consisting of repeating units of - [ (CH₂) ₅COO] - (hereinafter referred to as “PCL segments” ) in the copolymers, respectively, were calculated based on quantitative ¹³C NMR spectrum. The sum of CH₂OH end peak (61-62 ppm) integral and ester (C=O) -O peak (63-64 ppm) was set to 2, and the integral of C-O ether (68-72 ppm) and ester carbonyl (172-173 ppm) was obtained as Y and Z, respectively. The number of repeating units in PTMEG segments was calculated by equation: n₁= (Y+2) /2, and the number of repeating units in PCL segments was calculated by equation: n₂= Z/2. The average molecular weight of PTMEG segments was M₁= 72* (Y+2) /2, and the average molecular weight of PCL segments was M₂= 114* (Z+2) /2.

Then, the number average molecular weight of the polymer additive is calculated by: the sum of the obtained average molecular weight of PTMEG segments, and PCL segments if present, and the molecular weight of terminal groups of the polymer additive. Terminal groups of the polymer additive can be characterized according to the Characterization of Polymer Additives described above.

Volume Resistance Test

A silicone composition sample was casted into a mold (15 mm*5 mm*0.5 mm (thickness) ) on a glass slide and then cured at 150 ℃ for 30 min to form cured samples. The cured samples were cooled down to room temperature before volume resistance (VR) testing. The volume resistance of the obtained cured samples was measured by a four-probe method using a 4-probe volume resistivity tester (ST2253) from Suzhou Jingge Electronic Co., Ltd. (China) , in accordance with GB/T 1551-2009.

The as prepared cured samples on the glass slide were placed under the 4-probe VR tester and an initial volume resistance of the samples was measured, denoted as VR_Initial. The samples were then put into an oven for heat aging under the condition (i) or (ii) : (i) at 120 ℃ for 1000 hours, or (ii) 125 ℃ for 720 hours, followed by cooling to room temperature for more than 12 hours.

VR of the samples after heat aging was measured, denoted as VR_Aging. The variation of VR before and after heat aging, denoted as VR_Variation, is calculated according to the following equation:
VR_Variation= (VR_Aging/VR_Initial) .

Acceptable VR_Initial is less than 0.005 Ohm·cm. Acceptable VR_Agingis less than 0.01 Ohm·cm.

Density Test

Density was tested according to ASTM D792. A silicone composition sample (2 g) was cured under 150 ℃ for 30 min and then used for the density test. Acceptable density is less than 4.8 g/cm³.

Median Particle Size of Electrically Conductive Fillers

Median particle size, i.e., D50 particle size, of fillers was determined using Laser Diffraction particle size analyzer from Beckman Coulter (Model LS 13 320) by determining the volume weighted particle size distribution of 108 particles.

Inventive Examples (IEs) 1-22 and Comparative Exs (CEs) 1-7 Silicone Compositions

Formulations for electrically conductive silicone composition samples are in Tables 2-5, with the amount of each component reported in wt%relative to the total weight of components in each composition. Samples were prepared by using a dental mixer (DAC600 VAC mixer from Flack Tek, Inc. ) to mix the components together at room temperature.

To the mixing cup in the mixer, add certain amounts of Vi Polymer and Treating agents. Slowly add Fillers by two steps: Add a first part of fillers (Filler-2) into the mixing container and mixing using a dental mixer at 1000 rpm for 1 min, and then at 1500 rpm for another 1 min. Add the secondary part (Filler-1 and Filler-3) of fillers into the container, mix at 1000 rpm for 1 min, and at 1500 rpm for another 1 min. Then stop mixing and scrape material down from the walls of the mixing container. Mix again at 1000 rpm for 1 min and at 1500 rpm for another 1 min. Add the inhibitor, crosslinker, and polymer additives, and mixing for 2 min at 1000 rpm, and another 2 min at 1500 rpm. Cool the mixture down to 25 ℃, add Pt catalyst into the mixer, and then mix at 800 rpm for 2 min under vacuum. Stop mixing and release the vacuum to obtain the electrically conductive silicone compositions. The obtained compositions were characterized for density and VR properties according to the Density Test and Volume Resistance Test described above and characterization results are given in Tables 2-4 for IEs 1-22 and Table 5 for CEs 1-7.

As shown in Tables 2-4, IEs 1-22 silicone compositions comprise a novel combination of the electronically conductive fillers (A) , the vinyl polymers (B) , crosslinkers (C) , and specified PTMEG-based polymer additives (E) such as the PTMEG (Additive-1) , PTMEG copolymer (Additve-2) , acetyl-capped PTMEG (Additive-5) , or epoxy-capped PTMEG (Additive-6) . All these IEs silicone compositions provided cured samples with excellent electric conductivity, as indicated by low initial volume resistance (＜ 0.005 Ohm·cm) . At the same time, after aging at 125 ℃ for 720 hours or 120 ℃ for 1000 hours, the cured samples made from IEs silicone compositions still showed low VR_Aging so as to meet the requirement of less than 0.01 Ohm·cm, indicating excellent thermal stability. The VR_Initial for IE 1 was even lower than that of CE 2 that has higher loading of fillers. All IEs silicone compositions also provided cured samples with low density (＜ 4.8 g/cm³) at a filler loading up to 47.89 vol%.

In contrast, as shown in Table 5, the volume resistance of CE cured samples without additives increased by 2-3 orders of magnitude after aging. CE 1 silicone composition that does not contain any polymer additive provided cured samples with acceptable initial volume resistance, indicating the loading levels of electrically conductive fillers all have reached an electric conductive threshold. However, the volume resistance of the cured sample for CE 1 after aging significantly increased and failed to meet the VR_Aging requirement of less than 0.01 Ohm·cm, indicating poorer thermal stability (poorer electric conductivity retention after aging) than IEs 1 and 3-10. CE 2 silicone composition that does not contain any polymer additive after curing and aging showed poorer thermal stability (much higher VR_Aging) than IE 2. As compared to IE 11, CE 3 silicone composition that does not contain any polymer additive provided cured samples with poor electric conductivity with a VR_Initial higher than 0.005 Ohm·cm and the cured samples after aging showed significantly increased VR and failed to meet the requirement of less than 0.01 Ohm·cm, indicating poorer thermal stability. CE 4 silicone composition that does not contain any polymer additive provided cured samples with both higher VR_Initial and VR_Aging than IEs 13-20, particularly, CE 4 gave significantly increased volume resistance after aging (open circuit) . CEs 5 and 6 silicone compositions that contain polymer additives (E') either different in M_n or polymer types from the polymer additive (E) , after curing and aging, both failed to achieve the requirement for VR_Aging and showed significantly higher VR_Aging than IEs 17 and 18 silicone compositions. As compared to IEs 21 and 22, CE 7 silicone composition that is free of any PTMEG-based additive provided cured samples with higher VR_Initial and failed to achieve the requirement for VR_Aging, indicating poor thermal conductivity and thermal stability.

Table 2. Silicone compositions and properties

In Tables 2-5:

“Vol%Filler” refers to volume percentage of total fillers relative to the total volume of all components in the composition.

“SiH/Vi ratio” refers to molar ratio of silicon atom-bonded hydrogen atoms to vinyl groups for the composition. “VR_Initial” and “VR_Aging” were both determined according to the Volume Resistance Test. “Open circuit” means insulation, infinite resistance. “VR_Aging (i) ” refers to VR after aging at 120 ℃ for 1000 hours. “VR_Aging (ii) ” refers to VR after aging at 125 ℃ for 720 hours. “VR_Variation” refers to the ratio of VR_Aging to VR_Initial.

“Density” was measured according to the Density Test.

Table 3. Silicone compositions and properties

Table 4. Silicone compositions and properties

able 5. CE Silicone compositions and properties

Claims

A silicone composition comprising:

(A) from 29 to 49 volume percent, based on the volume of the silicone composition, of an electrically conductive filler;

(B) from 50 to 70 volume percent, based on the volume of the silicone composition, of an alkenyl-functional polyorganosiloxane having an average of at least two alkenyl groups per molecule;

(C) a silyl-hydride functional polyorganosiloxane having an average of at least two silicon atom-bonded hydrogen atoms per molecule and free of an alkenyl group; wherein the silyl-hydride functional polyorganosiloxane is present in an amount sufficient to provide a molar ratio of silicon-bonded hydrogen atoms to alkenyl groups for the composition of 0.5 to 3.0;

(D) a platinum-based hydrosilylation reaction catalyst; and

(E) from 0.025 to 2 weight percent, based on the weight of the silicone composition, of a polymer additive having a number average molecular weight in a range of greater than 1000 to 5000 grams per mole; wherein the polymer additive is selected from the group consisting of a poly (tetramethylene ether glycol) homopolymer, a poly (tetramethylene ether glycol) copolymer, and mixtures thereof.
The silicone composition of claim 1, further comprising one or both of the following components: (F) a hydrosilylation reaction inhibitor and (G) an adhesion promoter.
The silicone composition of claim 1 or 2, wherein the polymer additive has general formula (IV) :
(R¹O) -L-A-L- (OR¹) (IV)

where A is - [ (CH₂) ₄-O] _n (CH₂) ₄-, where n is in a range of from 13 to 50; L is - [ (CH₂) _pCOO] _m-, where m is in a range of from 0 to 10, and p is in a range of from 3 to 19; and each R¹ is independently H, an alkyl group having 1 to 12 carbon atoms, an acetyl group, or an epoxy group.
The silicone composition of claim 3, where, in formula (IV) , m is 0, and each R¹ is independently H, an acetyl group, or an epoxy group.
The silicone composition of claim 3, where, in formula (IV) , m is in a range of from 1 to 7, p is in a range of from 3 to 5, and each R¹ is H.
The silicone composition of claims 1 or 2, wherein the polymer additive comprises a poly (tetramethylene ether glycol) homopolymer having a number average molecular weight of from 1050 to 2500 grams per mole and having terminal groups selected from the group consisting of hydroxyl, methyl, an acetyl group, an epoxy group, and combinations thereof.
The silicone composition of claims 1 or 2, wherein the polymer additive comprises a poly (tetramethylene ether glycol) -polycaprolactone copolymer having a number average molecular weight of from 1200 to 3000 grams per mole.
The silicone composition of any one of claims 1-7, wherein the alkenyl-functional polyorganosiloxane has an average chemical structure of formula (I) ,
R _(3-c) R’_cSiO- (R’RSiO) _a- (R₂SiO) _b-SiR’_dR _(3-d) (I)

where each R is independently an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms, each R’ is independently an alkenyl group, a ≥ 0, b ＞ 0, c is 0 to 1, d is 0 or 1, (a+b) is in a range of from 10 to 1000, and (a+c+d) ≥ 2.
The silicone composition of any one of claims 1-8, where the silyl-hydride functional polyorganosiloxane has an average chemical structure of formula (III) :
R_3-hH_hSiO- (HRSiO) _e- (R₂SiO) _f-SiH_h’R_3-h’ (III)

where each R is independently an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms; h and h’ each independently have a value of 0, 1, 2 or 3; e is in a range of from 0 to 50; provided that the combination of e, h, and h’ is at least 2; f is in a range of from 0 to 200, provided that a quantity (e+f) ＞ 0.
The silicone composition of any one of claims 1-9, wherein the electrically conductive filler comprises silver coated nickel particles, silver coated glass particles, silver coated aluminum particles, silver coated copper particles, particles consisting of silver or alloys thereof, or mixtures thereof.
A process for preparing the silicone composition of any one of claims 1-10, comprising: admixing the electrically conductive filler (A) , the alkenyl-functional polydiorganosiloxane (B) , the silyl-hydride functional polyorganosiloxane (C) , the platinum-based hydrosilylation reaction catalyst (D) , and the polymer additive (E) .
A silicone adhesive comprising a cured product of the silicone composition of any one of claims 1-10.