WO2019083914A1

WO2019083914A1 - Curable siloxane adhesives

Info

Publication number: WO2019083914A1
Application number: PCT/US2018/056973
Authority: WO
Inventors: Gang Lu; Ryan C. THOMAS; Nick Shephard
Original assignee: Dow Silicones Corporation
Priority date: 2017-10-27
Filing date: 2018-10-23
Publication date: 2019-05-02
Also published as: TW201917148A

Abstract

The invention is siloxane polymer comprising a backbone of the following siloxane repeat units and end groups clusters formed from siloxane units. The clusters are functionalized by the presence of at least two functional reactive groups per cluster and at least one functional reactive group is a free radical polymerizable group and at least one functional reactive group is an alkenylalkoxysilane groups and the amount of free radically polymerizable group is at least 2 mole percent of the total moles of functional reactive groups in the polymer. The invention is also an adhesive made using such polymers.

Description

CURABLE SILOXANE ADHESIVES

Field of the Invention

[001] This invention relates generally to curable siloxane polymers.

Introduction

[002] Siloxanes having clustered ring end groups are known (see, e.g. U.S. 9593209,

US 2016/0009865, WO2014/124364, WO 2014/124388, WO 2014/124367, WO2014/124382). At least some of these are taught to be curable.

[003] Certain curable siloxane polymers may be useful as adhesives. One approach to cure of such polymers is by free radical polymerization using acrylate or methacrylate groups. However, free radical curable compositions sometime suffer from under cure of the surface region and surface wetness due to oxygen quenching of the free radicals at the surface where there is exposure to air.

[004] There is a desire to have an improved curable siloxane polymer that has faster cure and drying times while maintaining other important adhesive properties such as lap shear strength, tensile strength, elongation and modulus.

Summary of Invention

[005] The present inventors have discovered an improved curable siloxane polymer useful as an adhesive component that has improved cure and drying times while maintaining other important adhesive properties such as lap shear strength, tensile strength, elongation and modulus.

[006] Thus, according to one aspect, the invention is curable siloxane polymer comprising a backbone of the following siloxane repeat units:

Rl

I

-[Si-0]j- I

Rl where j is an integer of at least 50, and j is preferably no more than 10,000 and Rl is independently in each occurrence H or an alkyl group of 1 to 4 carbon atoms or an aryl group of 6-12 carbon atoms. Rl is preferably alkyl and most preferably methyl. If Rl is aryl, it is preferably phenyl. The siloxane polymer may be branched provided each branch has at least j of the repeat units. Linear polymers are preferred.

[007] The siloxane polymer is characterized by end groups that form clusters. The clusters may be cyclical groups, cages or the like. Preferably the clusters are formed from siloxane units. Each cluster has at least 3 and preferably no more than 12 siloxane groups, more preferably no more than 10. The clusters are functionalized by the presence of at least two functional reactive groups, preferably at least 3 reactive groups per cluster. Preferably, the number of functional reactive groups is no more than 5. At least one functional reactive group is a free radical polymerizable group such as an acrylate or akylacrylate group and at least one functional reactive group is an alkenylalkoxysilane groups. The amount of alkenylalkoxysilane groups is at least 2 mole percent of the total moles of functional reactive groups (i.e. the sum of the number of acrylate or alkylacrylate groups and the number of alkenylalkoxysilane groups) in the polymer. Preferably the amount of alkenylalkoxysilane groups is less than 30 mole based on total moles of functional reactive groups. Alternatively, the mole ratio of acrylate or alkylacrylate to alkenylalkoxysilanes is no less than 1 : 1, preferably is at least 2:1, more preferably is at least 8: 1, and preferably is no more than 20:1.

[008] If ratio of acrylate or alkylacrylate groups to alkenyl alkoxysilane groups is important. If the ratio is too high (i.e. too few alkenylalkoxysilane groups are present) the polymer has inadequate drying (dry times are too long) for practical use as an adhesive. If the ratio is too low (i.e. too many alkenylakloxysilance groups are present) the adhesive may suffer from one or more of decreased or poor lap shear strength, tensile strength, elongation and modulus.

[009] According to a second embodiment the invention is an adhesive comprising

A) the curable siloxane polymer as described above,

B) optionally, a poly-alkoxy endblocked silicone resin-polymer blend,

C) optionally, a condensation reaction catalyst, and

D) a free radical initiator.

Detailed Description

The Curable Siloxan Polymer— Component A of the Adhesive

[0010] According to one embodiment the invention is curable siloxane polymer comprising a backbone of the following siloxane repeat units:

Rl

I

-[Si-0]j- I

Rl

where j is an integer of at least 50, more preferably at least 100, more preferably still at least 150, still more preferably more than 500, and n is preferably no more than 10,000, more preferably no more than 1500; and R¹ is as defined above.

[0011] The siloxane polymer is characterized by end groups that form clusters. The clusters may be cyclical groups, cages or the like. Preferably the clusters are formed from siloxane units. Each cluster has at least 3, more preferably at least 4, and preferably no more than 10, more preferably no more than 8, still more preferably no more than 6 siloxane groups. The clusters are functionalized by the presence of at least two functional reactive groups, preferably at least 3 reactive groups per cluster. Preferably the number of functional reactive groups is no more than 5. At least one functional reactive group is an acrylate or alkylacrylate group and at least one functional reactive group is an alkenylalkoxysilane groups. The amount of alkenylalkoxysilane groups is at least 2 mole percent of the total moles of functional reactive groups (i.e. the sum of the number of acrylate or alkylacrylate groups and the number of alkenylalkoxysilane groups) in the polymer. Preferably, the amount of alkenylalkoxysilane groups is at least 5 mole percent of the total moles of functional reactive groups. Preferably the amount of alkenylalkoxysilane groups is less than 30 mole %, more preferably less than 25 mole %, more preferably still less than 20 mole %, yet more preferably less than 15 mole % and most preferably less than 13 mole % based on total moles of functional reactive groups. Stated alternatively, wherein mole ratio of acrylate or alkylacrylate to alkenylalkoxysilanes is no less than 1 :1, preferably is at least 2:1, more preferably is at least 8: 1, and preferably is no more than 20:1. The end groups are preferably cyclical groups of at least 3, preferably at least 4 but no more than 25, preferably less than 10, preferably less than 8, more preferably less than 6, siloxane repeat units (e.g.

R2

-[Si-O]-

atoms, preferably 1-5 carbon atoms, more preferably 2-4 carbon atoms, and alkenyl alkoxysilanes).

[0012] According to one preferred embodiment the curable polymer has cyclic end groups and may be represented by the formula:

the where j and R1 is as defined above. is a single bond or is a divalent hydrocarbon group of 1 to 20 carbon atoms. Each subscript k is independently in each occurrence 0, preferably at least 1, and no more than to 12 (i.e., such that each ring has 3, preferably 4 to 15 silicon atoms), more preferably k is no more than 8, more preferably still no more than 6, more preferably still no more than 4, and most preferably no more than 2. R is, independently in each occurrence, (a) a monovalent hydrocarbyl groups or monovalent hydrocarbyl groups substituted with a halogen or a hetero atom such as oxygen or nitrogen, (b) free radical polymerizable group such as an acrylate or alkylacrylate containing group or (c) an alkenylalkoxysilane group, provided at least two of R on each ring are (b) or (c), and the amount of alkenylalkoxysilane is at least 2 mole percent, preferably at least 5 mole % and no more than 30, preferably no more than 25, more preferably no more than 20, most preferably no more than 15 mole percent based on total moles of acrylate, alkylacrylate, and alkenylalkoxysilane present.

[0013] The monovalent hydrocarbyl groups and monovalent halogenated hydrocarbon groups may have 1 to 18 carbon atoms. Suitable monovalent hydrocarbon groups for R include, but are not limited to, alkyl and aryl groups. Suitable alkyl groups are exemplified by methyl, ethyl, propyl, butyl and hexyl. Suitable aryl groups are exemplified by phenyl, tolyl, xylyl, and phenyl-methyl. As noted these may be substituted with a halogen atom such as fluorine or chlorine as in, for example, lH,lH,2H,2H-trifluoropropyl, lH,lH,2H,2H-perfluorobutyl, 1H,1H,2H,2H- perfluoropentyl, lH,lH,2H,2H-perfluorohexyl, lH,lH,2H,2H-perfluoroheptyl, 1H,1H,2H,2H- perfluorooctyl. Further as noted, hydrocarbyl groups with heteroatoms may be used. Examples of such heteroatom containing groups include alky lthio alkyl groups, such as alkylthiomethyl, alkylthioethyl, alkylthiopropyl, alkylthiobutyl, and alkylphosphorous alkyl groups, such as alkylphosphorousmethyl, alkylphosphorousethyl, alkylphosphorouspropyl, alkylphosphorousbutyl.

[0011] Examples of suitable acrylate and alkyl acrylate groups include methyl methacrylate, methyl acrylate, butyl methacrylate, 2-ethylhexylacrylate, and 2-ethylhexylmethacrylate.

[0014] Examples of suitable alkenylalkoxylsilane groups include vinyltrimethoxysilane, vinylmethyldimethoxysilane, allyltrimethoxysilane, allylmethyldimethoxysilane,

3-butenyltrimethoxysilane, 3-butenylmethyldimethoxysilane, 4-pentenyltrimethoxysilane, 4- pentenylmethyldimethoxysilane, 5-hexenyltrimethoxysilane,

5- hexenylmethyldimethoxysilane, 6-heptenyltrimethoxysilane,

6- heptenylmethyldimethoxysilane, 7 -octenyltrimethoxysilane,

7- octenylmethyldimethoxysilane, 8-nonenyltrimethoxysilane,

8- nonenylmethyldimethoxysilane, 9-decenyltrimethoxysilane,

9- decenylmethyldimethoxysilane, 10-undecenyltrimethoxy silane, and

10- undecenylmethyldimethoxy silane . [0015] The polyorganosiloxane terminated with clustered mixed functionalities of this invention may be made by reacting a linear siloxane polymer with ethenyl termini ( for example, vinyl, allyl, 1-butenyl, 1-pentenyl, 1-hexenyl, etc.), a cylic or cage methylhydrogen siloxane polymer, a (me th) aery late monomer with ethenyl functionality, and a trimethoxysilane or a dimethoxysialne with ethenyl functionality in the presence of a hydrosilylation catalyst (typically Pt, Ru, Ni- containing species). The reaction is typically carried out at 50 °C and above under inert atmosphere. The reaction can be done with or without solvents. At the end of the reaction, the catalysts can be quenched by the addition of a ligand, such as diallyl maleate. Instead of quenching, the catalysts can also be removed by pass the reaction mixture through a carbon black bed.

[0016] When used as a component in the adhesive formulation of this invention, the amount of the curable polyorganosiloxane with clustered end groups and the dual cure functionality is preferably at least 10% by weight, preferably at least 20% by weight, more preferably at least 30% by weight, and according to some embodiments more preferably still at least 40% by weight, alternatively at least 50% by weight, alternatively at least 60% by weight, but preferably no more than 99.9, 99.8 or 99.7 weight %, more preferably no more than 98, 97 or 95 weight %. When component B is present component A is preferably present at no more than 90 weight percent, and more preferably no more than 85 weight percent. Alternatively it is present at no more than 65 weight percent, no more than 60 weight percent, and no more than 50 weight percent with all percentages being based on total amounts of those components A through D which are used in the adhesive formulation.

Component B

[0017] Optional component B in the adhesive composition described above is a poly-alkoxy endblocked resin-polymer blend. The poly-alkoxy endblocked resin-polymer blend preferably comprises a reaction product of

i) a siloxane resin comprising units of formulae (R^ 3S1O1 ₂) and (S1O4/2), where each is independently a monovalent hydrocarbon group, with the proviso that at least one R2' per molecule has terminal aliphatic unsaturation, wherein the siloxane resin has a molar ratio of

(R²'₃SiOi/2) units ("M" units) to (S1O4/2) units ("Q" units) ranging from 0.5:1 to 1.5:1 (M:Q ratio),

ii) a polydiorganosiloxane comprising units of formulae (R^ 3SiOi/2)ii and (R¾i02/2)hh ("D" units), where subscript hh is 20 to 1000 and subscript ii has an average value of 2, and

iii) an alkoxy-functional organohydrogensiloxane oligomer. The alkoxy-functional organohydrogensiloxane oligomer has unit formula

independently a monovalent hydrocarbon group as described above for R, subscript b is 0 or 1, subscript c is 0, subscripts f, h, i, and k have values such that 5 > f > 0, 5 > h > 0, subscript i is 0 or 1, subscript kk is 0 or 1, subscript m > 0, and a quantity (m + n + f + o + h + i + p + kk) < 50, with the proviso that > 90 mol% of all D groups in the endblocker are linear; and

iv) a hydrosilylation reaction catalyst.

Starting material i)

[0018] The siloxane resin used to prepare starting material B) is i) a siloxane resin comprising units of formulae (R^ 3S1O1 /2) and (S1O4/2), where each R^ is independently a monovalent hydrocarbon group, with the proviso that at least one R2' per molecule has terminal aliphatic unsaturation, where the siloxane resin has a molar ratio of (R^ 3S1O1 2) units (M units) to (S1O4/2) units (Q units) ranging from 0.5: 1 to 1.5: 1 (M:Q ratio), Starting material i) may contain an average of 3 to 30 mole percent of aliphatically unsaturated groups, alternatively 0.1 to 30 mole percent, alternatively 0.1 to 5 mole percent, alternatively 3 to 100 mole percent. The aliphatically unsaturated groups for R²' may have 2 to 18 carbon atoms. The aliphatically unsaturated groups for

R2' may be alkenyl groups, alkynyl groups, or a combination thereof. The mole percent of aliphatically unsaturated groups in the siloxane resin is the ratio of the number of moles of unsaturated group-containing siloxane units in the resin to the total number of moles of siloxane units in the resin, multiplied by 100. The remaining monovalent hydrocarbon groups for R^ may be, for example, alkyl or aryl groups of 1 to 18 carbon atoms.

[0019] Methods of preparing resins are known in the art. For example, resin may be prepared by treating a resin copolymer produced by the silica hydrosol capping process of Daudt, et al. with at least an alkenyl-containing endblocking reagent. The method of Daudt et al., is disclosed in U.S. Patent 2,676, 182.

[0020] The method of Daudt, et al. involves reacting a silica hydrosol under acidic conditions with a hydrolyzable triorganosilane such as trimethylchlorosilane, a siloxane such as

hexamethyldisiloxane, or mixtures thereof, and recovering a copolymer having M units and Q units. The resulting copolymers generally contain from 2 to 5 percent by weight of hydroxyl groups. [0021] The siloxane resin, which typically contains less than 2% of silicon-bonded hydroxyl groups, may be prepared by reacting the product of Daudt, et al. with an unsaturated organic group- containing endblocking agent and an endblocking agent free of aliphatic unsaturation, in an amount sufficient to provide from 3 to 30 mole percent of unsaturated organic groups in the final product. Examples of endblocking agents include, but are not limited to, silazanes, siloxanes, and silanes. Suitable endblocking agents are known in the art and exemplified in U.S. Patents 4,584,355;

4,591,622; and 4,585,836. A single endblocking agent or a mixture of such agents may be used to prepare the siloxane resin used as starting material i).

Starting material ii)

[0022] The polydiorganosiloxane used to prepare starting material B) comprises units of formulae (R² 3S101 2)11 and (R2Si02/2)hh (D units), where R and R² are as described above, subscript hh is 20 to 1000 and subscript ii has an average value of 2.

[0023] Alternatively, starting material ii) may comprise a polydiorganosiloxane of

Formula (Γ): R²R²SiO(R₂SiO)_a(RR²SiO)_bSiR²R²,

Formula (IF): R₃SiO(R₂SiO)_c(RR²SiO)_dSiR₃,

or a combination of both (Γ) and (IF);

where R is as described above and each R² is independently a monovalent hydrocarbon group having terminal aliphatic unsaturation, as described above for R² . Subscript a may be 0 or a positive number. Alternatively, subscript a has an average value of at least 2. Alternatively subscript a may have a value ranging from 2 to 2000. Subscript b may be 0 or a positive number. Alternatively, subscript b may have an average value ranging from 0 to 2000. Subscript c may be 0 or a positive number. Alternatively, subscript c may have an average value ranging from 0 to 2000. Subscript d has an average value of at least 2. Alternatively subscript d may have an average value ranging from 2 to 2000. Alternatively, each R is a monovalent hydrocarbon group exemplified by alkyl such as methyl and aryl such as phenyl. Alternatively, R² is exemplified by alkenyl groups such as vinyl, allyl, butenyl, and hexenyl; and alkynyl groups such as ethynyl and propynyl.

[0024] Starting material ii) may comprise a polydiorganosiloxane such as

i) dimethylvinylsiloxy-terminated polydimethylsiloxane,

ii) dimethylvinylsiloxy-terminated poly (dime thylsiloxane/methylvinylsiloxane) ,

iii) dimethylvinylsiloxy-terminated polymethylvinylsiloxane,

iv) trimethylsiloxy-terminated poly(dimethylsiloxane/methylvinylsiloxane),

v) trimethylsiloxy-terminated polymethylvinylsiloxane,

vi) dimethylvinylsiloxy-terminated poly(dimethylsiloxane/methylvinylsiloxane),

vii) dimethylvinylsiloxy-terminated poly(dimethylsiloxane/methylphenylsiloxane), viii) dimethylvinylsiloxy-terminated poly(dimethylsiloxane/diphenylsiloxane), ix) phenyl,methyl,vinyl-siloxy-terminated polydimethylsiloxane,

x) dimethylhexenylsiloxy-terminated polydimethylsiloxane,

xi) dimethylhexenylsiloxy-terminated poly(dimethylsiloxane/methylhexenylsiloxane), xii) dimethylhexenylsiloxy-terminated polymethylhexenylsiloxane,

xiii) trimethylsiloxy-terminated poly(dimethylsiloxane/methylhexenylsiloxane),

xiv) trimethylsiloxy-terminated polymethylhexenylsiloxane

xv) dimethylhexenyl-siloxy terminated poly(dimethylsiloxane/methylhexenylsiloxane), xvi) dimethylvinylsiloxy-terminated poly(dimethylsiloxane/methylhexenylsiloxane), or xvii) a combination of two or more of i), ii) iii), iv), v), vi), vii), viii), ix), x), xi), xii), xiii) xiv), xv), and xvi).

[0025] Methods of preparing polydiorganosiloxanes suitable for use as starting material ii) to prepare starting material B), such as hydrolysis and condensation of the corresponding

organohalosilanes or equilibration of cyclic polydiorganosiloxanes, are known in the art.

Starting material iii)

[0026] Starting material iii) is an alkoxy-functional organohydrogensiloxane oligomer. Starting material iii) may be prepared by a method comprising

1) reacting starting materials comprising:

(a) a polyorganohydrogensiloxane oligomer of unit formula (I):

(HR₂Si0_1/2)e( 3Si0_1/2)f(HRSi02/2)g( 2Si02/2)h(RSi03/2)i(HSi03_/2)_jj(Si04_/2)_kk, where R is as described above, and subscripts e, f, g, h, i, jj, and kk have values such that 5 > e > 0, 5 > f > 0, 10 > g > 0, 5 > h > 0, subscript i is 0 or 1, 5 > jj > 0, subscript kk is 0 or 1, with the proviso that a quantity (e + g + jj) > 2, and a quantity (e + f + g + h + i + jj + kk) < 50;

(b) an aliphatically unsaturated alkoxysilane of formula (II):

R²(R_c)Si(OR³)(3__c), where R and R² are as described above, each R^ is independently a monovalent hydrocarbon group of 1 to 8 carbon atoms, and subscript c is 0 or 1 ; and

(c) a selective hydrosilylation catalyst; and

optionally 2) isolating the alkoxy-functional organohydrogensiloxane oligomer prepared in step 1). Starting material iv)

[0027] Starting material iv) is a hydrosilylation reaction catalyst other than the catalyst used in preparation of starting material iii). Conventional catalysts for catalyzing hydrosilylation reaction are suitable, are known in the art, and are commercially available. Such hydrosilylation catalysts can be a platinum group metal, such as platinum. Alternatively, the hydrosilylation catalyst may be a compound of such a metal, for example, chloroplatinic acid, chloroplatinic acid hexahydrate, platinum dichloride, and complexes of said compounds with low molecular weight organopolysiloxanes or platinum compounds microencapsulated in a matrix or core/shell type structure. Complexes of platinum with low molecular weight organopolysiloxanes include 1,3- diethenyl-l,l,3,3-tetramethyldisiloxane complexes with platinum. These complexes may be microencapsulated in a resin matrix. Exemplary hydrosilylation catalysts are described in U.S. Patents 3,159,601; 3,220,972; 3,296,291; 3,419,593; 3,516,946; 3,814,730; 3,989,668; 4,784,879; 5,036,117; and 5,175,325 and EP 0 347 895 B. Microencapsulated hydrosilylation catalysts and methods of preparing them are known in the art, as exemplified in U.S. Patents 4,766,176 and 5,017,654. Combining the starting materials may be performed at elevated temperature, such as heating at 50°C to 250°C.

[0028] The polyalkoxy functionalized silicone resin-polymer blend are synthesized by reacting starting materials i), ii), and iii), in the presence of catalyst iv) in the temperature range of 50-250°C.

[0029] The amount of component B in the adhesive of this invention, when used, is present in amounts of at least 5 weight%, alternatively at least 10 weight percent, alternatively at least 15 weight percent but no more than 90 weight percent, alternatively no more than 50 weight percent, alternatively no more than 35 weight percent with all percentages being based on total amounts of those components A-D which are used in the adhesive formulation.

Component C

[0030] Optional component C in the adhesive composition described above is a condensation reaction catalyst. The condensation reaction catalyst may be selected from common condensation catalysts that are effective for silanol-silanol condensation reaction, include organometallic compounds, amines, and a wide range of organic and inorganic bases and acids. Organometallic compounds include organic compounds of tin, titanium, zinc, zirconium, hafnium, and others. The condensation reaction catalysts can be an organotin compound and an organotitanium compound.

Exemplary organotin compounds may be selected from the group consisting of: a) stannic salts of carboxylic acids such as i) dibutyl tin dilaurate, ii) dimethyl tin dilaurate, iii) di-(n-butyl)tin bis- ketonate, iv) dibutyl tin diacetate, v) dibutyl tin maleate, vi) dibutyl tin diacetylacetonate, vii) dibutyl tin dimethoxide, viii) carbomethoxyphenyl tin tris-uberate, ix) dibutyl tin dioctanoate, x) dibutyl tin diformate, xi) isobutyl tin triceroate, xii) dimethyl tin dibutyrate, xiii) dimethyl tin di- neodeconoate, xiv) dibutyl tin di-neodeconoate, xv) triethyl tin tartrate, xvi) dibutyl tin dibenzoate, xvii) butyltintri-2-ethylhexanoate, xviii) dioctyl tin diacetate, xix) tin octylate, xx) tin oleate, xxi) tin butyrate, xxii) tin naphthenate, xxiii) dimethyl tin dichloride; b) tin (II) salts of organic carboxylic acids such as xxiv) tin (II) diacetate, xxv) tin (II) dioctanoate, xxvi) tin (II) diethylhexanoate, xxvii) tin (II) dilaurate, c) stannous salts of carboxylic acids such as xxviii) stannous octoate, xxix) stannous oleate, xxx) stannous acetate, xxxi) stannous laurate, xxxii) stannous stearate, xxxiii) stannous naphthanate, xxxiv) stannous hexanoate, xxxv) stannous succinate, xxxvi) stannous caprylate, and a combination of two or more of i) to xxxvi). Exemplary organotitanium compounds may be selected from the group consisting of: i) tetra-n-butyl titanate, ii) tetraisopropyl titanate, iii) tetra-t-butyl titanate, iv) tetrakis(2-ethylhexyl) titanate, v) acetylacetonate titanate chelate, vi) ethyl acetoacetate titanate chelate, vii) triethanolamine titanate chelate, and a combination of two or more of i), ii), iii), iv), v), vi) and vii).

[0031] The amount of condensation reaction catalyst in the adhesive composition depends on various factors including the selection of the other starting materials, whether any additional starting materials are added, and the end use of the adhesive composition. However, the condensation reaction catalyst, when used, is preferably present in an amount of at least 0.01 weight %, more preferable at least 0.1 weight % and in some embodiments at least 0.5 weight %, but preferably no more than 25 weight%, preferably no more than 15 weight%, more preferably no more than 10 weight percent, more preferably still no more than 5 weight percent and most preferably in some embodiments no more than 1 weight % based on based on total amounts of those components A-D which are used in the adhesive formulation.

Component D

[0032] Component D in the adhesive composition described above is a free radical initiator. The free radical initiator may comprise an azo compound or an organic peroxide compound. Suitable azo compounds include azobenzene, azobenzene-p-sulfonic acid, azobisdimethylvaleronitrile, azobisisobutyronitrile, and a combination thereof. Suitable organic peroxide compounds include dialkyl peroxides, diaryl peroxides, diacyl peroxides, alkyl hydroperoxides, and aryl

hydroperoxides. Specific organic peroxide compounds are exemplified by benzoyl peroxide; dibenzoyl peroxide; 4-monochlorobenzoyl peroxide; dicumyl peroxide; tert-butylperoxybenzoate; tert-butyl cumyl peroxide; tert-butyloxide 2,5-dimethyl-2,5-di-tert-butylperoxyhexane; 2,4- dichlorobenzoyl peroxide; di-tertbutylperoxy-diisopropyl benzene; l, l-bis(tert-butylperoxy)-3,3,5- trimethylcyclohexane; 2,5-di-tert-butylperoxyhexane-3,2,5-dimethyl-2,5-bis(tert-butylperoxy) hexane; cumyl-tert-butyl peroxide; or combinations of two or more thereof.

[0033] The amount of free radical initiator added to the adhesive composition depends on various factors including the type and amount of condensation reaction catalyst selected and the selection of other starting materials in the adhesive composition, however, the free radical initiator may be present in an amount of at least 0.1 weight %, alternatively 0.2%, and preferably 0.3weight % but no more than 5 weight %, alternatively no more than 3 weight %, and alternatively no more than 2 weight%, based on total amounts of those components A-D which are used in the adhesive formulation.

Optional additives [0034] The adhesive composition described above may further comprise one or more optional ingredients (distinct from and added in addition to component A), B), C), and D) described above). The optional ingredients selected from the group consisting of E) a dual cure compound, F) an adhesion promoter, G) a corrosion inhibitor, H) a rheology modifier, I) a drying agent, J) a crosslinker, K) a filler, L) a spacer, M) an acid scavenger, N) a silanol functional

polydiorganosiloxane, O) a fluorescent optical brightener, P) a chain transfer agent, Q) a

(me th) aery late monomer, R) a poly-alkoxy terminated polydiorganosiloxane, S) a colorant, and two or more of E), F), G), H), I), J), K), L), M), N), O), P), Q), R), and S).

[0035] The adhesives are used simply by applying the adhesive and curing. The cure of the adhesives can be achieved thermally in 50-170°C range, preferably 70°C or higher. The adhesive composition provides excellent performance on variety of metals without priming or surface treatment. The adhesion performance on plastics with medium to high surface energy was satisfactory as well. It can be sued for metal-metal bonding and metal-plastic bonding.

Ingredients and Components

SFD-120 Vinyl terminated polydimethylsiloxane, Reactant (Dow Silicone DP=600-700 Corporation)

3-1719 Trimethoxysilyl terminated Adhesion promoter (Dow polydimethylsiloxane, DP=300-400 Silicone Corporation)

OS-20 Hexamethyldisiloxane Solvent (Dow Silicone

Corporation)

ETS-900 Dimethyldiacetoxysilane: Reactant (Dow Silicone (OFS-1579) Diethyldiacetoxysilane=50:50% wt Corporation)

Stripped MH-1109 Mixture of tetramethylcyclotetrasiloxane, Reactant (Dow Silicone pentamethylcyclopentasiloxane, and Corporation) hexamethylcyclothexsiloxane, overall Si-H

1.6% wt

Allyl methacrylate Reactant

(Mitsui)

2-0707 Platinum(O)- 1 ,3-divinyl- 1,1,3,3- Hydrosilylation catalyst tetramethyldisiloxane complex in PDMS, (Dow Silicone

Pt concentration=5,000 ppm Corporation)

Butylated Free radical inhibitor hydroxytoluene (BHT) (Sigma-Aldrich)

MTM (Z-6070) Methyltrimethoxysilane Drying agent and

crosslinker (Dow Silicone Corporation)

VTMS Vinyltrimethoxysilane Reactant (Dow Silicone

Corporation)

ATMS Allyltrimethoxysilane (structure below) Reactant (Dow Silicone

Corporation)

—o

Diallyl maleate Pt chelator/quencher

(Bimax Chemicals)

Allyltrimethylsilane (structure below) Reactant (Dow Silicone

Corporation)

1-Octene Reactant

Method of measurement of surface wetness of the adhesives.

[0036] The thin films of adhesives in this invention were made by a draw-down bar with 50 mil gap (1.27 mm) on aluminum Q-panels (3.5x10 inches) obtained from Q-Lab. The films were cured in an oven in air at 100 °C for an hour. The films were allowed to cool to room temperature for 15 minutes, before their surface wetness was measured.

[0037] The surface wetness is quantified by the impact test.

[0038] The impact test was carried out on a drop impact tester (Qualtech Products). A pre-weighed filter paper (Gilman, quantitative, Grade 2) was place on a cured adhesive film (Thickness: 50 mil, 1.27 mm) on aluminum Q-panel (3.5x10"). A steel block (0.3 Kg) was dropped from a height of 30 cm onto a cylindrical metal bar which makes an imprint on the filter paper. The drop was repeated a couple of times at different areas of the filter paper. The filter paper was carefully peeled off the specimen and weighed. The difference before and after the impact in milligrams is referred as the surface wetness of the sample.

Synthetic example 1 (Comparative)

A. Preparation of siloxane with end clusters and only alkylacrylate reactive groups. (Comparative)

[0039] In a typical synthesis, to a 10 liter Turello mixer was added MB-2030 (2897 grams), SFD- 120 polymer (1636 grams), OS-20 fluid (271 grams), and ETS-900 (aka OFS-1579, 4.89 grams). The mixture was inerted using nitrogen purge and stirred for 10 minutes (dissolving blades=500 rpm; scraper blade=20 rpm). To the homogenized mixture was added butylated hydroxytoluene (1.4 grams), stripped MH-1109 (98.8 grams), and allyl methacrylate (233 grams). The mixture was stirred for an additional 10 minutes at room temperature (250 rpm; 20 rpm), at which point a platinum catalyst (2-0707, 6.4 grams) was added to the mixture. The mixture was stirred for 10 additional minutes (250 rpm; 20 rpm) before setting the temperature at 60 °C. The temperature was held for 30 minutes at 60 °C before cooling, and diallyl maleate (6.4 grams) was added when temperature dipped below 50 °C. The mixture was then cooled to less than 30°C before adding MTM (Z-6070, 44.2 grams). The mixture was then heated to 60°C and held for 30 minutes (250 rpm; 20 rpm), wherein the temperature was increased to 85°C and a vacuum of 5-6 Torr was applied for 40 minutes. This polymer was obtained as a white viscous paste. Yield: 4500 grams.

B. Formulation of the adhesive from component A. (Comparative)

[0040] In a 10 liter Turello mixer, the polymer of Comparative Example 1, part A above (2200 grams), IT EA-3013 ETM Resin/Polymer (593 grams), 3-1719 (3 grams), and Tinopal OB (0.61 gram) were loaded. The mixture was mixed for 10 minutes at 10 °C (200 rpm; 20 rpm). To the homogeneous mixture was added benzoyl peroxide paste (Perkadox L-50S-ps, 90.48 grams), Z-6030 silane (60.4 grams), triallyl isocyanurate (15 grams), and a solution of 2-mercaptobenzothiazole (4.6 grams) in A186 (aka KBM-303, 18.1 grams). The mixture was mixed again for 10 minutes at 10 °C (200 rpm; 20 rpm). Solutions of tri-n-butyl titantate (18.7 grams) in IBTMS (Z-2306, 56.7 grams) and Al 110 (3.4 grams) in IBTMS (3.4 grams) were added. The prep was mixed again for 10 minutes at 10 °C (200 rpm; 20 rpm). The final product was degassed at 10 °C at 200 Torr of vacuum for 30 minutes.

[0041] Comparative example a and b are prepared substantially following Synthetic example 1.

Synthetic example 2. Preparation of inventive adhesive.

A. Synthesis of alkoxysilyl-modified polymer with cyclic clustered end groups

[0042] In a typical synthesis, to a 10 liter Turello mixer was added MB-2030 (2897 grams), SFD- 120 polymer (1636 grams), OS-20 fluid (271 grams), and ETS-900 (aka OFS-1579, 4.89 grams). The mixture was inerted using nitrogen purge and stirred for 10 minutes (dissolving blades=500 rpm; scraper blade=20 rpm). To the homogenized mixture was added butylated hydroxytoluene (1.4 grams), stripped MH-1109 (98.8 grams), an alkoxysilane with vinyl functionality (5-25% mol based on allyl methacrylate), and allyl methacrylate (217.5 grams). The mixture was stirred for an additional 10 minutes at room temperature (250 rpm; 20 rpm), at which point a platinum catalyst (2- 0707, 6.4 grams) was added to the mixture. The mixture was stirred for 10 additional minutes (250 rpm; 20 rpm) before setting the temperature at 60 °C. The temperature was held for 30 minutes at 60 °C before cooling, and diallyl maleate (6.4 grams) was added when temperature dipped below 50 °C. The mixture was then cooled to less than 30°C before adding MTM (Z-6070, 44.2 grams). The mixture was then heated to 60°C and held for 30 minutes (250 rpm; 20 rpm), wherein the temperature was increased to 85°C and a vacuum of 5-6 Torr was applied for 40 minutes. Alkoxysilyl-modified dumbbell polymer was obtained as a white viscous paste. Yield: 4500 grams.

B. The alkoxysilyl-modified dumbbell polymer was formulated into adhesive following step B in the Comparative Synthetic Example 1. Sample 1-6 are prepared following Synthetic example 2.

Comparative Synthetic example 3. Preparation of adhesive with alkylsilane-modified dumbbell polymer.

A. Synthesis of alkylsilyl-modified dumbbell polymer

[0043] In a typical synthesis, to a 10 liter Turello mixer was added MB-2030 (2897 grams), SFD- 120 polymer (1636 grams), OS-20 fluid (271 grams), and ETS-900 (aka OFS-1579, 4.89 grams). The mixture was inerted using nitrogen purge and stirred for 10 minutes (dissolving blades=500 rpm; scraper blade=20 rpm). To the homogenized mixture was added butylated hydroxytoluene (1.4 grams), stripped MH-1109 (98.8 grams), an alkylsilane with vinyl functionality or a hydrocarbon alkene (5-25% mol based on allyl methacrylate), and allyl methacrylate (217.5 grams). The mixture was stirred for an additional 10 minutes at room temperature (250 rpm; 20 rpm), at which point a platinum catalyst (2-0707, 6.4 grams) was added to the mixture. The mixture was stirred for 10 additional minutes (250 rpm; 20 rpm) before setting the temperature at 60 °C. The temperature was held for 30 minutes at 60 °C before cooling, and diallyl maleate (6.4 grams) was added when temperature dipped below 50 °C. The mixture was then cooled to less than 30°C before adding MTM (Z-6070, 44.2 grams). The mixture was then heated to 60°C and held for 30 minutes (250 rpm; 20 rpm), wherein the temperature was increased to 85°C and a vacuum of 5-6 Torr was applied for 40 minutes. Alkylsilyl-modified dumbbell polymer was obtained as a white viscous paste. Yield: 4500 grams. B. The alkylsilyl-modified dumbbell polymer was formulated into adhesive following step B in Comparative Example 1.

[0044] Comparative Samples 7-8 are prepared following Synthetic example 3. Example 4. The efficacy of the alkoxysilyl-modified dumbbell

[0045] Surface wetness comparison of unmodified adhesive (Comparative example a, b) and vinyltrimethoxysilane (VTMS) modified adhesive at 3 different loading levels (Sample 1-3). As is shown the VTMS modified adhesive dried in 22 hours or less compared to over 200 hours for the adhesives like those from Comparative example 1.

Table 1. Comparison of the performance of unmodified adhesive (Comparative example a, b) and

VTMS modified adhesives (Sample 1-3).

[0046] Surface wetness comparison of unmodified adhesive (Comparative example a, b) and allyltrimethoxysilane (ATMS) modified adhesive at 3 different loading levels (Sample 4-6). As shown in the tables the ATMS modified inventive adhesive polymer dried in less than about 20 hours as compared to over 200 hours for the Comparative Example 1.

Table 2. Comparison of the performance of adhesives in Comparative example a, b and ATMS modified adhesives (Sample 4-6).

Example 5. Alkoxysilyl vs. Alkylsilyl group.

[0047] 1-ocetene and allyltrimethylsilane-modified adhesives were prepared according to Example

3 (Sample 7 and 8). Surface wetness of an ATMS-modified new adhesive (Sample 6) and Sample 7 and 8 were compared (Table 3). The loading level of all modifiers is 12.5% mol. This example demonstrates that having a hydrolysable functional group is important to reducing drying time as allylmethylsilane and 1-octene-modified adhesives still have dry times in excess of 40 hours. Table 3.

Example 6. Adhesion performance.

[0048] Adhesion performance of Comparative Example a, b and sample 1-8 were compared in Table 4. The adhesion strength was determined by lap shear method.

Table 4.

Claims

WHAT IS CLAIMED IS:

1. A curable siloxane polymer comprising a backbone of the following siloxane repeat units:

Rl

I

-[Si-0]j- I

Rl where j is an integer of at least 50, and Rl is independently in each occurrence H or an alkyl group of 1 to 4 carbon atoms or an aryl group of 6-12 carbon atoms, wherein the siloxane polymer is characterized by end groups are clusters formed from siloxane units and the clusters are functionalized by the presence of at least two functional reactive groups per cluster and at least one functional reactive group is a free radical polymerizable group and at least one functional reactive group is an alkenylalkoxysilane groups and the amount of free radically polymerizable group is at least 2 mole percent of the total moles of functional reactive groups in the polymer.

2. The polymer of claim 1 wherein there are at least 3 functional reactive groups per cluster.

3. The polymer of any of the preceding claims wherein the amount of free radically polymerizable group is less than 30 mole based on total moles of functional reactive groups.

4. The polymer of claim 1 wherein having the formula

where DMs a single bond or is a divalent hydrocarbon group of 1 to 20 carbon atoms, k is independently in each occurrence from 0 to 12, R is independently in each occurrence (a) a monovalent hydrocarbyl groups or monovalent hydrocarbyl groups substituted with a halogen or a hetero atom such as oxygen or nitrogen, (b) free radical polymerizable group or (c) an

alkenylalkoxysilane group, provided at least two of R on each ring are selected from (b) and (c), and the amount of alkenylalkoxysilane is at least 2 mole percent and no more than 30 mole percent based on total moles of free radical polymerizable groups and alkenylalkoxysilane groups present.

5. The polymer of claim 4 wherein k is 1 or 2.

6. The polymer of any one of the preceding claims wherein the free radical polymerizable group is an aery late or alkylacrylate containing group.

7. The polymer of any one of the preceding claims wherein the alkeylalkoxysilane group is selected from the group consisting of vinyltrimethoxysilane, vinylmethyldimethoxysilane, allyltrimethoxysilane, allylmethyldimethoxysilane, 3-butenyltrimethoxysilane,

3-butenylmethyldimethoxysilane, 4-pentenyltrimethoxysilane, 4-pentenylmethyldimethoxysilane,

5- hexenyltrimethoxysilane, 5-hexenylmethyldimethoxysilane, 6-heptenyltrimethoxysilane,

6- heptenylmethyldimethoxysilane, 7-octenyltrimethoxysilane, 7-octenylmethyldimethoxysilane,

8- nonenyltrimethoxysilane, 8-nonenylmethyldimethoxysilane, 9-decenyltrimethoxysilane,

9- decenylmethyldimethoxysilane, 10-undecenyltrimethoxy silane, and

10- undecenylmethyldimethoxy silane .

8. The polymer of any one of the preceding claims wherein the free radical polymerizable group is selected from the group consisting of methyl methacrylate, methyl acrylate, butyl methacrylate, 2-ethylhexylacrylate, and 2-ethylhexylmethacrylate.

9. The polymer of any one of claims 4-8 wherein the alkenylalkoxysilane is o more than 15 mole percent based on total moles of free radical polymerizable groups and

alkenylalkoxysilane groups present.

10. An adhesive comprising the polymer of any one of claims 1-9 and a free radical initiator.

11. The adhesive of claim 10 further comprising a poly-alkoxy endblocked silicone resin-polymer blend.

12. The adhesive of claims 10 or 11 further comprising a condensation reaction catalyst.

13. The adhesive of claim 12 wherein the amount of the polymer a is at least 10 weight percent, the amount of the poly-alkoxy endblocked silicone resin-polymer blend is in the range of 10 to 50 weight percent, the amount of condensation reaction catalyst is in the range of 0.1 to 5 weight percent, and the amount of free radical initiator is in the range of 0.1 to 3 weight percent based on total weight of the polymer, the poly-alkoxy endblocked silicone resin-polymer blend, the condensation reaction catalyst, and the free radical initiator.

14. The adhesive of any one of claims 10-13 further comprising one or more of the following ingredients dual cure compound, an adhesion promoter, a corrosion inhibitor, a rheology modifier, a drying agent, a crosslinker, a filler, a spacer, an acid scavenger, a silanol functional polydiorganosiloxane, a fluorescent optical brightener, a chain transfer agent, a (meth)acrylate monomer, a poly-alkoxy terminated polydiorganosiloxane, and a colorant.

15. A process comprising applying the adhesive of any one of claims 10-14 to a substrate and curing at a temperature of at least 70°C.