REDOX-INDUCED CATIONICALLY POLYMERIZABLE COMPOSITIONS WITH LOW CURE TEMPERATURE

BACKGROUND OF THE INVENTION

[0001] This invention relates to a redox-induced cationically polymeπzable composition that exhibits reduced cure temperature and to a method for reducing the cure temperature of a cationically polymeπzable composition.

[0002] In many manufacturing processes, processing speed leads to higher throughput and lower assembly costs When the use of an adhesive, coating, or encapsulant is part of the manufacturing process, processing speed can be increased if the adhesive, coating, or encapsulant can be cured quickly at a relatively low curing temperature

[0003] In the electronics packaging industry, for example, low temperature, fast (snap) cure adhesives and encapsulants are desired for various applications. A common mode of eiectronic packaging involves affixing semiconductor devices onto substrates by means of an adhesive or encapsulant. The more prominent uses are the bonding of integrated circuit chips to metal lead frames or organic substrates, and the bonding of circuit packages or assemblies to printed wire boards, including, for example, die attach for array package, die attach for RFID package, and component attach for ink jet cartridge assembly. For ink jet cartridge, low temperature cure assembly can minimize jetting trajectory distortion and improve printing quality For temperature-sensitive components or substrates, such as, the paper-based antenna in RFID application and camera sensor in organic substrates, low temperature interconnect is very desirable Thus, there is a need for polymeπzable compositions that cure at low temperatures, preferably iess than 100 ⁰ C

SUMMARY OF THE INVENTION

[0004] This invention is a polymeπzable composition comprising (ι) a cationicaliy polymeπzable resin, (ιι) an onium salt, (in) an azo or peroxide initiator, and (iv) an

electron-rich vinyl resin

[0005] In another embodiment, this invention is a polymeπzable composition comprising (i) a cationicaiiy polymerizable resin, (ιι) an onium salt, (iii) an azo or peroxide initiator, and (iv) a catalytic or substoichiometric amount of an electron-rich vinyl resin

[0006] In another embodiment, this invention is method for reducing the cure temperature of a cationicaiiy poSymeπzable resin, in which the cure of the resin is catalyzed by the addition of an onium salt and an azo or peroxide initiator to the resin, the method comprising adding an electron-rich vinyl resin to the mixture of resin, onium salt and azo or peroxide initiator

[0007] In another embodiment, this invention is method for reducing the cure temperature of a cationicaiiy polymerizable resin, in which the cure of the resin is catalyzed by the addition of an onium salt and an azo or peroxide initiator to the resin, the method comprising adding a catalytic or substoichiometric amount of an eiectron-rich vinyl resin to the mixture of resin, onium salt and azo or peroxide initiator

DETAILED DESCRIPTION OF THE INVENTION

[0008] The reaction scheme for the cationic polymerization using onium salt and an azo initiator, in the presence of an electron-rich vinyl species, occurs as depicted here-

cationic polymerization actual initiating species in which R and R ¹ are any organic moiety.

[0009] Peroxide can also be used to generate a radical for reaction with the onium salt

[0010] As used within this specification and claims, a curable resin is one that is polymeπzable with or without crosslinking Curable and poiymeπzable are used interchangeably and a cationically curable resin or composition is one that is poiymeπzable Any cationically polymeπzable resin may be used in the above reaction Exemplary cationically polymerizable resins include oxetanes, epoxies, spiroorthocarbonates, spiroorthoesters, and benzoxazines, or a mixture of any of those

[0011] Suitable oxetane resins are those disclosed in US patents 7,034,064, 6,982,338, 6,953,862, 6,943,258, 6,753,434, and those available from Toagosei Corporation under the tradenames OXT-221 , OXT-121 , OXT-101 , OXT-212, OXT-211 , CHOX ₁ OX-SC, PNOX-1009, having the structures

OXT-101 OXT-221 OXT-212

[0012] Suitable epoxy resins include bisphenol epoxies, naphthalene epoxies, and aliphatic type epoxies Commercially available materials include bisphenol type epoxy resins (for example, those sold under the tradenames EPICLON 830LVP, 830CRP, 835LV, 850CRP, available from Dainippon Ink & Chemicals, lnc ), naphthalene type epoxy resins (for example, those sold under the tradenames EPICLON HP4032, available from Dainippon Ink & Chemicals, lnc ), aliphatic epoxy resins (for example, those sold under the tradenames ARALDITE CYI 79, 184, 192, 175, 179, available from Ciba Specialty Chemicals, EPOXY 1234, 249, 206, available from Dow Corporation, and EHPE-3150, available from Daicel Chemical Industries, Ltd )

[0013] Other suitable epoxy resins include cycloaliphatic epoxy resins, for example, 3,4- epoxy-cyciohexylmethyl 3,4-epoxycyclohexanecarboxylate , available as ERL-4221 from Union carbide and ARALDITE CY-179, available from Ciba-Geigy, diglycidylester of hexahydro-phthahc anhydride, available as CY-184 from Ciba-Geigy, bιs(3,4- epoxycyclohexylmethyl)-adιpate, available as ERL-4229 from Union carbide, and other bisphenol-A type epoxy resins, bisphenol-F type epoxy resins, epoxy novolac resins, biphenyl type epoxy resins, naphthalene type epoxy resins, and dicyclopentadienephenol type epoxy resins, all commercially available from different sources

[0014] Exemplary spiroorthocarbonate and vinyl spiroorthocarbonates include those having the following structures

[0015] Exemplary electron-rich vinyl spirocarbonates include those having the following structures:

[0016] Exemplary spiroorthoesters include

which Piv is a trimethylacetyl group

[0017] An exemplary electron-rich vinyl spiroorthoester is

[0018] Suitable benzoxazines include those compounds containing the structure

which R and R are any organic moiety, including another benzoxazine structure

[0019] Exemplary benzoxazine compounds include those of the formulae

in which R ¹ is a divalent radical that may be aliphatic, aromatic, or a combination of aliphatic and aromatic, and that may contain heteroatoms, such as oxygen, nitrogen, sulfur, phosphorous, or halogen, or that may be a single bond, or that may be S, S ₂ , SO, SO ₂ , O, or CO, and R ² is hydrogen, an alkyl or substituted alkyl, an aromatic or substituted aromatic

[0020] Specific suitable benzoxazine compounds include

[0021] In addition to compounds such as the above, the benzoxazine may also be present in a polymeric species, such as depicted in the following structure:

which R ¹ is as described above, π is an integer that will vary depending on the polymeric composition from which the benzoxazine depends, and each Q is a polymeric entity, for example, polyurethane, polyether, polyester, poly(butadιene) or polystyreπic

[0022] Exemplary onium salts include iodonium salts, sulfonium salts, diazonium salts, ammonium salts or a mixture of those salts In one embodiment, the onium salt is an

X iodonium salt of the formula © in which R is independently seiected from phenyl, halophenyl, (for example, chlorophenyl) and C ₁ -C ₂₀ alkylphenyl (for example, dodecyl phenyl) X is any suitable counter anion, for example, a halogen anion, CF ₃ SO ₃ , C ₆ H ₅ SO ₃ ^' , NO ₃ ^" , AsF ₆ ^" , SbF ₆ ^" , FeCI ₄ ^" , SbCI ₆ ^" , BF ₄ ^" , PF ₆ ^" , and (C ₆ F ₅ )B ^"

[0023] Commercially available iodonium salts include (p-lsopropylphenyj)(p- methylphenyl) iodonium tetrakιs(pentafluorophenyl)borate from Gelest as RHODORSIL 2074, and bisdodecyl phenyliodonium hexafluoroantimonate as UV 9380 from General Electric The onium salts are used in an effective amount In one embodiment, an effective amount is in the range of 0 1 to 10% by weight of the total resin

[0024] Exemplary azo initiators include, for example, azoisobutylonitπle, 2,2"- azobispropane, 2,2'-azobis(2-methylbutanenitnle), and m.m'-azoxystyrene Commercially available azo initiators are those available from Wako Specialty Company, such as those sold under the tradenames VA-044, VA-057, VA-085, V-70, VF-096, V-65, V-601 , V-59, V-40, VF-096, V-30, and those available from Akzo Nobel, such as those sold under the tradenames PERKADOX ACCN, PERKADOX AIBN ₁ PERKADOX AMBN-GR, and those available from Dupont, such as those sold under the tradenames VAZO-52, VAZO-64, VAZO-67 and VAZO-88 The azo initiators are used in an effective amount In one embodiment an effective amount ranges from 0 1 to 10% by weight of the total resin

content

[0025] Exemplary peroxide initiators include those commercially available from Akzo Nobel, such as those sold under the tradenames PERKADOX and TRIGONOX Other peroxide initiators are suitable, provided they generate radicals with the vinyl resin for reaction with the onium salt Exemplary peroxides include benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, butyl peroctoate, dicumyl peroxide, acetyl peroxide, para- chlorobenzoyl peroxide and di-t-butyl diperphthalate The peroxide initiators are used in an effective amount In one embodiment an effective amount ranges from 0 1 to 10% by weight of the total resin content

[0026] Exemplary electron-rich vinyl resins include vinyl ethers, spirocyctic vinyl ethers, styrenics (compounds containing a styrene moiety), cinnamyls (in this specification and claims compounds containing a cinnamyl moiety), N-vιnylamιdes, and N-vinylamines

[0027] Suitable vinyl ether resins include, for example, poly(butadιenes), poly(carbonates), poiy(urethanes), poly(ethers), poly(esters), simple hydrocarbons, and simple hydrocarbons containing functionalities such as carbonyl, carboxyl, amide, carbamate, urea, ester, or ether, which also contain vinyl ether functionality Suitable commercially available vinyl ether resins include cyclohexane-dimethanol divinylether, dodecylvinylether, cyclohexyl vinylether, 2-ethylhexyl vinylether, dipropyleneglycol divinylether, hexanediol divinylether, octadecylvinylether, and butandiol divinylether, available from International Specialty Products (ISP), vinyl ethers sold under the tradenames VECTOMER 4010, 4020, 4030, 4040, 4051 , 4210, 4220, 4230, 4060, 5015 available from Sigma-Aldrich, lnc

[0028] Suitable spirocyciic vinyl ethers include, for example, those having the structures

[0029] Suitable styrenic resins include, for example, those disclosed in US patents

6,953,862, 6,908,969, 6,908,957, 6,809,155, 6,803,406, 6,716,992, 6,441 ,213, 6,441 ,121, 6,307,001 , 6,300,456, and those commercially available styrene, substituted styrenics, divinyl benzene, diphenylethylene, and any other resins possessing styrenic functionality (hereinafter styrenics) Such resins can be, for example, polyesters, carbamates, ureas Exemplary styrenic resins include compounds having the following structures in which R is an aliphatic or aromatic hydrocarbon, including those with heteroatoms.

[0030] Suitable cinnamyl resins include, for example, those disclosed in US patents 6,943,258, 6,753,434, 6,716,992, 6,908,969, 6,908,957, 6,809,155, 6,803,406, 6,753,434, 6,570,032, 6,441,121, 6,307,001 , 6,300,456 The cinnamyl compounds can be any small molecule, oligomeπc, or polymeric material that contains a cinnamy! functionality

represented by the structural formula , hereinafter, cinnamyls

[0031] Suitable commercially available N-vinylamide resins include, for example, N-vιnyl- pyrrohdone, N-vinylformamide, and N-vinylcaprolactone

[0032] Suitable commercially available N-vιnylamιnes include, for example, N- vinylcarbazole, N-vinylpyrrole, N-vinylimidazole, and 2-methyl-N-vιnylιmidazole

[0033] In another embodiment, this invention is a method for polymerizing a cationically polymeπzable composition of one or more cationically polymeπzable monomers comprising reacting the cationically polymeπzable composition in the presence of an onium salt, an azo or peroxide initiator, and an electron-rich vinyl resin The components

of such cationically poiymeπzable composition are as described earlier in this specification

[0034] In another embodiment, this invention is a method for polymerizing a cationically poiymeπzable composition of one or more cationically polymeπzable monomers comprising reacting the cationically polymeπzable composition in the presence of an oπium salt, an azo or peroxide initiator, and a catalytic or substoichiometric amount of an electron-rich vinyl resin The components of such cationically polymeπzable composition are as described earlier in this specification

[0035] In another embodiment, this invention is a method for lowering the cure temperature of a cationically polymeπzable composition comprising one or more cationically polymeπzable monomers, an onium salt, and an azo or peroxide initiator, the method comprising adding to the cationically polymeπzable composition an electron-rich vinyl resin. The components of such cationically polymerizable composition are as described earlier in this specification

[0036] In another embodiment, this invention is a method for lowering the cure temperature of a cationicaliy polymerizable composition comprising one or more cationically polymerizable monomers, an onium salt, and an azo or peroxide initiator, the method comprising adding to the cationically polymerizable composition a catalytic or substoichiometric amount of an electron-rich vinyl resin The components of such cationically polymerizable composition are as described earlier in this specification.

[0037] In another embodiment, this invention is a two-part cationicaiiy polymerizable composition, one part comprising cationically poiymeπzable monomer and an onium salt, and the second part comprising cationically poiymeπzable monomer and an azo or peroxide initiator Either the first part or the second part, or both, will contain an electron- rich vinyl resin. The components of these parts have been described earlier in this specification The two parts may be mixed mechanically just before dispensing

[0038] In another embodiment, this invention is a two-part cationically polymerizable composition, one part comprising cationically polymerizabie monomer and an onium salt,

and the second part comprising cationically polymeπzable monomer and an azo or peroxide initiator Either the first part or the second part, or both, will contain a catalytic or substoichiometric amount of an electron-rich vinyl resin The components of these parts have been described earlier in this specification The two parts may be mixed mechanically just before dispensing.

[0039] These two part polymerizations can occur simultaneously or independently, depending on the choice of specific azo or peroxide initiator and the temperature at which the initiator decomposes and forms the initiating radical species. Both the cationic polymerization of the cationic polymeπzable materials and the radical polymerization of the viny! monomers will occur below 100°C with the appropriate choice of initiator

[0040] In other embodiments, the polymerization of one or more cationically polymenzable monomers, in which the polymerization mix further comprises an onium salt, an azo or peroxide initiator, and an electron-rich vinyl resin, can be performed in the presence of one or more other vinyl monomers, such as, acrylates, methacrylat.es, maleimides, maleates, or fumarates, or a mixture of those {that is, vinyl monomers that are not typically denominated as electron-rich) In this polymerization, the azo or peroxide initiator will initiate the radical polymerization of these other vinyl monomers The cationic polymerization of the cationic polymeπzable materials and the radical polymerization of these vinyl monomers can occur simultaneously or independently, depending on the choice of specific azo or peroxide initiator and the temperature at which the initiator decomposes and forms the initiating radical species In any case, the initiators can be chosen so that curing occurs at 100 ^D C or lower

[0041 ] In other embodiments, the polymerization of one or more cationically polymenzable monomers, in which the polymerization mix further comprises an onium salt, an azo or peroxide initiator, and an electron-rich vinyl resin can be performed in the presence of a substoichiometric amount of one or more other vinyl monomers, such as, acrylates, methacrylates, maleimides, maleates, or fumarates, or a mixture of those In this embodiment, the cationic polymerization is initiated by a cationic macroinitiator generated by radical polymerization and followed by oxidation as shown in the below reaction scheme. The two polymerization processes are dependent To generate the

macroinitiator, the electron-rich vinyl resin should be present in slight excess in comparison to the other vinyl resin. This embodiment works well in a two part system, in which one part contains the cationically polymerizable resin and the second contains the electron-rich vinyl resin and the other vinyl resin.

[0042] Suitable acrylate and methacrylate resins include those having the generic

which n is 1 to 6, R ¹ is -H or -CH ₃ . and X ² is an aromatic or aliphatic group. Exemplary X ² entities include poly(butadienes), poly-(carbonates), poly(urethanes), poly(ethers), poly(esters), simple hydrocarbons, and simple hydrocarbons containing functionalities such as carbonyl, carboxyl, amide, carbamate, urea, ester, or ether. Commercially available materials include butyl (meth)acrylate, isobutyl (meth)acryiate, 2-ethyi hexyl (meth)acrylate, isodecyl (meth)acrylate, n-laury! (meth)acrylate, alkyl (meth)-acrylate, tridecyl (meth)acrylate, n-stearyl (meth)acrylate, cyclohexyl(meth)-acrylate, tetrahydrofurfuryl(meth)acrylate, 2-phenoxy ethyl(meth)- acrylate, isobornyl(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1 ,6- hexanediol di(meth)acrylate, 1,9-nonandiol di(meth)acrylate, perfluorooctylethyl (meth)acryiate, 1 ,10 decandiol di{meth)acry!ate, nonylphenol polypropoxylate (meth)acrylate, and polypentoxylate tetrahydrofurfuryl acrylate, available from Kyoeisha Chemical Co., LTD; polybutadiene urethane dimethacrylate (CN302, NTX6513) and polybutadiene dimethacrylate (CN301 , NTX6039, PRO6270) available from Sartomer Company, inc; polycarbonate urethane diacrylate (ARTRESIN UN9200A) available from Negami Chemical Industries Co., LTD; acrylated aliphatic urethane oligomers (EBECRYL 230, 264, 265, 270,284, 4830, 4833, 4834, 4835, 4866, 4881 , 4883, 8402, 8800-20R, 8803, 8804) available from Radcure Specialities, Inc; polyester acrylate oligomers (EBECRYL 657, 770, 810, 830, 1657, 1810, 1830) available from Radcure Specialities, Inc.; and epoxy acrylate

resins (CN104, 111 , 112, 115, 116, 117, 118, 119, 120, 124, 136) available from Sartomer Company, Inc. In one embodiment the acrylate resins are selected from the group consisting of isobornyl acrylate, isobornyl methacrylate, lauryl acrylate, lauryl meth acrylate, poly(butadiene) with acrylate functionality and poly(butadiene) with methacrylate functionality.

[0043] Suitable maleitnide resins include those having the generic structure

which n is 1 to 3 and X ¹ is an aliphatic or aromatic group. Exemplary X ¹ entities include, poly(butadienes), poly(carbonates), poly(urethanes), poly(ethers), poly(esters), simple hydrocarbons, and simple hydrocarbons containing functionalities such as carbonyl, carboxyl, amide, carbamate, urea, ester, or ether. These types of resins are commercially available and can be obtained, for example, from Dainippon Ink and Chemical, Inc.

[0044] Additional suitable maleimide resins include, but are not limited to, solid aromatic bismaleimide (BMI) resins, particularly those having the structure

in which Q is an aromatic group. Suitable bismaleimide resins having aromatic bridging groups are commercially available, and can be obtained, for example, from Sartomer (USA) or HOS-Technic GmbH (Austria).

[0045] Other suitable maleimide resins include:

in which C ₃₆ represents a linear or branched chain hydrocarbon chain (with or without cyclic moieties) of 36 carbon atoms;

[0046] Suitable fumarates and maleates include, for example, dioctyl maleate, dibutyl maieate, dioctyl fumarate, and dibutyi fumarate.

[0047] In all embodiments, the cationically polymerizable composition may further comprise an additional monofuπctional and/or polyfunctional cationicaily polymerizable resin, and/or a reactive cationically polymerizable diluent.

[0048] Jn all embodiments, the cationically polymerizable composition may further comprise a filler. Examples of suitable nonconductive fillers include alumina, aluminum hydroxide, silica, fused silica, fumed silica, vermiculite, mica, wollastonite, calcium carbonate, titania, sand, glass, barium sulfate, zirconium, carbon black, organic fillers, and haiogenated ethylene polymers, such as, tetrafluoroethylene, trifluoroethylene, vinylidene fluoride, vinyl fluoride, vinylidene chloride, and vinyl chloride. Examples of suitable conductive fillers include carbon black, graphite, gold, silver, copper, platinum, palladium, nickel, aluminum, silicon carbide, boron nitride, diamond, and alumina.

[0049] The filler particles may be of any appropriate size ranging from nano size to several mm. Appropriate filler sizes can be determined by the practitioner, but, in general, will be within the range of 20 nanometers to 100 microns. The choice of such size for any particular end use is within the expertise of one skilled in the art. Filler may be present in

any effective amount, and typically, an effective amount will range from 10 to 90% by weight of the total composition. More than one filler type may be used in a composition and the fillers may or may not be surface treated.

[0050] Other materials, such as adhesion promoters, dyes, pigments, and rheology modifiers, may be added as desired for modification of final properties. Such materials and the amounts needed are within the expertise of those skilled in the art.

[0051] In those cases in which the cationic polymerizable monomer is not an epoxy, the worklife of the composition can be lengthened by the addition of an epoxy resin or a radical inhibitor. As an additive to increase worklife, the epoxy resin will be present in an amount of 1 to 90% by weight of total resin. Suitable epoxy resins are those previously disclosed in this specification. In those cases in which a radical inhibitor is used to lengthen worklife, the radical inhibitor will be present in an amount of 10ppm to 2000ppm. Suitable radical inhibitors include, for example, hydroquinone, methylhydroquiπone, t- butylcatechol, phenothiazine, and NPAL having the structure

EXAMPLES

[0052] EXAMPLE 1. EFFECT OF ELECTRON-RICH VINYL COMPOUND ON CURE TEMPERATURE OF CATIONICALLY POLYMERIZABLE COMPOSITION

[0053] A cationically polymerizable composition was prepared as a control to contain oxetane (OXT-221) having the structure shown above in this specification, an iodonium salt (RHODORSIL-2074), and an azo initiator (VAZO-52). Additional compositions were prepared to contain the control composition and a catalytic amount of vinyl ether I, vinyl ether II, or a styrene compound, having the structures shown below. Samples of the compositions were cured and their peak temperature (Tpeak) recorded. Other samples of the same composition were stored at room temperature and gel times recorded to measure worklife.

styrene compound

[0054] The formulations for the compositions and the results are reported in TABLE 1. The results show that the addition of vinyl ether to the cationically polymerizable oxetane in the presence of an iodonium salt and an azo initiator decreased the cure temperature of the composition (compare entry 1 control to entry 2). Increasing the amount of iodonium salt from 1 moi% to 2 mol% (entry 3) increased the gel time, without affecting the cure temperature. Vinyl ether alone had the lowest cure temperature, but had a short gel time (entry 5). The difunctional styrenic compound, another electron-rich vinyl compound, lowered the cure temperature similarly to the vinyl ether (entry 6). Isothermal Differential Scanning Calorimetry was run on two samples: the sample shown in entry 2 with a peak temperature of 76°C cured in about 45 seconds at 85 ⁰ C; and the sample shown in entry 5 with a peak temperature of 65 ^C C cured in 30 seconds at 85°C.

[0055]

[0056] EXAMPLE 2. EFFECT OF EPOXY OR RADICAL INHIBITOR ON WORKLIFE OF CATIONICALLY POLYMERIZABLE COMPOSITION

[0057] In order to improve the worklife of the compositions, epoxy or a radical inhibitor was added to the formulations. A control cationically polymerizable composition was prepared to contain oxetane (OXT-221) having the structure shown above, an iodonium salt (RHODORSIL), an azo initiator (VAZO-52) and vinyl ether I or N having the structures shown above. To this was added epoxy resin or methyihydroquinone (MeHQ) as a radical inhibitor. The epoxy resins used were a cycloaliphatic epoxy sold under the tradename CYRACURE UVR6128 from Dow chemicals or epoxy resin sold under the tradename EPON 834 from Hexion chemicals.

[0058] The composition components and results are reported in TABLE 2 and show that the addition of epoxy to the composition stabilized the formulation and improved gel times (entries 2 and 3). The epoxy system without oxetane and a catalytic amount of vinyl ether

showed a peak temperature of 95°C with good work life (entry 4) Changing from vinyl ether I to vinyl ether Il increased the gel time slightly (entry 5), indicating that the workhfe may depend on the type of vinyl ether used Use of radical inhibitors improved the work life of the formulations, although there was an accompanying increase in the peak temperature, which corresponded to the amount of inhibitor used (entries 6, 7, 8, 9).

[0059]

[0060] EXAMPLE 3. EFFECT OF PEROXIDE INITIATOR ON THE CURE TEMPERATURE OF CATIONICALLY POLYMERIZABLE COMPOSITIONS

[0061] Azo initiators can liberate N ₂ gas upon decomposition, which is undesirable in applications where low outgassing is required. The successful substitution of peroxides for the azo initiators will be dependent on the peroxide chosen. Cationically polymerizable compositions were prepared as in the previous examples with the substitution of benzoyl peroxide and a commercial peroxide sold under the tradename TRIGONOX-23 for the azo initiators. The formulations of the compositions and the results are reported in TABLE 3. The data show that the (TRIGONOX) peroxide was more effective than benzoyl peroxide as an initiator.

[0062]