Toughened Cyanoacrylate Compositions

 US00739085lBl (12) Ulllted States Patent (10) Patent No.: US 7,390,851 B1 Misiak (45) Date of Patent: Jun. 24, 2008 (54) TOUGHENED CYANOACRYLATE 4,440,910 A 4/1984 O’Connor ................. .. 525/295 COMPOSITIONS 4,444,933 A 4/1984 Columbus etal. ......... .. 524/292 4,477,607 A 10/1984 Litke ........................ .. 523/212 (75) Inventor: Hanns Roland Misiak, Dublin (IE) 4,533,422 A 8/1985 Litke ........... .. 156/307 4,556,700 A 12/1985 Harris etal. .............. .. 523/209 (73) Assigneei Loetite (R&D) Limited, Dublin (IE) 4,560,723 A 12/1985 Milletetal. .............. .. 524/486 Notice: subjecno anycusciaimer, merennomus 3323212‘; 2 11/133? ¥;‘§ZrZfZ1".‘.‘.‘ ......... .jjj‘5§§§’2/ii Patent is extended Or adjusted under 35 4,695,615 A 9/1987 Leonard etal. ........... .. 526/194 U~S~C~ 154(b)bY112daYS- 4,713,405 A 12/1987 Koga etal. ............ .. 523/212 4,718,966 A 1/1988 Harris etal. ........... .. 156/331.2 (21) APP1~N°* 11/279307 4,855,461 A 8/1989 Harris ...................... .. 549/348 . 4,906,317 A 3/1990 ' 156/307.3 (22) Ffled" APr'14’2006 5,312,864 A 5/1994 Wenz ....................... .. 524/716 Related US Application Data 5,340,833 : 8‘/13:: 1VI_1tr§_r ........................ (63) Continuation-in-part of application No. ll/001,244, 5,994,464 A 11/1999 Ohsawa et al. .............. .. 525/85 filed on Nov. 30, 2004, which is a continuation of 6,475,331 B1 11/2002 O’C0nn0r ................. .. 156/331 application No. 10/336,697, filed on Jan. 6, 2003, now abandoned. (51) Int. Cl. C08L 27/06 (2006.01) (52) U.S. Cl. ...................... .. 525/193; 524/492; 524/565; 524/568; 525/295 (58) Field of Classification Search ............... .. 524/492, 524/565, 568; 525/193, 295 See application file for complete search history. (56) References Cited U.S. PATENT DOCUMENTS 4,102,945 A 7/1978 Gleave ..................... .. 260/879 Primary Examiner—D. S Nakarani (74) Attorney, Agent, or Firm—SteVen C. Bauman (57) ABSTRACT This invention relates to toughened cyanoacrylate composi- tions which exhibit improved peel strengths and fixture speeds. The toughened cyanoacrylate compositions include a toughening agent comprising poly(Vinychloride-co-Vinyl acetate) and poly(methylmethacrytlate). 10 Claims, N0 Drawings US 7,390,851 B1 1 TOUGHENED CYANOACRYLATE COMPOSITIONS RELATED APPLICATIONS This application continues in part from co-pending, com- monly assigned U.S. patent application Ser. No. 11/001,244, filed Nov. 30, 2004, which itself continues from U.S. patent application Ser. No. 10/336,697, filed Jan. 6, 2003, which has now been abandoned. BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to toughened cyanoacrylate compo- sitions which exhibit improved peel strengths and fixture speeds. The toughening agent used in the present invention comprises poly(vinychloride-co-vinyl acetate) in combina- tion with poly(methylmethacrytlate). 2. Brief Description of Related Technology Cyanoacrylate compositions are well known as one com- ponent reactive adhesives, quick bonding and suitable for a variety of substrates. However, traditional cyanoacrylate- based adhesives tend to be brittle, and to have low peel strengths. A variety of additives and fillers have been pro- posed for addition to cyanoacrylate adhesive compositions to improve toughness and peel strengths. U.S. Pat. No. 4,102,945 (Gleave) describes a cyanoacrylate adhesive having enhanced peel strengths in which a cyanoacrylate is thickened by a copolymer or terpolymer including vinylidene chloride-acrylonitrile copolymers. U.S. Pat. No. 4,440,910 (O’Connor) is directed to cyanoacrylate compositions having improved toughness, achieved through the addition of elastomers, i.e., acrylic rub- bers. These rubbers are either (i) homopolymers of alkyl esters of acrylic acid; (ii) copolymers of another polymeriz- able monomer, such as lower alkenes, with an alkyl ester of acrylic acid or with an alkoxy ester of acrylic acid; (iii) copolymers of alkyl esters of acrylic acid; (iv) copolymers of alkoxy esters of acrylic acid; and (v) mixtures thereof. U.S. Pat. No. 4,444,933 (Columbus) suggests the addition of a vinyl chloride/vinyl acetate copolymer to a cyanoacrylate adhesive to reduce adhesion to human skin. U.S. Pat. No. 4,560,723 (Millet) discloses a cyanoacrylate adhesive composition containing a toughening agent com- prising a core-shell polymer and a sustainer comprising an organic compound containing one or more unsubstituted or substituted aryl groups. The sustainer is reported to improve retention of toughness after heat aging of cured bonds of the adhesive. U.S. Pat. No. 4,713,405 (Koga) discloses an 0t-cyanoacry- late adhesive composition of matter consisting essentially of ot-cyanoacrylate, fumed silica having a surface treated with a dimethyldichlorosilane, and trialkyl borate. U.S. Pat. No. 5,340,873 (Mitry) discloses a cyanoacrylate adhesive composition having improved toughness by includ- ing an effective toughening amount of a polyester polymer derived from a dibasic aliphatic or aromatic carboxylic acid and a glycol. U.S. Pat. No. 5,739,205 (Nishino) discloses an 0t-cy- anoacrylate adhesive composition which comprises (a) 100 parts by weight of an ot-cyanoacrylate compound, (b) 10 through 20 parts by weight of (I) polyalkyl methacrylates having a weight average molecular weight of 100,000 through 300,000, or (II) copolymers of alkyl methacrylates and other methacrylates or acrylates, said copolymers having the same weight average molecular weight as that of the polyalkyl methacrylates (I), (c) 2 through 20 parts by weight of ultrafine anhydrous silicas, and (d) 0.001 through 20 parts 10 15 20 25 30 35 40 45 50 55 60 65 2 by weight of certain quick curing additives, (b)-(d) being on the basis of (a) 100 parts by weight of ot-cyanoacrylate com- pounds. U.S. Pat. No. 5,994,464 (Oheawa) discloses a cyanoacry- late adhesive composition containing a cyanoacrylate mono- mer, an elastomer miscible or compatible with the cyanoacry- late monomer, and a core-shell polymers being compatible, but not miscible, with the cyanoacrylate monomer. U.S. Pat. No. 6,475,331 (O’Connor) discloses and claims a cyanoacrylate adhesive composition comprising: (a) a cyanoacrylate components; and (b) an accelerator component consisting essentially of (i) calixarenes, oxacalixarenes, or a combination thereof, and (ii) at least one crown ether, wherein said composition exhibits a fixturing speed of less than 20 seconds for bonding two substrates, at least one of which is constructed of a material selected from steel, epoxy glass, and balsawood. Despite the state of the technology, there continues to be a need for cyanoacrylate adhesives with improved toughness and peel strengths, while maintaining a high fixture speed. SUMMARY OF THE INVENTION As used herein, all compositions values are given in weight percent unless otherwise noted. The present invention is directed to, in a first aspect, a cyanoacrylate composition which demonstrates enhanced touglmess such as improved peel strength, and fixturing speeds including a cyanoacrylate component; and a toughen- ing agent comprising poly(vinychloride-co-vinyl acetate) (“PVCVA”) in combination with poly(methylmethacrytlate) (“PMMA”). Cyanoacrylate compositions in accordance with the present invention containing PVCVA in combination with PMMA show increased toughness, measured for instance as an increased peel strength. In another aspect, the present invention is directed to a cyanoacrylate composition which demonstrates enhanced touglmess including a cyanoacrylate material; a toughening agent comprising PVCVA in combination with PMMA; and one or more additives selected from plasticizers, accelerators, fillers, opacifiers, inhibitors, thixothrophy conferring agents, stabilizers, dyes, thermal degradation reducers, and combi- nations thereof, where upon cure, the cyanoacrylate compo- sition has an average T peel strength on mild steel of more than about 3 N/mm after curing at room temperature for about 72 hours and a fixture speed on EPDM-foam rubber of less than 40 seconds. In yet another aspect, the present invention is directed to a method of bonding two or more substrates including the steps of providing at least two substrates; dispensing, on at least a portion of a surface of one or both of the at least two sub- strates, a cyanoacrylate composition including about 1 to about 20% by weight of the toughening agent comprising PVCVA in combination with PMMA; contacting the surfaces of the at least two substrates having the cyanoacrylate com- position therebetween; and curing the cyanoacrylate compo- sition. In still another aspect, the present invention is directed to a bonded assembly including: a first substrate having a first surface; another substrate having a second surface; and a cured cyanoacrylate composition disposed between the first and second surfaces, the composition having included prior to cure a cyanoacrylate component; and a toughening agent comprising about 1 to about 20% by weight of PVCVA in combination with PMMA. Preferably, the T peel strength on mild steel is greater than about 3 N/mm after room tempera- ture cure for about 72 hours, and fixture speed on EPDM rubber of less than 40 seconds. US 7,390,851 B1 3 DETAILED DESCRIPTION OF THE INVENTION The cyanoacrylate compositions of the present invention include toughening agents which provide enhanced tough- ness, such as improved peel strengths in the cured composi- tions. The toughening agent comprises PVCVA in combina- tion with PMMA. A method of bonding substrates and the resultant bonded assembly are disclosed herein as well. The cyanoacrylate compositions of the present invention include a cyanoacrylate component which include cyanoacrylate monomers, such as those represented by the structure: OR’ \ \N where R1 is selected from CH6 alkyl, alkoxyalkyl, cycloalkyl, alkenyl, aralkyl, aryl, allyl and haloalkyl groups. Preferably, the cyanoacrylate monomer is selected from methyl cyanoacrylate, ethyl-2-cyanoacrylate, propyl cyanoacrylates, butyl cyanoacrylates (such as n-butyl-2-cy- anoacrylate), octyl cyanoacrylates, allyl cyanoacrylate, [3-methyoxyethyl cyanoacrylate and combinations thereof. A particularly desirable cyanoacrylate monomer is ethyl-2-cy- anoacrylate. The cyanoacrylate component should be included in the compositions in an amount within the range of about 70% by weight to about 90% by weight, preferably about 75% by weight to about 85% by weight. The compositions of the present invention may also con- tain additives such as stabilizers, accelerators, plasticizers, fillers, opacifiers, inhibitors, thixotrophy conferring agents, dyes, fluorescence markers, thermal degradation reducers, adhesion promoters, and combinations thereof, and the like. These additives are known to those of skill in the art. The cyanoacrylate monomers (and the compositions in which the cyanoacrylate monomers are used) are preferably stabilized using acid stabilizers of the Lewis or protonic types although combinations of nonvolatile sulfonic acids with gas- eous stabilizers such as N0, S02, S03, BF3, C02 and HF can provide a synergistic effect. A preferred stabilizer system for the present invention includes methane sulfonic acid (“MSA”) and S02. Preferably, the amount of MSA is about 5 to about 25 ppm and a preferred amount of S02 is about 2 to about 30 ppm based on the amount of the cyanoacrylate monomer. More preferably, BF3, another acidic gaseous sta- bilizer, may also be added in amounts of about 5 ppm to about 50 ppm based on the amount of the cyanoacrylate monomer. Advantageously, such small amounts of stabilizers used with the compositions of the present invention provide optimal performance without stability concerns. Inhibitors or free radical scavengers that may be useful in the cyanoacrylate compositions are of the phenolic type such as hydroquinone, t-butyl catechol, p-methoxy-phenol, and the like. A preferred inhibitor of the present invention is hydroquinone,. The inhibitor is present in an amount of about 0.001% by weight to about 2.0% by weight, preferably about 0.02% to about 0.5% by weight. 0ther inhibitors suitable for use herein include butylated hydroxytoluene and butylated hydroxyanisole. 10 15 20 25 30 35 40 45 50 55 60 65 4 Accelerators that may be useful in the cyanoacrylate com- positions include for example calixarenes, oxacalixarenes, and combinations thereof. 0f the calixarenes and oxacalix- arenes, many are known, and are reported in the patent litera- ture. See e.g. U.S. Pat. Nos. 4,556,700, 4,622,414, 4,636,539, 4,695,615, 4,718,966, and U.S. Pat. No. 4,855,461, the dis- closures of each of which are hereby expressly incorporated herein by reference. Another potentially useful accelerator component is a crown ether. A ho st of crown ethers are known. For instance, examples which may be used herein either individually or in combination, or in combination with the calixarenes and oxacalixarenes described above include 1 5 -crown-5, 18-crown-6, dibenzo-18-crown-6, benzo-15 -crown-5, dibenzo-24-crown-8, dibenzo-30-crown-10, tribenzo-18- crown-6, asym-dibenzo -22-crown-6, dibenzo-14-crown-4, dicyclohexyl-18-crown-6, dicyclohexyl-24-crown-8, cyclo- hexyl-12-crown-4, 1,2-decalyl-15-crown-5, 1,2-naphtho-15- crown-5, 3,4,5 -naphthyl-16-crown-5, 1,2-methyl-benzo-18- crown-6, 1,2-methylbenzo-5, 6-methylbenzo-18-crown-6, 1 ,2-t-butyl-18-crown-6, 1 ,2-vinylbenzo-15-crown-5, 1,2-vi- nylbenzo-18-crown-6, 1,2-t-butyl-cyclohexyl-18-crown-6, asym-dibenzo -22-crown-6 and 1,2-benzo-1,4-benzo-5 -oxy- gen-20-crown-7. See U.S. Pat. No. 4,837,260 (Sato), the dis- closure of which is hereby expressly incorporated here by reference. 0ther suitable accelerators include those described in U.S. Pat. No. 5,312,864 (Wenz), which are hydroxyl group deriva- tives of an (X-, [3- or y-cyclodextrin which is at least partly soluble in the cyanoacrylate; in U.S. Pat. No. 4,906,317 (Liu), which are silacrown compounds to accelerate fixturing and cure on de-activating substrates such as wood, examples of which are within the following structure: R4 I R3—Si—Oj |—(OCH2C|H>n R5 where R3 and R4 are organo groups which do not themselves cause polymerization of the cyanoacrylate monomer, R3 is H or CH3 and n is an integer of between 1 and 4. Examples of suitable R3 and R4 groups are R groups, alkoxy groups such as methoxy, and aryloxy groups such as phenoxy. The R3 and R4 groups may contain halogen or other sub stitutents, an example being trifluoropropyl. However, groups not suitable as R4 and R3 groups are basic groups such as amino, substi- tuted amino and alkylarnino. Specific examples of silacrown compounds useful in the inventive compositions include: H3C CH3 \ ./ S1 0/ \0 E I 0 0 US 7,390,851 B1 dimethylsila-1 1-crown-4; K“. E} O\s/O / \ H3C CH3 dimethylsila-14-crown-5; H3C CH3 / \Si 5‘ “.3 LU) and dimethylsila-17-crown-6. The accelerator component should be included in the com- positions in an amount within the range of from about 0.01% to about 10% by weight, with the range of about 0.05% to about 2% by weight being desirable, and about 0.1% to about 1% by weight of the total composition being particularly desirable. Phthalic anhydride may also be added to the cyanoacrylate component to further aid in durability and impact, heat, and moisture resistance. Plasticizers may also be added to the cyanoacrylate com- ponent, and when so added are preferably present in an amount of about 25% by weight to about 50% by weight, more preferably about 10% by weight to about 25% by weight of the total composition. The inventive compositions may also be rendered thixotro- pic by the addition of thixoprophy conferring agents, such as fumed silica. See U.S. Pat. No. 4,533,422 (Litke) and U.S. Pat. No. 4,477,607 (Litke). These agents, when used, should be used in an amount less than about 15% by weight, such as within the range of about 0.5% by weight to about 10% by weight of the total composition. The combination of the cyanoacrylate monomer and the additives will be referred to herein as the cyanoacrylate com- ponent. The cyanoacrylate compositions of the present invention are typically cured using an anionic mechanism. The layer of moisture inherently adsorbed on the surfaces of virtually all materials is sufiicient to initiate polymerization of the cyanoacrylate component. Further, most substrates also con- tain alkaline or nucleophilic ingredients or as impurities which can initiate the anionic polymerization. The hydroxyl groups of the water molecules effectively act to initiate poly- 10 15 20 25 30 35 40 45 50 55 60 65 6 merization as carbanions are generated at a rapid rate. The polymerization reaction will continue until all available monomer is consumed or until growth is inhibited by an acidic species. As noted, the toughening agent of the present invention comprises PVCVA in combination with PMMA. The inventive cyanoacrylate compositions are readily pre- pared by adding predetermined amounts of the toughening agent components to the cyanoacrylate component and stir- ring or agitating for a sufiicient time at an appropriate tem- perature to achieve a homogeneous solution or suspension. Typically, temperatures much above room temperature are not necessary, though in formulations containing high levels of fillers, thickeners, and the like, moderate heating may be desirable to speed dissolution of the various additives. The cyanoacrylate compositions of the present invention are useful in bonding two or more substrates. A sufficient portion of the composition may be placed on a surface of one of the two or more substrates. The other substrate is then positioned adjacent to the cyanoacrylate composition and the two substrates are placed in contact to one another to form an assembly, upon curing of the cyanoacrylate. Unexpectedly, typical fixturing speeds of the cyanoacrylate compositions of the present invention for bonding EPDM rubber were less than about 40 seconds. The improved toughness of the cured compositions of this invention is manifested through various physical properties, such as 180° peel strength. High peel strengths are indicative of tough bonds. Peel strength was determined in accordance with American Standard Test Method (ASTM) No. D-903- 49, the substance of which is hereby expressly incorporated herein by reference. The present invention may be better understood through consideration of the following examples which are intended to be illustrative rather than limiting. EXAMPLES The following examples describe the preparation and use of the cyanoacrylate compositions of the present invention. These examples are presented for the purpose of further illus- trating and explaining the invention, and are not to be taken as limiting the scope of the invention. It was found that the addition of PVCVA to cyanoacrylate monomer significantly increases the T peel strength of the cured cyanoacrylate composition, if PMMA is present as well. Cured cyanoacrylate compositions are typically rigid, brittle materials, having low crack resistance and therefore low T peel strength. In order to modify these physical prop- erties, additives may be included as noted herein. A toughening agent is the focus of the examples in which a series of cyanoacrylate compositions was prepared by agita- tion/mixing/tumbling a closed vessel to obtain a homogenous dispersion or solution of the cyanoacrylate composition. Peel strengths were evaluated by bonding flexible steel strips together and curing for 24 hours at a temperature of 25° C. The force required to cause the bond to fail was measured, the results being presented in units of force per unit length of bond. The peel test procedure was performed according to ASTM D-903-49. The fixture time was also measured, with shorter fixture times required to develop a bond on EPDM rubber samples, generally being preferred. Certain of these compositions and test results therefor are presented below in Table I. US 7,390,851 B1 TABLE I Feel Strength EPDM Composition 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 to CA OCTITE 424 OCTITE 380 OCTITE 480 CA + 7.5% PVeneCAN CA + 9% PVeneCAN CA + 10% PVeneCAN CA + 15% PVeneCAN CA + 20% PVeneCAN CA + 30% PVeneCAN CA + 10% PVeneCAN + 0.4% Calix. CA + 9% PVeneCAN + 4% PMMA CA + 9% PVeneCAN + 3% Silica CA + 9% PVeneCAN + 4% Silica CA + 11% PVeneCAN + 3% Silica CA + 11% PVeneCAN + 6% Silica CA + 9% PVeneCAN + 4% BzBuPht CA + 9% PVeneCAN + 4% GTA CA + 9% PVeneCAN + 4% nBuCA uoctite 424 + 10% PVeneCAN uoctite 431 + 5% PVeneCAN uoctite 431 + 5% PVeneCAN + 4% Silica uoctite 431 + 9% PVeneCAN + 4% Silica EtCA + 10% PVCVA(1) EtCA + 10% PVCVA(H) EtCA + 10% PVCVA(11I) EtCA + 15% PVCVA(11I) EtCA + 20% PVCVA(11I) uoctite 431 + 5% PVeneCAN + 5% PVCVA(111) {Loctite 431 + EtCA [1 :1]} + 4.5% PVeneCAN {Loctite 431 + EtCA [1 :1]} + 4.5% PVeneCAN + 4% Silica EtCA + 7% PVeneCAN + 5% PMMA + 2.75% Silica EtCA + 7% PVeneCAN + 5% PMMA + 2.75% Silica + 4% GTA EtCA + 7% PVeneCAN + 5% PMMA + 2.75% Silica + 4% TEAC PrCA + 10% PVeneCAN PrCA + 10% PVeneCAN + 4% Silica uoctite 431 + 10% ’VCVA(H1) uoctite 431 + 10% ’VCVA(H) + 3% Silica {Loctite 431/EtCA 19:3]} +6% PVCVA(H) + 3% Silica L L LU LU LU LU LU LU LU LU LU LU LU LU LU LU LU L 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 BzBuPht = Benzyl butyl phtalate Calix = Calixarene derivative (fixture speed accelerator) EPDM = Fixture time on EPDM foam rubber cord EtCA = Ethylcylancecry ate monomer GTA = Glycerol triaceta e 1PrCA = Iso-Propyl cyanoecrylate monomer nBuCA = nButyl cyanoecrylate momomer Peel Strength = Peel Strength on degreased mild steel PMMA = Polymerylme iacrylate (thickening agent) PVCVA(I) = Poly(vinylchloride-co-vinyl acetate), 86% vinylchloride PVCVA(H) = Poly(vinylchloride-co-vinyl acetate), 90% vinylchloride PVCVA(HI) = Poly(vinylchloride-co-vinyl acetate), 81% vinylchloride PVeneCAN = Poly(viny idene chloride-co-acrylonitrile), 20% acrylonitrile TEAC = Trieltryl-O-ace yl citrate The substrates used in determining T peel strength in Table I are sand blasted steel bonded to sand blasted, flexible steel shims. Unexpectedly, typical fixture speeds of the cyanoacry- late compositions of the present invention for these substrates were less than about 70 seconds, and in most cases, from 12-40 seconds. Non-toughened cyanoacrylate compositions that are evaluated in adhesive applications have low T peel strengths, typically from about 0.2-0.4 N/mm. Samples 01 and 02 illus- trate the low peel strengths of such non toughened cyanoacry- late compositions. The cyanoacrylate compositions of the present invention exhibit improved T peel strengths in comparison with cyanoacrylate compositions toughened with known tough- ners, such as BLACK MAX® (Loctite® 380 cyanoacrylate adhesive, an adhesive known for its high peel strength). In Table 11, twenty six of the twenty seven samples are based on ethyl cyanoacrylate, whereas the twenty seventh [N/mm] 0.4 0.4 2.9 4.1 2.3 3.3 2.9 2.5 2.1 0.5 3.1 2.8 3.2 3.4 3.1 3.6 2.9 3.6 2.6 4.2 1.3 1.6 3.7 1.3 1.4 1.1 1.1 0.7 2.2 2.1 4.8 5.4 5.6 5.0 2.1 2.6 1.99 0.9 2.3 50 55 60 65 [s] Remark control control control control 120 75 20 30 22 17 18 28 After 1/2 yr: 30s; 1.68 N/mm After 1/2 yr: 24s; 3.61 N/mm 26 28 35 40 40 50 60 12 18 17 After 1/2 yr: 32s; 1.67 N/mm After 1/2 yr: 30s; 3.99 N/mm Afterl/2 yr: 65s; 3.48 N/mm 6 6 (Sample AA) is based on isopropyl ester cyanoacrylate. Samples A-D are used as controls, with Sample A being an ethyl ester control with no PMMA or PVCVA. Samples B-D are commercially available products that report a toughness property. The substrates used in determining T peel strength in Tables 11 and 111 are aluminium bonded to aluminium and mild steel bonded to mild steel. TABLE 11 PVCVA Amt. of VA in PVCVA* Sample PMMA (% by wt.) (% by wt.) A 0.0 0.0 — B* 0.0 0.0 — C** 0.0 0.0 — D*** 0.0 0.0 — US 7,390,851 B1 9 TABLE II-continued PVCVA Amt. of VA in PVCVA* Sample PMMA (% by wt.) (% by wt.) 3 2.0 0.0 — 7 0.0 10.0 2% VA (“063” from SP2) G 0.0 10.0 0% VA (“068” from SP2) 1 0.0 20.0 9% VA (grade from Polysciences) 2.0 10.0 2% VA (“063” from SP2) 2.0 10.0 0% VA (“068” from SP2) { 2.0 15.0 % VA (“Vinno /59” rom Wac (er) 1 7.5 7.5 % VA (“Vinno /59” rom Wac (er) M 5.0 2.5 % VA (“Vinno /59” rom Wac (er) N 7.5 2.5 % VA (“Vinno /59” rom Wac (er) 0 0.0 2.5 % VA (“Vinno /59” rom Wac (er) ’ 2.5 2.5 % VA (“Vinno /59” rom Wac (er) Q 5.0 5.0 % VA (“Vinno /59” rom Wac (er) { 7.5 5.0 % VA (“Vinno /59” rom Wac (er) S 0.0 5.0 % VA (“Vinno /59” rom Wac (er) T 5.0 7.5 % VA (“Vinno /59” rom Wac (er) J 2.5 10.0 % VA (“Vinno /59” rom Wac (er) V 5.0 10.0 % VA (“Vinno /59” rom Wac (er) W 2.5 12.5 % VA (“Vinno /59” rom Wac (er) X 0.0 3.0 % VA (“Vinno /59” rom Wac (er) Y 6.5 6.5 % VA (“Vinno /59” rom Wac (er) Z 3.0 10.0 % VA (“Vinno /59” rom Wac (er) AA 0.0 2.5 % VA (“Vinno /59” rom Wac (er) *LOCTTTE ® 480 * *CYBERBOND 2241 ***DEVCON HV1200 +Commercial source of vinyl acetate noted TABLE 111 T peel strength N/mm Fixture Speed (ees) Sample Al MS* EPDM A 0.0 0.2 1 0.2 6 3 2.7 1 0.4 3.6 1 0.5 45 c 2.6 1 0.5 3.5 1 0.5 45 ) 2.0 1 0.1 1.8 1 0.3 40 3 0.3 1 0.2 0.4 1 0.3 — 5 — 0.6 1 0.4 — G — 0.7 1 0.3 — 1 — 0.7 1 0.3 — — 1.4 1 0.2 4 — 4.8 1 0.6 13 < — 2.5 1 0.2 24 1 1.8 1 0.34 4.9 1 0.3 20 M — 3.1 1 0.5 — N — 2.9 1 0.2 — o 1.2101 4.110.3 24 3 — 2.9 1 0.2 — Q — 3.4 1 0.6 21 1 — 3.4 1 0.6 21 s — 2.8 1 0.8 — T — 3.1 1 0.2 — J 1.7 1 0 5 4.5 1 0.3 22 V — 3.3 1 0.1 — W — 3.3 1 0.3 — x — 2.5 1 0.6 — Y 1.3 102 2.3 10.6 14 z — 1.8 1 0.2 — AA — 1.7 1 0.4 — *mild steel As is evident from a review of the information presented in the tables above, neither cyanoacrylate monomers them- selves, nor the presence of either PMMA or PVCVA, result in the development of an appreciable T peel strength after curing on EDPM rubber substrates. (See e.g. Samples A and E-H of Tables 11 and 111.) More specifically, Sample E demonstrates the effect of adding PMMA to an ethyl cyanoacrylate monomer. Virtually 10 15 20 25 30 35 40 45 50 55 60 65 10 no effect is seen on added peel strength over the ethyl cyanoacrylate monomer used as a control. However, when the PMMA and PVCVA are together pre- sented in a cyanoacrylate formulation, T peel strength mea- surements show a significant increase. (See e.g. Samples I-W and AA.) Samples X-Z contain the thixotrophy agent, silica, at a 3.5% by weight level. What is claimed is: 1. A cyanoacrylate composition comprising: a cyanoacrylate component; and a toughening agent comprising poly(vinychloride-co-vi- nyl acetate) in combination with poly(methylmethacry- late). 2. The composition of claim 1 wherein said cyanoacrylate component comprises a monomeric structure represented by: OR’ %N wherein R1 is CH5 alkyl, alkoxyalkyl, cycloalkyl, alkenyl, aryl, aralkyl, allyl, alkylhalide, or haloalkyl and mixtures thereof. 3. The composition of claim 2 wherein said cyanoacrylate component comprises a member selected from the group consisting of methyl cyanoacrylate, ethyl-2-cyanoacrylate, propyl cyanoacrylate, butyl cyanoacrylates, octyl cyanoacry- lates, allyl cyanoacrylates, [3-methoxyethyl cyanoacrylate, and mixtures thereof. 4. The composition of claim 3 wherein said cyanoacrylate component comprises ethyl-2-cyanoacrylate. 5. The composition of claim 1 wherein said poly(vinychlo- ride-co-vinyl acetate) is present in an amount of about 1% to about 20% by weight. 6. The composition of claim 1 further comprising fumed silica. 7. The composition of claim 6, wherein said fumed silica is present in an amount (by weight) of from about 0.5 to about 10%. 8. The composition of claim 1 further comprising at least one additive selected from the group consisting of stabilizers, accelerators, plasticizers, fillers, opacifiers, thickeners, vis- cosity modifiers, inhibitors, thixotrophy conferring agents, dyes, thermal degradation inhibitors, and combinations thereof. 9. The composition of claim 1 wherein upon cure, the cyanoacrylate composition has an average peel strength in excess of about 1.0 N/mm after 72 hours at room temperature cure. 10. A cyanoacrylate composition consisting essentially of: a cyanoacrylate component; a toughening agent comprising poly(vinychloride-co-vi- nyl acetate) in combination with poly(methylmethacryt- late); and one or more additives selected from the group consisting of stabilizers, accelerators, plasticizers, fillers, opacifiers, thickeners, viscosity modifiers, inhibitors, thixotrophy conferring agents, dyes, thermal degradation inhibitors, and combinations thereof, wherein upon cure, the cyanoacrylate composition has an average tensile shear strength in excess of about 1.0 N/mm. * * * * *