Mixed Alpha-Cyanoacrylate Adhesive Compositions

 United States Patent it-Oflice 2,776,232 Patented Jan. 1, 1957 .1 2,776,232 %MIXED .':xEC~Y AN OACRYLATEIADIIESIV E JCOMFOSITIONS Newton. H.‘ Shearer, "J1-., and»Harry'W. Coover, Jr.,-‘Kings- "port, Tenn., assignors to Eastman ‘Kodak Company, “-Rochester, N.*Y_., ‘a' corporation of New ‘Jersey No Drawing. *Application~Jun’e 2,-1954, .. Serial No. 434,080 11’ Claims. 5 (Cl. 'l54=-I-46) Thisinventionrel-atessto »adhe‘sive:con1positions particu- ‘larly adapted for‘forming:'flexi'ble adhesivebonds and is par-ticularly concerned with adhesive compositions com- ,,prising .a mixture of at ‘least two different esters of a-cyanoacrylic acid. The .oc-cyanoacrylate esters, in monomeric niorm, ‘have .found excellentutility for ‘a ,-great variety of adhesive ap- t])llG3i:l.O1’1‘S.‘ .~These ‘monomeric Lcompositions fform ‘strong adhesive bonds at room temperature and without -the application of ‘pressureor the :use of a polymerization zcatalyst. Such adhesive compositions and ;their use is ‘.d'l.‘SCl.0SCd and claimed in the copending application of -,Coover.and Shearer, Serial No. ‘31‘8,'325, filed November 1, 1952. t :It :is -an object of :this invention "to provide newand "improved wcyvanoacrylate adhesive compositions ‘which form adhesive bonds '-which :-are.=rnor.e flexible than the adhesive ‘bonds ordinarily obtained from the single on-cyanoacrylate ‘adhesives. :Another object of the invention is to prepare new -mixed monomeric ‘oz-cyanoacrylates by .a :process which lendsvitself tozready depolymerizationtof the low.mdlecu- Tlaruweight polymeric cc-cyanoacrylates which -are nor- .mally ‘formed ‘in the ~manu-tacturing process. Another object of the invention is ‘toxprovide adhesive compositions which areparticularly adapted for bonding together ‘flexiblematerial-s without giving .a relatively in- rfiexible bond. Another object of the invention is :to providea means for zregulatingrthe bonding -speedof or-cyanoacrylate ad- ~hesives"b.y adjusting ..the composition :of ‘the adhesive .com- positions. -Other objects willbeapparent from the descriptionand claims -.-which follow. These and other objects of the invention are attained as -described more Ifully hereinafterwithéparticular refer- .ence to certain preferred -embodiments of the invention. The adhesive compositions of .this invention comprise mixtures of at least two diflerent ix-cyanoacrylates ‘from -:the class . having . the "formula ‘O.H2=(I}—C o o R ‘ON "-in which ‘R is an alkyl -group of from ‘1‘to -1'6 carbon atoms, a cyclohexyl ‘group, ~o’r”a phenyl -group. In the compositions of ‘-the invention, each ‘of the monomeric ester‘-siforms at -least 5% -‘of the ‘total ’weightv‘oi the mix- ture. The compositions —’de'sirably ‘include an acidic poly- merization inhi-b‘i_tor-in “an~amount suflicient§1:o3inhibit'the -bulk polymerization of said mixture. * Monomer-ic cc-cyanoacrylate esters are “readily prepared by reacting a suita’=ble or-‘cyanoacetate with ‘formaldehyde ‘in the presence of a ‘basic condensation catalyst to ‘form .a ‘low molecular weight ‘polymeric on-‘c.ya‘noa’crylat'e ester. This ‘low molecular "weight polymer ‘is'th‘en ‘heated ‘under vacnurn :an'd.in the presence "of 'apolymeriza’tion'inhibitor, whereby monomeri_c_ vapors ‘are evolved which “can “be 10 1...: C71 20 25 30 35 40 45 O! U1 60 70 0.5% ‘by weight is adequate. used but are notnecessary ‘and may ‘be disadvantageous ‘in some cases, particularly if they are ‘carried over into ‘the polymeric product and hence -into the monomeric -product, ‘since ‘basic materials catalyze the polymerization ‘of ac-cyanoacrylate monomers. The reaction -between the .2 condensed wand collected. The condensation of -the ‘cc-cyanoacetate "with the ‘formaldehyde can be efiected using aqueous solutions of‘~formaldehyde, or it can be -elfected in a ‘-nonaqueous isystem employing anhydrous forrnaldehyde.‘or.a polymeric form thereof ‘such as p- ‘formal'dehy‘de. =The.~' nature of the monomeric oc-cyano- acrylatewill depend‘ upo'n’the:’pa"rticular—cyanoacetate es- ter’ which is employedin the condensation. In practicing this invention,..un’mixe’d:monomeric oc-cyanoacrylates can be ‘prepared "by any ‘-of the welliknown methods such as -thoseidescribed in the copending /application of Joyner and Hawkins, Serial No. ’415,422,"filed‘March-l0, 1954, in which unmixed vcornpositions are prepared “ by depoly- merizing the‘-in'div«i'dual polymeric a‘-cyanoacrylat‘es;'or the rnixed ‘monomeric esters can ‘be prepared together :'by reactinga mixture-of oz-cyanoacetate est~ers‘with1the formaldehyde, whereby a mixed polymer is obtained which can ‘be depolymerized to ‘give the compositions ofthis invention directly. , Thus any of the ac-cyanoacetates wherein the ester group is either an alkyl group of -from 1 to l6c‘arbon atoms, -a cycl‘ohexy1‘group, or a phenyl group can be used in ‘practicing the invention. The condensation is readily catazlyzedby any of the basic condensation cata- :lysts which are known tothe art. Thus the catalysts can include such materials «as the ‘inorganic bases such as sodium or potassium hydroxide, ammonia or ammonium -hydroxide, the organic bases such as quinoline, pyridine, piperidine, isoquinoline, dialkyl amines such as diethyl ‘amine, alkali metal alkoxides such as sodium or potas- ‘sium metlroxide or ethoxide, -or similar well known basic materials. The amount ofcatalyst is not critical and can ‘be varied as desired. Ordinarily, a relatively small amount of basic catalyst such as about 0.001% to about Larger amounts can be cyanoacetate and the formaldehyde is readily effected by hcatingthe reaction ‘mixture to a temperature-of about 50 -to 90° C. When the compositions -of ‘this invention are prepared ‘by admixing tpreformed or-cyanoacrylate monomers, a single u-cyanoacetate as ‘defined is used in the prepara- tion. :'For example, -the cyanoacetate can be methyl cyanoacetate, ethyl cyanoacetate, propyl cyanoacetate, butyl icyanoacetate, capryl cyanoacetate, decyl cyano- acetate, cyclohexyl cyanoacetate, phenyl cyanoacetate, -l-auryl cyanoacetate, or any of the other cyanoacetates wherein the -alkyl group contains from 1 to 16 carbon atoms. In practicing -the -invention, the reaction is ‘desirably carried out in solution in a nonaqueous organic solvent which distills at ‘a temperature below the depolymeriza- tion ‘temperature of the low molecular weight ‘polymer ‘formed -by the reaction. The solvent used can be any of the vnorbionizable organic solvents which do not af- fect the icour-se of the reaction. After the condensation reaction ‘has been -completed, a quantity of the solvent may be removed by distillation. In carrying out the proc‘e'ss, it -is then desirable to introduce into the reaction mixture an organic ‘solvent which is capable of forming an ‘azeotrope with the water, whereby the removal of the water -with the remaining solvent is facilitated. The azeotropic ‘solvent -can -be introduced initially and form the ‘solvent medium for the reaction itself, or it can be introduced initially in admixture with another organic solvent, or it can “be introduced into the reaction mixture after the reaction has been effected and prior to the 3 separation of the reaction solvent. In most cases, the solvent which is employed will be one which is at least partially miscible with water, although solvents which are immiscible with water can be used in some cases with slightly less advantageous results. Among the reaction solvents which are preferably employed are the mono- hydric alcohols, and particularly the lower alkyl mono- hydric alcohols such as methanol, isopropanol, butanol or the like; aliphatic ethers, and particularly the lower di- alkyl ethers such as diethyl ether, diisopropyl ether and the like; benzene, chloroform, cyclohexane, or similar well known organic solvents which distill at a temperature below the temperature of that employed for depolymeriz- ing the cc-cyanoacrylate polymer. To remove the water formed during the reaction, benzene and «similar solvents which readily form wazeotropes with water are desirably employed. They may be the sole solvent for the reaction, or, alternately, they may be added at any time after the completion of the reaction to facilitate removal of the water formed. Following the reaction between the cyanoacetate and the fomialdehyde, the solvent and water are separated from the polymeric product. This separation is readily effected by distilling out the mixture of organic solvent and water from the reaction mixture. Using an azetrope-forming solvent such as benzene, the reaction solvent, water, and the benzene can usually be distilled off as a tenary azeo- trope, and the water content of the polymer is reduced to a value of less than 0.4%. In some cases, it may be desirable to distill off part of the reaction solvent from the reaction mixture when such solvent is not an azeo- trope-forming solvent. This is done in the preferred method before adding to the reaction mixture an azeo- trope-forming solvent, such as benzene, since the water formed during the reaction stage remains in the reaction mixture even when the solvent content has been reduced by as much as 80 to 90 percent. It is necessary, of course, that the azeotrope distill at a temperature below the depolymerization temperature of the polymeric product. In most cases, however, this is not a problem using the volatile organic solvents, since depolymerization is usually effected by heating the polymeric product at a tempera- ture of the order of 100—150° C. under a vacuum of the order of 1 mm. Hg. The substantially anhydrous. crude polymer thus ob- tained as a residue can then be directly depolymerized without the necessity of a further drying operation. De- polymerization is usually effected by heating the poly- mer under reduced pressure and in the presence of a polymerization inhibitor. In some cases, it may be desira- ble to include a plasticizer such as tricresyl phosphate to give a low melting and readily depolymerized polymer, although this is not necessary for successful operation. Because of the inherent instability of the monomeric oucyanoacrylates, it is desirable to elfect the depolymeriza- tion in the presence of a polymerization inhibitor, even though the low water content of the polymer gives in- creased stability to t11e monomer. Any of the acidic inhibiting substances can be used, including phophorus pentoxide, antimony pentoxide, picric acid, hydroquinone, tertiary butyl catechol, metaphosphoric acid, maleic an- hydride, ferric chloride, or the like. A particularly desira- ble group of polymerization inhibitors are the acidic gaseous inhibitors such as sulfur dioxide, nitric oxide, hydrogen fluoride, and the like. Usually it is desirable to include a polymerization inhibitor in the reaction vessel containing the polymer being depolymerized, and also to collect the monomeric vapors in a receiving ves- sel also containing a polymerization inhibitor. Best re- sults are obtained by also introducing into the system a stream of gaseous inhibitor which mixes with the mono- meric vapors evolved during the depolymerization and dissolves in such vapors to some extent when the vapors are condensed. Phosphorus pentoxide is desirably em- ployed in the depolymerization vessel, and sulfur dioxide 2,776,232 10 15 20 26 30 35 40 Q7! 3! (‘>0 65 70 75 4 is desirably introduced into the system as the gaseous in- hibitor. A particularly stable composition is obtained when the receiving flask contains a small amount of hy- droquinone, whereby a monomer composition is obtained which contains a mixture of sulfur dioxide and hydro- quinone. ’ Since the polymers prepared in accordance with this invention melt readily at a temperature of 75 to 95° C., the process can be readily carried out in continuous fash- ion since the solvent can be removed from the crude reaction mixture, the polymers melted and caused to flow into a depolymerization vessel. If desired, however, the process can be carried out batchwise with good re- sults. The improved stability which is obtained by means of a mixture of sulfur dioxide and hydroquinone are dis- closed in the copending application of Coover and Dickey, Serial No. 409,756, filed February 11, 1954. The individual monomeric oz-cyanoacrylate esters pre- pared in this manner can then be admixed in amounts of from 5 to 95% by weight of one monomer with from 95 to 5% by weight of a different monomer prepared as described. Desirably, however, the mixed monomers are prepared by using a mixture of any two or more of the a-cyanoace- tates as defined herein. In many cases, it is desirable to employ methyl wcyanoacetate as one of the cyanoace- tates used in preparing the compositions of the invention. Good results are obtained, however, using many mixtures of at least two alkyl cyanoacetates or mixtures of one or more alkyl cyanoacetates with phenyl cyanoacetate or cyclohexyl cyanoacetate. In the preparation of the monomers the use of mixed at-cyanoacetates has the ad- vantage of giving a mixed polymer which is more readily depolymerized than are the unmixed cyanoacrylate poly- mers. Thus the depolymerization can be effected at a lower temperature using such mixed oucyanoacetates. The relative proportions of the monomers in the com- positions of this invention can be varied as desired de- pending upon the characteristics desired. Generally speaking, the higher esters of ac-cyanoacrylic acid bond more slowly than those of the lower alkyl esters. As a consequence, a mixture of capryl ac-cyanoacrylate with methyl ac-cyanoacrylate results in a composition which polymerizes more slowly than does monomeric methyl cc-cyanoacrylate alone. This more gradual setting of the adhesive bond has advantages in certain applications. For example, it is often desirable to ‘make minor adjustments in the positions of the two articles being bonded before the bond sets up. One of the primary advantages of the compositions embodying this invention is the fact that the adhesive bonds formed therefrom are considerably more flexible after polymerization than are the bonds of homopolymers of at-cyanoacrylates. This is particularly desirable when bonding films, textiles, rubbery materials, and similar articles wherein a pliable rubbery bond is desired. It may also be desirable in bonding rigid articles where the bonded article may be subject to sudden shocks, and where it is desired to have an adhesive bond which per- mits a slight cushioning efiect in the bonded layer. In many cases, the mixed compositions of this invention have superior adhesive properties, particularly in the case of flexible materials, to the unmixed esters. The adhesive compositions can be eflectively stabilized by the inclusion of any of the acidic gaseous polymeriza- tion inhibitors such as sulfur dioxide, nitric oxide, boron trifluoride, hydrogen fluoride, and similar materials. Usually it is necessary to employ the stabilizer in an amount of at least 0.001% by weight based on the weight of the monomeric mixture for adequate stabiliza- tion. Usually the stabilizer content in the adhesive com- position is maintained below about 2% by weight based on the weight of monomer in order that the composition will polymerize rapidly when spread in a thin film. The 2% level of stabilizer is etfective to prevent bulk polymeri- 2,773,232 5 zation of the adhesive over prolonged periods of shelf storage. ’ Compositions containing above 2% by weight of stabilizer are within the scope ‘of the invention, how-' ever, and the stabilizer content can be reduced to the desired level immediately before use. Thus, for ex- ample, when the stabilizer is a normally gaseous material such as sulfur dioxide, the content can be reduced below 2% by subjecting the adhesive composition to reduced pressure immediately before use. An important advantage of the ac-cyanoacrylate adhesive compositions is the fact that no heat or catalyst is nor- mally required to cause setting up of the adhesive bond. This is of particular advantage in the fabrication of articles from irregularly shaped elements where the application of heat or pressure is difficult. If desired, however, a basic catalyst or heat or pressure-, or a combination of these, can be employed for accelerating the polymerization of the adhesive film. This is particularly true when at least one of the esters in .the mixed ester compositions of this invention is a higher ester which normally poly- merizes less rapidly than the lower alkyl esters such as methyl oucyanoacrylate. As l1as been indicated, the bonding of flexible articles is readily carried out by merely spreading a thin film of the adhesive composition on one or more of the surfaces to be bonded and bringing the coated surfaces into con- tact. The bond which is formed by the compositions of this invention has a flexible character, whereby the bonded area does not become hard and inflexible in contrast to the remainder of the article. This is a particular advan- tage when bonding such flexible materials as plastic films, textiles, paper and the like where the presence of a rigid area is undesirable. The compositions of the invention normally possess a relatively low viscosity which permi-ts the adhesive com- position to completely cover the surface to be bonded and to flow into any minor irregularities in the surface. In some cases, however, it may be desirable to increase the viscosity of the adhesive composition in order to pre- vent undue flow of the composition during application. This can be readily accomplished by adding up to 25% by weight of a suitable polymeric material which is solu- ble in the mixed monomer. Typical polymeric materials which can be used for increasing viscosity include the polymeric alkyl cyanoacrylates, polyacrylates, polymeth- acrylates, cellulose esters, and similar well known poly- meric additives. The invention is illustrated by the following examples of certain preferred embodiments‘ thereof. It will be understood, however, that the examples are included to illustrate the invention and are- not intended to limit the scope of the invention as defined herein unless otherwise specifically indicated. ~ Example I A mixture of 38 g. of’ ethyl cyanoacetate, 33 g. of methyl cyanoacetate, and 8 drops of piperidine was added dropwise over a period of 20 minutes to 54 g. of 37% aqueous formaldehyde preheated to 80° C. The reac- tion was exothermic and no external heating was re- quired to maintain the reaction temperature at 80—90° C. during the addition. Heating was continued at 80-90“ C. for 30 minutes after the addition was completed. The resulting mixed low molecular weight or-cyanoacrylate polymer was light yellow in color and could be poured while molten into a suitable vessel in which it was al- lowed to harden. This polymer was then separated from unreacted reactants, ground, dried and mixed with 4% phosphorus pentoxicie and 1.5% hydroquinone. This mixture was then heated under reduced pressure to eifect depolymerization. The. depolymerization began at a tem- perature below 200° C. which was in marked contrast to depolymerization temperatures of at least 220° C. which are required ordinarily with homopolymers. During the depolymerization sulfur dioxide was introduced into the reaction system and allowed to mix with the monomeric 10 15 29 25 30 40 50 G0 70 75 6 vapors which were evolved.» The niénoiner vapofs con: taining sulfurdioxide were condensed and collected in an 80%’ yield of the mixed monomer. This monomeric mixture was then used directly for bonding such articles as cellulose acetate films, polyterephthalate films, and polyester films, and the bonded areas showed improved flexibility over bonds which were obtained using either of the monomers alone. Example 2 The proportions of the monomers can be varied widely over the range of 5 to 95% by weight of each monomer. Thus, for example, a mixture of 90 parts by weight of methyl wcyanoacrylate and 10 parts by weight of ethyl cyanoacrylate was prepared by admixing the individual preformed monomers. This composition showed excel- lent adhesive properties and gave flexible rubbery bonds. Example 3 Similar results were obtained usinga mixture of 10 parts by weight of methyl at-cyanoacrylate and 90 parts by weight of ethyl cyanoacrylate. Example 4 Although mixtures of alkyl esters of cc-cyanoacrylic acid are‘ usually employed for convenience, any of the alkyl esters can be admixed with phenyl cc-cyanoacrylate in amounts of from 5 to 95% by weight based on the combined monomer weight. Thus 20 parts by weight of phenyl ac-cyanoacrylate was admixed with 80 parts by weight of ethyl cyanoacrylate to give a composition which gave rubbery flexible bonds when employed for adhering together film materials. Example 5 The polymerization period of the adhesive composi- tion is lengthened by admixing methyl cyanoacrylate with a higher alkyl cyanoacrylate. A mixture of 30 parts by weight of isobutyl oc-cyanoacrylate with 70 parts by weight of methyl cyanoacrylate gave excellent adhesion, and the rubbery flexible bond formed more slowly than was the case with mixtures of methyl and ethyl oc-cyano- acrylates. The polymerization period can be further ex- tended using a higher alkyl ester as, for example, mix- tures including capryl a-cyanoacrylate. This permits minor adjustments in the positioning of the elements being bonded before the adhesive bond has completely set up. Example 6 A mixture of 40 parts by weight of cyclohexyl a-cyano- acrylate and 60 parts by weight of methyl ac-cyanoacrylate was an excellent adhesive for a variety of different mate- -rials. It showed particular utility in bonding flexible ma- terials since it gave flexible rubbery bonds. Example 7 A mixture of 5 parts by weight of monomeric phenyl at-cyanoacrylate and 95 parts by weight of isobutyl cyano- acrylate gave the desired flexible bonds when employed for adhering together cellulose acetate films. Similar advantageous results are obtained with other combinations of the monomers as defined herein over the range of proportions as described. Usually mixtures of two monomers are employed, although three or more monomers can be admixed if desired. Desirably, when the adhesive composition is to be stored for any prolonged period of time before use, the composition contains a suitable polymerization inhibitor which is desirably sulfur dioxide. The compositions embodying this invention can be used for bonding together a great variety of similar or dissimilar materials, including rigid materials such as metals, glass, wood, and the like, or flexible materials as already described. Although the invention has been described in con- siderable detail with particular reference to certain pre- 2,776,232 7 ferred embodiments thereof, variations and modifica- tions can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims. We claim: 1. An adhesive composition adapted to ‘form flexible adhesive bonds and comprising a mixture of monomeric wcyanoacrylate esters consisting of 5—95% by weight of a monomeric ester of at-cyanoacrylic acid from the class having the formula CH2=C—COOR éu wherein R is a member of the group consisting of alkyl groups of 1 to 16 carbon atoms, cyclohexyl groups and phenyl groups, and 95—5% by weight of a different monomeric ester of ac-cyanoacrylic acid from said class, said mixture being stabilized by incorporation therein of at least 0.001% by weight based on the weight of said mixture of an acidic gaseous polymerization inhibitor of the group consisting of sulfur dioxide, nitric oxide, boron trifluoride and hydrogen fluoride. 2. An adhesive composition adapted to ‘form flexible adhesive bonds and consisting of a mixture of 5—95% by weight of monomeric methyl oucyanoacrylate and 95—5% by weight of a different monomeric ester of et- cyanoacrylic acid of the formula CH2=C|3~C00R ON wherein R is from the group consisting of alkyl groups of 1 to 16 carbon atoms, cyclohexyl groups and phenyl groups, said mixture containing 0.001 to 2% by weight based on the weight of said mixture of sulfur dioxide as a polymerization inhibitor. 3. An adhesive composition adapted to form flexible adhesive bonds and consisting of a mixture of at least two alkyl esters of at-cyanoacrylic acid wherein each alkyl group contains 1 to 16 carbon atoms, said mix- ture containing 0.001 to 2% by weight based on the weight of said mixture, of sulfur dioxide. 4. An adhesive composition adapted to form flexible adhesive bonds and consisting of a mixture of an alkyl ester of oc-cyanoacrylic acid in which the alkyl group tains from 1 to 16 carbon atoms and a phenyl ester of at-cyanoacrylic acid, said mixture containing 0.001 to 2% by weight based on the weight of said mixture, of sulfur dioxide. 5. An adhesive composition adapted to form flexible adhesive bonds and consisting of a mixture of a cyclo- hexyl ester of oz-cyanoacrylic acid and an alkyl ester of cyanoacrylic acid wherein the alkyl group contains from 1 to 16 carbon atoms, said mixture containing 0.001 to 2% by weight basedon the weight of said mixture, of sulfur dioxide. 6. An adhesive composition consisting of from 5 to 95% by weight of monomeric methyl oz-cyanoacrylate and 95 to 5% by weight of a different monomeric alkyl 10 15 20 25 30 35 40 45 U1 U1 8 ester of wcyanoacrylic acid in which the alkyl group contains 2 to 16 carbon atoms, said mixture containing 0.001 to 2% by weight of sulfur dioxide. 7. An adhesive composition consisting of a mixture of 5—95% by weight of monomeric methyl oc-cyano- acrylate and 95 % by weight of monomeric ethyl a-cyano- acrylate, said composition including 0.001 to 2% by weight of sulfur dioxide based on the weight of said mixture. 8. An adhesive composition consisting of a mixture of a major proportion of methyl on-cyanoacrylate and a minor proportion of cyclohexyl or-cyanoacrylate stabilized with 0.001 to 2% by weight of sulfur dioxide based on the weight of said mixture. 9. A laminated article comprising at least two ele- ments adhered together by a flexible polymerized fihn resulting from the polymerization in situ of a mixture of polymerizable monomers consisting of on-cyano- acrylate esters of the formula CH2-—iC—OOOR éu wherein R is selected from the group consisting of alkyl groups of 1 to 16 carbon atoms, cyclohexyl groups and phenyl groups. 10. A flexible laminated article comprising at least two flexible elements adhered together by a flexible polymerized film resulting from the polymerization in situ of a mixture of polymerizable monomers consisting of on-cyanoacrylate esters of the formula CH2=C—C O O R I ON wherein R is selected from the group consisting of alkyl groups of 1 to 16 carbon atoms, cyclohexyl groups and phenyl groups, a major portion of said mixture being a lower alkyl on-cyanoacrylate. 11. A flexible laminated article comprising at least two flexible elements adhered together by a flexible poly- merized film resulting from the polymerization in situ of a mixture of polymerizable monomers consisting of wcyanoacrylate esters of the formula CH2=(I3—C 0 OR ON wherein R is selected from the group consisting of alkyl groups of 1 to 16 carbon atoms, cyclohexyl groups and phenyl groups, a major portion of said mixture being methyl oucyanoacrylate. ‘ ' References Cited in the file of this patent UNITED STATES PATENTS 2,346,858 Mighton ____________ __ Apr. 18, 1944 2,467,927 Ardis _______________ __ Apr. 19, 1949 2,492,170 Mast et al. ___________ __ Dec. 27, 1949 2,535,827 Ardis et al. __________ __ Dec. 26, 1950 2,672,477 Heinemann __________ __ Mar. 16, 1954