Adhesive Composition

United States Patent [19] Kimura et al. [54] ADHESIVE COMPOSITION [75] Inventors: Kaora Kimura; Kyoji Sugiura, both of Nagoya, Japan Toagosei Chemical Industry Co., Ltd., Tokyo, Japan [21] Appl. No.: 209,253 [73] Assignee: [22] Filed: Nov. 21, 1980 [30] Foreign Application Priority Data Dec. 24, 1979 [JP] Japan .............................. .. 54/166932 [51] Int. Cl.3 .......................................... .. C08F 120/36 [52] U.S. Cl. ....................... .. 524/549; 526/270; 526/298; 524/555 [58] Field of Search ................. .. 260/29.6 WQ, 465.4; 526/270, 298 [56] References Cited U.S. PATENT DOCUMENTS 2,784,215 3/1957 Joyner ...................... .. 526/298 3,465,027 9/1969 Hawkins . .. 260/465.4 3,527,841 9/1970 Wicker 526/298 3,559,652 2/1971 Banitt .... .. 526/298 3,728,375 4/1973 Coover ........................... .. 260/465.4 OTHER PUBLICATIONS Japanese Patent Application Kokai 130438/74. [11] 4,321,180 [45] Mar. 23, 1982 Journal of the Japanese Society of Adhesion, vol. 4, No. 2, 1968, pp. 67-70. Primary Examz'r1er—Paul R. Mich] Attorney, Agent, or Firm—Cooper, Dunham, Clark, Griffin & Moran [57] ABSTRACI‘ An adhesive composition consisting essentially of (A) an alkyloxyalkyl 2-cyanoacrylate represented by the formula, CN I Cl-lp_=C-COO-R-0—R’ wherein R is an alkylene group having 2 to 4 carbon atoms and R’ is an alkyl group having 2 to 6 carbon atoms, or tetrahydrofurfuryl 2-cyanoacrylate, (B) 300 to 2,000 ppm. of water, (C) a radical-polymerization inhibitor, and (D) an anionic-polymerization inhibitor. This adhesive composition is useful as an instant-setting adhesive for metals, plastics, rubbers, glass, wood and the like, is excellent in instant-setting properties, bond strength and storage stability, and neither emits an irri- tating odor nor causes whitening of the adherend sur- face. 12 Claims, No Drawings 4,321,180 1 ADHESIVE COMPOSITION This invention relates to an adhesive‘ comprising an ether-linkage-containing alkyl 2-cyanoacrylate, that is, an alkyloxyalkyl 2-cyanoacrylate, or tetrahydrofurfuryl 2-cyanoacrylate. Since 2-cyanoacrylate adhesives generally become ‘hardened instantaneously at room temperature by the moisture adsorbed in a minute quantity on the surface of an adherend, they are widely utilized in various indus- trial fields to bond metals, plastics, rubbers, glass, wood and the like. However, conventional alkyl 2-cyanoacrylate adhe- sives have such defects that they emit an irritating odor and have a tendency to cause whitening, that is, such a phenomenon that white powder has been scattered on the adherend surface on application of the adhesive. Further, there is such a disadvantage that when the alkyl 2-cyanoacrylate adhesive has been cured, the re- sulting polymer per se is hard and brittle and lacks flexibility, and hence is insufficient in resistance to im- pact or flexure. » Among the known adhensives of the alkyl 2-cyanoa- crylate type, those in actual use are methyl 2-cyanoa- crylate, ethyl 2-cyanoacrylate, n-propyl 2-cyanoacry- late, n-butyl 2-cyanoacrylate and isobutyl 2-cyanoacry- late. Other alkyl 2-cyanoacrylate adhesives have never been put into practical use. These monomeric esters are all alike in chemical and physical properties and in ad- hesive activity. As a consequence, the adhesive activi- ties of all the adhesive compositions comprising the above-noted alkyl esters resemble closely the adhesive activity of ethyl 2-cyanoacrylate adhesive which is used most widely at present. Higher alkyl 2-cyanoacrylates have been known to be lower in bonding speed and, in addition, in tensile, shear and impact strengths of the bonds. Further, it has been well known that conven- tional alkyl 2-cyanoacrylate adhesives have an irritating odor and a tendency to cause whitening. A conventional process of manufacturing alkyl 2- cyanoacrylates has been publicly known in U.S. Pat. Nos. 2,721,858; 2,756,251; and 2,763,677. An alkyl cya- noacetate and formaldehyde are allowed to react at 50° to 90° in an organic solvent in the presence of a basic condensation catalyst such as piperidine or the like to form a condensation product and the water. set free by the reaction is removed by distillation. After the re- moval of the solvent by distillation, the condensation product is depolymerized in the presence of phosphorus pentoxide (P205) at a temperature of 100° to 185° C. under a pressure of 15 mmHg or less to give an alkyl 2-cyanoacrylate. Although the above process is most generally used, there are specific processes. In one of said processes, tricresyl phosphate is added in depolym- erizing the condensation product to dissolve the latter (U.S. Pat. No. 2,756,251). Japanese Patent Publication No. l4,567/ 63 discloses a process by which the conden- sation product of an alkyl cyanoacetate and formalde- hyde is depolymerized after washing it with an aqueous acidic solution to yield an alkyl 2-cyanoacrylate mono- mer, chiefly monomeric methyl 2-cyanoacrylate. The above production examples all pertain to those for alkyl 2-cyanoacrylate adhesives. The performance characteristics and the stability of a 2-cyanoacrylate adhesive are very ‘sensitive to the contamination with minute amounts of moisture, basic or acidic substances. Accordingly, the process and conditions for manufac- 5 10 15 20 25 30 35 45 50 55 60 65 2 ture and adhesive performance of a monomeric 2- cyanoacrylate must be properly selected for each kind of esters. It has been well known to those skilled in the art that it is impossible to apply the knowledge about the manufacturing conditions and properties of such conventional alkyl 2-cyanoacrylates as methyl 2- cyanoacrylate and ethyl 2-cyanoacrylate to the cases of other specific monomeric 2-cyanoacrylate esters. The alkyloxyalkyl 2-cyanoacrylates of the general formula CH2=C(CN)—COO—IR--O——R’ wherein R is an alkylene radical of 2 to 4 carbon atoms and R’ is an alkyl group of 2 to 6 carbon atoms, are known cou- pounds as disclosed in U.S. Pat. No. 2,784,215. How- ever, if they are prepared by applying without modifi- cation the process and conditions for manufacture de- scribed in said patent specification or those for conven- tional alkyl 2-cyanoacrylates, the yield will be as low as 10 to 20% by weight owing to marked repolymerization of the alkyloxyalkyl 2-cyanoacrylate in the vapor phase during depolymerization; in fact, gas-chromatographic analysis revealed that the purity was as low as 70 to 80% and large amounts of an alkyloxyalkyl cyanoace- tate and an alkyloxyalkanol were detected. Thus, in spite of purification by repeated distillation, the al- kyloxyalkyl 2-cyanoacryaltes prepared by conventional processes do not exhibit sufficient adhesive characteris- tics and stability for the practical use. Although the reason is yet to be elucidated, such phenomena are originated from the difference in chemi- cal structure between the alkyloxyalkyl 2-cyanoacry- late and the conventional alkyl 2-cyanoacrylate. It is presumable that when a substance promoting an abnor- mal decomposition is present in the depolymerization mixture, abnormal decomposition of the alkyloxyalkyl group results in an ether, alcohol or the like, which accelerates the vapor phase-polymerization. Such ac- celerated polymerization plus its synergistic effect with autocatalysis due to the ether linkage of the alkyloxyal- kyl 2-cyanoacrylate itself seem to give rise to the above behavior which is different from that of alkyl 2-cyanoa- crylate. A cyanoacetate seems also to be formed by the abnor- mal decomposition in this case. When a large amount of cyanoacetate is present in an alkyloxyalkyl 2-cyanoa- crylate after depolymerization, it is very diffecult to purify the latter by distillation because of the close proximity of the boiling points. As described above, the alkyloxyalkyl cyanoacetate and alkyloxyalkanol which contaminate the alkyloxyal- kyl 2-cyanoacrylate during the preparation thereof ad- versely affect the performance characteristics of the adhesive such as bond strength, instant-setting ability, storage stability, etc. The present inventors have con- ducted further studies on the effect of the above con- taminants and found that when the alkyloxyalkyl 2- cyanoacetate or alkyloxyalkanol content exceeds 5% by weight, the above-mentioned characteristics become rapidly deteriorated, thus rendering the adhesive sub- stantially useless. It has been further found that minute amounts of impurities affect the depolymerization to deteriorate the product quality. The present inventors have consequently found that in order to render an alkyloxyalkyl 2-cyanoacrylate or tetrahydrofurfuryl 2-cyanoacrylate excellent in perfor- mance chracteristics and life (storage stability) as an adhesive, it is necessary, prior to the depolymerization step, to remove or consume by reaction minute amounts 4,321,180 3 of impurities promoting the abnormal decomposition, which have been produced as by-products or incorpo- rated in the condensation step while maintaining the viscosity of the condensation product within a certain range, whereby the subsequent depolymerization pro- ceeds easily and a high quality adhesive may be ob- tained. Further, it has been known that although excellent in adhesive performance, a high purity 2-cyanoacrylate is unsuitable for a long-term storage owing to its high activity and instability. The present inventors have, therefore, carried out extensive research to eliminate the said defect and, as a result, have found that an adhe- sive composition free from said defect is obtained by allowing the composition to contain a specified amount of water. An object of this invention is to provide an adhesive composition comprising an alkyloxyalkyl 2-cyanoacry- late or tetrahydrofurfuryl 2-cyanoacrylate. Another object of this invention is to provide an adhesive composition excellent in instant-setting ability, bond strength and storage stability, unsusceptible to whitening of the adherend surface, and free from an irritating odor. Other objects and advantages of this invention will become apparent from the following description. According to this invention, there is provided an adhesive composition consisting essentially of (A) an alkyloxyalkyl 2-cyanoacrylate represented by the gen- eral formula, CN I Cl-l2=C—COO-R-0-R’ wherein R is an alkylene group having 2 to 4 carbon atoms and R’ is an alkyl group having 2 to 6 carbon atoms, or tetrahydrofurfuryl 2-cyanoacrylate, (B) 300 to 2,000 ppm. of water, (C) a radical-polymerization inhibitor, and (D) an anionic-polymerization inhibitor. The alkyloxyalkyl 2-cyanoacrylate and tetrahydro- furfuryl 2-cyanoacrylate employed in this invention must be of a high purity, and can be prepared by wash- ing with water or an aqueous acidic solution the con- densation product of formaldehyde with an alkyloxyal- kyl cyanoacetate represented by the formula, NC—CH- 2—CO2—R—O—R’, wherein R and R’ are as defined above or tetrahydrofurfuryl cyanoacetate, while main- taining the viscosity of the condensation product within the range of from 1 to 500 centipoises, thereafter depo- lymerizing the washed condensation product and then distilling the depolymerization product. The above method is described in more detail below. An alkyloxyalkyl cyanoacetate of the formula, NC—CH2—CO2——R—O~—R', or tetrahydrofurfuryl 2-cyanoacetate is allowed to condense with formalde- hyde in the presence of 0.01 to 10 mole %, based on said cyanoacetate, of a basic catalyst, that is, a basic com- pound such as an amine, e.g. piperidine, sodium hydrox- ide, potassium hydroxide, or an alkali metal alkoxide. The molar ratio of the alkyloxyalkyl or tetrahydrofurfu- ryl cyanoacetate to formaldehyde in the reactant mix- ture is preferably l:O.7—1.3, more preferably 1:1. A solvent is usually used in the condensation reac- tion. As the solvents, there may be used inert solvents such as benzene, toluene, ethyl alcohol, chloroform, trichloroethylene, tetrahydrofuran, water and the like. It is also possible to use a binary solvent, such as a mix- ture of water and toluene. The amount of the solvent 10 15 20 25 30 35 40 45 50 55 60 65 4 used is preferably in the range of 50 to 300 ml per mole of the alkyloxyalkyl orgtetrahydrofurfuryl cyanoace- tate. The condensation reaction is carried out preferably at a temperature of 30° to 150° C., more preferably at a reflux temperature of 50° to 100° C. A reaction time of from several hours to 24 hours is suitable. The conden- sation product of an alkyloxyalkyl or tetrahydrofurfu- ryl cyanoacetate with formaldehyde is a high-viscosity liquid or a brittle solid containing a trace to small amounts of the condensation catalyst, unreacted reac- tants, an acid, an alcohol, by-products of the reaction, lower condensation products, and the like. As previously described, no success is obtained by depolymerizing the above condensation product as such in the presence of a depolymerization catalyst such as P205 or the like. The condensation product should be washed with an aqueous acidic solution or water, and, although the reason is not clarified, it is essential, during the washing treatment, to maintain the viscosity of the condensation product within the range of 1 to 500, preferably 20 to 250, centipoises. When a condensate having a viscosity outside the said range is washed, the washed product is difficult to depolymerize in the next step, or even if depolymerization is possible, no good quality adhesive is obtained. The maintenance of the viscosity of the condensation product within the range of 1 to 500, preferably 20 to 250, centipoises can be achieved by elevating the temperature up to about 100° C. or by employing in the condensation step a predeter- mined amount of a solvent, for example, an aromatic hydrocarbon such as benzene, toluene or the like; a ketone such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone or the like; an ester such as ethyl acetate, butyl acetate or the like, a chlorohydrocarbon such as trichloroethylene, dichloroethane or the like; an ether such as methyl ethyl ether or the like or a furan compound such as tetrahydrofuran, or by diluting the condensation product with said solvent. The washing is carried out at a temperature in the range of 0° to 100° C. The acids used in the washing treatment include those which show acidity in aqueous solution, such as sulfuric acid, hydrochloric acid, phos- phoric acid, p-toluenesulfonic acid, benzenesulfonic acid, formic acid,» acetic acid and the like. The concen- tration of the acid is preferably in the range of 0.01 to 5% by weight. The condensation product washed under the above- mentioned conditions is depolymerized in a conven- tional manner. That is to say, the depolymerization is effected by heating the condensation product at a tem- perature in the range of 100° to 250° C., preferably 140° to 200° C. in vacuo in the presence of a depolymeriza- tion catalyst such as phosphorus pentoxide, phosphoric acid, or polyposphoric acid, whereby a crude monomer is obtained in a high yield. On redistilling the crude monomer, there is obtained a high quality alkyloxyalkyl or tetrahydrofurfuryl 2- cyanoacrylate. _ In the above case, only by the process by which the condensation product is washed while maintaining its viscosity within the range of 1 to 500, preferably 20 to 250, centipoises, there is obtained an alkyloxyalkyl or tetrahydrofurfuryl 2-cyanoacrylate having an unre- acted 2-cyanoacetate content of 5% by weight or less, preferably 2% by weight or less, most preferably 1% by weight or less, an alcohol content of 5% by weight or 4,321,180 5 less, preferably 2% by weight or less, most preferably 1% by weight or less, and a low moisture content. The alkyloxyalkyl 2-cyanoacrylates used in this in- vention include, for example, 2-ethoxyethyl 2-cyanoa- crylate, 2-propoxyethyl 2-cyanoacrylate, 2-butoxyethyl 2-cyanoacrylate, 2-hexyloxyethyl 2-cyanoacrylate, 2- ethoxybutyl i 2-cyanoacrylate, 2-amyloxyethyl 2- cyanoacrylate, and the like. It has heretofore been considered that the smaller the moisture content in the alkyl 2-cyanoacrylate, the bet- ter. U.S. Pat. No. 3,728,375 discloses that when the monomeric 2-cyanoacrylate is prepared in a production apparatus which has been dried the moisture content in the monomer obtained becomes 50 to 200 ppm., the setting time is short (in other words, the bonding speed is high), and the storage stability is excellent. The rapid deterioration in adhesive performance of a 2-cyanoa- crylate having a moisture content exceeding 200 ppm. during storage is due to an increase in acidic substance content by decomposition of the 2-cyanoacrylate caused by the water molecules contained therein. It is also known, as is clear from Japanese Patent Applica- tion Kokai (Laid-Open) No. 130,438/74, that an alkyl 2-cyanoacrylate of a moisture content of 5,000 to 10,000 ppm. has a short setting time and an excellent storage stability. Therefore, a conventional alkyl 2-cyanoacry- late adhesive has been considered to exhibit excellent adhesive performance characteristics when its moisture content is in the range of from 50 to 200 ppm. or in the range of 5,000 to 10,000 ppm., whereas when the mois- ture content is in the intermediate range of 200 to 5,000 ppm., the storage stability becomes lower, the perfor- mance characteristics deteriorate rapidly during stor- age, and the adhesive activity becomes also low. The alkyloxyalkyl or tetrahydrofurfuryl ‘ 2-cyanoa- crylate obtained as described above is of a high purity and is excellent in bonding performance, but owing to its high activity and low stability, it is unsuitable for the long-term storage. The present inventors have carried out extensive research to ameliorate the adhesive performance as well as the storage stability of the alkyloxyalkyl cyanoacry- late and have, as a result, found that quite contrary to the case of conventional alkyl 2-cyanoacrylate, an al- kyloxyalkyl 2-cyanoacrylate monomer exhibits a high activity short setting time, high bond strength and opti- mum storage stability when the monomer has a mois- ture content in the range of 300 to 2,000 ppm., prefera- bly 400 to 1,500 ppm. In the case of this invention, when the moisture con- tent in the alkyloxyalkyl 2-cyanoacrylate or tetrahydro- furfuryl 2-caynoacrylate is less than 300 ppm., the stor- age stability of the adhesive is markedly low. Although the reason therefor is not entirely understood, the low storage stability seems to result from the ether linkage of the monomer. The ether linkage has a tendency to cause or promote free-radical or anionic polymerization of the 2-cyanoacrylate, and when the moisture content in the adhesive composition becomes less than 300 ppm., the adhesive composition becomes too active and the viscosity thereof is consequently increased with the lapse of time during storage until the hardening occurs finally. Further, when the adhesive composition has a moisture content of less than 300 ppm., wetting of the adherend surface with the adhesive composition be- comes markedly inferior, the penetration of the compo- sition into the adherend surface layer becomes also low, and the bond strength thereof tends to decrease. 10 20 25 30 35 45 50 55 65 6 On the other hand, when the: moisture content ex- ceeds 2,000 ppm., the storage stability decreases, and the setting time becomes remarkably long with the lapse of time. At the same time, the bonding strength de- creases, so that the composition has lost completely its function as an instant-setting adhesive. If the moisture content is further increased to reach more than 5,000 ppm., the viscosity of the adhesive composition, of course, increases in a relatively short period of time until the composition hardens finally. It is well-known from U.S. Pat. Nos. 3,728,375 and 3,465,027 that with the decrease in moisture content, the alkyl 2-cyanoacrylate becomes better in adhesive per- formance and in storage stability, and particularly, a moisture content of 50 to 200 ppm. is preferable. Quite contrary to the conventional knowledge, in the case of the alkyloxyalkyl 2-cyanoacrylate or tetrahydrofurfuryl 2-cyanoacrylate of this invention, it is necessary that the moisture content be in the range of 300 to 2,000 ppm., preferably 400 to 1,500 ppm. If the moisture content falls outside the said range, it is difficult to obtain an adhesive satisfactory in both storage stability and adhe- sive activity. As described previously, the allkyloxyalkyl 2-cyanoa- crylate of this invention is represented by the general formula, CN l CHg=C-COO--R—O—R’ wherein R is an alkylene radical of 2 to 4 carbon atoms and R’ is an alkyl group having 2 to 6 carbon atoms. A 2-cyanoacrylate having the above formula wherein R has one carbon atom cannot be employed in this invention because of its instability and susceptibility to hydrolysis with a minute amount of moisture, whereas a 2-cyanoacrylate having 5 or more carbon atoms in R is difficult to obtain in a highly pure form, so that an adhe- sive inferior in both adhesion performance and stability will result. A 2-cyanoacrylate having one carbon atom in R’ cannot be freed from malodor, is of low stability (this stability is difficult to improve even by the control of moisture content), and gives an adhesive inferior in adhesive performance, particularly in water resistance and durability. When R’ has 7 or more carbon atoms, a high-purity monomer is difficult to obtain and the adhe- sive obtained therefrom is deficient in performance characteristics and stability. The adhesive composition of this invention compris- ing an alkyloxyalkyl 2-cyanoacrylatebr tetrahydrofur- furyl 2-cyanoacrylate should contain an anionic-polym- erization inhibitor to protect the composition from vis- cosity increase and gelation caused by the moisture during storage. Specific examples of the inhibitors in- clude S02, S03, NO, N02, HCl, H3PO4, esters of hy- drogen phosphate, aromatic sulfonic acids, alkylsul- fonic acids, propanesultone, triflluoromethanesulfonic acid, perfluoroalkylcarboxylic acids and the like. These are used in an amount of preferably 1 to 10,000 ppm., more preferably 5 to 1,000 ppm. Further, the adhesive composition of this invention must contain a radical-polymerization inhibitor. This is for preventing the composition from radical polymeri- zation during storage and is, at the same time, an antiox- idant to inhibit the formation or accumulation of perox- ides caused by the ether linkage of the alkyloxyalkyl 2-cyanoacrylate or tetrahydrofurfuryl 2-cyanoacrylate. 4,321,180 7 Typical examples of the radical-polymerization inhibi- tors are aryl alcohols such as phenol, cresols, hydroqui- none, benzoquinone, a-naphthol, /3-naphthol, catechol, pyrogallol, Bisphenol-A, Bisphenol-S, 2,6-di-tert-butyl- phenol, 2,6-di—tert-butylcresol, 2,2’-methylene-bis(4- methyl~6-tert-butylphenol), 4,4’-butylidene-bis(3-meth- yl—6-tert-butylphenol), 4,4’-thiobis(3-methyl-6-tert- butylphenol), 4,4’-thiobis(3-methyl-6-tert-butylphenol), hydroquinone monomethyl ether, 2-hydroxybenzophe- none, phenylsalicylic acid, 1,3,5-trimethyl-2,4,6-tris(3,5- di-tert-butyl-4-hydroxybenzyl)benzene, and the like. These are used in an amount of preferably 1 to 10,000 ppm., more preferably 10 to 5,000 ppm. Conventional alkyl 2-cyanoacrylates are not liable to peroxide formation and, hence, do not necessarily re- quire a radical-polymerization inhibitor. However, in the case of the alkyloxyalkyl 2-cyanoacrylate or tetra- hydrofurfuryl 2-cyanoacrylate of this invention, the methylene radical involved in an ether linkage is liable to peroxide formation so that it becomes necessary to inhibit the peroxide formation or to decompose the formed peroxide by the addition of an antioxidant of the aromatic alcohol type. The adhesive composition of this invention may have incorporated thereinto, if necessary, thickners, plasticiz- ers, dyes, pigments, solvents, diluents, perfumes, etc. The adhesive composition of this invention is very useful as an instant-setting adhesive which is hardly susceptible to whitening, is free from irritating odor, and is more flexible than conventional alkyl 2-cyanoa- crylates. The invention is illustrated below with reference to Examples which are merely illustrative and not limita- tive. In the Examples, all percentages and parts are by weight unless otherwise specified. EXAMPLE 1 Into a four-necked flask provided with a stirrer, a thermometer, a water trap and a dropping funnel were charged 60 parts of paraforrnaldehyde, 200 parts of toluene and 0.2 part of piperidine. To the mixture was added dropwise at 80° to 90° C. with stirring 314 parts of 2-ethoxyethyl cyanoacetate. After the completion of the dropwise addition, the mixture was allowed to react 10 15 20 25 30 35 40 under reflux, while removing the water formed by the 45 reaction, until all of the theoretical amount of water had been distilled out. The reaction mixture was then cooled down to room temperature. To the resulting condensa- tion mixture having a viscosity of 200 centipoises was 8 added 300 parts of a 1% aqueous solution of p-toluene- sulfonic acid. The mixture was shaken at 70° C., and then allowed to stand, upon which it separated into two layers. The oil layer thereof was taken out. The oil layer was distilled under reduced pressure to remove the toluene. To the condensation product left in the pot were added 3 parts of each of phosphorus pen- toxide and hydroquinone. The mixture was subjected to depolymerization by heating at 150° to 200° C. under a pressure of 3 to 5 mmHg to obtain 266 parts (83% yield) of a crude monomer. The crude monomer had a purity of 96.8% and contained 0.50% of 2-ethoxyethyl 2-cyan- oacetate, 1.20% of 2-ethoxyethanol, 0.15% of moisture, and 1.3% of other impurities in total. After the addition of 0.5% of phosphorus pentoxide and 0.5% of hydroquinone to the crude monomer, the resulting mixture was redistilled to obtain 220 parts of 2-ethoxyethyl 2-cyanoacrylate containing 0.48% of 2-ethoxyethyl cyanoacetate, 0.50% of 2-ethoxyethanol, and 0.05% of moisture, the boiling point and the purity having been l00°—l02° C./ 3 mmHg and 98.8%, respec- tively. An adhesive composition was prepared by add- ing to the above monomer 50 ppm. of S02 and 100 ppm. of hydroquinone. On the other hand, water was added to the ethoxyethyl 2-cyanoacrylate containing 0.05% (500 ppm.) of moisture, to prepare adhesive composi- tions containing, respectively, 1,000 ppm., 1,500 ppm., 1,800 ppm. (these are Examples of this invention), 2,500 ppm. and 5,000 ppm. (these are Comparative Examples) of moisture based on the weight of the ethoxyethyl 2-cyanoacrylate. . Further, an adhesive composition containing 200 ppm. of moisture was prepared by drying the ethox- yethyl 2-cyanoacrylate coptaining 0.05% of moisture with a molecular sieve (3 A) (Comparative Example). USE EXAMPLES 1 TO 4 AND COMPARATIVE USE EXAMPLES 1 TO 3. The adhesive compositions of the Examples and the Comparative Examples obtained in Example 1 were tested for forced storage stability including the adhesive characteristics. The results obtained were as shown in Table 1. Each adhesive was placed in a polyethylene container, 2 ml in volume, and kept in a thermostat at 60° C. to examine the deterioration with the lapse of time. Fifty days of the forced deterioration correspond to about one year of allowing to stand at room tempera- ture in the dark. TABLE 1 Early-stage bonding per- After 30 days of After 50 days of forced formancc forced deterioration deterioration Tensile Tensile Tensile Composition shear shear shear Mois- Hydro- Setting strength Setting strength Setting strength ture S02 quinone time of bond time of bond Vis- time of bond Vis- (ppm) (ppm) (ppm) (sec.) (kg/cmz) , (sec.) (kg/cm?-) cosity (sec.) (kg/cmz) cosity Use Example - No No 1 500 50 200