Stabilized Alpha-Cyanoacrylate Compositions

United States Patent [191 Sweeny et al. [541 [751 [731 [221 [21] ‘[1621 [52] [51] 158] STABILIZED ALPHA-CYANOACRYLATE COMPOSITIONS Inventors: Norman P. Sweeny, North Oaks, Minn.; Karl Friedrich Thom, Cologne, Gennany Assignee: Minnesota Mining and Manufacturing Company, St. Paul, Minn. Filed: Aug. 27, 1975 Appl. No.: 608,267 Related U.S. Application Data Division of Ser. No. 445,862, Feb. 26, 1974, Pat. No. 3,943,146, which is a division of Ser. No. 262,557, June 14, 1972, Pat. No. 3,839,282. U.S. Cl. ........................ .. 260/465 D; 2.60/465.4 Int. Cl.2 .............. .. C07C 121/30; C07C 121/52 Field of Search ............ .. 260/464, 465 D, 465.4 [.11] 3,993,678 145] Nov. 23, 1976 [56] References Cited _ UNITED STATES PATENTS 2,794,788 6/1957 Coover, Jr. et al. ....... .. 260/465.4 X Primary Examiner—.Ioseph Paul Brust Attorney, Agent, or Firm—-Alexander, Sell, Steldt & DeLaHunt [57] ABSTRACT The disclosed compounds are adducts of imidazole or derivatives thereof and sulfur dioxide. The adducts are apparently of the Lewis acid-Lewis base type,‘and are useful as latent curing agents for epoxide resins. The adducts are prepared by interacting the imidazole and sulfur dioxide under anhydrous conditions. Equimolar imidazole—SO2 adducts can serve as a source of sulfur dioxide at room temperature. 4 Claims, No Drawings 3,993,678 1 . STABILIZED ALPHA-CYANOACRYLATE COMPOSITIONS This application is a division of copending applica- tion Ser. No. 445,862 filed Feb. 26, 1974, now U.S. Pat. No. 3,943,146, which in turn is a division of appli- cation Ser. No. 262,557f1led June 14, 1972 and now US. Pat. No. 3,839,282. . — FIELD ‘OF THE INVENTION This invention relates to sulfur 'dioxide—imidazole adducts and methods for making them, the “imidazole” portion of the adduct being either imidazole itself (C3H.,N2) or a derivative thereof; An aspect of this invention relates to latent epoxy curing agents and latent curable epoxide resin systems containing sulfur dioxide-imidazole adducts. further aspect of . this invention relates to _a source for ‘an, acid stabilizerin a closed system. ’ ' . I ‘ DESCRIPTION OF THE PRIOR ART It is well known that sulfur dioxide is a Lewis acid, though not nearly so strong a Lewis acid as, for exam- ple, boron trifluoride. It is also known that nitrogen bases (e.g. amines) are Lewis bases and can react with sulfur dioxide to form adducts. The literature relating to such adducts is extensive, representative examples being W. C. Fernelius, Ed., Inorganic Synthesis, II, McGraw-Hill, NY. (1946); W. E. Byrd, Inorganic Chemistry 1, p. 762 (1962); K. R. Hoffman et al, J. Am. Chem.‘ Soc. 68, p. 997 (1946), H. A. Hoffman et al, J. Am. Chem. Soc._ 70, p. 262 (1948). The Byrd article indicates that the exact structure of aromatic amine—sulfur dioxide complexes is not well understood, since it is possible that the sulfur dioxide could be bound to the adduct via the pi-complex of the aromatic ring. The picture is further complicated by‘. data in the Byrd article and both Hoffman et al articles indicating that some of these aromatic (or heterocyclic-aromatic) amine—sulfur dioxide adducts or complexes are.unsta- ble, though there is little doubt that true adducts, rather than simple mixtures, are formed. . According to U.S. Pat. No. 2,270,490 (Wood), is- sued Jan. 1942, morpholine and sulfur dioxide react to form a compound useful as a photographic developer, local anesthetic, or antioxidant, but in this case it is suggested that the compound can be a true salt, i.e. a salt of the cation-anion type. Some of .the aromatic . amine-sulfur dioxide adducts exhibit crystalline charac- ter and have sharp melting.points, but probably lack this high degree of ionic character. The nature of the amine (aliphatic, aromatic, aromatic heterocyclic, non- aromatic heterocyclic, etc.) appears to have significant effects upon,the nature of the sulfur dioxide adduct or compound, b'ut_these effects have not been explored fully enough to postulate any general rules for all the possible adducts‘. - Apparently none of -these prior art adducts or com- pounds has been investigated) for use as a latent catalyst or initiator or curvature in epoxy resin technology, though amines per_se have been investigated exten- sively. Several different Lewis acid-Lewis base adducts of the amine-boron trifluoride type have been carefully studied by epoxy resin ychemists,-and various theories have been proposed to explain theirpotency or latency, 10 15 20 25 30 35v 40 45 50 2 ample, Harris etval, J. Appl. Polymer Science 10, p. 523 (1966). The Harris et al article provides little or no guidance for one attempting to use a Lewis acid-Lewis base adduct derived from sulfur dioxide instead of boron trifluoride. The degree of latency of an amine — BF3 adduct appears to be independent of its stability (Harris et al, op cit., pp. 523-525 and 527), but the stability of amine — S02 adducts is so variable that latency might very well be a function of the stability of the adduct. Imidazole and its derivatives have been used as non- latent initiators or curative-catalysts for epoxide resins, and various approaches have been used to make latent compounds or complexes containing imidazole nuclei; see, for example, U.S. Pat. No. 3,553,166 (Anderson et al), issued Jan. 5, 1971. Apparently, imidazole-sulfur dioxide adducts have never been reported in the litera- ture and have never been proposed for use as epoxy curing agents or for any other purpose. In view of the variations in the stability of different types of amine- sulfur dioxide adducts and the lack of guidance in the prior art as to their behavior as epoxy initiators, it would be difficult at best to predict the stability and utility of an imidazole-sulfur dioxide adduct. Nor is it even possible-to predict with certainty from the avail- able prior art if such an adduct can even be made and what its structure might be. Analogies between imidaz- ole and other heterocyclic and/or aromatic and/or ali- phatic amines are difficult to draw, due to the unique- ness of the imidazole nucleus (N-c=N—c=C). I I I I Accordingly, this invention contemplates synthesiz- ing adducts from imidazole or derivatives thereof and sulfur dioxide. This invention further contemplates using these adducts in polymer chemistry and formulat- ing either curable latent epoxy resin systems or stabi- lized acrylate monomers containing the adducts. SUMMARY OF THE INVENTION Briefly summarized, the present invention involves the synthesis of imidazole-sulfur dioxide adducts and the discovery that these adducts are useful both as a source for an acidic stabilizer and in the formulation of latent curable epoxides. These latent curable systems have a shelf life of weeks or months (e.g. at least 6 months) and-are rendered non-latent at elevated tem- ’ peratures (e.g. above 50° C., preferably above 130° 55 60 65 as the case may be, in curing diglycidyl ether-bisphenol . A epoxides at various cure temperatures. See, for ex- . C.); that is, the typical epoxide curing reactions can be made to occur expeditiously at these elevated tempera- tures. The compounds of this invention can be pre- pared by exposing imidazole or a derivative thereof (optionally dissolved in a solvent) to liquid or gaseous sulfur dioxide, or a saturated solution thereof, under anhydrous conditions for a period of several minutes until the compound precipitates out as a solid sulfur dioxide-imidazole adduct. The apparent behavior of these solid products in the presence of curable epoxy resins is evidence not only of utility, but also of a stable, adduct-like structure, as. _opposed to a mere physical mixture. The adducts decompose upon heating into sulfur dioxide and imidazole (or an imidazole deriva- 3,993,678 3 tive) and thereby serve as a latent source for either the imidazole or sulfur dioxide. DETAILED DESCRIPTION Adduct-like compounds made according to the pre- sent invention can be represented by the following formula: (lmid),..SO.,, (1) wherein lmid is imidazole or a derivative thereof, i.e. a nucleus of the formula R-I wherein R‘, R2, R‘, and R5 represent substituents se- lectcd from the group consisting of hydrogen, an ali- phatic radical, and an aromatic radical, and, together R‘ and R5 can be the residue of a fused ring. The n term represents a small number less than 4, preferably an integer. The exact structure of the vari- ous species encompassed by n is not a known, but avail- able evidence substantiates the formation of Lewis acid-Lewis base adducts wherein n=l, 2, or 3 or mix- tures of these species. When rt=l, these compounds have a tendency to lose sulfur dioxide slowly until the n=2 species (the most stable) is formed. The terms R‘, R’, R‘, and R5 represent suitable sub- stituents or hydrogen, the preferred substituents being non-hindering organic radicals such as alkyl or aryl radicals or, particularly in the case of R‘ and R5, fused rings. For convenience, the term “an imidazole" or “an imidazole nucleus" is used in this specification to de- note both imidazole itself (C3N,H.,) and the imidazole derivatives of formula (II), set forth previously. The term curing agent is used to denote agents which 2 (lmid). assist or participate in hardening or crosslinking or polymerization reactions which solidify or increase the viscosity of liquid epoxide monomers or prepolymers or convert solid epoxides to tough, durable thermoset materials. Curing agents are referred to as “hardeners“ or “crosslinkers" in some contexts, because of their ability to convert even the liquid monomers or prepoly- mers to thermoset solids. It is also common in the art to (lmid). . so, en [mid + so, (gas) (1) refer to imidazole as a catalyst or initiator since it-as- sists in the opening of the oxirane ring. However, it is established that imidazole can make a contribution to the properties of the cured epoxide and is thus more than a simple catalyst. For consistency of terminology, the term curing agent is used in this specification. 5 l() 15 20 25 30 35 40 50 55 65 4 In the art of curing or hardening epoxide resins, a latent curing agent is one which is effective only under certain specific conditions, e.g. temperatures above 50° or 100° C. A latent curing agent can therefor be in- cluded in a one-part curable system which is storable for long periods of time at normal ambient tempera- tures, and the storable system can be said to have good storage ability or a‘ long shelf life or pot life. The shelf life of a liquid one-part system can be conveniently determined by observing its viscosity; any tendency toward premature gelation will, of course, be evi- denced by an increase in viscosity. Adducts of an imidazole and sulfur dioxide can be synthesized by one of the following methods, provided that anhydrous conditions are maintained. 1. An imidazole is dissolved in a solvent such as ace- tonitrile and gaseous sulfur dioxide is bubbled through the solution. An exothermic reaction occurs. Upon dilution with the solvent, a white precipitate forms which is the imidazole-sulfur dioxide adduct. 2. Gaseous sulfur dioxide can be passed over an imid- azole and the adduct forms. The. solid adduct may be recovered from the reaction mass by treating it with a solvent. ' 3. A solution of an imidazole in a solvent can be added to another portion of a similar or the same sol- vent which is saturated with sulfur dioxide. A precipi- tate is formed which is the imidazole-sulfur dioxide adduct. 4. Liquid sulfur dioxide can be added to an imidazole (either as the pure compound or as a solution of the compound) and the adduct forms. The mixture is treated with a solvent to recover the solid adduct. 5. A solution of an imidazole can be placed in an autoclave and the autoclave pressurized with sulfur dioxide. The adduct precipitates out of solution. The sulfur dioxide gas reactions may utilize diluent gases to act as carriers and controls for the exothermic reaction. The 2:l adducts (2 imidazole: 1 S02) are more stable than the 1:1 adducts. Sulfur dioxide loss occurs with 1:1 adducts at room temperature over a period of 3 to 4 days. The equation for this decomposition is: 23° C. so, ——>(imid), . so, + so, (gas) (Eq. 1) wherein [mid is as defined previously. It is difficult to remove the last traces of solvent from the compounds of Formula (I), and mixture of com- pounds wherein n has more than one value, e.g. 2 and 3, can form. The adduct-like compounds of this invention decom- pose or dissociate according to the following equation: heat (Eq. 2) (H) For a given lmid moiety, the dissociation temperatures of the compounds of formula (I) can vary when n var- ies. For example, for 1,2-dimethylimidazole, the disso- ciation temperature of the n=2 species is higher than that of the n=l species. The properties of cured epox- ide systems which have been obtained by heating the 3,993,678 5 curable latent systems containing formula (1) com- pounds can also vary with n for a’ given Imid moiety. The dissociation temperatures are not fixed precisely, but generally appear to be significantly higher than room temperature. Under normal ‘ambient temperature and pressure, e.g. 23° C./760 mm of Hg, dissociation of the 1:1 (i.e. n=1), 2:1 (n=2), and 3:1 (n=3) adducts according to Equation 2 is, to say the least, difficult to detect. Experimentation with curable epoxide materi- als such as diglycidyl ethers of bisphenol A shows that the adducts have little, if any, effect upon the viscosity of the epoxide over a period of months, indicating an epoxide pot life longer than 6 months. This pot life data indicates that little or no free imidazole or imidazole derivative is available for interaction with the vicinal epoxide (oxirane) ring, since free imidazole can cure typical curable epoxide systems in a manner of minutes at room temperature; see Farkas et al, J. Appl. Polym. Sci. 12, 159 (1968). Even the latentizing the imidazole with acetic acid to form imidazole acetate salts extends the pot life of the epoxide system to only about three weeks; see U.S. Pat. No. 3,356,645 (Warren), issued Dec. 5, 1967. Thus, a simple comparison with known curable epoxide systems provides further evidence that the adducts of the present invention are reasonably stable compounds at normal ambient temperature and pressure, at least insofar as loss of the imidazole moiety is concerned. Some clearly detectible loss of imidazole can occur at temperatures above the melting points of the adducts, particularly in the range of 100° - 200° C., as is subsequently shown by the data Table II. Since the adducts have varying degrees of stability at tempera- tures above 100° C., the rate or extent of dissociation can be selected in accordance with the desired rate of cure or gel time, as the case may be. To illustrate: given a temperature of 180° C. and a typical latent curable system containing a formula (1) compound of this in- vention, the gel time is much longer for Imid = benz- imidazole than for Imid = imidazole (C3N2H.,). At 160° C., the benzimidazole adduct appears to have little or no effect upon a diglycidyl ether-bisphenol A epoxide prepolymer; but the ‘imidazole adducts are very effec- tive at this temperature. The 1-alkyl imidazole species of Formula (1) also exhibit longer gel times. The prop- erties of the cured epoxides obtained according to this invention are generally satisfactory. The compounds of Formula (I) are generally solids with fairly small melting ranges, typically not more than 5° C. These data can be compared to the 80°—85° C. . melting range of morpholine-sulfur dioxide, which is reported to be a salt-like chemical compound in the U.S. Pat. No. 2,270,490 referred to previously. The compound (1mid)3-S0,, where Imid = 2-ethyl-4- methylimidazole, appears to be a viscous liquid, but, as shown subsequently by Table I, this is not typical. Formulation of curable epoxide systems containing curing agents of this invention can be carried out along the lines generally laid down by latent imidazole epox- ide curing technology, e.g. the technology described in the aforementioned 3,553,166 and 3,356,645 patents. The U.S. Pat. No. 3,553,166 also describes suitable co-curatives (e.g. of the dicyandiamide type) which can be included in the curable system. It is preferred to introduce at least 0.1% by weight, based on the weight of the epoxide monomer or prepolymer, of a com- pound of Formula (1) into the curable‘ system, and levels of l—20% by weight are particularly useful. Lev- els higher than 20% — even 50% or more — are per- 10 15 20 25 30 35 40 45 50 55 60 65 6 missible but excessively increase the cost of the system without any significant beneficial result. Typical one-part curable epoxy resin systems formu- lated according to this invention comprise (1 ) 0.1 — 20 parts by weight ‘of a curing agent of Formula (I), (2) at least 80 parts by weight of a suitable cycloaliphatic, aliphatic, aromatic, or heterocyclic epoxide, and (3) O — 300 parts by weight of suitable fillers, extenders, flexibilizers, pigments, and the like, e.g. colloidal silica. These one-part systems have sufficient shelf—1ife at normal ambient temperature to allow for most ordinary shipping and inventory procedures, although the stabil- ity of the system can be further enhanced, if desired, by special precautions such as careful temperature control during storage. It is generally not necessary to formu- late two-part systems (with the epoxide in one con- tainer and the curing agent in another). If a two-part system is made up, however, the benefits of this inven- tion will still be apparent to industrial users who blend the two parts and then carry out one or more coating, molding, laminating, casting, or impregnating steps prior to curing at cure temperatures above 100° C. These steps can be carried out in a leisurely fashion, taking advantage of the long room temperature pot life prior to curing at elevated temperatures. Epoxides suitable for use in this invention can be aliphatic, cycloaliphatic, aromatic or heterocyclic and will typically have an average epoxy equivalency (i.e. the number of epoxy groups contained in the average molecule) of from about 1.7 to 6.0, preferably 2 or 3, this value being the average molecular weight of the epoxide divided by the epoxide equivalent weight. The epoxy equivalent weight, which is determined by multi- plying the sample weight by 16 and dividing by the number of grams of oxirane oxygen in the sample, is typically greater than 100 for commercially useful cur- able systems. These materials are variously referred to as epoxide monomers or prepolymers and in any event can contain repeating units, e.g. repeating ether units. Typical of such epoxides are the glycidyl-type epoxy resins, e.g. the diglycidyl ethers of polyhydric phenols and of novolak resins, such as described in “Handbook of Epoxy Resins”, by Lee and Neville, McGraw-Hill Book Co., New York (1967). Another useful class of epoxides has a structure of the following type: Ep — CR2 — O—R'—O—CR2—CROH-CR, , 0 — R'—O—CR, — Ep (111) 01' R‘(OCR2 — Ep),, (IV) where Ep is an epoxide ring, . R is hydrogen, or a non-hindering aliphatic group (e.g. methyl); R‘ is an aliphatic or aromatic radical; and .z is a number from O to about 5. In Formula IV, n is a number from 1 to 6. Typically, these epoxides are glycidyl ethers of poly- hydric phenols obtained by reacting a polyhydric phe- nol or aliphatic polyol with an excess of chlorohydrin, such as epichlorohydrin, e.g. the diglycidyl ether of Bisphenol-A or of resorc_inol, 1,4-butane diol, or the like. Further examples of epoxides of this type which can be used in the practice of this invention are de- 3,993,678 7 scribed in U.S. Pat. No. 3,018,262 (Schroeder), issued Jan. 23, 1962. The preferred cycloaliphatic epoxide monomers or prepolymers preferably contain at least one 5- or 6- membered carbocyclic ring (or heterocyclic ring with equivalent properties) on which is substituted the epox- ide functional group. In polycyclic cycloaliphatic epox- ides, the two rings are preferably independent and preferably joined by a bridging radical containing at least one ester or ether linkage. A plurality of these ester or ether linkages can provide flexibilizing proper- ties in the cured system. Further examples of cycloali- phatic epoxide compounds are described in U.S. Pat. No. 3,117,099 (Proops et al), issued Jan. 7, 1964. There are a host of commercially available epoxides which can be used in this invention, including the di- glycidyl ether of Bisphenol-A (e.g. “Epon” 828, “._piRez" 522-C, “Araldite” 7072, “Epon” 1002 and “DER” 332), mixtures of the diglycidyl ether of Bis- phenol A with an alkyl glycidyl ether (e.g. “ERL” 2795), vinylcyclohexene dioxide (e.g. “ERL” - 4206), .3,4-epoxycyclohexylmethyl—3, 4-epoxycyclohexane carboxylate (e.g. “ERL”-4221), 3,4-epoxy-6-methyl- cyclohexylmethyl-3,4—epoxy-6-methylcyclohexane car- boxylate (e.g. “ERL”-4201 ), bis(3,4-epoxy-6-methyl- cyclohexy1methyl)adipate (e.g. “ERL"-4289), bis(2,3- epoxyeyclopentyl)ether (e.g. “ERLA”-0400), ali- phatic epoxy modified with polypropylene glycol (e.g. “ERLA”-4050 and “ERL”—4052), dipentene dioxide (e.g. “ERL"-4269), epoxidizcd polybutadiene (e.g. “Oxiron” 2001), silicone epoxy (e.g. “Syl-Kem" 90), 1,4-butanediol diglycidyl ether (e.g. “araldite" RD-2), polyglycidyl ether of phenolformaldehyde novolak (e.g. “DEN”-431 and “DEN”-438) resorcinol diglyci- dyl ether (e.g. Ciba “ERE”-1359), and epoxidized unsaturated esters of carboxylic acids having more than six carbon atoms, e.g. epoxidized soybean oil. (“Epon" is a trade-mark of Shell Chemical Co.; “EpiRe2" is a trademark of Jones-Dabney Co.; “Araldite” is a trade- mark of Ciba Products Co.; the various “DER" and “DEN” designations are trade designations of Dow Chemical Co.; the “ERL” designations are trade desig- nations of Union Carbide Plastics Division; “Syl Kem” is a trade designation of Dow Corning; “Oxiron” is a trademark; and “ERE—1359” is a trade designation of Ciba Products Co.) The compounds of Formula (I) and the nuclei of Formula (II) have already been described in some de- tail. As will be apparent from this description, the sub- stituents R‘, R2, R4, and R5 can be varied considerably without any adverse effect upon the operability of this invention. The teachings of the aforementioned US. Pat. Nos. 3,356,645 and 3,553,166, and of U.S. Pat. No. 3,361,150 (Green), issued Dec. 28, 1971, are gen- erally applicable here with respect to selection of imid- azole substituents, which can also include 5- and 6- member fused or separate heterocyclic or carbocyclic rings. Substitution at the 1- position (i.e. R‘ percent H) is least preferred. Lower alkyl substituents (including substituted lower alkyl) are generally most preferred, although higher alkyl substituents (containing, for ex- ample, 7 — 36 carbons) can be used. Other aliphatic (including substituted aliphatic) radicals can be substi- tuted, as is conventional. Included among these are the alkenyl and alkinyl radicals such as allyl. Fused rings ( such as fused benzene or other 6-member carbocyclic rings) are preferably attached to the 4 and 5 positions; thus R‘ and R5 together can comprise the three or four 10 15 20 25 30 35 40 45 50 55 60 65 8 carbons or heterocyclic atoms of a fused ring. Separate aromatic rings can be substituted at the 1-, 2-, 4-, or 5- (preferably the 2-, 4-, or 5-) positions and can be mon- ocyclic (e.g. phenyl, tolyl, xylyl, etc.) or polycyclic (preferably di- or tri-cyclic, e.g. naphthyl). As pointed out previously, the compounds of For- mula (I) are generally useful when a latent source or other controlled release of either an imidazole or sulfur dioxide is needed. For example: alpha-cyanoacrylate monomers of the formula CH2 = C(CN)COOR, wherein R can be alkyl, phenyl, etc., polymerize by an ionic mechanism and are sensitive to contaminants, e.g. moisture. A consider- able body of patent and scientific literature is available concerning the use and storage of these monomers; see U.S. Pat. No. 2,776,232 (Shearer et al), issued January 1, 1957, British Pat. No. 1,159,548 (Rice et al) pub- lished July 30, 1969, U.S. Pat. No. 3,483,870 (Coover et al), issued Dec. 16, 1969, and British Pat. No. 1,048,906 (Halpern et al), published Nov. 23, 1966. A commercially available example of a cyanoacrylate monomer is “Eastman 910”, trade designation of East- man Kodak Company. Sulfur dioxide has convention- ally been used to stabilize these monomers. It has now been found that a compound of Formula (1), preferably one wherein n = 1, can be used as a source of constant sulfur dioxide pressure to preserve these monomers in a closed system. The principle and practice of this invention is illus- trated by the following non-limiting Examples, wherein all parts are by weight unless otherwise specified. EXAMPLE 1 Ten grams of imidazole were placed in a 250 ml. Erlenmeyer flask and exposed to gaseous sulfur dioxide for fifteen minutes. Immediate reaction takes place as is indicated by an exotherm. A light yellow viscous liquid is obtained. An increase in weight of nine grams‘ resulted. (This liquid will cure epoxy resins immedi- ately and shows no latency). The viscous liquid is sub- sequently treated with 150 ml. CHCI3 and stirred rap- idly. A fine white precipitate is formed and slow evapo- ration of the solvent yields 18.5 gms. of product. Dry- ing at room temperature under vacuum for three hours yields 16.5 gms. of material. (m.p. = 100° — 104°; 19.9% N; 19.8%S; [N]/[S] = 2.30.) The onezone adduct of imidazole and sulfur dioxide is a latent curing agent for epoxy resins. Five parts of the adduct admixed with 95 parts of epoxy resin (Epon 828) shows no increase in viscosity over a period of months. At 100° C., this mixture has a gel time in ex- cess of 30 minutes, whereas a similar mixture ofimidaz- ole and epoxy has a gel time of 5 minutes. The onezone adduct shows a slow decomposition to the twozone adduct. This decomposition is shown by an almost linear decrease in sample weight over a period of about 75 hours. There was no further change in sample weight from the 80th to the 135th hour, and weighings were then discontinued. EXAMPLE 2 Two moles (136 gm) of imidazole were placed in a three-neck flask fitted with a condensor, a gas inlet tube, and a stirrer. The imidazole was dissolved in 200 cc. of chloroform. Gaseous sulfur dioxide (one mole) was bubblediinto the solution through the inlet tube as the solution was stirred. After the addition of the sulfur dioxide,‘ stirring was continued for one hour. The solu- '3,'993-,6"78 9 tion was transferred to a Rotovapor and the solvent evaporated off at room temperature. A white solid was obtained upon removal of the solvent. (M.p. = 70° C; 21.0% N; 12.9% S; [N]/[S] = 3:71.). The elemental analysis indicated that the compound is lmid.,SO2, where lmid = imidazole. The solid showed no weight loss over a period of months. . Five parts of the solid were added to 100 parts of “Epon” 828 (Trademark of Shell Chemical Company) 10 imidazole (Example 3); 2-methyl imidazole (Example 4);‘ 1,2-dimethyliimidazole» (Example 5); 2-ethyl, 4- methyl imidazole '( Example 6); and benzimidazole (Ex- ample 7). Data on these compounds or adducts is set forth in Table l.=The melting point of morpholine-sulfur dioxide is also given in Table l‘f0r comparison. Examples 8 — 11 are tabulated’ in Table [I and illus- trate the use of the compounds of Examples 1, 2, 5, and 7 with a curable epoxide. The curable epoxide mono- resin, which is a diglycidyl ether of Bisphenol A. A 10 mer (sometimes referred to as a “prepolymer”) is portion of this mixture was immediately heated to 160° “Epon” 828 (trademark of Shell Chemical Corp. for a C. The sample cured to a hard resin in less than three viscous liquid diglycidyl ether of bisphenol A having an months. The Barcol hardness of the resulting cured epoxide equivalent weight slightly greater than the sample was 85. Another portion of the mixture was theoretical 170 and an epoxide functionality of slightly stored on the laboratory shelf for 3 months,’ during 15 less than 2.0). In Examples 8, 9, 10A, and HA, 95% by which time no change in the consistency of the resin weight of the liquid epoxide monomer is combined with was noted. The 3-month-old portion was warmed to 5% by weight of the compound of Examples 1, 2, 5, and 160° C., and cured at this temperature to a hard resin in 7, respectively; in Examples 10B and 1 1B 90 wt. % of less than 3 minutes. The Barcol hardness of this cured the epoxide is combined with 10 wt. % of the com- resin was 85. (A resin system is considered “cured” 20 ‘pound of Examples 5 and 7, respectively. For compari- when it has reached the most advanced state of harden- son, data on 5 ‘wt. % imidazole, benzimidazole, and ing for that system.) 1,2-dimethyl imidazole are also shown in Table II; the E I H epoxide is again “Epon” 828. g . Xamp es‘ to ; In‘ Table II, the Barcol Hardness test is the standard In Examples 3 to 7, imidazole-sulfur dioxide adducts 25 935 ASTM Test. “Gel time” is a measure of the length were prepared in_the same manner as Example 2 from of time a sample of resin may be maintaned in a pliable sulfur dioxide and the following imidazoles: 1-methyl form at a given temperature. TABLE I d ts mi ' 01 s n Sulf r Dioxide EQUND CALCULATED Ex. Adduct m.p. % N % S [N]/[Sl ”/I N. '/I 5 1 100-104" 19.9 19.8 2.30 21.2 24.2 I . I , N N—H . so, ‘ \/ 2. _ V 65-70’ 21.0 12.9 3.71 28.0 9 l6.() ' 5°‘ 3. ' 9 - i60—65° 20.7 10.2 4.73 24.5 14.0 l\l\\/l’~«l—CH_., . so, 4." 60-65“ 19.3 12.5 ’ 3.51 24.5 14.0 I l _ r~1\/1~I—H . so, CH3 2 5 |=__._________l 138-l40°» 16.7 15.3 2.50 17.5 20.0 N \/N—CH, . so, CH. 6. » vi_scqus 14.5 5.6 5.9 19.7 11.2 C L'q""d 1>~1\\%~1-11 . so, 3,993,678 ' TABLE ll-continued cs lmida ol s an ulfur Dioxide K ‘ 7 ‘ . ' ' ' ND gA! gm ATED- Ex. Adduct ’ m.p. % N i "/c S ‘[N]/[S] ’/c N. 7! S 7. H . i35;14o° 1x.3 7.5‘ 5.58 2 13.? 1017 / ~' 7 i . l . , .: N = , N V V . l ‘ 5| * _ /_‘\ i i V V 80-85“ 0- N—H . SO, v ‘US. Pal. Nn. 2.270.490 TABLE II I Examples 8 — ll Amount GEL TIME’ (minuteszscconds) ’ At: Barcol Hardness Example Compound of -‘ (wt. ‘7() ‘ 100° C. l20° C.. l40° C. l60° C. l80° C. 200° C. of Cured Product 8 Example 1 ’ ' 5 30 min: ' 9 min: 2 min: 1 min: ' ' 84 _ 2] sec. 19 sec. 21 sec. — 41 sec. - 9 Example 2 p 5 41 min: 21 min; 4 min: 2 min: 1 min: r— 84 V ' 5 sec. ‘ g 27 sec. 40 sec. 10 sec. 44 sec. l0A ‘ Example 5 ' 5 ~ — . — —— >90 min. 93 min: 85 min: 85' . _ e ; I e _ - . 35 sec. l0B Example 5 l_0 — — — — 17 min: 2 min: . 85 ‘ - 4 sec. I3 sec. ‘ llA Example 7 5 — — — >90 min. >90 min. >90 min. 80 HB Example 7 l0 — —— — — 11 min: 4 min: 80 ‘ 30 sec. I I see. imidazole _5 5 min: > 2 min: l min. _ _ _3 sec. 40 sec. 24 sec. .15 sec. —— henzimidazole 5 . _ — . -— 55 min: 2 min: l min: - ~ - - 18 sec. 40 sec. ll sec. 47 sec; l,2-dimcthyl ‘ V 4 imidazole 5 — — 49 sec. 41‘ sec. 27 sec. I8 sec. What is claimed is: 1. A stabilized composition comprising an alpha- - _ _ _ cyanoacrylate monomer of the formula ‘"l:''‘_’‘“ R!» Rlzv R‘; ?“d l"d5Pe“deml_Yt‘YePT€‘%5:“t CH2=C(CN)COOR, wherein R IS alkyl or phenyl, ad- 40 5“ Smuems 5‘? °°t°_ ''.°‘_“ 5 g"°“P °°“515_"‘g °_ Y’ mixed with a stabilizing amount of a compound of the dmgenv 3" allphauc radlcal am an ammatlc radwalr formula and together R‘ and R5 can be the residue of a fused (lmid),. - so, ring. \ wherein Z. A composition according to claim 1 wherein R‘, »n is 1, 2, or 3 or mixtures thereof, and 45 R‘, R3 and R‘ are independently selected from the group consisting of hydrogen and lower alkyl of l to 6 carbon atoms. 3. A‘ composition according to claim I wherein said fused ring is a benzene ring. 4. A composition according to claim 1 wherein R‘, [mid is a compound of the formula R4_c 1- c._Rs g 50 R’, R”, R‘ and R5 independently represent substituents Ill IL__Rl 3 selected from the group consisting ofhydrogen, alkyl of \\ / up to 36 carbon atoms, alkenyl, alkmyl; phenyl; tolyl; xylyl and naphthyl; and together R‘ and R5 can be the 2 ‘lg 55 residue of a fused benzene ring. ' * * * * * 60 65 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENTNO. : 3,993,678 DATED : November 23, 1976 4 |NVENTQm$); ,Norman P. Sweeny and Karl Friedrich Thom Hbcmmmdmmmmrwmmsmtmamw—mmmmdmmmamtmtwmLammPmmt amhmwywnmmdmsmwnmmw Column 1, line 61, change "curvature" to —- curative —- ; Column 3, line 23, insert the formula number —— (II) —- ; line "4, insert quotation marks around "curing agent"; line 63, insert quotation marks around "catalyst" mm'%nflimmf3 line 68, insert quotation marks around "curing agent"; Column 4, line 2, insert quotation marks around "latent"; line H, change "therefor" to —- therefore -- ; line 8, insert quotation marks around "shelf life" and "pot life"; Column 5, line 19, change "the" (second occurrence) to -- of — lines 38-39, insert quotation marks around "Imid"; Column 6, line 25, insert quotation marks around ' —- "pot life" —- ; line 39, insert quotation marks around "monomers" and "prepolymers"; line #8, insert brackets in the formula so it reads: —— Ep - CR2-E O—Rl-O-CR2—CROH-CR23-Z O—Rl-O-CR2-Ep -- . Column 7, line 29, change "ERL" to -— ERLA -- so it reads -- "ERLA"-4052 -— ; line 58, change "percent" to —- # —- , so it reads: —- (i.e. R1 aé H).--. Signcd and Scaled this Twelfth Day of April 1977 [SEAL] Arrest: C‘ RUTHC MASON . C.MARSHALLDANN AF 16’-"U18 Off???’ (‘mmnissimzer ofPaten!s and Trademarks