the α - cyanoacrylate adhesive compositions of this invention contain as their principal ingredient one or more α - cyanoacrylate monomers of the formula : ## str1 ## where r represents a c 1 - 16 alkyl , cycloalkyl , alkenyl , alkynyl , cycloalkenyl , alkaryl , aralkyl or aryl group , any of which may be optionally substituted or , interrupted with non - basic groups , such as oxo , halo and ether oxygen , which do not interfere with the stability and functioning of the monomer as an adhesive . specific examples of the groups for r are a methyl group , an ethyl group , an n - propyl group , an isopropyl group , an n - butyl group , an isobutyl group , a pentyl group , a hexyl group , an allyl group , a methallyl group , a crotyl group , a propargyl group , a cyclohexyl group , a benzyl group , a phenyl group , a cresyl group , a 2 - chlorobutyl group , a trifluoroethyl group , a 2 - methoxyethyl group , a 3 - methoxybutyl group and a 2 - ethoxyethyl group . ethyl cyanoacrylate is the preferred monomer for use in the inventive compositions . a single α - cyanoacrylate monomer or a mixture of two or more of these α - cyanoacrylate monomers can be used . for a number of applications , the above α - cyanoacrylate monomer alone is not sufficient as an adhesive , and at least some of the components set forth below are typically added . ( 4 ) special additives such as cure accelerators , plasticizers tougheners and heat stabilizers ; a suitable amount of the α - cyanoacrylate monomer present in the adhesive composition is about 75 to 99 by weight , based on the total weight of the adhesive composition . an anionic polymerization inhibitor is added to the α - cyanoacrylate adhesive composition , e . g ., in an amount of about 1 to 1000 ppm based on the total weight of the adhesive composition , to increase the stability of the adhesive composition during storage , and examples of known inhibitors are sulfur dioxide , sulfur trioxide , nitric oxide , hydrogen fluoride , and certain sultones , as discussed above . particularly preferred for purposes of this invention are combinations of methane sulfonic acid ( msa ) or hydroxypropane sulfonic acid ( hpsa ) with sulfur dioxide . preferred concentrations of sulfonic acids range from about 5 to about 100 , more preferably about 10 to 50 , parts per million ( based on monomer weight ). the preferred concentrations of so 2 range from about 15 to about 50 ppm for either acid . while not essential , the cyanoacrylate adhesive compositions of this invention generally also contain an inhibitor of the free radical polymerization . the most desirable of these inhibitors are of the phenolic type , such as quinone , hydroquinone , t - butyl catechol , p - methoxyl - phenol , etc . the above inhibitors may be used within wide ranges , but the following general guidelines are representative of the adhesive composition : acid gases , from about 0 . 001 % to about 0 . 06 % by weight ; hydrolyzed or hydrolyzable sultones , from about 0 . 1 % to about 10 % by weight ; sulfonic acids , from about 0 . 0005 % to about 0 . 1 % by weight ; and free radical inhibitors , from about 0 . 001 % to about 1 % by weight of the composition . a thickener frequently is added to increase the viscosity of the α - cyanoacrylate adhesive composition . the α - cyanoacrylate monomer generally has a low viscosity of about several centipoises , and therefore , the adhesive penetrates into porous materials such as wood and leather or adherends having a rough surface . thus , good adhesion strengths are difficult to obtain . various polymers can be used as thickeners and examples include poly ( methyl ) methacrylate , methacrylate - type copolymers , acrylic rubbers , cellulose derivatives , polyvinyl acetate and poly ( α - cyanoacrylate ). a suitable amount of thickener is generally about 20 % by weight or less based on the total weight of the adhesive composition , preferably 3 %- 10 % based on the total weight of the adhesive composition . a number of conventional polymer additives may also be added for toughening purposes . examples include acrylic elastomers , acrylonitrile copolymer elastomers and fluoro elastomers . in approproate amounts such materials may serve as both thickener and toughener . certain fumed silica fillers may also be usefully employed as cyanoacrylate thickeners . various hydrophobic silicas are reported in the art to give satisfactory storage stable gels with cyanoacrylates . see , for instance u . s . pat . nos . 4 , 477 , 607 , 4 , 533 , 422 , 4 , 686 , 247 , 4 , 837 , 260 and gb 2 , 204 , 872 , all incorporated herein by reference . preferred silicas are polydimethylsiloxane , octyltrimethoxysilane or hexamethyldisilazane treated silicas such as cab - o - sil ® ts - 720 ( cabot corp . ), aerosil ® r202 ( degussa co . ), aerosil ® r805 ( degussa co .) or cab - o - sil ® ts - 530 ( cabot corp .). mixtures of such silicas may also be employed . suitable levels of such silicas are in the range of 3 %- 12 % based on total composition weight , preferably 4 %- 8 %. as examples of cure accelerators there are known , for instance , calixarene compounds as described in u . s . pat . no . 4 , 556 , 700 and u . s . pat . no . 4 , 695 , 61 5 and silacrown compounds as described in u . s . pat . no . 4 , 906 , 317 . other accelerators are well known to those skilled in the art . the naphthosultone additives utilized in the invention have at least one strong electron group substituent . as examples of strong electron withdrawing groups there may be mentioned , for instance , nitro , trifluoromethyl , cyano , sulfonyl , halo and carboxylalkoxy groups . particularily preferred are nitro substituted naphthosultone compounds , especially nitronaphthosultone additives utilized include specifically nitronaphthosultone 6 - nitronaphth -[ 1 , 8 ,- cd ]- 1 , 2 - oxathiole s , s - dioxide ) and diniteonaphthosultone ( 6 , 8 - dinitronaphth -[ 1 , 8 , cd ]- 1 , 2 - oxathiole s , s - dioxide ). these compounds are usefully employed at levels in the range of 0 . 1 %- 10 % by weight of the formulation , preferably at least 0 . 25 % and no more than the ambient temperature solution saturation level of the additive in the particular cyanoacrylate composition . saturation for nitronaphthosultone compounds in typical ethyl cyanoacrylate adhesive formulations is about 2 %. most preferably the nitronaphthosultone compound is employed at a level of 1 %- 2 % by weight of the formulation . the nitronaphthosultone compounds do not substantially affect the shelf life of the cyanoacrylate adhesive formulations in which they are employed . the cyanoacrylate polymers produced from the adhesive formulations of the invention have higher thermal decomposition temperatures than compositions employing no additive . by way of contrast , formulations of the invention can be readily formulated to provide cured polymers having an onset of decomposition temperature , when heated at 10 ° c . per minute , of more than 200 ° c . whereas additive free polymers provide a decomposition onset temperature of only 155 ° c . additionally , typical polymers of the invention are characterized by a weight loss of 10 % or less ( 5 % or less with some embodiments of the invention ) when heated at 150 ° c . for 900 minutes , as opposed to greater than 95 % weight loss under identical conditions for an additive free composition . it has been observed that use of naphthosultone as a cyanoacrylate additive can also give some improvement of thermal properties in the cured polymer , but the improvement is less substantial even at much higher concentrations . example 2 illustrates the comparative performance of nitronaphthosultone additives and naphthosultone . other additives which may be added to the cyanoacrylate adhesive compositions of the invention are plasticizers . plasticizers serve to make the cured bonds less brittle and , therefore , more durable . the most common of these plasticizers are c 1 to c 10 alkyl esters of dibasic acids such as sebasic acid and malonic acid . other plasticizers , such as diaryl ethers and polyurethanes , also may be used , and a variety of other plasticizers are also known . the plasticizers , as well as cyanoacrylate compatible perfumes , dyes , pigments , etc ., may be added depending on desired uses in amounts which do not adversely affect the stability of the α - cyanoacrylate monomer . the use of such additives is within the skill of those practicing in the cyanoacrylate adhesive art and need not be detailed herein . the effects of nitronaphthosultone compound additives on the thermal properties of cured cyanoacrylate polymers were investigated in several ways . thermal analyses of cyanoacrylate polymers to which had been added amounts of additive as shown in table i were conducted dynamically to determine temperature at which decomposition onset occurred and isothermally at 150 ° c . to determine relative weight loss of polymer on heat aging . fixture speeds and 82 ° c . stability were performed on monomer formulations containing the additives to ascertain whether the additive affected the cure speed or storage stability of the formulation . thermal analysis was done using two different instruments . the dupont 2100 thermal system with 951 thermogravimetric analyzer attached , and seiko ssc5245hm2 controller attached to tg / dta220 thermogravimetric differential thermal analyzer . isothermal thermal runs were started from 30 ° c . and heated at 50 ° c ./ minute up to 150 ° c . and held at that temperature for 900 minutes under 250 cc / min nitrogen gas flow . temperature dynamic runs were started at 30 ° c . and heated at 10 ° c ./ min up to 450 ° c . under 250 cc / min nitrogen gas flow . samples for dynamic analyses were all prepared by intimate mixing with a mortar and pestle of a prepolymerized cyanoacrylate polymer and the additive followed by heating of the mixture at 100 ° c . for two hours . samples for isothermal analyses were either prepared in the same way or from a film prepared by placing a droplet of a monomer formulation containing the additive between pressed santoprene ™ blocks for 72 hours at room temperature , followed by post - curing at 100 ° c . to completely polymerize all residual monomer present , and then separating the resulting polymer film . both methods of sample preparation were found to give equivalent results . freshly distilled ethyl cyanoacrylate monomer containing methane sulfonic acid ( 10 ppm ), sulfur dioxide ( 2 ppm ) and hydroquinone ( 3000 ppm ) was used in preparing thermogravimetry analysis samples . fixture speeds were measured on formulations containing a polymethyl methacrylate ( 6 wt %), hydrophobic silica ( 6 wt %), calixarene ( 0 . 5 wt %) and silacrown ( 0 . 5 wt %) in ethyl cyanoacrylate monomer . table i__________________________________________________________________________ onset of % wt loss 82 ° c . fixture speed ( sec ) decomposition at 150 ° c . stability balsa cowadditive % temp (° c .) in 900 min ( days ) wood leather__________________________________________________________________________invention formulationsnnod * 2 210 5 20 25 40dnnod * 2 210 5 20 25 40comparative formulationnone ( control ) -- 155 98 20 25 37__________________________________________________________________________ * nnod is nitronaphthosultone s , sdioxide ). ** dnnod is dinitronaphthosultone s , sdioxide ). from table 1 it can be seen that the onset of thermal decomposition and outgasing properties of the polymers were improved when a nitronaphthosultone additive was employed , compared to an additive free formulation . loctite ® superbonder 498 , a commercial ethyl cyanoacrylate based adhesive formulation containing a conventional shelf - life stabilization system , was used as a control formulation to compare the effect of adding a nitronaphthosultone additive versus naphthosultone . steel lap shear coupons were bonded with the control adhesive or the control adhesive to which an amount of additive had been added , as shown in table 2 . each bonded assembly was aged at 121 ° c . for the periods indicated in table 2 . tensile shear strengths were determined on bonded samples which had been allowed to return to room temperature before testing and other samples which were tested at 121 ° c . after the heat aging . the results , provided in table 2 , demonstrate the superiority of the nitronaphthosultone additive over both the control and the naphthosultone additive , even when the naphthosultone was added at substantially higher levels . table 2__________________________________________________________________________ tensile shear strength tensile shear strength ( psi ) ( psi ) heat aged at 121 ° c . heat aged at 121 ° c . tested at room temp tested at 121 ° c . formulation % 2 wks 4 wks 6 wks 8 wks 2 wks 4 wks 6 wks 8 wks__________________________________________________________________________comparative formulationsnone -- 2419 1215 579 508 1938 1102 361 232nps *** 5 2093 1330 1264 1003 1223 973 799 771nps 2 . 5 1977 1337 934 699 1748 1323 618 250invention formulationsnnod 2 2575 2012 1871 1783 1758 1690 1542 1773nnod 1 2879 2139 1979 1765 2125 1921 1684 1842__________________________________________________________________________ *** nps is naphthosuftone the test procedures of example 2 were utilized with a control rubber modified cyanoacrylate adhesive formulation sold under the trademark black max ® by loctite corporation . quantities of additives and tensile shear strengths obtained at room temperature and at 121 ° c . as shown in table 3 . table 3______________________________________ tensile shear tensile shear strength ( psi ) strength ( psi ) heat aged at heat aged at 121 ° c . tested 121 ° c . at room temp tested at 121 ° c . formulation % 2 wks 4 wks 2 wks 4 wks______________________________________comparitive formulationsnone -- 1802600242152nps . 25 1630924299221nps . 5 1805790285357nps 1 2451 1280392309nps 2 2373 1445454489invention formulationsnnod . 25 2982 2577 1041 1122nnod . 5 3425 3122 1174 1126nnod 1 3814 2817 1210 1210______________________________________