Cyanoacrylate ester

Table 2. Cured Bulk Properties of Common 2-Cyanoacrylic Esters...

Table 3. Adhesive Bond Properties of 2-Cyanoacrylic Esters with Metals and Various Polymeric Materials...

Acrylic Ester Polymers, 2-Cyanoacrylic Ester Polymers" ia ECT 3rd ed., VoL 1, pp. 408—413, by H. W. Coover, Jr., andj. M. Mclatire, Tennessee Eastman Company. 

Because they are acrylic monomers, alkyl cyanoacrylate esters still require the addition of radical polymerization inhibitors, such as hydroquinone or hindered phenols, to prevent radically induced polymerization over time [3j. Since basic initiation of alkyl cyanoacrylate monomers is the predominant polymerization mechanism, large quantities of free radical inhibitors can be added, with little or no effect on adhesive performance. 

All of the eommereial alkyl eyanoaerylate monomers are low-viseosity liquids, and for some applications this can be an advantage. However, there are instances where a viseous liquid or a gel adhesive would be preferred, sueh as for application to a vertical surface or on porous substrates. A variety of viscosity control agents, depending upon the desired properties, have been added to increase the viscosity of instant adhesives [21]. The materials, which have been utilized, include polymethyl methacrylate, hydrophobic silica, hydrophobic alumina, treated quartz, polyethyl cyanoacrylate, cellulose esters, polycarbonates, and carbon black. For example, the addition of 5-10% of amorphous, non-crystalline, fumed silica to ethyl cyanoacrylate changes the monomer viscosity from a 2-cps liquid to a gelled material [22]. Because of the sensitivity of cyanoacrylate esters to basic materials, some additives require treatment with an acid to prevent premature gelation of the product. 

Michael addition in the absence of any catalytic agent has been reported for dialkyl and diaryl phosphites and thiophosphites with a-cyanoacrylate esters and a-cyanoacrylic acid.444 Yields of the conjugate addition products were moderate to good. The regiochemistry of this process is the opposite of that previously reported for similar additions to ketene acetals, the latter presumably proceeding by initial protonation of the distal olefinic carbon site.445... 

ACRYLIC ESTER P OLYMERS - 2-CYANOACRYLIC ESTER POLYMERS] (Vol 1)... 

Ihe polymers of the 2-cyanoacrylic esters, more commonly known as the alkyl 2-cyanoacrylates, are hard glassy resins that exhibit excellent adhesion to a wide variety of materials. The polymers are spontaneously formed when their liquid precursors or monomers are placed between two closely fitting surfaces. Tile spontaneous polymerization of these very reactive liquids and the excellent adhesion properties of the cured resins combine to make these compounds a unique class of single-component, ambient-temperature-curing adhesive of great versatility (Table 3). The materials that can be bonded run the gamut from metals, plastics, most elastomers, fabrics, and woods to many ceramics. 

TABLE 3. ADHESIVE BOND PROPERTIES OF 2-CYANOACRYLIC ESTERS WITH METALS AND VARIOUS POLYMERIC MATERIALS... 

Manufacture and Processing. The cyanoacrylic esters are prepared via the Knoevenagel condensation reaction, in which the corresponding alkyl cyanoacetale reacts with formaldehyde in the presence of a basic catalyst to form a low molecular weight polymer. The polymer slurry is acidified and the water is removed. Subsequently, the polymer is cracked and redistilled at a high temperature onto a suitable stabilizer combination to prevent premature repolymerization. Strong protonic or Lewis acids arc normally used in combination with small amounts of a free-radical stabilizer. 

Adhesives formulated from tile 2-cyanoacrylic esters typically contain stabilizers and thickeners, and may also contain tougheners, colorants, and other special property-enhancing additives. 

Economic Aspects, Production of the 2-cyanoacrylic ester adhesives on a worldwide basis is estimated to be approximately 2400 metric tons. This amounts to only 0.02% of the total volume of adhesive produced but about 3% of the dollar volume. 

HeaUh and Safety Factors. The 2-cyanoacrylic esters have sharp, pungent odors and arc lacrimators. even at very low concentrations. The TLV for methyl 2-eyanoacrylate is 2 ppm and the sliort-tenii exposure limit is 4 ppm. Good ventilation when using the adhesives is essential. 

Both the liquid and cured 2-cyanoacrylic esters support combustion. 

The bulk physical properties of tire polymers of the 2-cyanoacrylic esters appear in Table 2. All of these polymers are soluble in -nu-tlivlpvrmlidiinmi-. Y. Y-dimet 1 nil< >rni mride. and nitrornethane. The adhesive bonding properties of typical formulated adhesives are listed in Table 3. 

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