Cyanoacrylate adhesives monomers

Cyanoacrylate adhesives (Super-Glues) are materials which rapidly polymerize at room temperature. The standard monomer for a cyanoacrylate adhesive is ethyl 2-cyanoacrylate [7085-85-0], which readily undergoes anionic polymerization. Very rapid cure of these materials has made them widely used in the electronics industry for speaker magnet mounting, as weU as for wire tacking and other apphcations requiring rapid assembly. Anionic polymerization of a cyanoacrylate adhesive is normally initiated by water. Therefore, atmospheric humidity or the surface moisture content must be at a certain level for polymerization to take place. These adhesives are not cross-linked as are the surface-activated acryhcs. Rather, the cyanoacrylate material is a thermoplastic, and thus, the adhesives typically have poor temperature resistance. 

Acryhc stmctural adhesives have been modified by elastomers in order to obtain a phase-separated, toughened system. A significant contribution in this technology has been made in which acryhc adhesives were modified by the addition of chlorosulfonated polyethylene to obtain a phase-separated stmctural adhesive (11). Such adhesives also contain methyl methacrylate, glacial methacrylic acid, and cross-linkers such as ethylene glycol dimethacrylate [97-90-5]. The polymerization initiation system, which includes cumene hydroperoxide, N,1S7-dimethyl- -toluidine, and saccharin, can be apphed to the adherend surface as a primer, or it can be formulated as the second part of a two-part adhesive. Modification of cyanoacrylates using elastomers has also been attempted copolymers of acrylonitrile, butadiene, and styrene ethylene copolymers with methylacrylate or copolymers of methacrylates with butadiene and styrene have been used. However, because of the extreme reactivity of the monomer, modification of cyanoacrylate adhesives is very difficult and material purity is essential in order to be able to modify the cyanoacrylate without causing premature reaction. 

Cyanoacrylate adhesives are particularly valuable because of their speed of action, which allows the joining of intricate parts without the need for complex jigs and fixtures. Within very broad limits the more monomer that is used to make a joint the less will be the strength. These adhesives have in fact no gapfilling ability, nor can they be used on porous substrates. Whilst they have good heat and solvent resistance their weathering behaviour is limited and joints should not be in frequent contact with water. 

Crosslinking has been claimed to improve thermal resistance of the cyanoacrylate adhesive [18]. However, in other reports [6], little or no improvement in thermal resistance of the adhesive was demonstrated by the addition of a difunctional monomer. As seen in Fig. 2, the addition of varying amounts of crosslinker 7 provided no improvement in the tensile adhesive strength of ethyl cyanoacrylate on steel lapshears after thermal exposure at 121 °C for up to 48 h. 

Care must also be taken in the choice of rubber to insure that the rubber, or one of its additives, does not initiate the premature polymerization of the monomer. Even very low concentrations of a basic or nucleophilic material in the rubber or elastomer will cause the premature polymerization of an alkyl cyanoacrylate adhesive formulation. 

For surfaces which do not readily polymerize alkyl cyanoacrylate monomers, the adhesive monomer can be applied, a part assembled and repositioned, if... 

Cyanoacrylate adhesives, the famous consumer Super glue , is a monomer that polymerizes when it comes in contact with moisture, even with atmospheric moisture. 

The chemistry of cyanoacrylate adhesives contains no co-reactants but can polymerise at room temperature on any substrate that is exposed to atmospheric moisture or alkaline surfaces. Synthesised cyanoacrylate esters can be methyl, ethyl, n-propyl, n-butyl, allyl, ethoxyethyl and methoxyethyl. The basic structure of the cyanoacrylate monomer is ... 

Results. The results in Table 6.1 are the determination of Nb complex salt added to cyanoacrylate adhesive as a tracer added at a concentration of 1.5 ig g 1 (ppm = 1500 ngg1) Nb using three non-destructive methods. The results obtained are similar to 0 % PMMA. Figure 6.1 shows the intensity of Nb in cyanoacrylate monomers with and without PMMA thickening agent. 

With certain exceptions, cyanoacrylate monomer formulations containing additives e.g. rubbers, high-density neutral resins, silicon dioxide, etc., may hinder accurate and precise analysis using dilution methods. In such cases it may be necessary to prepare samples using destructive techniques, particularly where the levels are very low. Solvent selection for dilution of cyanoacrylate adhesive must be compatible for the entire journey of the sample solution from sample vessel to torch. Failure to do this could cause the cyanoacrylate to polymerise locally and block the entire sample transport system in ICP-OES and can cause serious damage requiring expensive replacements. The solvents suggested in the above dilution methods were found to be satisfactory. 

Cyanoacrylates are marketed as contact adhesives. Often popularly known as superglue, they have found numerous applications. In dry air and in the presence of polymerization inhibitors, methyl- and ethyl-2-cyanoacrylates have a storage life of many months. As with many acrylic monomers, air can inhibit or severely retard polymerization of cyanoacrylates. These monomers are, however, prone to anionic polymerization, and even a very weak base such as water can bring about rapid polymerization. 

Cyanoacrylates are one-part, highly polar thermoplastic polymers. The resin monomers cure in seconds when in contact with a weak base such as the moisture that is present on most surfaces. Many cyanoacrylate-adhesive formulations are commercially available, but not widely used in electronics assembly because of their poor resistance to solvents and moisture at elevated temperatures (>70 °C). Cyanoacrylates have relatively low impact and peel strengths and may be brittle unless toughened by the addition of elastomeric resins. 

With cyanoacrylate adhesives, the reactor used to convert the liquid monomer to the hard solid is the space between the parts being bonded. When conditions vary in this space, the performance of the adhesive will vary. Such parameters as temperature, humidity, space between the parts, and the type of surface being bonded can vary considerably in a given application. 

Cyanoacrylate adhesives were introduced in 1958 by Easttnan Kodak. They are based on alkyl-2-cyanoacrylate monomers. 

Cyanoacrylate adhesives consist mainly of alkylcyanoacrylate monomer, which undergo rapid anionic chain polymerization when the adhesive bond is closed. Hydroxide ions in absorbed water are generally thought to be the initiators, and the rapidity of anionic polymerization is due to two electron-withdrawing groups (-CN and -COOR), which stabilize the propagating anion. The initiation step is... 

Cyanoacrylate adhesives are rapid curing one part adhesives based on alkyl-2-cyano-acrylate monomers (I). 

Plasticizers These are required to reduce the inherent brittleness of poly(alkyl-2-cyanoacrylates). This can be achieved by using non-copolymerizing plasticizers such as esters or higher alkyl cyanoacrylates, which copolymerize with the basic adhesive monomer. Toughness properties can be improved by the inclusion of rubber toughening materials such as ABS (acrylonitrile-butadiene-styrene) or MBS (methacrylate-butadiene-styrene) copolymers. Whichever approach is adopted, toughness is only achieved at the expense of reduced cure speed. 

Cyanoacrylate adhesives are relatively low viscosity fluids based on acrylic monomers and characterised by extremely fast rates of cure. When placed between closely fitting surfaces, some will cure to give a strong joint in two to three seconds. 

The cyanoacrylate adhesives sold today are quite similar to the first product, Eastman 910. This is due to the fact that changes in the structure of the monomer have dramatic effects on the adhesive properties, and because there are very few modifying monomers which will successfully coreact with the cyanoacrylates under normal application conditions. Also, the monomers with the best adhesive properties were discovered early in the development of cyanoacrylates. Finally, research toward improving the deficiencies of these products had a slow start owing to the early manufacturing problems. Beginning in the late 1970s, however, a number of adhesives with improved performance were introduced. 

Adhesives based on cyanoacrylic acid esters differ significantly from most other reactive adhesives because they consist in large part of pure monofunctional monomers. Epoxy, acrylic, and isocyanate based adhesives typically include di-, tri-, and tetrafunctional reactants, and usually contain significant quantities of curatives or coreactants. Cyanoacrylate adhesives rarely contain significant amounts of coreactants because they are able to homopolymerize rapidly at room temperature. Also, non-neutral additives drastically alter the cure rate of shelf life of the compounded adhesives. 

While the bulk of any cyanoacrylate formulation consists of monomer, a large number of modifiers have been used to impart desired properties to the composition. These include stabilizers, inhibitors, thickeners, plasticizers, dyes or colorants, adhesion promoters, and others. Each of these classes of modifier will be dealt with in subsequent parts of this chapter. Because of the variety of modifiers, and the variety of applications for cyanoacrylates, a bewildering number of cyanoacrylate adhesives are now commercially available. These can be generally divided into the following classifications adhesives of different viscosities and cure rates, adhesives based on different monomers, adhesives for the bonding of metal, plastic, rubber, or wood, various types of improved performance adhesives, i.e., heat, moisture, or impact resistant, and adhesives for bonding low surface... 

Over-stabilization is a temptation, in order to ensure long shelf lives for cyanoacrylate adhesive. This practice should be avoided because it leads to sluggish cure rates and inferior bond strengths. The use of strong protic acids can lead to hydrolysis of the cyanoacrylate ester group, producing alcohol which will destabilize the adhesive as its concentration increases. Because of the hydrolytic susceptibility of cyanoacrylate monomers, the water content of these adhesives should be kept as low as possible. Over-stabilization with strong acids should also be avoided in order to minimize hydrolysis. 

The thermal instability of polycyanoacrylate is of particular importance both to the manufacturer and the consumer of cyanoacrylate adhesives. The degradation of cyanoacrylate oligomer has been described in general terms previously, as an important step in the production of cyanoacrylate monomer. Heating PECA above 150°C results in the steady production of cyanoacrylate monomer in high yield. This process is end group-initiated... 

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