Cyanoacrylic adhesives polymerization

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 cure by anionic polymerization. This reaction is catalyzed by weak bases (such as water), so the adhesives are generally stabilized by the inclusion of a weak acid in the formulation. While adhesion of cyanoacrylates to bare metals and many polymers is excellent, bonding to polyolefins requires a surface modifying primer. Solutions of chlorinated polyolefin oligomers, fran-sition metal complexes, and organic bases such as tertiary amines can greatly enhance cyanoacrylate adhesion to these surfaces [72]. The solvent is a critical component of these primers, as solvent swelling of the surface facilitates inter-... 

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. 

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

The water molecules present on the adherend surfaces that cause the polymerization (Section 4.3) of the cyanoacrylate adhesives (Section 4.3.1). 

Thumwanit, V. et al., Cytotoxicity of polymerized commercial cyanoacrylate adhesive on cultured human oral fibroblasts, Austr. Dent.., 44, 248, 1999. 

In practice, a trace of moisture occurring on a substrate is adequate to cause polymerization of the cyanoacrylate monomer to provide strong bonding within a few seconds of closing the joint and excluding air. Cyanoacrylate adhesives are particularly valuable because of their speed of action, which... 

The initiator that drives the polymerization or curing reaction of cyanoacrylate adhesives can be any of the chemicals that generate free radicals. Electromagnetic... 

For closing parenchymatous renal hemorrhages, a needleless injector was used [468]. This method consists in obtaining a hemostatic infiltrate on the wound surface, which is achieved by introducing easily polymerized cyanoacrylate adhesives into the organ parenchyma using a needleless injector. A thin adhesive film that is formed... 

Acrylic adhesives are based on the esters of acrylic and substituted acrylic acids and can be categorized into two main groups the acrylates and methacrylates (I), which cure by free radical-catalysed addition polymerization, and the cyanoacrylates (II), which cure by anion-catalysed addition polymerization. The term acrylic adhesives is normally restricted to include the former, while the latter is usually considered separately (see Cyanoacrylate adhesives) this categorization is adhered to here. 

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... 

As already stated, formulated cyanoacrylate adhesives contain low levels of additives that improve the performance profile of the product. They can be divided into two general groups those that modify the polymerization process and those that alter the properties of the final polymer. 

Cyanoacrylate adhesives J GUTHRIE Anionic polymerization, additives, applications, advantages and disadvantages... 

Cyanoacrylate adhesives n. alkyl -2-cyano-crylates polymerize rapidly via anionic initiation in the presence of weak bases (water, alcohol) at ambient temperatures highly exothermic reaction yielding brittle polymers very useful for quickly setting anaerobic adhesives also useful for suture less topical tissue adhesives (e.g.. Derma-bond ) and industrial grades are commonly known as super glue . 

Methyl-2-cyanoacrylate n. A fast setting adhesive used for bonding cellulosics, nylon, polyesters, acrylics, polystyrene, and polyurethanes to each other and to other materials such as woods, metals, and glass. Catalyzed by atmospheric moisture or lightly applied methanol, the adhesive polymerizes without loss of solvent. For best results, the surfaces to be bonded should mate closely. 

The two types of inhibitors used in cyanoacrylate adhesives are radical polymerization inhibitors and anionic polymerization inhibitors. The former type are usually phenolic, for example, hydroquinone, p-methyloxyphenol, or hindered phenolics. They are generally employed in 0.1-1.0% concentrations. The amine- or sulfur-based inhibitors and the metal-chelating inhibitors should be avoided owing to their nucleophilic character. Radical inhibitors are used to protect the adhesive during storage from polymerization induced by heat or light and other adventitious radical sources. These... 

A common feature of all of the adhesion promoters discussed here is the presence of one or more carboxylic acid groups, anhydrides, or phenolic hydroxyls. Presumably these groups complex with the metal surface during bonding and/or coreact with the cyanoacrylate during polymerization. Also, the improvement in adhesive performance can be attributed to improved adhesion, regardless of the manner in which that performance is measured. 

More recently, the monofunctional cyanopentadienoates (2) were shown to improve the heat resistance of cyanoacrylate adhesives. In one case, when more than 50 weight % of 2 was combined with a standard cyanoacrylate monomer, the impact, peel, heat, and water resistance were greatly improved. " The improved heat resistance was attributed to the crosslinking of the residual olefin (28) after the anionic polymerization of 2 (see Eq. 8). The cyanopentadienoate was used in 50-90% concentration. The slow cure rate of the dienoate was overcome by the addition of an accelerator, in this case, a small quantity of an alcohol. Improvements in the heat, water, and water vapor resistance of alkyl cyanoacrylates can also... 

---