Acrylic acid Anaerobic adhesives

The use of monomethacrylates in anaerobic formulations was disclosed in a patent assigned to Loctite. Specifically mentioned were hydroxyethyl (XIX), hydroxypropyl (XX), cyclohexyl (XXI), tetrahydrofurfuryl (XXII), dimethylaminoethyl (XXIII), and glycidyl methacrylates (XXIV), and cyanoethyl acrylate [26]. Methacrylate esters containing residual carboxylic add groups were prepared by the reaction of hydroxyethyl methacrylate with phthalic anhydride (XXV), pyromellitic dianhydride (XXVI), and benzophenonetetracarboxylic add dianhydride (XXVII). The residual acid provided improved adhesion [27,28]. The reaction product of hydroxyalkylmethacrylates with maleic anhydride (XXVIII) also produced monomers with residual acid as well as additional curable unsaturation [29]. The dimethacrylates of the bisglycol esters of dicarboxylic adds were used to formulate anaerobic adhesives. Among the dicarboxylic acids mentioned were phthalic (XXIX), maleic (XXX), fumaric (XXXI), and malonic (XXXII) [30]. 

Pike and Lamm, in a contribution from United Technologies, describe the preparation of acrylic modified polyester adhesives which exhibited anaerobic cure behavior. The hydroxyl containing polyester was synthesized from dimethyl terephthalate, isophthalic acid, trimellitic acid and diethylene glycol or ethylene glycol using a butyl titanate catalyst. A series of model compound reactions was carried out to establish optimum conditions for the acid-catalyzed addition of glycidyl methacrylate with the hydroxyl containing polyester. Sulfuric acid and... 

This adhesive group has been promoted for use as a sealant. The adhesives used are acrylate acid diesters (polyester-acrylic). They are essentially monomeric thin liquids that polymerize to form a tough plastic bond when confined between closely fitting metal joints. Contact with air before use keeps the monomeric adhesive liquid. Metal surfaces accelerate the polymerization in the absence of air (anaerobic conditions). These materials will bond all common metals, glass, ceramics, and thermosetting plastics to each other. Phenolic plastics and some plated metals, such as cadmium and zinc, require a primer such as ferric chloride. Polymerization is essentially a free-radical-type addition polymerization. " ... 

Solvent adhesives and reactive adhesives are made from homo- and copolymers of methacrylates, generally methyl and ethyl methacrylate and, occasionally, butyl methacrylate. Monomeric (meth)acrylates are also used in reactive adhesive systems (polymerization adhesives). Poly(ethyIene glycol) dimethacrylates are the basis of anaerobically curing liquid resins (reactive adhesives). They also are added as adhesion promoters to plastisol adhesives. Acrylate-ethylene copolymers, in some cases with a small content of carboxyl groups, are used instead of ethylene-vinyl acetate copolymers as fusible polymers for special hot-melt adhesives. Salts of polyacrylate and acrylate - acrylic acid copolymers are used as thickeners for aqueous adhesive solutions and emulsion-based adhesives. 

Anerobic adhesives. Acrylate acid diester and cyanoacrylate resins are called anaerobic adhesives because they cure when air is excluded from the resin. Anaerobic resins are noted for being simple to use, one-part adhesives, having fast cure at room temperature and high cost. However, the cost is moderate when considering a bonded-area basis because only a small volume of adhesive is required. Most anaerobic adhesives do not cure when gaps between adherend surfaces are greater than 10 mils, although some monomers have been developed to provide for thicker bond-lines. 

Anaerobic stmctural adhesives are typically formulated from acryhc monomers such as methyl methacrylate [80-62-6] C Hg02, and methacrylic acid [79-41-4] (see Acrylic ester polymers). Very often, cross-linking agents such as dimethacrylates are also added. A peroxide, such as cumene... 

Acidic monomers, particularly methacrylic acid, are used in both high-and low-odor acrylics. As with anaerobics, methacrylic acid provides improved adhesion and high temperature resistance. In acrylic adhesives the acid may further promote the cure. Maleic acid plays an important role in certain formulations,providing improved curing properties in oxygen-exposed areas. 

Anaerobics are usually formulated with di- or trifunctional methacrylate monomers that can be polymerised rapidly to form a tightly crosslinked thermoset polymer. Typical examples are triethylene glycol dimethacrylate, and ethoxylated bisphenol A dimethacrylate. Other monomers are used to modify the properties. Examples are hydroxyethyl or hydroxypropyl methacrylate and acrylic or methacrylic acid these help to adjust viscosity, cure speeds and adhesive strength as seen in Equations 2.3-2.S ... 

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