Chain polymerization acrylic adhesives

Acrylic acid esters Free-radical-initiated chain polymerization Fiber modification, coatings, adhesives, paints... 

Acrylic adhesives cure by addition polymerization reactions. These chain reactions are initiated by the formation of free radicals that result in the adhesive curing by way of a very rapid polymer chain growth. This cure chemistry is significantly more rapid than a typical cure curve (i.e., condensation type) found in epoxy and urethane adhesives. A comparison of the cure profile of condensation (epoxy and urethane) versus addition... 

The polymerization of acrylic adhesives via free radicals (chain reaction) allows acrylic adhesives to be dispensed and cured using unique techniques. Other types of adhesive products often cure by condensation polymerization reactions which dictate certain cure characteristics and handling techniques. 

The growing polymer chain can be terminated by a number of mechanisms including two radicals joining to form a molecular species, abstraction of hydrogen, or radical transfer. Oxygen is particularly effective in terminating free-radical polymerization and is responsible for the familiar air inhibition property (wet or tacky surface) noted by users of acrylic adhesives. The absence of oxygen or air is, therefore, required in order to obtain the most complete cure (polymerization) and hence, the best properties of acrylic adhesives. 

The second means of transforming a liquid adhesive entirely into a solid without the loss of a solvent or dispersion medium is to produce solidification by a chemical change rather than a physical one. Such reactive adhesives may be single-part materials that generally require heating or exposure to electron beam or UV or visible radiation (see Radiation-cured adhesives) to perform the reaction, and which may be solids (that must be melted before application), liquids or pastes. The alternative two-part systems require the reactants to be stored separately and mixed only shortly before application. The former class is exemplified by the fusible, but ultimately reactive, epoxide film adhesives and the latter by the two-pack Epoxide adhesives and Polyurethane adhesives and by the Toughened acrylic adhesives that cure by a free-radical Chain polymerization mechanism. 

Anaerobic adhesives and sealants are based on acrylic (usually meth cryXic) functional monomers and cure by a redox-initiated free radical polymerization (see Chain polymerization). They are so named because of the characteristic of requiring a relatively air-free condition to allow curing. Hence, anaerobic adhesives are very suitable for the bonding and sealing of close-fitting metal components. 

There are several polymers that form the basis of adhesives, and which are made by free radical chain polymerization. These include the carbon-chain synthetic rubbers. Acrylic adhesives. Ethylene vinyl acetate copolymers and polymer lattices. 

Reactive acrylic adhesives generally consist of a solution of a toughening rubber (chlorosulphonated polyethylene) in a partly polymerized mixture of monomers this is mainly methylmethacrylate but ethane diol dimethacrylate is added as a cross-linking agent. The remaining monomer is polymerized in a free radical chain polymerization redox initiation involves an organic peroxide and a tertiary amine. Acrylic cements consist of a partly polymerized acrylic monomer containing an initiator. Cure is established by the thermal or UV decomposition of the initiator (see Radiation-cured adhesives). 

The tacky polymeric microspheres that comprise the pressure-sensitive adhesive layers of repositionable notes are patented inventions. One such material (U.S. Patent 5,714,237) is prepared by a free-radical polymerization reaction of isooctyl acrylate (Fig. 14.3.1) in the presence of polyacrylic acid with a chain-... 

The curing reaction of an acrylic structural adhesive is the chain-growth polymerization of the acrylic monomer. The monomer units are not reactive with each other but react only with a growing chain having an active site on one end. In order to begin a chain, one must generate an initiator in the monomer solution. In the case of acrylic structural adhesives, this initiator nearly always is a free radical, a species having an unpaired, reactive electron. 

The fundamental chemistry of the structural adhesives described here can change very little. Vinyl and acrylic monomers polymerize by chain growth polymerization initiated by free radicals or ions. Isocyanate and epoxy compounds react with compounds containing active hydrogen in step growth polymeriza-... 

Nitrile polymers used for the manufacture of adhesives generally contain 25% or more acrylonitrile, but in the base polymer the acrylonitrile content can vary from 15% to 50%. Increasing the acrylonitrile content improves the oil and plasticizer resistance and increases the polarity of the compound. However, higher levels of acrylonitrile also increase the hardness and modulus of the polymer, reducing the elasticity of the resulting polymer. Nitrile rubber can be produced by a cold (5°C) or hot (25-50°C) process, with most adhesive polymers produced by the hot process which induces more chain branching. Nitriles can be combined with other monomers in solution polymerization which increases functionality and improves compatibility with other reactive resins like acrylics, epoxies, and polyurethanes. 

In practice, many commercial process employ a chain transfer agent to control molecular weight at a reduced level. Processes of commercial importance are the copolymerization of butadiene with styrene or acrylonitrile to produce synthetic rubber and the polymerization of acrylic esters, vinyl chloride, vinylidene, and vinyl acetate to produce latexes for adhesives and paints. 

Uses Antioxidant for lubricants, rubber, waxes monomer stabilizer insecticide mfg. of dyes polymerization inhibitor for acrylic ester monomers chain transfer agent in rubber prod. polymerization control agent in food-pkg. adhesives food and feed additive treatment of food-producing animals mfg. of chlorpromazine and related antipsychotic drugs anthelmintic drug antioxidant in dry rosin size in mfg. of paper/paper-board in contact with aq./fatty foods in food-contact rubber articles for repeated use... 

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