Acrylic polymers adhesives

Dynamic mechanical properties vs. temperature for untackfied (acrylic A , ) and tackified (acrylic B [tackfied A] , A) acrylic polymers. Adhesive properties are in O Table 15.1... 

Acrylates are primarily used to prepare emulsion and solution polymers. The emulsion polymerization process provides high yields of polymers in a form suitable for a variety of appHcations. Acrylate polymer emulsions were first used as coatings for leather in the eady 1930s and have found wide utiHty as coatings, finishes, and binders for leather, textiles, and paper. Acrylate emulsions are used in the preparation of both interior and exterior paints, door poHshes, and adhesives. Solution polymers of acrylates, frequentiy with minor concentrations of other monomers, are employed in the preparation of industrial coatings. Polymers of acryHc acid can be used as superabsorbents in disposable diapers, as well as in formulation of superior, reduced-phosphate-level detergents. 

Adhesives. Acryhc emulsion and solution polymers form the basis of a variety of adhesive types. The principal use is in pressure-sensitive adhesives, where a film of a very low T (<—20 " C) acrylic polymer or copolymer is used on the adherent side of tapes, decals, and labels. Acrylics provide a good balance of tack and bond strength with exceptional color stabiUty and resistance to aging (201,202). AcryUcs also find use in numerous types of constmction adhesive formulations and as film-to-film laminating adhesives (qv). 

In addition to poly(methyl methacrylate) plastics and polyacrylonitrile fibres, acrylic polymers find widespread use. First introduced in 1946, acrylic rubbers have become established as important special purpose rubbers with a useful combination of oil and heat resistance. Acrylic paints have become widely accepted particularly in the car industry whilst very interesting reactive adhesives, including the well-known super-glues are also made from acrylic polymers. 

Acrylics are some of the most common and most versatile materials used in the PSA industry. Although the basic monomers and some of the acrylic polymers have been known for about a century, their commercial application as pressure sensitive adhesives did not happen until after the Second World War. 

Acrylic acid, the main precursor to acrylic adhesives had been synthesized in the mid 1800s and the first acrylic acid esters were made and characterized at the turn of the century [62]. The first commercial launch of acrylic polymers in the form of poly(methylmethacrylate) took place in 1927 when the German company Rohm and Haas AG introduced this new plastic to the market. Soon after, other companies such as BASF introduced acrylic dispersions. 

Natural rubber adhesives were traditionally used as contact adhesives. However, synthetic polymers are more generally used today. Polychloroprene adhesives are the most common contact adhesives based on synthetic rubber, although recently some have been displaced by polyurethane and acrylic polymers [2]. 

Acrylic polymers are also important in the preparation of other classes of adhesives, especially pressure sensitive adhesives. This discussion will be limited to adhesives that cure by the reaction of unsaturated acrylic functional groups. These adhesives are also sometimes termed Methacrylate , Methacrylic or Structural Acrylic adhesives. This is consistent with the long-standing habit of organic chemists to assign multiple names to the same substance. 

A different approach, although stdl working with essentially non-fiinctional polymers has been exemplified [114,115], in which, a 100% solid (solvent free) hot melt has been irradiated to produce pressure-sensitive adhesives with substantially improved adhesive properties. Acrylic polymers, vinyl acetate copolymers with small amounts of A,A -dimethylaminoethyl methacrylate, diacetone acrylamide, A-vinyl pyrrohdone (NVP) or A A have been used in this study. Polyfunctional acrylates, such as trimethylolpropane trimethacrylate (TMPTMA) and thermal stabilizers can also be used. 

The polymerization of alkyl vinyl ethers is of some commercial importance. The homopolymers, which can be obtained only by cationic polymerization, are useful as plasticizers of other polymers, adhesives, and coatings. (The copolymerization of vinyl ethers with acrylates, vinyl acetate, maleic anhydride, and other monomers is achieved by radical polymerization but not the homopolymerizations of alkyl vinyl ethers.)... 

Acrylics. There are two principal classes of acrylic sealants latex acrylics and solvent-release actylics. High molecular weight latex acrylic polymers are prepared by emulsion polymerization of alkyl esters of acrylic acid, The emulsion polymers are compounded inlo sealants by adding fillers, plasticizers, freeze-thaw stabilizers, thickeners, and adhesion promoters. As is true of the silicone lalex sealants, die acrylic latex sealants are easy to apply and clean with water. 

To conclude this discussion on zirconium, it is appropriate to look at the adhesion promotion effects of various zirconium compounds in flexographic and gravure ink printed on corona discharge-treated polyolefins and polyester. Flexographic and gravure inks are basically a pigment (often titanium dioxide) suspended in a polymer (normally called the binder) dissolved in a solvent. Actual commercial ink formulations are rather more complicated. These inks are either water-based when acrylic polymers and co-polymers are typically the binders, or solvent-based (usually ethanol-ethyl acetate mixtures) when the binder is typically nitrocellulose or cellulose acetate propionate. 

Another photoconductive acrylic polymer, poly(N-acryloylaminopropylcarba-zole)93) is claimed to have good flexibility and adhesion properties. 

Ethylene Copolymers. Ethylene copolymers probably are the most important materials in hot-melt formulations. Ethylene-vinyl acetate and ethylene-ethyl acrylate polymers are very versatile and available in a wide range of grades offering different co-monomer contents and viscosities. The melts are stable and compatible with various modifying resins, waxes, extenders, and fillers. Adhesion to many substrates is good—including the polyolefin plastics, which are difficult to bond with most other types of adhesive unless the surfaces are pre-treated. 

All acrylic structural adhesives consist basically of a solution or a mixture of polymers and unsaturated, low-molecular-weight, free-radical-polymerizable monomers with other materials added as needed for the particular intended use. In addition, some precursor of the polymerization initiator will be present. 

The choice of monomers that are useful in acrylic structural adhesives is rather limited. Cost always is an important factor, and because acrylic structural adhesives consume only a very small portion of the world s output of acrylic monomer, the formulator usually must rely on acrylic monomers that are made in large quantity for other uses. In addition, the monomers must polymerize readily at room temperature. If a mixture of monomers is to be used, the monomers must copolymerize easily. Finally, the monomers must be good solvents or dispersants for the polymers used in formulating the adhesive. The acrylic monomers finding most use in acrylic structural adhesives are methyl methacrylate and tetrahydrofurfuryl methacrylate. The later, albeit more expensive, has a much higher flashpoint and a generally perceived low odor, yet maintains good solvency. 

A technology developed at Du Pont75 combines the use of reactive sites on the oligomers with the initiation reaction. The resulting family of acrylic structural adhesives has become popularly known as second generation acrylics. They consist essentially of solutions of chlorosulfonated polyethylene (Du Pont Hypalon ) in acrylic or methacrylic monomers. The chlorosulfonyl groups present on the polymer will react with... 

The influence of parameters such as crosslinking agent aluminium acetylacetonate content, introduction time of monomers, amount of reactor charge, distribution of N-vinyl caprolactam (VC), diverse crosslinkers, viscosity and molar mass of the synthesised pressure-sensitive adhesives (PSA) and solvent balance and transfer agent kind and content on such important parameters of PS A as shrinkage, plasticity, adhesion to steel and deformation are examined. Synthesised pressure-sensitive adhesives based on acrylic polymers and containing 2-ethylhexyl acrylate (2-EHA), methyl acrylate (MA), acrylic acid (AA) and VC are used for production of self-adhesives containing PVC carrier. 4 refs. 

Emulsion Polymerization. Emulsion polymerization is the most important industrial method for the preparation of acrylic polymers. The principal markets for aqueous dispersion polymers made by emulsion polymerization of acrylic esters are the paint, paper, adhesives, textile, floor polish, and leather industries, where they are used principally as coatings or binders. Copolymers of either ethyl acrylate or butyl acrylate with methyl methacrylate are most common. 

Water-thinnable acrylic polymers dissolved in cosolvent aggregate on dilution. The aggregates are highly swollen with water in the region of the functional groups and with cosolvent around the hydrophobic backbone. Clearly, the nature of the cosolvent-water-polymer interaction is a major factor in the polymer conformation. The effect on the orientation of the carboxyl groups, on which adhesion and water sensitivity depend, is unknown. 

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