Polyacylates are an important class of polymers that are soft, tough and rubbery. Their glass transition temperature is well below room temperature. They are known for their high transparency, good impact toughness and elasticity, and have fairly good heat resistance up to ca. 450 K under dry heat. They also have good weatherability and ozone resistance since they do not have double bonds in the backbone.
The two most important acrylic polymers are poly(methyl acrylate) and poly(ethyl acrylate). Both polymers are tough, rubbery materials with little or no tack at room temperature. However, poly(ethyl acrylate) is considerably softer and more extensible than poly(methyl acrylate). These two acrylates are often copolymerized to achieve the desired hardness, flexibility and strength. Two other important acrylic comonomers are butyl and 2-ethylhexyl acrylate; both increase the flexibility and elasticity.
Sometimes small amounts of comonomers with other functionality such as carboxyl, ether, hydroxyl, amine or amide are added to further adjust / improve the properties. Some important functional monomers are acrylic, methacrylic and itaconic acid, 2-hydroxyethyl acylate and N-hydroyxethyl acrylamide, to name only a few.
For the production of acrylic elastomers, acrylic monomers are quite often copolymerized with other monomer such as acrylonitrile (ANM) or ethylene (AEM). AEMs are usually terpolymers of ethylene, acrylics and some other monomers, whereas ACM elastomers are composed solely of acylics. Both have similar mechanical properties, however, AEM's can withand a wider temperature range than ACM's and hydrogenated nitriles (HNBR). Unlike butadiene-based rubbers (SBS, NBR), acrylic elastomers have good resistance to mineral oils, oxygen, ozone, ultraviolet radiation and withstand higher temperatures.
COMMERCIAL PolyacrylatesMajor manufacturers of acrylic monomers and resins are Sartomer (now part of Arkema), DOW Chemical, Arkema, San Esters Corp., and Lucite Int.
Major applications are coatings, paints, textiles, leather finishing, automotive products, tape adhesives, and oil-resistant and high-temperature-resistant elastomers. They are also used as comonomers to increase the plasticity of rigid and brittle plastics.
Acrylic elastomers are often a cheap alternative to fluorocarbon polymers (FKM), silicones (VMQ) and fluorosilicones (FVMQ) for elevated temperature applications (< 430 (450) K). They are extensively used in the automotive industry for hoses, seals, gaskets and dampers that must function under long-term exposure to elevated temperatures and hydrocarbon oils.
Another important application of acrylics are emulsion paints. Acrylic latices are the main ingredient of many interior and exterior water-based paints. The waterborn paints and coatings market is expected to reach $ 43 billion by 2020.1
Acrylics are also used in solventborn coatings and printing inks for applications that require fast drying rates. These products have excellent performance and are extensiviely used as automotive lacquers and industrial coatings. They are formulated as one- or two-part systems and are usually applied by spray gun, aerosol spray or by dipping. The majority of these products contain flammable solvents which require proper precautions for safe handling. Furthermore, most organic solvents are regulated due to environmental concerns with emissions.
Besides paints, inks, and coatings, acrylics are used in pressure sensitive adhesive formulations. They can be formulated with a large variety of adhesion properties, from low adhesion (barely tacky) to very high tack that bond permanently to surfaces.
The three most important acrylic monomers used for coatings, paints, inks, and pressure sensitive adhesives are poly(ethyl acrylate), poly(butyl acrylate), and poly(ethylhexyl acrylate) and blends thereof that are often copolymerized in various ratios with other monomers such as methacrylates, styrenes, acrylamide, acrylonitrile to modify their properties. Methacrylates, styrenes and acrylonitrile are usually added to increase the cohesive strength (hardness) and to reduce or to eliminate the tack after drying, whereas (meth)acrylamide, (meth)acrylic acid, glycidyl acrylates and maleic anhydride are added as crosslinkers and/or as cure accelerators. Some of these monomers, like acrylonitrile and methacylamide, also improve the solvent and oil resistance.
1Source: bcc Research / PRNNewswire, August 13, 2014
- Poly(acrylic acid)
- Poly(benzyl acrylate)
- Poly(butyl acrylate)
- Poly(4-chlorophenyl acrylate)
- Poly(2-cyanoethyl acrylate)
- Poly(cyanomethyl acrylate)
- Poly(cyclohexyl acrylate)
- Poly(ethyl acrylate)
- Poly(2-ethylhexyl acrylate)
- Poly(hexyl acrylate)
- Poly(isobutyl acrylate)
- Poly(methyl acrylate)
- Poly(propyl acrylate)
- Poly(sec-butyl acrylate)
- Poly(tert-butyl acrylate)