Published: Jan 2012
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ACRYLIC POLYMERS, WHICH ARE USED AS COAT-ings binders, are comprised chiefly of esters of acrylic and methacrylic acid that are polymerized by addition polymerization, usually using a free radical mechanism: Interest in acrylic technology dates back to the 1920s when Dr. Otto Rohm developed a practical process for making acrylate esters from ethylene. Shortly afterwards, his associate, Otto Haas, established the first commercial production of methyl and ethyl acrylate in the United States . The first commercial use of an acrylic polymer was as an adhesive-like interlayer for laminated safety glass. Probably the highest profile use of an acrylic began in 1936 with the introduction of thermoplastic, transparent methacrylate sheet. With the advent of World War II, methacrylate sheet became invaluable as a tough, weather-resistant glazing material for military aircraft. Since it could be formed easily and had excellent optical properties, the transparent plastic was used for aircraft canopies, bomber noses, and gun turrets . Acrylic technology soon expanded into the coatings industry in the form of acrylic solution polymers, followed later by acrylic emulsions. The acrylics gained widespread market acceptance as coatings binders due to such outstanding properties as color stability, transparency, and resistance to weathering and aging. The good weathering resistance of acrylic polymers is primarily due to their resistance to hydrolysis and their lack of absorption of ultraviolet (UV) light, the high-energy portion of the light spectrum most responsible for degradation. Acrylic solution polymers (often referred to as acrylic resins) are generally copolymers of acrylate and methacrylate esters prepared by direct solution polymerization in a solvent that has a solubility parameter similar to that of the polymer. Typical solvents include aromatics such as toluene and xylene, as well as ketones and esters. Acrylic resins are typically supplied at about 30 % to 50 % solids by weight, with viscosities ranging from a few hundred to a few thousand centipoise. In later years, 100 % solid-grade versions became popular since they reduced the cost and safety concerns associated with shipping resins containing high solvent levels. The coatings manufacturer is then able to dissolve the solid-grade acrylic in a wide range of solvents, thereby having greater control over the formulation ingredients.
Friel, John M.
The Dow Chemical Company, Spring House, PA
Scientist, The Dow Chemical Company, Spring House, PA