Acrylonitrile Polymers, Survey and Styrene‐Acrylonitrile (SAN)

Abstract

AbstractAcrylonitrile (AN) is a versatile and reactive monomer that can be polymerized under a wide variety of conditions and copolymerized with an extensive range of other vinyl monomers due to its polar nature and reactivity. Because of the difficulty of melt processing acrylonitrile homopolymer, acrylonitrile is usually copolymerized to achieve a desirable thermal stability, melt flow and physical properties. As a comonomer, acrylonitrile provides rigidity, chemical and solvent rsistance, and gas‐impermeable properties. Acrylonitrile‐continuing polymers are used in the areas of textile fibers, carbon fiber percursors, adhesives, binders, antioxidants, medicines, dyes, electrical insulations, emulsifying agents, graphic arts materials, insecticides, leather, paper, plasticizers, soil‐modifying agents, solvents, surface coatings, textile treatments, viscosity modifiers, azeotropic distillations, artificial organs, lubricants, asphalt additives, water‐soluble polymers, hollow spheres, cross‐linking agents, and catalyst treatments. Styrene is the largest volume acrylonitrile comonomer for thermoplastic applications. Styrene–acrylonitrile (SAN) copolymers are inherently transparent plastics with high heat resistance and excellent gloss and chemical resistance. They are also characterized by good hardness, rigidity, dimensional stability, and load‐bearing strength. In general, the styrene component of SAN resins offers clarity, stiffness, and processability, while the acrylonitrile provides chemical and heat resistance. Because of their inherent transparency, SAN copolymers are most frquently used in clear application. These optically clear materials can be readily processed by extrusion and injection molding, but they lack real impact resistance. SAN resins show considerable sesistance to solvents and insouble in carbon tetrachloride, ethyle alcohol, gasoline, and hydrocarbon solvents. Polar solvents such as acetone, chlorofrom, and pryidine will dissolve SAN. The properties of SAN are significantly altered by water absorption. Commercially, SAN is manufactured by three processes: emulsion, suspension, and continuous mass polymerization. More than 75% of the SAN resin produced is believed to be used captively for ABS compounding and in the production of acrylonitrile–styrene–acrylate (ASA) and acrylonitrile–EPDM–styrene (AES) weatherable copolymers. Overall, U.S. SAN consumption other than ABS compounding and ASA/AES polymers production has been relatively stable for the past few years, ranging from 43 to 44.5 × 103metric tons between 1994 and 1996. SAN resins themslaves appear to pose few health problems, and they have been approved by the FDA for direct food contact. Copolymers of acrylonitrile and methly acrylate and terpolymers of acrylonitrile, styrene, and methyl methacrylate are used as barrier polymers. Acrylonitrile multipolymers containging indene, methyl methacrylate, and α‐methyl methacrylate are used as PVC modifiers for HDT and processability improvement. Well‐defined acrylonitrile polymers can be prepared by an atom transfer radical (living radical) polymerization process.