General-purpose polystyrene (also called crystal polystyrene because of the clarity of resin granules) is a clear, hard, glassy material with a bulk density of 1.05 g/cm-3. These desirable physical characteristics, as well as easy moldabil-ity, low water absorbancy, and good color range in which the resin was available, made it a popular general-purpose resin. Its brittleness, which limited the range of products in which the resin could be used, was soon overcome when the high-impact toughened grades of polystyrene containing rubber became available. The resin is available as a general-purpose grade, high-impact resin, high-molecular-weight resin (for improved strength), high-heat grades with a higher softening point, and easy flow grades for sophisticated molding applications. High-heat resins are high-molecular-weight resins with melt flow rates of 1.6 g/10 min. The medium and easy flow grades contain 1 -4% added mineral oil or other lubricant to obtain higher flowrates of about 7.5 and 16 g/10 min, respectively. Impact-grade resin accounts for about half of the demand for polystyrene and is widely used in injection molding of consumer products. Some copolymers such as (acry-lonitrile-butadiene-styrene) copolymers (ABS), styrene-acrylonitrile copolymers (SAN), and styrene-maleic anhydride copolymers (SMA) are also commercially available . Copolymer of styrene with butadiene (SBR) is an important elastomer widely used in passenger tire applications.
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