SAN is similar in use to polystyrene. Like polystyrene itself, it is optically transparent and brittle in mechanical behavior. The copolymer has a glass transition temperaturegreater than 100°C owing to the acrylonitrileunits in the chain, thus making the material resistant to boiling water. Uses include food containers, kitchenware, computer products, packaging material, battery cases and plastic optical fibers. It is structurally related to ABSplastic, where polybutadiene is copolymerised with SAN to give a much tougher material. The rubber chains form separate phases which are 10-20 micrometers in diameter. When the product is stressed, crazing from the particles helps to increase the strength of the polymer. The method of rubber toughening has been used to strengthen other polymers such as PMMAand nylon.