2.4 POLYSTYRENES

Except where high temperatures are involved, polystyrenes may be used for some electronic applications. They have very low dielectric constants and power factors (Table 2.5), placing them in a class with polyethylenes, fluorocarbons, and silicones. Polystyrenes also have high dielectric strength values (comparable to mica) and volume resistivities that do not vary much at high frequencies or in the presence of moisture. Because of these properties, polystyrenes are especially suited as capacitor dielectrics, especially in commercial markets where moderate temperatures are encountered. Another outstanding property is their transparency. Unmodified polystyrene coatings are clear, colorless, and capable of transmitting 88 to 92% of light. Their refractive index is 1.59 to 1.60. They are, therefore, used in coating lenses and other optical equipment. Polystyrenes also have very good tinting and coloring properties, giving them a wide range of transparent, translucent, and opaque colors for decorative uses.

Among the more serious limitations of polystyrenes are their inherent flammability and their upper temperature limit of 85 C, which is much too low for most military electronic applications.