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Polycarbonates
are high-molecular weight, amorphous engineering thermoplastics that have
exceptionally high impact strength over a wide temperature range. Polycarbonate resins are produced in the U.S. principally by
General Electric Co. (Lexan) and by Mobay Chemical Corp. (Merlon).
The Dow Chemical Co. has recently become the third producer of
polycarbonate resins, (Calibre).
The
resins are available in general-purpose molding and extrusion grades and in
several special grades that provide specific properties or processing
characteristics. These include
flame-retardant formulations, grades that meet FDA regulations for parts used in
food-contact and medical applications, blow-molding grades, glass-reinforced
grades for applications requiring maximum strength and stiffness, and
structural-foam grades. Polycarbonate
is also available in extruded sheet. The
natural resin is water clear and transparent.