Chemical Industry-Polycarbonate

Polycarbonates are transparent thermoplastic polymers which are mainly used as moulding compounds.  CD-roms and baby bottles are well known examples of this use.

The great commercial success of polycarbonate (Lexan®, Makrolon®) is due to its unique combination of properties: extreme toughness, outstanding transparency, excellent compatibility with several polymers, and high heat distortion resistance.

The production of polycarbonate can be splitted in two stages:

• production of phosgene (COCl₂) starting with chlorine (Cl₂) and carbon monoxide (CO) according to the following reaction:

•                 CO + Cl₂  ®  COCl₂

• reaction between phosgene and bisphenol-A in a solution of methylene chloride:

• Cl-CO-Cl + HO-C₆H₄-C(CH₃)₂-C₆H₄-OH   ® 

  HO-C₆H₄-C(CH₃)₂-C₆H₄-O-CO-]_{80 till 100} + 2 HCl

Large quantities of caustic soda lye are added during the second stage in order to form bisphenolate and to catalyse this reaction via neutralisation of the formed hydrochloric acid.

The polycarbonate obtained in this way is precipitated as a solid substance after purification and centrifugation and subsequently dried until a powder remains.

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