There are many synthetic methods for bisphenol a-type polycarbonate. The industrial production mainly includes phosgenation (interfacial polycondensation) and transesterification (melt polycondensation), which respectively obtain phosgene polycarbonate and transesterification polycarbonate. Two products.
Both methods can be produced in batch or continuous mode
PC production process - phosgenation
1 phosgenation method: mainly includes two parts of polycondensation and post-treatment. Under intense stirring, phosgene is introduced into an aqueous solution of an inert solvent and bisphenol a in sodium hydroxide, and a polycondensation reaction is carried out at the interface of the two phases, and a catalyst may be added during the reaction. The reaction product is demulsified, separated, washed with water and dried to obtain a white polycarbonate powder.
The advantage of this method is that the reaction is carried out under normal temperature and normal pressure, and the equipment is simple, and a high molecular weight polymer (molecular weight 30,000 to 100,000) can be obtained.
The disadvantage is that the phosgene is highly toxic and requires special protection. The product needs to be post-treated and granulated. The solvent needs to be rectified and recovered, and the process is complicated.
2 transesterification method: mainly includes three parts of transesterification, polycondensation and acid leaching, and the reaction of diphenyl carbonate with bisphenol a to obtain a polycarbonate having a molecular weight of 25,000 to 50,000.
The advantage of the method is that the raw material diphenyl carbonate is easy to prepare and has high purity, and the produced polycarbonate can be post-treated, and the resin can be directly granulated and packaged after being discharged from the polycondensation reactor.
Disadvantages are harsh production conditions, high temperature and high vacuum, high melt viscosity of the material, special stirring equipment, and difficulty in producing high molecular weight polycarbonate.
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