| 摘要 |
A method is provided for the preparation of polycarbonates by the reaction of a diaryl carbonate, such as DPC and a dihydric phenol, such as BPA. The method utilizes the steps of successively processing the diaryl carbonate and the dihydric phenol in a melt in a first reaction stage, a second reaction stage and at least a first polymerization stage, and shifts the processing conditions such that the desired low viscosity/high end-cap product is obtained. This is achieved by having the ratio of diaryl carbonate to dihydric phenol in the melt prior to the first reaction stage greater than 1.08; and by controlling the temperature and residence time in the first polymerization stage are selected to provide a polycarbonate product having a melt flow rate at 250� C. of greater than 10 g/10 min and an end-cap level of at least 90%. The method of the invention can be used in a linear manufacturing process, in which there is one product produced. The method of the invention can also be incorporated into a multi-line manufacturing process for the simultaneous production of more than one product. Thus, a stream of product produced from the first polymerization stage may be split into two or more lines which are further processed to produce, for example, a low viscosity, high end-cap product and a medium viscosity, moderate end-cap product. |
