Polycarbonate Synthesis and Characterization

Example 1

Polycarbonate was continuously produced using an apparatus as schematically shown in FIG. 1. BPA and DPC are introduced in a monomer mixing device which is kept at a temperature of 170 QC at a pressure of about 1050 mbar. 1000 ppm of tetra butyl phosphonium acetate (TBPA) was also added as a beta catalyst.

The monomer mix is then introduced in the first oligomerisation reactor operating at a temperature of 257° C. and a pressure of 180 mbar. The initial DPC/BPA ratio (molar ratio) is adjusted with additional DPC to 1.040 and an amount of NaKHPO₄ as alpha catalyst is added. The carbonate oligomer formed in the first oligomerisation reactor is fed to the second oligomerisation reactor operating at a temperature of 280° C. and a pressure of 37 mbar.

The so formed carbonate oligomer is then introduced to a first and second polymerisation reactor operating at 300 and 302° C., respectively. The pressure was selected to accommodate the formation of the desired molecular weight.

The residence time in the oligomerisation section was 1.8 hours (1.1. hour in the first oligomerisation reactor, 0.7 hours in the second polymerisation reactor) and the residence time in the polymerisation section was 1.0 hours (0.5 hour in each polymerisation reactor).

After polymerisation the polymer is fed to an extruder where a catalyst quencher (butyl tosylate) is added to deactivate the catalyst. The molten polymer was extruded, filtered, cooled and cut to pellets.

During the oligomerisation PCP as endcapping agent was added to the first oligomerisation reactor. In order to increase the level of PCP end-capping while maintaining the desired molecular weight, the amount of alpha catalyst was adjusted resulting in somewhat higher amount of Fries branching as shown in the Table 1 below.

In Example 1, two different polycarbonates were made with this process, indicated below as Example 1a and Example 1 b.

Polycarbonate was produced using a process similar to Example 1 except that the end-capping agent, PCP, is added to the second polymerisation reactor. In order to reach the desired weight average molecular weight of 40,000 Daltons the present inventors observed s strong increase in the level of Fries branching. The present inventors further found that the amount of PCP end-groups was much lower as compared to the level in Examples 1-3.

Example 2

Polycarbonate was produced using a process similar to Example 1, but with the difference that the end-capping agent, PCP, was added to the first polymerisation reactor. The inventors observed that at similar levels of Fries more similar levels of bulky end-groups could be obtained, yet with a somewhat lower molecular weight.