Process for the manufacture of polycarbonate compositions

A continuous process for the manufacture of a polycarbonate comprising:

• combining an aromatic dihydroxy compound stream and a diaryl carbonate stream to form a mixture;
• controlling a weight or molar ratio of the diaryl carbonate to the aromatic dihydroxy compound by:
• measuring a sound velocity, Vs, in the mixture at an operating temperature of the controlling step;
• and
• determining the weight or molar ratio of the diaryl carbonate to the aromatic dihydroxy compound in the mixture based on Equation 3 or Equation 4:
• WR=[100−(a+b×Vs)]/(a+b×Vs) (Equation 3)
• MR=(Mw1/Mw2)×[100−(a+b×Vs)]/(a+b×Vs) (Equation 4)
• wherein Mw1 is the molecular weight of the aromatic dihydroxy compound, Mw2 is the molecular weight of the diaryl carbonate, WR is the weight ratio of the diaryl carbonate to the aromatic dihydroxy compound, MR is the molar ratio of the diaryl carbonate to the aromatic dihydroxy compound, and a and b are constants;
• and
• adjusting a flow rate of at least one of the aromatic dihydroxy compound stream and the diaryl carbonate stream, if needed, to achieve a desired weight or molar ratio of the diaryl carbonate to the aromatic dihydroxy compound;
• and
• polymerizing the aromatic dihydroxy compound and the diaryl carbonate in the presence of a catalyst to produce the polycarbonate.

A process for monitoring a relative level of an aromatic dihydroxy compound or a diaryl carbonate in a mixture comprising the aromatic dihydroxy compound and the diaryl carbonate, the process comprising:

• measuring a sound velocity, Vs, in the mixture at an operating temperature of the process;
• and
• determining the relative level of the aromatic dihydroxy compound or the diaryl carbonate in the mixture based on Equation 1, 2, 3 or 4:
• WP1=a+b×Vs (Equation 1)
• WP2=100−(a+b×Vs) (Equation 2)
• WR=[100−(a+b×Vs)]/(a+b×Vs) (Equation 3)
• MR=(Mw1/Mw2)×[100−(a+b×Vs)]/(a+b×Vs) (Equation 4)
• wherein
• WP1 is the weight percent of the aromatic dihydroxy compound in the mixture,
• WP2 is the weight percent of the diaryl carbonate in the mixture,
• Mw1 is the molecular weight of the aromatic dihydroxy compound,
• Mw2 is the molecular weight of the diaryl carbonate,
• WR is the weight ratio of the diaryl carbonate to the aromatic dihydroxy compound,
• MR is the molar ratio of the diaryl carbonate to the aromatic dihydroxy compound, and
• a and b are constants, further comprising:
• calculating the weight ratio WR or molar ratio MR of the diaryl carbonate to the aromatic dihydroxy compound;
• comparing the calculated weight ratio WR or molar ratio MR to a desired weight ratio or molar ratio of the diaryl carbonate to the aromatic dihydroxy compound;
• and
• if needed, adjusting the amount of the aromatic dihydroxy compound or the amount of the diaryl carbonate added to the mixture to achieve the desired weight ratio WR or molar ratio MR, wherein the standard deviation of a calculated weight ratio WR or molar ratio MR to a desired weight ratio or molar ratio is less than 0.02.