Patent ID: 8426531
Filing Date: 2013-04-23
Classification: C08G,G01N

Abstract:
1. A method for controlling a dihydric phenol to chain terminator ratio in an interfacial polycarbonate polymerization process by measuring the concentration of dihydric phenolate, hydroxide, or both in an aqueous dihydric phenolate solution prior to reacting said solution with a carbonate precursor and chain terminator to produce a polycarbonate polymer, comprising the steps of: i setting a target range for the dihydric phenol to chain terminator ratio; ii introducing dihydric phenol and base at specific and independent feed rates into said solution; iii setting target concentration ranges for dihydric phenolate and/or hydroxide in said solution; iv introducing said solution, the carbonate precursor, and the chain terminator into a polymerization reactor at specific and independent feed rates; v analyzing said solution, online prior to entering the polymerization reactor by vibrational spectroscopy measuring the absorbance or scattering intensity of at least one wavelength as a reference wherein said solution has little to no absorbance, at least one wavelength wherein the dihydric phenolate absorbs, at least one wavelength wherein hydroxide absorbs, and at least one wavelength for temperature compensation; vi calculating the concentration of the dihydric phenolate and/or hydroxide in said solution based on the vibrational spectrometer analysis; vii comparing the calculated concentrations to the target concentration ranges; and viii using process control, when necessary, to adjust the feed rates of one or more of the dihydric phenol, the base, the chain terminator, and/or the dihydric phenolate solution to maintain the dihydric phenolate to chain terminator target range.