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Process for the production of polycarbonate of constant viscosity

  • US 5,412,060 A
  • Filed: 01/31/1994
  • Issued: 05/02/1995
  • Est. Priority Date: 08/20/1991
  • Status: Expired due to Fees
First Claim
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1. A process for the production of polycarbonates by the two-phase interfacial method in at least two reaction steps, in which a phosgene-containing organic phase and a bisphenol-containing water phase with or without alkali hydroxide or chain terminator are mixed in a first step to form a first input stream and in a second step polycarbonate producing catalyst with or without chain terminator is added as a second input stream, said first input stream and said second input stream being controlled by the value of the relative viscosity Of the polycarbonate, wherein the relative viscosity of the resulting polycarbonate is measured at the end of the reaction, a viscosity number (VZ*) defined as V-number=100×

  • (relative viscosity -1) is calculated from the measured concentration and quantity of phosgene, bisphenol, catalyst and alkali hydroxide and applying an empirical relation conforming to
    
    
    space="preserve" listing-type="equation">V-number=a+b.n+c.n.sup.2in which n denotes the average number of bisphenol units in the polymer chain which is calculated from the measured concentrations and quantities in which a, b, c . . . are empirical constants and the variation in time of the V number is calculated from the measured variations in time of the input streams and concentrations;

    a V number VZ** is then formed by adding a correction term Δ

    VZ to VZ* resulting in a minimization of the deviation between VZ** and the measured V number;

    the correction term Δ

    VZ.sup.(new) =Δ

    VZ.sup.(old) +f (VZ measured-VZ**) is recalculated every time a new measured V number is available, and the calculated VZ** together with the concentrations of the input streams are converted into control variables which set the input streams of the running reaction and with or without converting correspondingly the concentration of the alkali hydroxide or of the alkali carbonate or of both at the end of the reaction into controlled variables to set the input streams of the running reaction.

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