Continuous low moisture catalytic method for polymerization of

Abstract

This invention is an improvement to the continuous method to polymerize caprolactam at temperatures over 220.degree. but below 280.degree. C. in the presence of free water, a catalyst capable of generating phosphoric acid at the reaction conditions, in the hydrolyzer to form a prepolymer, with subsequent stripping of water and other low boiling compounds, and with completion of polymerization in a final finisher under a vacuum. The improvement comprises limiting the amount of free water fed to the polymerization process to less than about 1.5 percent but above 0.5 percent by weight of polymer and limiting the amount of catalyst being fed to the polymerization process to between about 5 ppm and 100 ppm of polymer of measured phosphorus so that (a) the rate of the process increases at the same temperature and pressure, or dimer content of the final polymer decreases or both, (b) the molecular weight of prepolymer from the hydrolyzer of the process increases, (c) less water is removed from the polymer and prepolymer during processing, (d) conditions required to remove water and other low boiling compounds from the finisher are less severe, resulting in a lower temperature of the polymer delivered to spinning from the final finish or a lower cost for vacuum removal or both, and (e) there is a reduction of deposits on the screen for molten final polymer prior to spinning.