Production of High-Molecular-Weight Nylon 6 Using Prepolymerization Process -Study on the Polymerization of Nylon. I.-

Abstract

On the conventional polymerization of Nylon 6, excess water is evaporated at the degassing stage from the reaction product which is already well-polymerized towards polymerization equilibrium. For the high-molecular-weight polymer, the degassing does not proceed always smoothly, because of high melt viscosity of the product at the degassing stage.
Then, production of high-molecular-weight polymer using prepolymeriza tion process has been studied, in which the degassing takes place from the prepolymer with lower melt viscosity.
First, prepolymer range which leads to polymer even after the degassing is determined through batchwise experiment (Fig.3). Then, in continuous polymerization, in fluence of prepolymer condition and degassing temperature on relative viscosity of polymer has been tested (Fig.6).
Meanwhile, solidification point is found to be a practical parameter to characterize the prepolymer and melt viscosity of the prepolymer is measured.
Melt viscosity of the prepolymer is about 50 poise at 240°C and increases rapidly as it approaches to the polymer in equilibrium (Fig.7).
Optimum prepolymer condition at the degassing stage is determined by experiment to be 170-175°C of solidification point. This corresponds to the prepolymer range where melt viscosity is still low and polymerization reaction has sufficiently proceeded, Under these conditions smooth and flash vaporization of water from the prepolymer at the degassing stage is observed. Thus the steady production of high-molecular-weight Nylon 6 can be proved.