Liquid-phase hydrolytic polymerization of caprolactam at 483 K

Abstract

Experimental confirmation of the thermodynamic identity of condensation reactions of amino and carboxyl groups in PCA melt and amorphous phase was obtained. It was shown that the Huggins constant of PCA uniformly increases with an increase in the time the polymer is in the molten state and the moisture content of the melt. The expediency of synthesis of PCA prepolymer in stages with k H ≤ 0.25 for two different values of the moisture content of the melt in a reactor with adjustable water vapor pressure was substantiated.Liquid-phase hydrolytic polymerization of caprolactam (CL) at 483 K, i.e., below the melting point of polycaproamide (PCA), is possible if the moisture content of the polymer melt is at the level of ~1 wt. % [1].If we use the relation inwhich correlates the equilibrium degree of polymerization of the polymer with the initial moisture content of the CL melt ([H 2 O] 0 ), expressed in moles per mole CL converted to linear chain units (base-mole),* and the amide equilibrium constant (K) at the given temperature, then it is possible to show that at 483 K (K = 946 [3], α = 0.92 [3]) and initial CL moisture content of 1 wt. %, the equilibrium degree of polymerization of PCA will be equal to ~125. This is already at the level of a fibre-forming polymer, especially in the case of use of technology that provides for nonaqueous extraction of low-molecular-weight compounds (LMC) in the stage of preparing the polymer for fibre spinning and combined drying demonomerization [4]. For this reason, the question regularly arises concerning the duration of such low-temperature synthesis and the possibility of obtaining a polymer with a Huggins constant (k H ) equal to 0.25, which allows spinning fibres with high physicomechanical indexes [5].The results of a study of the kinetics of polymerization of CL at 483 K and the effect of the duration of synthesis and moisture content of the PCA melt on the value of k H are examined below. . 18 16 113 0 2 0 2. is the initial CL moisture content, g/g; 113.16 and 18 are the molecular weight of CL and water, respectively; α = (1 -LMC) is the degree of conversion of CL in linear chain units and LMC is the equilibrium mass fraction of CL and cyclic oligomers in the polymerizate.0015-0541/07/3901-0007

Sustainable Production of Polyamide 6 Fibers: Direct Melt Spinning and Efficient Reuse of Residual Oligomers during Polymerization

“…Bazarov proved that CPL hydrolysis polymerization below the melting point of PA6 (210 °C) can effectively reduce the monomer content after equilibrium and recalculated the reaction equilibrium constant according to different water contents. 17 Mizerovskii further studied melt polymerization at a temperature 10−15 °C below the melting point of PA6. 18 Although the molten state can still be maintained at low temperature, it is a metastable state and is not suitable for large-scale application.…”

“…Reduction of the reaction temperature is an effective way to control the content of oligomers. Bazarov proved that CPL hydrolysis polymerization below the melting point of PA6 (210 °C) can effectively reduce the monomer content after equilibrium and recalculated the reaction equilibrium constant according to different water contents . Mizerovskii further studied melt polymerization at a temperature 10–15 °C below the melting point of PA6 .…”

Unveiling the Mechanisms of Hydrolytic Ring-Opening Polymerization of Caprolactam and Amino-Assisted Ring Opening of Cyclic Dimers: A DFT Study

“…In addition to water, the production of cyclic oligomers is also affected by the reaction temperature and time. , Therefore, a few studies have reported that the formation of cyclic oligomers can be reduced by adjusting the polymerization process. Bazarov et al opened caprolactam at 210 °C for 8–12 h to obtain the PA6 prepolymer with 6.5–7.0 wt % oligomer and then reduced the monomer and water content by a vacuum method so that the polymerization degree of PA6 reaches 120, and the oligomer content can be reduced to the spinning requirements. Isaeva et al first prepared the PA6 prepolymer from caprolactam, then removed the water in the prepolymer by controlling the pressure, and then placed it in a superheated steam environment for solid-phase polymerization so that the degree of polymerization of the polymer can reach 200, and the oligomer mass fraction is 3.0–4.0%.…”