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

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The point of view was advanced that in spinning fibres from polymer melts, the molecular inhomogeneity of the melts is not due to the polydispersity of the polymer but to important differences in the average molecular mass of the individual granules. Using the example of three industrial samples of hydrolytic PA 6, it was shown that the standard deviation of the average molecular mass of the polymer with respect to the individual granules from its mean statistical values is at the level of 10-11% for a practically significant (for up to several percent of granules) deviation of 30-50%. The use of samples of PA 6 with the mass provided by GOST 18245-72, OST 6-06-S9-76, and GOST 11034-82 in determining the viscosity a solution of the polymer in H 2 SO 4 allows correctly estimating its average molecular mass but makes it impossible to obtain reliable information relative to the real degree of inhomogeneity of the granulate based on this index.In analyzing the dependence of the physicomechanical properties of fibres spun both from solution and from polymer melt on the molecular-weight characteristics of the polymer, it is believed that the molecular inhomogeneity of these liquid systems is exclusively due to the polydispersity of the initial polymer. However, if this assumption can be considered valid when applied to solutions of polymers, the validity of extending it to melts is doubtful.Actually, in preparing solutions of polymers (due to their relatively low viscosity in comparison to melts and the duration of the process), it is always possible in principle to attain a degree of homogenization of the system at which the differences in the average molecular mass and degree of polydispersity with respect to microvolumes of the initial (solid) polymer are totally leveled. Conversion of polymer granules into a melt is very rapid and a degree of homogenization similar to that attained in solution is probably practically impossible to attain. For this reason, inhomogeneity of the polymer granules with respect to the average molecular mass could be the basic cause of the molecular inhomogeneity of the melt on the microvolume level. The seriousness of the problem becomes evident if we consider that several meters of fibre can at the minimum be formed from a microvolume of melt formed in melting an ordinary granule weighing approximately 3⋅10 -2 g.We report the results of an analysis of polyamide 6 (PA 6) from Shchekinsk Khimvolokno Co. taken directly after the stage of synthesis on a cascade polyamidation line (polymer I) and PA 6 from Kuibyshevazot Co. (Tol'yatti) having gone through the stage of extraction of low-molecular-weight compounds and drying (polymer II), as well as treatment with an aqueous solution of a thermostabilizer and additional drying (polymer III).The essence of the experiment consisted of establishing the character of distribution of the polymer granules with respect to the average molecular mass based on determination of this quantity for 100 granules.

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