Nylon 6 type polyamide equilibrium products prepared from t-caprolactam and water in closed systems at temperatures of 222 and 254" C have been investigated. Unconverted caprolactam, higher membered cyclic compounds, chain fractions and end-groups (-NH, and -COOH) were determined quantitatively. Percentages of caprolactam and higher rings increase with increasing temperature and/or increasing water content (corresponding to decreasing DP) of equilibrium products. Numberaverage DP of chain fractions varied from -100 --+ 10 in the range investigated. The results have been evaluated in terms of equilibrium constants on the basis of plausible theoretical considerations including the Flory-Schulz distribution of chain lengths.The equilibrium constant of the polycondensation reaction has been found to decrease with decreasing DP of products. This bchaviour is in accordance with similar results obtained for different polyamide equilibrium products.Possible explanations are discussed. A comparison with some data available from the literature is included.

In this first‐paper of a series of publications on the mechanism of the polymerization of ϵ‐caprolactam (CL), an investigation of the kinetics of the polymerization initiated by ϵ‐aminocaproic acid (ACA) is reported. Experiments were performed at 254°C. for three different initial ratios (ACA/CL)0:0.05, 0.022, and 0.011 mole/mole. The concentration (x) of unconverted CL and that of end groups (c) were determined by extraction with water at room temperature and by potentiometric titration, respectively. The method of kinetic evaluation consists in the direct checking of rate equations making use of the quantities dx/dt and dc/dt which were determined graphically from the curves of x and c versus time. In this way tedious integration procedures are avoided and the testing of rather different mechanisms is much easier. Moreover, it is not necessary to make the assumption of constant rate coefficients which, of course, will seldom apply. Thus the inadequacy of the “polycondensation mechanism” has been proved for every time instant separately, although accidentally the rate constant of the main reaction is fairly constant. In this polycondensation mechanism it is assumed that polymer formation can take place only by polycondensation of ACA, the supply of which is provided for by the reaction of CL with water formed in the process of polycondensation. It turns out that even when the rate of hydrolysis of CL is so high that the polycondensation reaction is rate determining, this latter rate is to small by a factor of 10 or more to account for the rate of CL conversion observed. It is shown that this difficulty can be overcome only by incorporating a third reaction in the mechanism, a reaction which must provide for the main consumption of CL. We have assumed this reaction to be a reversible polyaddition reaction, i.e., a reaction in which CL is added to one of the end groups of the polymer molecules. The rate constant for this reaction derived from the experiments appears to be in good agreement with the value derived from the experiments on the polymerization of CL initiated with water.

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Simultaneous measurements of osmotic pressure and permeation of solute have been made for a nonfractionated polystyrene with a number of membranes of widely different permeability. It is shown that, even after many days, no real equilibrium is reached in an osmometer with a membrane permeable to part of the polymer. The theory of equilibria in such osmometers is developed and shows that, in first approximation, the distribution of permeating solute over the two osmometer cells is not affected by the presence of nonpermeating solute. In second approximation, this distribution is affected indeed, but in this approximation the osmotic pressure is not affected by this unequal distribution. Some short‐time experiments also show that when the number of permeated molecules is negligible (t → 0) the contribution of a molecular species to the osmotic pressure is less than the value given by equilibrium thermodynamics if the membrane is not completely impermeable to that molecular species. This phenomenon is in accordance with the theory of permeability of membranes based upon nonequilibrium thermodynamics.

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