Equilibria in polyamide systems from ϵ‐caprolactam and water

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Abstract
Nylon 6 type polyamide equilibrium products prepared from ε‐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 (−NH2 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. Number‐average 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 behaviour 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.