Modeling Equilibrium Behavior of Nylon 6, Nylon 6,6 and Nylon 6/6,6 Copolymer

Abstract

Nylon 6 and nylon 6,6 reaction equilibria depend in a complex way on water concentration and temperature. For example, data sets from six research groups reveal that the apparent equilibrium constant for polycondensation increases with water at low water concentrations, reaches a maximum, and then decreases as the water concentration rises further. In this article, semi‐empirical expressions are proposed to describe the experimentally observed equilibrium behavior for the five main reactions that occur during nylon 6 and nylon 6,6 polymerization. Nine side reactions involving amidine ends, cyclopentanone ends, and hydrated carboxyl ends are used to develop expressions that account for the influence of both water and temperature on these equilibrium constants. Excellent fit to the data, over the entire range of the available nylon 6 and nylon 6,6 literature data, suggests that the proposed equations will be helpful for modeling reaction equilibria for nylon 6/6,6 copolymerization.

Improved Kinetic Rate Constants for Nylon 6, Nylon 6,6, and Nylon 6/6,6 Copolymer

“…Parameter values from both Step 1 and Step 2 result in overprediction of the rate of polycondensation at high [ W ] (i.e., for experiments with initial water ≥3.5 wt%) and to underpredict the rate of polycondensation at low [ W ] (e.g., for experiments with initial water ≤1.18 wt%). This result is not particularly surprising because many authors have commented on the complex influence of water on polycondensation equilibrium and reaction rates 14–28. In our previous reaction equilibrium modeling study,28 side reactions involving amidine ends, cyclopentanone ends, and hydrated carboxyl ends (R7–R12 in Table 5) were used to develop a model for the complex behavior of K 2 a , which changes with [ W ] and T .…”

“…The parameter values in Equation were fitted using a portion of nylon 6 and 6,6 kinetic data in Table 6. Although Steppan's kinetic model provides a good match to a portion of the available nylon 6,6 literature data, it provides poor predictions for nylon 6 data, especially at long reaction times 17,21,22,28…”

“…Steppan's kinetic model provides a good match to a portion of the available nylon 6,6 literature data, it provides poor predic tions for nylon 6 data, especially at long reaction times. [17,21,22,28] Mallon and Ray used a more mechanistic approach to account for the complex effect of [W] on nylon kinetics and equilibrium, suggesting that ionization of endgroups is related…”

“…For example, it is well known that Arai's parameters do not account for the complex influence of water on nylon 6 and nylon 6,6 reaction equilibria that has been observed in the literature, especially for polycondensation reaction R2 17–27. To address the problem of complex equilibrium behavior for reactions R1–R5 in Table 1, we recently developed a series of mechanistically motivated semi‐empirical equilibrium expressions for nylon 6, nylon 6,6, and nylon 6/6,6 copolymer 28 . Table 4 provides these equilibrium expressions, which were derived by considering seven additional side reactions shown in Table 5 .…”

Special Issue: Innovative Processes and Enabling Technologies

“…Shifting gears from polyolefin production, McAuley and coworkers used models and literature data to study complex equilibrium behavior of nylon 6 and nylon 6,6 polymerizations, which has been a concern for many years. They reveal that side reactions involving hydration of carboxyl ends and dehydration of amine ends can explain the non‐linear dependence of water on the polycondensation equilibrium constant.…”