On the mechanism of the polymerization of ε‐caprolactam. IV. Polymerization in the presence of water and either an amine or a carboxylic acid

Abstract

In continuation of previous kinetic work on the hydrolytic polymerization of εcaprolactam (CL) (Part I–III) in which evidence was obtained that all the predominant reactions are catalyzed by endgroups, special experiments were undertaken in order to study the specific role played by the NH2 and COOH endgroups. To that end kinetic runs at 221°C. were performed with Cl‐water systems (containing 5–7 mole‐% of water) in which the symmetry of the concentrations of NH2 and COOH groups was disturbed by the addition of about 1 mole‐% of either an amine or a carboxylic acid [hexamethylenediamine (HMD), adipic acid (ADA), and sebacic acid (SBA) were used]. The concentrations of unconverted lactam and of amino and carboxyl groups were determined as previously described; special techniques were worked out for the determination of the small concentrations of unconverted HMD, ADA, and SBA. The main observations are: (1) added HMD disappears much more rapidly from the reaction mixture than added ADA or SBA; (2) the dicarboxylic acids have considerable accelerating effect on the formation of endgroups. Only a general qualitative discussion of these results is given. The principal deductions may be summarized as follows. (a) The initial reaction of the polymerization process, the hydrolysis of CL, is found to be catalyzed by COOH groups. (b) The main contribution to the increase in chain length is furnished by the addition of CL to NH2 endgroups exclusively (aminolysis of the lactam molecule). (c) This addition reaction is catalyzed by COOH groups. (d) Probably, the polycondensation reaction of NH2 and COOH groups is also catalyzed by COOH groups.

Mathematical Modeling of Nylon 6/6,6 Copolymerization: Beneficial Influence of Comonomers on Degree of Polymerization in Batch Reactor

“…To our knowledge, there is no published nylon 6/6,6 batch reactor kinetic data in either the academic or patent literature. However, there is pertinent data from two experimental data sets generated by Heikens et al that are available for testing the model predictions . These early experiments, conducted at 221 °C, were performed to obtain information about the specific roles of amine and carboxyl ends during nylon 6 production.…”

“…The reverse of reaction (1.3) is a back‐biting reaction to produce caprolactam. Note that addition of caprolactam to a growing polymer chain occurs primarily at amine ends rather than at carboxyl ends . Reactions (1.1) to (1.3) were considered as the nylon 6 polymerization mechanism in modeling studies by a variety of early researchers until Arai et al added reactions (1.4) and (1.5) related to formation and consumption of cyclic dimer (CD).…”

“…Hermans et al found that the propagation, ring‐opening and transamidation reactions shown in Table are catalyzed by the presence of carboxyl end groups in the reaction mixture, leading to expressions for forward rate constants of the formwhere is an “uncatalyzed” rate constant corresponding to nylon 6 polymerization when the concentration of carboxyl ends is very low and is a “catalyzed” rate constant used to account for the higher reaction rates that are observed at higher carboxyl‐end concentrations. To study the roles played by amine and carboxyl end groups in nylon 6 polymerization, Heikens et al performed experiments in a caprolactam/water system with either HMD or ADA added to perturb the balance of ends. Data from their experiments will be used in this article to compare with predictions of the proposed copolymerization model.…”

“…Intended uses of this model are to guide experiments being conducted in the lab‐scale batch reactor shown schematically in Figure and to assist with improved understanding of PA6/6,6 production in continuous commercial reactors. Model predictions are compared with batch reactor data generated by Heikens et al at a relatively low temperature of 221 °C . The model is then used to simulate batch reactor operation at conditions of industrial interest.…”

Polymers for Fibers

“…With these assumptions, the maximum stressfc increases directly with the cooling rate and the activation energy for viscous flow as well as the other factors shown in equation (18). (22) Next the possibility that elongational flow is non-Newtonian over at least the higher ranges of elongation rates or stress levels is considered. If this happens, it may be for the same reasons that shear flow becomes non-Newtonian, i.e.…”