The kinetics of hydrolytic polymerization of ϵ-caprolactam

A method to determine the concentration of ?-aminocaproic acid (ACA) in poly-?-caprolactam by high-pressure liquid chromatography is established. The polymerizations for initial water concentrations of 0.42, 0.82, and 1.18 mol/kg and temperatures of 230, 240, 250, 260, 270, and 280°C were performed and concentration-versus-time curves were obtained for ACA, ?-caprolactam (CL), and endgroups (EG). Each curve for ACA and EG has a maximum which increases monotonically in its value and shifts from right to left in position with increasing either the temperature or the initial water concentration. The reaction rates of CL, EG, and ACA were also evaluated numerically from the concentration data. The observed kinetic data were compared with those obtained by the numerical solution of the rate equations with Reimschuessel's kinetic constants. Good agreement is found in CL and EG concentrations but discrepancies in ACA concentration and rates are considerable, particularly in the early stage of the polymerization.     

The hydrolytic polymerization kinetics of ϵ-caprolactam

The three major kinetics of the polymerization of caprolactam, ring opening, condensation and addition, has already been investigated.In this paper, data and rate constants for the other two important reactions, termination and cyclic oligomer formation are given. The both reactions are catalysed by the carboxyl end groups and the termination reaction with a very small quantity of organic acid is also affected by the viscosity of the solution.The effects of operating conditions on the rates and products of the polymerization have been studied through process simulation. It is shown that, to realize the cyclic oligomer content low as possible, simple optimizing criterion as obtaining given degree of polymerization in the shortest possible reaction time gives quite unfavourable conditions to the oligomer content.     

The kinetics of hydrolytic polymerization of ε-caprolactam. II. Determination of the kinetic and thermodynamic constants by least-squares curve fitting

The kinetic and thermodynamic constants of the hydrolytic polymerization of ?-caprolactam were determined by least-squares curve fitting. The calculations were carried out using observed kinetic data such as concentration of ?-caprolactam ([CL]), endgroup ([EG]), and ?-aminocaproic acid ([ACA]) and time derivatives of each concentration (rates) ?[CL]/?t, ?[EG]/?t, and ?[ACA]/?t. The sets of the converged constants are obtained for the initial water concentrations of 0.42, 0.82, and 1.18 mole/kg. An averaged set of the constants applicable for this range of the initial composition was also evaluated. The compatibility between observed and calculated concentration and rate curves was improved by the use of the newly developed sets of the constants. The mechanism of the polycondensation reaction is also discussed, based on the rate and kinetic constants obtained by this work.     

The simulation of hydrolytic polymerization of ϵ-caprolactam in various reactors

The concrete simulation models dealing with the kinetic behavior of the hydrolytic polymerization of ?-caprolactam (CL) in various polymerization reactors used in the industry were described, and the method for their numerical solutions was presented. The characteristic data of the polymerization such as the concentrations of CL, end group, water, ?-aminocaproic acid, cyclic dimer, and the hot-water-soluble component, conversion, number average, and weight average molecular weights, and solution and melt viscosities can be calculated at every stage of the polymerization reaction, at every part of the reactors, and/or at the outlet of the reactors. The calculated values based upon the models were found to be quite compatible with the observed values for the reactors. The applicability of the technique was well confirmed for the quality control, process control, modification of existing plants, and development of new chemical process plants.     

Activation of the hydrolytic polymerization of ε-caprolactam by ester functions: Straightforward route to aliphatic polyesteramides

The hydrolytic polymerization of ε-caprolactam (CLa) was carried out in bulk (in absence of solvent) at 250 °C in the presence of carboxylic esters and aqueous H₃PO₂. It turned out that by conducting the ring opening polymerization (ROP) of CLa in the presence of PEO–C(O)–O–C₅H₁₁, a selected model ester (PEO = poly(ethylene oxide)), a remarkable activating effect of the ester function on the hydrolytic polymerization of the lactam was observed yielding PEO–b–PCLa diblock copolymers. The comparison of the CLa monomer conversions obtained with or without the model ester activated by H₃PO₂, as determined by ¹H NMR spectroscopy, has enabled to propose a multi-step mechanism in which three major reactions occurred: (i) ester and lactam hydrolysis, (ii) aminolysis of the carboxylic ester by the resulting primary amine of the hydrolyzed/opened lactam ring and (iii) condensation reactions between carboxylic acids and both amine/hydroxyl functions. The overall result of this multi-step mechanism can be assimilated as an “insertion” of the opened lactam into the ester function. By conducting the hydrolytic polymerization of CLa in the presence of an aliphatic polyester chain, such as poly(ε-caprolactone) (PCLo), polyesteramides were recovered with high yields and random distributions of the CLa and CLo repetitive units as determined by ¹³C NMR.     

Reaction-induced crystallization kinetics during the anionic polymerization of ϵ-caprolactam

The kinetics of crystallization during anioiiic polymerization of ?-caprolactam was studied by the adiabatic temperature rise method, A new kinetic model for the non-isothermal crystallization was derived and the possibility of its application was Investigated. By evaluating the parameters in the model for the given adiabatic system, the crystallization behavior during the; polymerization process was analyzed. The experimental and calculated temperature rise showed a very good agreement, which indicated that the model equation was appropriate to describe the non-isothermal reaction-induced crystallization kinetics in this study. The melting temperature of the reaction mixture increased steadily due to the change of the crystal structure with conversion. The equilibrium crystallinity was higher when the crystallization started in the presence of unreacted monomer than when the crystallization occurred after polymerization was completed. At lower conversion, the reaction mixture was less viscous, a condition that made transport to the liquid-crystal interlace easier, and thus the activation energy for transport decreased. On the other hand, the increasing mobility resulted in difficulty in forming stable nuclei arid the free energy of nucleation increased.     

A kinetic study of the activated anionic polymerization of ε-caprolactam

The diversities existing among published kinetic studies on activated anionic polymerization of ε-caprolactam are closely examined. A kinetic model derived from a regular, linear reversible reaction mechanism is employed to explain the experimentally observed autocatalytic character of the polymerization system and to examine the dependence of the apparent activation energy on the experimental method. Several existing kinetic models tested with our experimental data show that the autocatalytic type rate equation best describes the polymerization process.     

Structure of poly(ε-caprolactam) obtained in anionic bulk polymerization

The nascent structures of poly(ε-caprolactam) (N6), obtained during anionic polymerization in bulk in the presence of different additives, were investigated. The experimental data show that both the type and the quantity of activator influence significantly the process of polymerization as well as the chemical and the physical structures of N6. By means of WAXD, DSC, IR, light and transmission microscopy (TEM), and electron microdiffraction (ED) the changes in the morphological and the crystal structure were followed. The observed alterations in the physical structures of N6 samples are explained on the base of changes in the chemical structure and mobility of the polymer chains. © 1995 John Wiley & Sons, Inc.     

Effect of diacid stabilizers on kinetics of hydrolytic polymerization of ϵ‐caprolactam in industrial reactors

The rate constants in hydrolytic polymerization of ε‐caprolactam are dependent on the concentration of carboxylic acid groups in the reaction medium. Therefore, the use of diacid stabilizers for regulating molecular weight are likely to have favorable effect on the kinetics of polymerization compared to monoacid stabilizers, which are traditionally used in such polymerizations. To understand the kinetics of polymerization in the presence of diacid stabilizer compared to monoacid stabilizer, mathematical kinetic models were developed using the end group approach. These models were used to quantify the effect of both stabilizers on nylon‐6 synthesis in a closed isothermal batch reactor at different temperatures in the range of 245–265°C. The kinetic model for the diacid‐stabilized system was then extended to an industrial VK tube reactor using the process model developed earlier for the monoacid stabilized system. Both the mathematical modeling and experimental results showed that the presence of diacid stabilizer could significantly enhance the overall kinetics of the reaction compared to the monoacid stabilized system and in turn, resulted in reduction of the polymerization time by about 20–25%. The study suggests that diacid stabilizers may be used preferably over monoacid stabilizers in synthesis of nylon‐6 to reduce the cost of polymerization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Some effects of cocatalyst structure on the anionic polymerization of ϵ-caprolactam. II.

A study of the effect of catalyst (base) concentration and N-acylcaprolactam cocatalyst size and substitution on the fast anionic polymerization of caprolactam indicated that a steric effect due to cocatalyst size exists, and perhaps an electronic effect due to cocatalyst substitution was noted. The rate of polymerization, degree of polymerization, and yield of polymer are related to these effects. It was also noted that at high base concentrations, the rate and degree of polymerization along with the product yields all decrease. These latter observations suggest that reinterpretation of some of the reaction mechanism data may be important if polymer degradation is not an appreciable factor during the reaction.     

Mechanism and kinetics of adiabatic anionic polymerization of ϵ-caprolactam in the presence of various activators

Nylon 6 was prepared by adiabatic anionic polymerization of ?-caprolactam using hexamethylene dicarbamoyl dicaprolactam (HDC), cyclohexyl carbamoyl caprolactam (CCC), or phenyl carbamoyl caprolactam (PCC) as activators and sodium caprolactamate (NaCL) as a catalyst at various initial reaction temperatures ranging from 130 to 160°C. Adiabatic temperature rise was recorded as a function of polymerization time to investigate polymerization kinetics. Kinetic parameters for polymerization, which are more accurate than data reported to date, could be obtained by fitting the temperature rise data with a new polymerization kinetic equation involving crystallization exotherm and thermal conduction. The polymerization rate highly depended on the chemical structure of the activator used, which indicates that the initiating step where the activator is attacked nucleophilically by NaCL is a very important reaction step, affecting the overall polymerization rate. CCC showed the fastest polymerization rate, whereas HDC and PCC showed the medium and the slowest rate, respectively. The contributions of crystallization exotherm and thermal conduction to the resultant temperature rise during polymerization were significant, when the initial reaction temperature was lower than 140°C. In all cases, the molecular weight obtained from intrinsic viscosity measurement was greater than the expected molecular weight. This may be attributed to the branching and/or crosslinking reaction through Claisen-type condensation reactions. © 1995 John Wiley & Sons, Inc.     

The simulation of hydrolytic polymerization of ε-caprolactam in various reactors: A simulation model for the tubular reactor with heat exchanger and its numerical solution

A concrete simulation model which deals with the hydrolytic polymerization of ε-caprolactam (CL) in the tubular reactor (TR) with the heat exchangers (HEx's) was described, and a method for its numerical solution was presented. The numerical calculations were carried out for 13 cases, where the position and number of the HEx's in the TR were varied. The effects of the HEx on the distribution of the temperature in the TR and of the characteristic data of the polymerization (the concentration of CL and number average degree of polymerization) in the TR and at the outlet of the TR were investigated. The results suggested that the HEx positioned at the upper half of the TR and the HEx positioned at the lower half of the TR are effective to narrow the temperature distribution in the TR and to produce the polymer product with narrower molecular weight distribution, respectively.     

Analysis of the impurities in industrial ε-caprolactam. Hypothesis of formation

Analysis of an industrial ε-caprolactam by gas–liquid chromatography has been carried out using different stationary phases and operating conditions. The impurities in the ε-caprolactam are identified and hypotheses about their formation are presented. In some cases the presence either in cyclohexane or cyclohexanone of the possible impurity-producing compounds is shown.     

Dynamic mechanical properties of poly( ε-caprolactam)/polypropylene alloy

The results of a round-robin testing on the dynamic mechanical properties of a poly(ε-caprolactam)/polypropylene PA-6/PP compatibilized blend (an alloy) are reported. The alloy was a commercial product (Orgalloy R-6000, from Atochem). The samples were prepared by extrusion, injection or compression molding. The greatest difficulty in comparing the data arose from the moisture content since the position of the PA-6 transition peaks depend on the drying conditions. For the extruded specimens only minor effects could be attributed to the anisotropy introduced by the extrusion process. Overall, there was good agreement between the contributing laboratories for the frequency dependence of the transition peaks, but agreement between the measured values of the storage moduli was poor. This discrepancy is suspected to be partially due to the differences in sample geometry and in the processing conditions.     

Enzyme-catalyzed polymerization and degradation of copolyesters of ε-caprolactone and γ-butyrolactone

Copolymers of γ-butyrolactone (γ-BL) and ε-caprolactone (ε-CL) were successfully synthesized by ring-opening polymerization using Novozyme-435 (immobilized lipase B from Candida antartica) as catalyst. Copolymers with different compositions were obtained and characterized by ¹H NMR, ¹³C NMR, GPC, DSC and X-ray diffraction. Increasing the [BL]/[CL] feed ratio resulted in decreases of molecular weight (M_n) of copolymers and reaction yield. Moreover, the BL contents in the copolymers varied according to the feed ratio. The T_m of the copolymers decreased from 58 to 49 °C with increase in BL content from 0 to 14%. The resulting copolymers were all semicrystalline with a PCL-type crystalline structure. Solution cast films were allowed to degrade in a pH 7.0 phosphate buffer solution containing Pseudomonas lipase. Weight loss data showed that the degradation rate of copolymers in the presence of Pseudomonas lipase decreased with the increase of BL contents.     

Block polymers from isocyanate-terminated intermediates. IV. Properties of cured butadiene–ε-caprolactam block polymers

Butadiene–ε-caprolactam block polymers containing a high proporation of 1,2 units in the butadiene-segments were synthesized and physical properties were measured on the cured copolymers. Flexural strength and impact resistance both increase regularly with increasing ε-caprolactam content in peroxide cured copolymers. This behavior is explained by the higher values of flexural modulus and impact resistance for poly(ε-caprolactam) compared with peroxide-cured polybutadiene resins. Copolymers reinforced with silica showed higher heat distortion temperatures but lower impact resistance than corresponding unfilled samples. Arrhenius plots of flexural properties at various test temperatures were linear. Both flexural modulus and strength decreased regularly with increasing test temperature. Flexural properties of filled copolymers were relatively unaffected by heat aging up to 204°C for several weeks, however, dramatic decreases in these properties were noted in a matter of days when heat aging was done at 260–316°C. These results are explained by the rapid degradation of poly(ε-caprolactam) above its melting point. Block polymers whose butadiene segments contained a high proportion of 1,4 units were also synthesized. These copolymers were elastomeric when cured with either sulfur or peroxide.     

Flame-resistant polycaproamide by anionic polymerization of ϵ-caprolactam in the presence of suitable flame-retardant agents

Poly(?-caprolactam) (PCL) with improved flame-retardant (FR) properties can be easily obtained by activated anionic polymerization of the monomer, ?-caprolactam (C), in the presence of adequate amounts of red phosphorus (red P). Analogous results with reduced P content can be achieved by coupling red P with a synergistic compound such as a chlorinated hydrocarbon or magnesium oxide (MgO). A peculiar advantage of this method is the possibility of obtaining a very fine and homogeneous dispersion of the FR additive in the polymer matrix, meanwhile avoiding the typical compounding techniques, which are expensive, often unsafe, and require melt mixing of the ingredients. Molecular, thermal, and mechanical characterization, as well as morphology of the resultant products, have been determined: No significant properties change have been found when FR agents are present, apart from the relevant improvement of the flame-resistance. Thus, by this novel procedure it is possible to prepare FR poly-(?-caprolactam) without any appreciable deterioration of its typical properties.