Anionic Polymerization Of Caprolactam Research Articles

Monitoring of small‐scale anionic polymerization of caprolactam; a method to be used in an additive manufacturing process

The anionic polymerization of caprolactam using small quantities of reactants was investigated as part of a project aimed at producing polyamide parts by additive manufacturing. Various methods were used to monitor the polymerization and crystallization processes. Drop on drop small‐scale polymerization was carried out on a hot surface and monitored by Fourier transform infrared, which showed that PA6 had been polymerized successfully. PA6 synthesis was carried out in a differential scanning calorimetry cell to monitor the exothermic and endothermic processes during polymerization, and the processes were also observed by hot stage microscopy. It was found that polymerization and crystallization occurred simultaneously at slow heating rates. The amount of crystallinity produced during polymerization decreased as the heating rate increased. Copyright © 2013 John Wiley & Sons, Ltd.

Study of the Proper Sintering Conditions of Anionically-Polymerized Polyamide 6 Matrices for the Fabrication of Greencomposites

The present research work assesses the manufacture of long fiber thermoplastic matrix composite materials (GreenComposites). Thermoplastic matrices are too viscous to be injected into the conventional LCM (Liquid Composite Molding) molds, and then epoxy, polyester or vinylester resins are used. Nevertheless, the groundbreaking anionic polymerization of caprolactam allows such a synthesis of a thermoplastic APA6 matrix inside the mold. This matrix is sintered from the starting monomers, and presents high mechanical performance and recyclability. In order to do the reactive injection in a LCM mold, it is necessary to control the polymerization mechanism of such a thermoplastic matrix. This paper puts special emphasis on detecting and solving all problems which arose during synthesis. For instance, moisture values were assessed for all starting reactants, since humidity keeps polymerization from occurring. It is thought that once the synthesis and the resulting material characterization are well controlled, the manufacture of GreenComposites through in situ polymerization, as well as addition of state-of-the-art fabrics such as basalt, can proceed successfully.

One‐pot synthesis of polyamide 12,T–polyamide‐6 block copolymers

AbstractPolyamide 12,T–polyamide‐6 (PA‐12,T–PA‐6) block copolymers were synthesized by anionic polymerization of caprolactam using a PA‐12,T macrocoinitiator (McI). PA‐12,T McI and its precursors are soluble in molten caprolactam allowing for both the McI step‐growth polymerization and anionic polymerization to be performed in one‐pot. It was found that the competing reaction rates of caprolactam ring‐opening polymerization and McI transamidation are both deterred by a common ion effect using CaCl2 and soluble materials were obtained using >1 mol % CaCl2. Without CaCl2, the reaction mixture solidifies in less than 30 s and produces crosslinked materials. To understand this effect, PA‐12,T McI reactions with caprolactam were performed with 1–10 mol % CaCl2, and polymer structures were characterized using 13C NMR and dilute solution viscometry. These data were then correlated with unique thermal properties and swelling behavior of the block copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Reactive rotational molding process of PP/PA6 bilayer systems: experimental investigations

Rotational molding has been regarded as a plastic molding method with great potential. The process offers virtually stress-free products having no weld lines or material wastage, and utilizes relatively inexpensive molds. Yet its widespread growth is hindered due to long production cycle times, which are limited by the time required to heat up and cool down the mold and the product. This presentation is about the study of making multilayer PP/PA6 parts with the reactive rotational molding process. Different studies have already been made in the past about rotational molding or about reactive process of monolayer part. The aim of this work is to reduce cycle time by making a layer via anionic polymerization of caprolactam, and them to compare each process. This presentation is divided into two parts: the first part deals with rheological, dieclectric aland thermal analysis to investigate the effect of mixtures and the crystallization/polymerization effect; the second part deals with the processing of bilayer parts. Firstly, different mixtures of catalysts and activators were investigated by Rheology and thermal analysis in order to determine which mixture would be the most appropriate for the rotational molding process: 2–2 (2% of activator and 2% of catalyst), 3–3, 4–4 and 6–6. In the second step, different processing investigations have been done in order to study the influences of the parameters like oven time or cooling time. An experimental analysis of heat transfer in reactive rotational molding process was also lead. By using an instrumented mold associated with a radio transmission data acquisition system, we demonstrate that the rotational parts of the bilyar PP/PA6 (reactive way) can be obtained with optimised conditions in correlation with the results of rheology and dielectric measurements. Moreover, the results allows us that it is possible to make bilayer reactive part with the rotational molding process by using less energy in a shorter time.

Reactive Blends of Epoxy Resin (DGEBA) Cross-Linked by Anionically Polymerized Polycaprolactam: Adhesive Property and Chemical Resistance

Different ratios of epoxy resin (i.e., diglycidyl ether of bisphenol-A [DGEBA] and caprolactam) have been used to synthesize DGEBA/polycaprolactam reactive blends by carrying out anionic polymerization of caprolactam at 140°C. Anionic polymerization conducted by a strong base such as sodium hydride was used as a catalyst along with a cocatalyst such as N-acetyl caprolactam. The experiments were carried out to study the effect of composition on the adhesive property (i.e., lap shear strength and chemical resistance of the reactive blends). It was observed that the lap shear strength of the reactive blends increased with increasing DGEBA content from 50 to 70 wt% and increased drastically above 70 wt% DGEBA content with all metals (i.e., copper, aluminum, stainless steel, and mild steel). The lap shear strengths of all these reactive blends were observed to be maximum on mild steel. The study of chemical resistance indicates that the films of reactive blends Ep75Ca25 and Ep80Ca20 with 75 and 80 wt% DGEBA content showed better resistance to acids, alkalies, and solvents than the reactive blends Ep50Ca50 and Ep70Ca30 with 50 and 70 wt% DGEBA content. Among the solvents, methyl ethyl ketone, toluene, and methanol were found to be more attacking as compared to acetone, xylene, and ethanol.

Research on the Kinetics of Anionic Polymerization of Caprolactam to Nylon Using Adiabatic Method

Kinetic parameters were calculated based on the catalytic reaction systems of sodium caprolactam salt and N-75 biuret at the temperature of 145 ℃ to 160 ℃.The reaction order was approximately first order.The activation energy was between 73.2-77.1 kJ·mol-1 and the pre-exponential factor was between 2.9×1011-3.6×1011 mol1-n·s-1.The calculated reaction heat of 134.5-137.3 J·g-1 was in consonance with the literature value of 138.6 J·g-1.The adiabatic reaction kinetic model of caprolactam anion was constructed based on the existing research findings.The coincidence between the simulation results and the experimental data revealed that the model was reasonable and correct.

ANIONIC POLYMERIZATION OF LACTAMS IN MICRODISPERSION. I. KINETIC ASPECTS OF THE PROCESS OF CAPROLACTAM POLYMERIZATION

Kinetics of the anionic polymerization of caprolactam (CL) in microdispersion was investigated at temperatures between 90 and 130°C and at stirring rates between 500 and 2000 rpm, respectively. For the investigated range of temperature data analysis showed pseudo-first order kinetics with respect to the monomer concentration. The rate constants are strongly influenced by temperature, increasing with the increase in temperature. For the associated activation energy, a value of 22.51 kJ/mol was obtained. The reaction order is also influenced by the hydrodynamic regime. It seems that below a threshold value of Reynolds Number, the rate of the reaction is independent of the concentration of CL, following pseudo-zero-order kinetics, which is replaced by first-order kinetics above this threshold value of N Re. However, in the second region of N Re, the values of rate constant are almost independent of N Re.

Anionic polymerization of caprolactam in organic media. Morphological aspects

Crystalline entities formed during anionic polymerization of caprolactam (CL) in nonpolar solvents were examined, mainly by scanning electron microscopy and wide angle X-ray scattering. The morphological development of these entities is governed by the complex interaction between the competing polymerization and physical processes like phase separation and crystallization. The effect of the efficiency of catalytic systems on their interaction, the mechanisms of the phase separation and the crystal growth under topological restrictions set by the phase separation are discussed. Under reaction conditions, for these ones favouring high polymer yields, the final morphology of the polycaproamide (PCA) particles can be controlled by the efficiency of both catalytic species (activator and catalyst). Despite the large range of particle sizes two typical morphologies, namely – connected globules evolving to large blocks and macroporous powders are obtained using more or less efficient catalytic systems, respectively. An adequate selection of the catalytic pairs allows to control the particles’ size and their internal morphology, which is important for certain specific applications of PCA.

On the relationship between synthesis parameters and morphology of the anionic polycaproamide obtained in organic media. III. Macroporous powders obtained using CO2 and carbodiimides as activating compounds

The relationship between the type of activator and the morphology of polycaproamide (PCA) powders was investigated. The powders were prepared by anionic polymerization of caprolactam in ethylbenzene using sodium caprolactamate as initiator and CO2, diisopropylcarbodiimide, and dicyclohexylcarbodiimide as activators. The powders were characterized by optical and scanning electron microscopy, particle size distribution, extent of the specific area, porosity, pore size, and pore size distribution. The crystalline structure of PCA powders was also investigated using X-ray diffraction technique. Formation of PCA powders during phase separation is discussed. Powders morphology is simultaneously and competitively controlled by the rates of polymerization and phase separation processes. It seems that the determining factor in the obtainment of such macroporous powders is the stepwise manner in which the growing centers are formed in the reaction medium. In addition, the effect of the site where polymerization proceeds after the occurrence of phase separation on the ultimate morphology of the PCA powders is also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 231–243, 1998

On the relation between synthesis parameters and morphology of anionic polycaproamide obtained in organic media. II. Influence of the Na [O (CH2)2OCH3]2AIH2/aliphatic diisocyanates catalytic systems

The morphology and structure of polycaproamide granules obtained by anionic polymerization of caprolactam in ethylbenzene in the presence of different activators (isocyanates) were investigated. The granules, which consist of a large number of initially separated small particles, were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and wide-angle X-ray scattering. On keeping all the synthesis parameters identical, correlations between the type of activator used, on the one side, and the high polymer content, chemical structure, agglomerates size, and fine morphology, on the other side, were found. The chemical structure of the components of the catalytic system seems to be the determining factor for the obtaining of some kinetically controlled morphologies. The results suggest that an adequate selection of the catalytic species is able to orient the process toward the obtention of materials with desired morphologies, in agreement with certain specific applications. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2575–2583, 1997

On the relation between synthesis parameters and morphology of anionic polycaproamide obtained in organic media. I. Influence of the Na[O(CH2)2OCH3]2AlH2/ isophorone diisocyanate catalytic system

Polycaproamide granules were obtained by anionic polymerization of caprolactam in ethylbenzene, using the sodium bis(2-methoxyethoxy) aluminium hydride/isophorone diisocyanate catalytic system. Under these conditions, polymerization occurs heterogeneously and the nature of the particle growth seems to be essentially a microbulk one. The most suitable reaction conditions were established. The morphology of the granules was investigated by scanning electron microscopy. These granules result from the coalescence of a great number of small, spherical particles. the coalescence occurs during solidification of the separated polymer. Numerous globular formations were observed at the surface of the particles. The particles were individualized through mechanical dispersion and measured, and the average number of particles composing the aggregates was calculated. Using wide-angle X-ray scattering and differential scanning calormetry technics, the crystalline structure of the granular polycaproamide was studied. It contains almost entirely the α phase. The heat of fusion decreases slightly as compared with that corresponding to the anionic bulk polycaproamide. A schematic mechanism containing the stages involved in the obtaining of the granular polycaproamide is proposed. © 1996 John Wiley & Sons, Inc.

Thermal behaviour of nylon 6-poly (ether-esteramide) block copolymers

Block copolymers have been produced by anionic polymerization of caprolactam with end-functionalized soft-block components derived from polymeric polyols. This method of synthesis gives rise to linear segmented block copolymers with alternating polyether soft blocks and polyamide hard blocks. Copolymers with 10–50% w/w of polyether polyol prepolymer have been the particular focus of attention in this work because of their better physical integrity than copolymers of other compositions. Their phase inversion and morphology/property relationships have been examined by means of differential thermal calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). In this work, the polymers have been hand-cast, but the materials do find application in the reaction injection moulding field.

Mechanical relaxations of nylon–polyurea block copolymers

AbstractDynamic mechanical analysis from −150 to +150°C has been carried out on seven block copolymers that were prepared by the in situ anionic polymerization of caprolactam in the presence of a preformed polyurea. The various relaxations have been identified and activation energies calculated. Some polymer–polymer miscibility of the polyurea and amorphous nylon copolymer segments is indicated by the compositional dependence of the α relaxation.

The synthesis and use of three-dimensional structure activators based on N-acryloylcaprolactam in the anionic polymerization of caprolactam

A description is given of the synthesis of PA by the anionic polymerization of caprolactam in the presence of new macromolecular polyfunctional activators that promote a three-dimensional structure. PA of this type have a cross-linked structure (gel-fraction in cresol amounts to 100 wt%). The size of the inter-node fragment of the network has been determined as 9850-18500. The PA synthesized are distinguished by a high value of specific impact strength (12–34 kJ/m 2 in the Izod test) and are characterized by the existence of hyperelasticity in the temperature range 220–300°C.

Use of N-acryloylcaprolactam as an activator in the anionic polymerization of caprolactam

The anionic polymerization of caprolactam under adiabatic conditions and inthe presence of N-acryloylcaprolactum as activator is studied. Kinetic curves for the total increase in temperature and the increase in temperature resulting from polymerization and crystallization are obtained and compared with those for polymers synthesized in the presence of N-acetylcaprolactam and N-methacryloylcaprolactam. In the case of the anionic polymerization of caprolactam, N-acryloylcaprolactam was shown to be a polyfunctional activator, resulting in the formation of cross-linked polycaprolactam. The effective network parameters were determined, and the physicomechanical propetiies of the synthesized polymers were studied.

The preparation of copolymers with polydimethylsiloxane and polycaprolactam blocks by the anionic polymerization of caprolactam

Block copolymers of polydimethylsiloxane (PDMS) with polycaprolactam were obtained by the anionic polymerization of ε-caprolactam using bifunctional PDMS activators prepared by the partial aminolysis of N, N′-isophthaloyl-bis(ε-caprolactam) with α,ω-di(3-aminopropyl)-PDMS. Copolymers containing 10–43 wt% PDMS blocks were prepared by solvent-free polymerization (150°) or in boiling toluene and were characterized by extraction, PDMS content, viscosity of dilute solutions, light scattering and sorption of water vapour at relative humidities 65 and 93%.

DTA-comparison of activities of catalytic systems used in the anionic polymerization of caprolactam

DTA-comparison of activities of catalytic systems used in the anionic polymerization of caprolactam

Optimization of spinning, drawing, and annealing conditions in the production of highly oriented fibers from the polycaprolactam/3.7% LiCl system

AbstractA polycaprolactam/3.7% w/w LiCl system, obtained by anionic polymerization of caprolactam directly in the presence of salt, has been employed for the production of highly oriented fibers. More particularly, an optimization of spinning, drawing, and annealing conditions has been performed, finally obtaining fibers which shows very satisfactory mechanical results. Namely, average moduli values up to 12 GPa and strength values up to 1 GPa when fracture is far from clamps, have been observed.

Influence of processing conditions on some properties of anionically synthesized polycaprolactam in presence of lithium chloride

AbstractNylon 6–LiCl systems of various concentrations were prepared by anionic polymerization of caprolactam in the presence of salt. A depression of both crystallization rate and melting temperature was evidenced through x‐ray, density, and DSC analyses. Such a preliminary characterization allowed for choosing the proper conditions in order to obtain amorphous fibers from a spinning operation which was performed at a temperature lower than the pure polymer melting point. These results are of technological relevance, especially in view of obtaining, as in similar cases, large amorphous orientations through a spinning–drawing process and high‐modulus fibers after subsequent crystallization. Also, the possibility of restoring some crystallinity in the material has been proven.

Rheological characterization of polycaprolactam anionically synthesized in the presence of lithium chloride

AbstractMelt viscosity and dynamic‐mechanical data are reported for samples obtained by anionic polymerization of caprolactam, in the presence of LiCl. The full body of results is essentially in line with those previously reported relative to mixtures of inorganic salts and commercial nylon 6, In particular a drastic‐decrease of the melting point and of the rate of crystallization is confirmed as well as an increase of the glass transition temperature and of the melt viscosity. Some quantitative differences exist, which may be attributed to the different molecular weight distribution in the polymers employed in the present work.