Polymerization of lactams, 43. Hydrolytic copolymerization of 6-caprolactam with 12-dodecanelactam

The copolymerization of 6-caprolactam with 12-dodecanelactam with 2 mol-% 6-aminocaproic acid as the initiator was investigated at 260°C within a broad concentration range of both comonomers. With increasing content of 12-dodecanelactam in the initial mixture the equilibrium content of the copolymer increased and the rate of copolymerization decreased. In the initial stage of copolymerization 12-dodecanelactam disappeared very quickly from the initial mixture; it was not incorporated into the copolymer directly, but through oligomers, probably through a cyclic dimer. The effect of temperature on the copolymerization process was examined for an equimolar composition of the initial mixture. It was demonstrated that starting with the polymerization temperature of 260°C, the copolymers underwent degradation on long-termin heating. At 280°C, degradation occured already after 50 h of polymerization. The apparent activation energy of copolymerization, 62 kJ/mol, was calculated from the temperature dependence.     

Optimization of nylon 6 reactors with end-point constraints

Optimal temperature profiles for nylon 6 polymerization in plug–flow reactors have been obtained with end-point constraints involving the degree of polymerization and the cyclic dimer concentration, using the most recent kinetic information. Computations suggest that the temperature at the feed end of the reactor must be maintained close to the highest permissible level (determined by the boiling point of the ?-caprolactam). The temperatures in this region control the degree of polymerization more than other variables. Thereafter, the temperature should be reduced. This second zone controls the undesirable cyclic dimer concentration. The effect of a systematic change of values of the various design variables is studied. The profiles obtained herein are qualitatively similar to those obtained by earlier workers using similar formulations. However, they differ significantly from the profiles obtained by us earlier, using different objective functions which are more relevant to the design of new reactors. Attempts have also been made to obtain a global optimal scheme to produce polymer of a desired degree of polymerization and cyclic dimer content, using as short a reactor as possible, and using the water content and the modifier concentration in the feed as the independent variables.     

Modification of polyamide 6 with hycar ATBN

The preparation of block copolymers from 6-caprolactam and a liquid amine terminated butadiene-acrylonitrile copolymer Hycar ATBN 1300X21 having higher notched impact strength than ordinary poly(6-caprolactam) was studied. In the polymerization of 6-caprolactam initiated by an adduct of phosphoric acid with 6-caprolactam the influence of initiator concentration (0– 50 mol-%) and Hycar ATBN 1300X21 concentration (0–5 wt.-%) in the polymerization charge, of polymerization time (4 – 72 h) and of temperature (200–280°C) on the 6-caprolactam conversion and on the properties of the copolymers formed were followed. Notched impact strength of the block copolymers prepared under optimized conditions was as high as 13.5 kJ·m^?2.     

Polymerization of lactams, 48. Autocopolymerization of 6-caprolactam with 12-dodecanelactam

The homo- and copolymerization of 6-caprolactam and 12-dodecanelactam was studied in the absence of an intentionally added initator. Both the polymerization and the copolymerization of an equimolar mixture of the monomers exhibited an induction period, the length of which was reduced with increasing temperature. Above 260°C, the polymers and copolymers of 6-caprolactam were not stable and their intrinsic viscosities as well as the polymer content decreased during long polymerization periods. On the other hand, insoluble products were formed in the homopolymerization of 12-dodecanelactam at temperatures of 300°C and higher. As much as 35 wt.-% of oligomers, predominantly cyclic ones, were formed in the initial stage of polymerization and copolymerization.     

Crystallization of cyclic oligomers on the surface of nylon 6 fibers

When scoured nylon 6 filament was exposed to either water vapor or n-alcohol vapor, a portion of the cyclic [NH(CH₂)₅CO]_x, with x = 2 through 7, and the ?-caprolactam present migrated to the filament surface and crystallized. A variety of crystal forms were observed. The variations depended partly on the vapor to which the sample had been exposed. During water vapor exposures, the cyclic dimer migrated more easily to the filament surface than the cyclic monomer and the cyclic tetramer migrated more easily than the cyclic trimer. It is postulated that the secondary valence forces acting between the dimer and the nylon 6 polymer are weaker than that between the ?-caprolactam and the polymer since the dimer forms intramolecular hydrogen bonds. Consequently, the dimer migrates more easily than the monomer, which can form hydrogen bonds with the polymer. Also the cyclic trimer can form hydrogen bonds with the nylon 6 polymer and thus migrates less easily than the cyclic tetramer, which can form intramolecular hydrogen bonds. In alcohol vapor exposures, the n-alcohol used influenced the concentration of cyclic monomer and oligomer, which migrated to the surface of the nylon 6 filament. The variation of the monomer and oligomer concentration on the fiber surface with the alcohol used in the exposure is discussed.     

Optimal temperature profiles for nylon 6 polymerization in plug-flow reactors

Optimal temperature profiles for nylon 6 polymerization in plug-flow reactors have been obtained under different conditions using a reasonable objective function which gives more flexibility to a designer than those studied earlier. Computations suggest that the temperatures at the feed end of the reactor must be maintained at the highest permissible level (determined by the boiling point of the ?-caprolactam) so as to force the degree of polymerization rapidly to the desired value. Thereafter, the temperatures should be reduced in order to minimize the undesirable cyclic dimer concentration, and, finally, near the exit of the reactor, the temperature must once again be increased in order to attain higher monomer conversion. The effect of a systematic change of values of the various design variables, one by one, is studied. The profile obtained differs substantially from those obtained by earlier workers because of the difference in the objective function as well as in the kinetic mechanism associated with the formation of the cyclic oligomer. Attempts are also made to obtain a global optimal scheme to produce a polymer of a desired degree of polymerization.     

ε-Caprolactam polymerization in presence of polyhedral oligomeric silsesquioxanes (POSS)

Polyhedral oligomeric silsesquioxanes (POSS) have been covalently linked to polyamide 6 (PA6) chains with the aim of synthesizing hybrid organic/inorganic polymer materials. The synthesis has been achieved by in situ polymerization of ε-caprolactam (CL) in presence of increasing amounts of POSS molecules, using two polymerization mechanisms (hydrolytic and anionic). The latter method has been carried out by three different approaches, in order to get PA6 samples characterized by various morphologies and content of structural defects: (i) quasi-adiabatic bulk polymerization; (ii) isothermal bulk polymerization; (iii) quasi-isothermal suspension polymerization. The products obtained have been characterized in term of structure, morphology, thermal properties and molecular mass.     

Die polymerisation der lactame XI. Die copolymerisation von 6-caprolactam mit 12-laurolactam

The course of the incorporation of 6-caprolactam and 12-laurolactam into polymer chains during the hydrolytic, cationic and anionic copolymerization for an equimolar ratio of the monomers was studied. During the hydrolytic copolymerization 6-caprolactam is incorporated more rapidly at 260, 230 or 200°C at the beginning of the polymerization process; the differences between incorporation rates of the lactams into the copolymer increase with decreasing temperature. During the cationic copolymerization the incorporation of 12-laurolactam is more rapid by orders of magnitude for the above temperatures at the beginning of the process. Changes in the composition of cationic copolymers as compared to the hydrolytic copolymers are independent of the temperature during the copolymerization. The anionic copolymerization is characterized by a more rapid incorporation of 6-caprolactam into the polymer chain. The differences in the polymerization activity of the two lactams decrease with increasing temperature of the anionic copolymerization. The described course of incorporation of individual monomers, with the various mechanisms of the polymerization, also corresponds to melting points of copolymers in accordance with their composition.     

Effects of diffusional water removal and heat transfer in nylon 6 reactors

The effects of diffusional water removal and heat transfer on the polymerization of ε-caprolactam were investigated by solving the systems of differential mass and energy balance equations using a finite difference method. Two types of contacting scheme between inert gas and reaction mass have been chosen for study. One is a hollow sphere system and the other is a wetted-wall type hollow cylinder system. The reaction system was designed to be in equilibrium with respect to monomer conversion. The interfacial area per unit volume and the diffusional depth have profound effects on the water content and the temperature of the reaction mass, and consequently on the molecular weight of the polymer produced. Larger interfacial area per unit volume and smaller diffusional depth lead to a higher rate of water removal and heat transfer. In case of larger interfacial area per unit volume, the higher interfacial temperature gives rise to higher molecular weight polymer. For the interfacial area per unit volume of 26.67 m²/m³, the number average chain length reaches as high as 277 and the polydispersity as high as 2.06 when the interfacial temperature is 270°C. The heat transfer greatly affects the content of cyclic dimer in the product so that the hollow cylinder type reactor is preferred, because it is easier to control the temperature of the later portion of the reactor.     

The kinetics of hydrolytic polymerization of ε-caprolactam. V. Equilibrium data on cyclic oligomers

The concentrations of the cyclic oligomers (C_i; i = 3, 4, 5, and 6) in the polymeric products of ε-caprolactam were determined by high-performance liquid chromatography. The equilibrium data on the oligomers were obtained as a function of the polymerization temperature and initial water concentration. The concentration of each oligomer in the equilibrated polymer was found to increase with the temperature and/or initial water concentration. A set of the kinetic equations to express the oligomer formation during the polymerization was also proposed.     

Determination of the residual monomer concentration of ε-caprolactam in polyamide-6 using thermogravimetric analysis coupled with Fourier transform infrared spectroscopy gas analysis

For the anionic polymerization of ε-caprolactam to polyamide-6 the residual monomer concentration in the final polymer is an important characteristic. To determine this residual ε-caprolactam monomer concentration, a fast and fail-safe method was developed, which couples thermogravimetric analysis (TGA) with Fourier transform infrared spectroscopy (FTIR) gas analysis. FTIR allows an identification of the types of gasses released during heat treatment. Calibration of the infrared absorbance of ε-caprolactam and the corresponding mass loss in TGA allows a quantitative evaluation of the ε-caprolactam monomer release. Low-heating rates and powdery samples guarantee high-precision measurements.     

Composites of alkaline poly(6-caprolactam) and short glass fibers: one-step synthesis,structure and mechanical properties

If incorporation of short fibers precedes the polymerization process, their damage is reduced because the viscosity of a monomer is much lower than that of a corresponding polymer. One-step preparation of composites also leads to essential energy savings since polymer fusion and melt mixing are eliminated. Structure and properties of poly(6-caprolactam) matrix polymerized with the initiator/activator systems sodium dihydridobis(2-methoxyethoxo)aluminate/cyclic trimer of phenyl isocyanate are affected by rising concentration of (γ-aminopropyl)triethoxysilane sizing agent: polymerization is slower, but polymerization degree rises; yield strength and notched impact strength decrease, while crystallinity and modulus remain unaffected. When the initiation system sodium tetra(6-caprolactamo)aluminate/cyclic trimer of phenyl isocyanate is alternatively used, the polymerization is somewhat faster, but the polymer is insoluble in m-cresol due to side crosslinking reactions. Incorporated short glass fibers (SGF) (up to 13.2 vol.-%) do not markedly affect the matrix properties. As expected, SGF decrease the compliance (increase the moduli) of composites, but do not affect the time dependence of the creep. Increasing the fraction of SGF also decreases the yield strength of composites, which indicates poor interfacial adhesion; the latter is only slightly improved by fiber sizing. Impact strength decreases with the fraction of as-received SGF, while a moderate opposite trend can be seen for the composites containing silane treated fibers.     

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.     

Polymerization of lactams, 87. Block copolymers of poly(ϵ-caprolactam) and polybutadiene prepared by anionic polymerization. Part I: Preparation and properties

The effect of the polymerization conditions on the properties of poly(?-caprolactam)-polybutadiene block copolymers prepared by polymerization casting through anionic polymerization of ?-caprolactam initiated with potassium salt of ?-caprolactam in the presence of α,ω-dihydroxy-polybutadiene and isocyanates or their blocked derivatives as functionalizing agents was investigated. The influence of the content of telechelic polybutadiene, its molecular weight, type of diisocyanate, and polymerization temperature on the fundamental mechanical properties of the prepared materials and on the polymerization rate was evaluated.     

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.     

Die polymerisation der lactame VI. Die copolymerisation von 6-caprolactam und 8-capryllactam

The process of incorporating 6-caprolactam and 8-capryllactam into polymer chains was studied during the hydrolytic, cationic, and anionic copolymerization in the case of equimolar ratio of the above mentioned monomers. At the beginning of the hydrolytic copolymerization at temperatures between 200 and 260°C, 6-caprolactam was more rapidly incorporated into the chains. Decreasing temperature led to a decrease in the total rate of polymerization with increasing difference between rates of incorporating the two components. Contrary to this, at the initial stage of the cationic copolymerization, the incorporation of 8-capryllactam was faster by orders of magnitude than that of 6-caprolactam, the changes of the copolymer composition being independent of temperature. Under the conditions of interest, in the course of the anionic copolymerization the two monomers were characterized with the same rates of incorporation into the polymer chains. Different melting points of products separated at various stages of the copolymerization process corresponded to the above mentioned differences in rates of incorporating individual monomers into polymer chains when different reaction mechanisms were employed.     

Controlled synthesis of crosslinked polyamide 6 using a bis-monomer derived from cyclized lysine

The controlled synthesis of polyamide 6 chemical networks by anionic ring-opening copolymerization of ε-caprolactam (CL) with synthesized bis-ε-caprolactam derived from α-amino-ε-caprolactam, i.e. N-functionalized α-amino-ε-caprolactam bis-monomers, using sodium ε-caprolactamate as an initiator and hexamethylene-1,6-dicarbamoylcaprolactam as di-functional fast activator was examined in bulk at 140 °C. An urea-based bis-monomer and CL were first shown to copolymerize with a decreasing polymerization rate due to side reactions. On the contrary, quantitative copolymerization of CL with various amounts of bis-N(2-oxo-3-azepanyl)-1,6-tetramethylenediamide, an amide-based bis-monomer, leads to fast kinetics similar to the homopolymerization of CL. Crosslinked PA6 with network exhibiting elastic or viscoelastic behaviors, depending on the amount of crosslinker, were observed and characterized by swelling in hexafluoroisopropanol, dynamic mechanical analysis and rheology measurements. Crystallinity and swelling were shown to decrease with the increasing content of the crosslinking agent.     

Depolymerization of nylon 6: Some kinetic modeling aspects

Depolymerization reactions of nylon 6 [poly(?-caprolactam)] have been modeled based on an existing mechanism for reversible polymerization reactions. The method of moments proposed by Min has been used together with kinetic and equilibrium constants for polymerization reactions to simulate depolymerization reactions. Simulation results thus obtained for batch and semibatch processes compare well with the corresponding experimental results.     

Simulation of nylon 6 polymerization in tubular reactors with recycle

In the hydrolytic polymerization of ?-caprolactam, the ring opening of the monomer is much slower than the polyaddition reaction. Hence, the mixing of aminocaproic acid to the feed results in a faster conversion of the monomer. Industrially, this fact is exploited by using a recycle stream. An isothermal plug flow reactor (PFR) with a recycle is simulated in this study, using two techniques: the method of successive substitutions and Wegstein's method. It is found that, under certain operating conditions, the use of a recycle stream gives higher monomer conversions and lower cyclic dimer concentrations than either a PFR or a homogeneous continuous-flow stirred-tank reactor (HCSTR), with the degree of polymerization almost the same as that obtained in an HCSTR, and thus offers a considerable advantage. However, when a recycle reactor is coupled with a subsequent flashing operation and a finishing reactor, these advantages are considerably reduced.     

Polymerization of lactams, 38. Copolymerization of 6-caprolactam with some of its non-homopolymerizing derivatives

It was demonstrated that non-homopolymerizing derivatives of 6-caprolactam: 7-cyclohexyl-1-aza-2-cycloheptanone (I) and 7-isopropyl-5-methyl-1-aza-2-cycloheptanone (II) were polymerizing with 6-caprolactam under conditions of the socalled hydrolytic polymerization. With its increasing content in the initial reaction mixture the copolymerization rate, the equilibrium content of the copolymer, and the reduced viscosity decreased. Lactam (I) was a more reactive comonomer in comparison with lactam (II).