Polymerization of lactams, 49. Hydrolytic polymerization of 6-caprolactam in the presence of its cyclic dimer

The hydrolytic polymerization of 6-caprolactam has been studied at 260–280°C in the presence of 5, 10 and 15 mol-% of cyclic dimer of 6-caprolactam and 2 mol-% of 6-aminocaproic acid as an initiator. The content of monomer and cyclic oligomers, including pentamer, was determined by HPLC. It has been proved that the rate of polymerization decreases with increasing content of cyclic dimer in the initial mixture and the time required to attain the equilibrium content of polymer increases as much as by an order of magnitude. The cyclic dimer is incorporated into the polymer above all in the final reaction stage.     

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.     

Characterization and comparison of Asian lacquer saps

Five kinds of Asian lacquer saps, Thailand raw and kurome, China raw and kurome, and Vietnam raw lacquer, were characterized by IR, UV resistance, viscosity, rigid-body pendulum physical property-testing and NMR measurements. The results showed that although Thailand lacquer has the highest oligomer and polymer content, its drying speed is the slowest, and it has the best UV resistance. In addition, the monomer, dimer, trimer, and tetramer fractions of thitsiol of Thailand raw lacquer were separated by HPLC and analyzed by NMR spectroscopy. Almost all proton and carbon NMR peaks were assigned, and the structure of thitsiol was confirmed.     

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.     

Ab Initio Study on Interactions in Difluoroamine Clusters from one to four Molecules

Ab initio calculations at HF, MP2 levels of theory with 6‐311G* basis set in combination with counterpoise procedure for BSSE correction have been performed on difluoroamine clusters consisting of up to four molecules. The dimer, trimer and tetramer were all found to exhibit two minima. There are two types of clusters: cyclic and chain. The corrected bond energies are 9.19, 19.22 and 33.67 kJ/mol at the MP2/6‐311G*//HF/6‐311G* level for the more stable dimer, trimer and tetramer, respectively. The contribution of cooperative effect to the interaction energy is quite significant in the cyclic clusters, but negligible in the chain ones. There exist H‐bonds which involve six and eight F⋅⋅⋅H contacts at ca. 0.23–0.24 nm in cyclic trimer and cyclic tetramer, respectively. The intermolecular interaction is an exothermic process under 400.0 K accompanied by a decrease in the probability of complex formation, and the interactions become weak as temperature increases.     

脂肪酶催化降解PBS及改性共聚物的研究

在含少量水的混合有机介质中,采用固定化脂肪酶对数均分子质量达10万以上的PBS及改性共聚物P(BS/CHDM)进行催化降解,并采用质谱(MS)对降解产物进行分析.研究结果表明:在脂肪酶的作用下,常压、60℃、反应24 h得到的产物为淡黄色油状的环状低聚物,主要为一至四环状多聚体,并伴有少量线型低聚物.     

Oligomer composition and content in regenerated PA6 fiber and its effect on properties

The preparation process from waste fibers to regenerated fibers is an environmental significance work. In this work, liquid chromatography/time-of-flight mass spectrometry, advanced polymer chromatography/multi-angle laser-light-scattering/refractive index detector, and two-dimensional wide-angle X-ray diffractometry were employed to characterize the polycaprolactam(PA6) fibers above oligomers composition and content, molecular weight and distribution, crystallization and orientation, and analyzing the changes in mechanical properties. The total content of oligomers in physical and chemical regenerated PA6 fiber is 2.084 wt% and 1.812 wt%, individually, which is higher than that in waste PA6 fiber. And the oligomer content of C1–C4 (cyclic monomer, cyclic dimer, cyclic trimer, and cyclic tetramer) in the regenerated PA6 fiber is higher than that of waste PA6 fiber. The regenerated PA6 fiber sample contains more low-molecular-weight substances, making it easier to form crystal nuclei and crystallize. During the dyeing process of the regenerated PA6 fiber, the γ crystal transformed into α crystal. The tensile strength of physical and chemical regenerated PA6 fiber is lower than that of waste PA6 fiber. And after dyeing, the oligomers content of regenerated PA6 fiber is significantly decreased, especially in C1–C4 oligomer. However, the crystalliniy and orientation of regenerated PA6 fibers were improved, which also leads to the fracture strength increased by about 20% compared to undyed fibers.     

The cationic oligomerization of p-aminostyrene 1. Trifluoroacetic acid-catalyzed polyaddition

Summary It was found that p-aminostyrene (PAS) was easily oligomerized by CF₃COOH (TFA) in CCl₄ to give a low molecular weight oligomer 4 including phenylene, ethylidene and secondary amine groups in the backbone, i.e., the isomer of poly-p-aminostyrene 5. The NMR and IR spectra of the product are quite different from those of polymer 5 produced by 2,2'-azobisisobutyronitrile (AIBN) in toluene. The dimer D and trimer T were separated from the reaction solution through the preparative GPC. The reaction seems to proceed stepwisely to give D in the initial stage and finally the near pentameric oligomer 4 at the end of the reaction. Received: 27 July 2000/Revised version: 8 September 2000/Accepted: 18 September 2000     

Surface modification of a group of polymers using a low temperature cascade arc torch

Surface modification treatments were performed on six different types of polymers using low temperature cascade arc torch (LTCAT) of Ar with or without adding reactive gas of O₂ or H₂O vapor. The effects of the treatments on the wettability enhancement, surface degradation from oligomer formation, and surface stability from the mobility of surface moieties and hydrophobic recovery were investigated. Surface characterization techniques included the static Sessile droplet method and dynamic Wilhelmy balance method. Experimental results indicated that Ar LTCAT treatments of the polymers with shorter treatment times (2 s in most cases) resulted in stable and hydrophilic surfaces without any surface damage from oligomer formation, with the exception of nylon‐6. The excellent results from Ar LTCAT treatments were attributed to the CASING effect (crosslinking via activated species of inert gas). Addition of O₂ into Ar LTCAT resulted in greater wettability of the treated surfaces, but increased surface damage from oligomer formation. Adding H₂O vapor into Ar LTCAT produced extremely hydrophilic surfaces on the polymers, but pronounced surface damage. The surface oligomer formation was attributed to alkoxy degradation reactions and chain scission from overexposure to high energy species. Comparisons of the treatment outcomes for each type of polymer are discussed with respect to the degree of wettability enhancement, the stability of the treated surfaces, and the susceptibility to degradation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

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.     

Synthesis and properties of polyamide derived from piperazine and lower purity dimer acid as hot melt adhesive

Polyamide hot melt adhesive was synthesized from lower purity dimer acid (composition: ∼23% trimer acid, ∼75% dimer acid and ∼3% monomer acid), sebacic acid, ethylenediamine and piperazine. The effect of piperazine and dimer acid concentration on properties of polyamides such as thermal properties: fusion temperature (T_f), heat of fusion (H_f), crystallization temperature (T_c), heat of crystallization (H_c), softening point (T_s) and glass transition temperature (T_g), mechanical properties: tensile strength and hardness, adhesion properties like lap shear strength (LSS) and T-peel strength (TPS), and rheological properties were investigated. Concentration of piperazine was varied from 12.5 to 37.5 mol% while that of dimer from 37.5 to 42 mol%. Piperazine has one hydrogen atom on each of its two nitrogen atoms in the ring structure. When it undergoes reaction with acids to form polyamide, these hydrogen atoms get consumed, making the amide linkage unable to form hydrogen bonding with the neighboring polyamide polymer chains. This leads to decrease in crystallinity of the polyamide. Thus, as the mole percentage of piperazine in the polyamide increases, it becomes more amorphous, decreasing T_f, H_f, T_c, H_c, T_s, T_g, tensile strength, hardness, LSS, TPS and viscosity. Dimer acid and trimer acid are bulky compounds. As their percentages in the polyamide increase, it becomes difficult for the neighboring polyamide chains to come closer. Thus, inter-molecular hydrogen bonding decreases. This leads to decrease in crystallinity of the polyamide, lowering T_f, H_f, T_c, H_c, T_s, T_g, tensile strength, hardness, LSS, TPS and viscosity.     

Cyclic oligomers in the cationic polymerization of 3,3-diethyloxetane

Summary The cationic polymerization of 3,3-diethyloxetane leads to a mixture of polymer and cyclic oligomers. The cyclic tetramer is the most important oligomer and is formed in 20–35% yield. This behaviour is almost identical to that of the unsubstituted oxetane and 3,3-dimethyloxetane. The monomer consumption shows two distinct stages: a very fast stage is followed by a slow stage, leading to complete conversion. The cyclic oligomers are formed only during the second stage.     

High‐pressure synthesis of cyclic mesitylacetylene oligomer

Reaction of mesitylacetylene was carried out by annealing under high pressure (0.13 and 0.52 GPa). The products obtained were classified into soluble and insoluble products in chloroform. The insoluble product reacted under 0.13 GPa was the mesitylacetylene polymer. The soluble product reacted under 0.13 GPa was classified as the monomer and the oligomer [number‐average molecular weight (M̄_n): 390, weight‐average molecular weight (M̄_w): 453, Oligomer yield (O_y): 36%]. The oligomer yield was accelerated by pressure [pressure: 0.13–0.52 GPa, M̄_n: 390–315, M̄_w: 453–968, O_y: 36–98%]. Field desorption mass spectrum showed that the oligomer had cyclic structure. The result of the elementary analysis revealed that the insoluble product reacted under 0.52 GPa was a polycyclic aromatic compound. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1539–1542, 1999     

Characterization and transport properties of a novel aliphatic polyamide with an ethyl branch

The CO₂ gas and water vapor transport properties of a novel aliphatic polyamide with an ethyl branch were investigated. The polymer was characterized with density measurements, differential scanning calorimetry, thermogravimetric analysis, and wide‐angle X‐ray diffraction analyses, and the amorphous and glassy nature of the polymer at the ambient temperature were confirmed. The CO₂ sorption isotherm of the polymer appeared to obey the dual‐mode sorption isotherm, which was characteristic of the glassy state. The water vapor sorption below a relative humidity of 0.4 or 0.5 was explained in terms of the Brunauer–Emmett–Teller sorption mechanism, whereas that at a high relative humidity demonstrated a dissolution type of water vapor into the polyamide. The permeability coefficients of He, CO₂, O₂, and N₂ gases through the membrane were as follows: P(He) > P(CO₂) > P(O₂) > P(N₂). The novel polyamide membrane was more permeable to CO₂, O₂, and N₂ gases than nylon 6 and nylon 66 membranes, containing a crystalline and hydrogen‐bonding nature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1955–1960, 2005     

Thermal dimerization of fatty ester hypdroperoxides

Summary When autoxidized fatty esters and purified fatty hydroperoxides were decomposed in the absence of oxygen at 210°C., the principal reaction was dimerization of the fatty acid chains with elimination of the hydroperoxide groups. Dimers isolated by molecular distillation (60 to 90% of the polymer) have approximately 1 mole hydroxyl, 0.5 mole carbonyl, and two double bonds per mole of dimer. Diene conjugation in the dimers from polyunsaturated fat hydroperoxides varied from 10 to 23%. The infrared spectra of the dimers were similar to those of the original fatty esters except for one striking band at 2.9 μ, which is attributed to the secondary hydroxyl group. Thecis-trans diene in the polyunsaturated hydroperoxides was isomerized to thetrans-trans configuration on dimerization. The methyl oleate hydroperoxide dimer showed only absorption for isolatedtrans double bond. The dimer was not split either by catalytic hydrogenation or by hydrogen iodide, indicating a carbon-carbon bond between the monomer units. On oxidation with permanganate and periodate, the dimeric acids behaved like a monounsaturated mixture containing double bonds in the C₆, C₇, C₈, C₉, and C₁₀ positions in the oleate dimer and in the C₈, C₉, and C₁₀ positions in the safflower ester dimer. Although the dimers showed no peroxidic oxygen iodometrically with potassium iodide, a reduction occurred with hydriodic acid that may indicate the presence of intramolecular peroxide groups and/or allylic alcohol or carbonyl groups. Bromination with N-bromosuc-cinimide and dehydrobromination with N,N-dimethyl aniline produced no aromatization. Subsequent oxidation of the dehydrobrominated dimer yielded 2.6% residue, which was not aromatic. This evidence indicates that the dimer does not have a six-membered cyclic structure. Dimerization of the hydroperoxides is suggested as occurring through alkyl or alkoxy hydroperoxide radicals to give carbon-carbon linked fatty acid dimers and some higher polymeric units. Presented at 33rd fall meeting, American Oil Chemists’ Society, Los Angeles, Calif., Sept. 28–30, 1959. This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

Preparation of the composite consisting of nano‐sized gold particles and nylon‐11 oligomer

Nylon‐11 oligomer was utilized as a matrix to prepare a composite containing nano‐sized gold particles. Nylon‐11 oligomer was prepared by a thermal degradation of a commercial nylon‐11 in vacuum. Weight‐average molecular weight of the oligomer was in a range from 500 to 800. Nylon‐11 oligomer was formed into a film, and then gold was vapor‐deposited onto the oligomer film. The gold‐colored oligomer film turned a transparent red after a heat treatment at 120°C. Transmission electron microscopy showed an isolated distribution of nano‐sized gold particles in the red film of the oligomer. The gold particles were stable in the oligomer for more than a year, and they were dissolved in CH₂Cl₂ to produce a stable colloidal solution. These results suggest that the gold particles were not only dispersed in the oligomer film, but they were stabilized by the nylon‐11 oligomer to form a composite. IR spectrum of the composite showed that N H groups of the nylon‐11 oligomer were responsible for the interaction between the gold particles and the oligomer. Pulse ¹H‐NMR measurement suggested that an active molecular motion of the nylon‐11 oligomer caused the dispersion of the gold particles. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1654–1661, 1999     

Dynamic equilibrium of self-assembled cyclic trimer and tetramer of 1-methyl-5-imidazolylcobalt(III)porphyrin

Dynamic equilibrium of self-assembled multi-porphyrin systems is of interest in obtaining switchable photoresponsive material, but rarely reported. 1-methyl-5-imidazolylcobalt(III)porphyrin ( 1Co ) synthesized here assembled automatically into cyclic trimer and tetramer by intermolecular imidazolyl-cobalt(III) coordination. The trimer-tetramer equilibrium was dependent on concentration and solvent, as examined by NMR spectrometry. In CDCl₃, the tetramer formation was favored at high concentrations, as the ratio of the trimer to the tetramer was 1:2 at 14.8 mM 1Co , and shifted to 1:8 at 74 mM. Further, when the sample was concentrated from a CHCl₃ solution to dryness, the ratio increased to 1:24 on dissolution. In CD₃OD, on the other hand, only the trimer was observed in the wide concentration range. Accordingly, both the trimeric and the tetrameric structures could be prepared selectively by the choice of concentration and solvent.     

Multiobjective optimization of an industrial nylon‐6 semi batch reactor using the a‐jumping gene adaptations of genetic algorithm and simulated annealing

The elitist nondominated sorting genetic algorithm (NSGA‐II) and multiobjective simulated annealing (MOSA) with the robust fixed‐length jumping gene adaptation (aJG) are used to solve three computationally intensive multiobjective optimization problems for an industrial semi batch nylon‐6 reactor. In Problems 1 and 2, the batch time and the final concentration of the undesirable side‐product (cyclic dimer) are minimized while maintaining desired values of the degree of polymerization of the product and the monomer conversion (monomer conversion is maximized as a third objective in Problem 3). The histories of two decision variables, pressure [or vapor release rate] and jacket fluid temperature, are used to obtain the Pareto optimal fronts. The study predicts considerable improvement over earlier results when (i) a single‐stage steam jet ejector is used to create subatmospheric pressures in the reactor, (ii) when the jacket fluid temperature is taken as a function of time, and (iii) when some amino caproic acid (from the depolymerization of scrap nylon‐6) is added to the feed. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Cationic oligomerization of 1-hexene catalyzed by EtAlCl2–chloroacetic acid complexes

Lower oligomers (dimer to tetramer) of 1-hexene were obtained in high yield (65 wt %) with a new cationic complex catalyst, EtAlCl₂? CCl₃CO₂H, in n-hexane at 70°C, trimer being the major product. A strong oxo acid, CF₃SO₃H, yielded very similar products under the same conditions. Characteristics of the 1-hexene oligomerization by these two catalysts were the high selectivity for dimers to tetramers and the absence of cracking of the product. In contrast, EtAlCl₂ or AlCl₃ alone led to oligomers with a higher molecular weight (～10³) and a broad molecular weight distribution, the structure of which was very complicated because of extensive cracking of products. A series of EtAlCl₂? chloroacetic acid (CCl_nH₃–nCO₂H, n = 0–3) complexes were also examined as catalysts. The yield of dimer to tetramer increased with increasing acidity of the chloroacetic acids. The mechanism of the 1-hexene oligomerization with these complex catalysts was discussed on the basis of the structure of product oligomers.     

Anodic oxidation of 2,6-xylenol in acetonitrile on platinum

Anodic oxidation of 2,6-xylenol at the platinum electrode in acetonitrile was investigated by the various electrochemical and chemical methods. Conductivity measurements indicated that the phenolic hydroxyl of 2,6-xylenol is undissociated in acetonitrile solution containing lithium perchlorate. By cyclic voltammetry and chronopotentiometry, it was shown that anodic oxidation of 2,6-xylenol at the platinum electrode proceeds in two steps. 2 electrons are involved in the first step, as determined by cyclic voltammetry using hydroquinone and DPPH as a reference compound. Polarographic study suggested that the first step is an electrophilic attack on the aromatic nucleus of the non-ionized phenol. The electrolysis products were analysed by thin-layer chromatography, ir and uv spectrophotometry and mass spectrometry. It is estimated that dimer, trimer and tetramer are produced by the anodic oxidation of 2,6-xylenol and that the dimer is 2,2′-dihydroxyl-3,3′-dimethylstilbene. The formation reactions of trimer and tetramer probably proceed by the same mechanism as dimer formation.