Flame retardant polyamide 6 by in situ polymerization of ε-caprolactam in the presence of melamine derivatives

An improved method for preparing melamine cyanurate (MCA)based flame retardant polyamide 6 (FRPA6)materials has been proposed.This processing method,i.e.,improved in situ polymerization,was used to synthesize flame retardant PA6.In situ formed MCA nanoparticles were supposed to be linked to PA6 chains in the ε-caprolactam hydrolytic polymerization system to obtain startype polymers for the first time.Through TEM photographs,it can be found that the in situ formed MCA nanoparticles with diametric size of less than 50 nm,are nanoscaled,highly uniformly dispersed in the PA6 matrix.Synthesized flame retardant PA6 have good fire performance which can achieve UL-94 V-0 rating at 1.6 mm thickness with the presence of 7.34 wt.% MCA in the matrix.     

Flame retardant polyamide 6 by in situ polymerization of ε-caprolactam in the presence of melamine derivatives

An improved method for preparing melamine cyanurate （MCA） based flame retardant polyamide 6 （FRPA6） materials has been proposed. This processing method, i.e., improved in situ polymerization, was used to synthesize flame retardant PA6. In situ formed MCA nanoparticles were supposed to be linked to PA6 chains in the ε-caprolactam hydrolytic polymerization system to obtain startype polymers for the first time. Through TEM photographs, it can be found that the in situ formed MCA nanoparticles with diametric size of less than 50 nm, are nanoscaled, highly uniformly dispersed in the PA6 matrix. Synthesized flame retardant PA6 have good fire performance which can achieve UL-94 V-0 rating at 1.6 mm thickness with the presence of 7.34 wt.% MCA in the matrix.     

Anionic polymerization of ɛ-caprolactam in the presence of piperidine N-carboxamides

Piperidine N-carboxamides were shown to activate the anionic polymerization of ?-caprolactam. The activator structure affects properties of the resulting polycaproamide.     

Hydrogen bonding in ε-caprolactam dimer: a quantum-chemical study

The equilibrium geometries, vibrational frequencies, and IR band intensities were calculated for the monomer and hydrogen-bonded cyclic dimer of -caprolactam (1) by the density functional B3LYP/6-311++G(d,p) method and compared with the experimental data. The gas phase IR spectrum of monomer of 1 was first measured. The calculated hydrogen bonding enthalpy H/2 in the hydrogen-bonded dimer in the gas phase (–5.93 kcal/mol) is consistent with the published data. The computed scaled (scaling factor 0.97) vibrational frequencies of the monomer and dimer are in good agreement with the experimental data. The geometry of the -caprolactam monomer remains nearly unchanged in its dimer except for the N-H, C-O, and C-N bond lengths that respectively change from 1.012, 1.230, and 1.369 in the former to 1.029, 1.246, and 1.350 in the latter. The frequencies, eigenvectors, and IR intensities of the amide modes of the monomer and dimer differ dramatically. The calculated NH and CO frequency shifts due to hydrogen bonding are in good agreement with the experimental data, but theoretical intensification of the NH IR band is much greater than that observed experimentally (by nearly 69 times vs. 11 times, respectively). The calculated N...O intermolecular distance in the structure of -caprolactam dimer equals the experimental value (2.89 ). The influence of the basis set employed on the results of calculations is discussed.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1818–1825, September, 2004.     

Dual catalysis with an N-heterocyclic carbene and a Lewis acid: Thermally latent precatalyst for the polymerization of ε-caprolactam

So far, the earlier reported strong correlation between basicity of an N-heterocyclic carbene (NHC) and its reactivity in poly(ε-caprolactam) (PA6) synthesis resulted in a substantial limitation of applicable carbenes. Here, to overcome this issue, 1,3-dimethylimidazolium-2-carboxylate, an easily accessible, air and moisture-stable NHC, was applied as thermally latent initiator. In order to compensate for its low basicity, reactivity was enhanced by the addition of both a Lewis acid and an activator to ease the initial polymerization step. The resulting mixtures of ε-caprolactam, the CO₂-protected NHC, a Lewis acid and N-acylazepan-2-one constitute homogeneous, thermally fully latent “single-component” blends for the anionic polymerization-based synthesis of PA6. They can be stored both in the liquid and solid state for days and months, respectively, without any loss in activity. The role of the Lewis acid as well as technical implications of the prolonged pot-times are discussed.     

Cationic polymerization of 1,3-pent adiene in the presence of arenes

The cationic polymerizations of 1,3-pentadiene initiated by AlCl3 in n-hexane at 30℃ have been carried out in the presence of various arenes,i.e.,benzene,toluene,p-xylene,o-xylene,m-xylene and mesitylene.The presence of all these arenes have reduced in different degrees the formation of crossliuked products.Namely,the crosslinking reaction,a major side-reaction during the cationic polymerization of 1,3-pentadiene,has been suppressed by adding the aromatic compounds.The results showed that a chain transfer to arene took place and this transfer process hindered the generation of the crosslinked polymer.IR and 1H NMR spectra have confirmed the existence of the corresponding aryl groups in the resulting polymers.     

468—the study of the BLM reversible electrical breakdown mechanism in the presence of UO22+

The nature of the reversible decrease (by more than 7 orders of magnitude) of the resistance for bilayer lipid membranes (BLM), modified by UO₂²⁺ ions, in the electrical field is studied. It is shown that the process of BLM current growth during a reversible breakdown is accompanied by not more than a 2% change in the membrane capacitance. This result, the reproduced character of current oscillograms and the linear increase of breakdown current point to the appearance in the BLM, modified by UO₂²⁺, of a considerable number of local defects developed due to the effect of the electrical field. The nature of such defects is discussed.     

Polymerization of lactams. 98: Influence of water on the non-activated polymerization of ε-caprolactam

The sensitivity of so-called non-activated polymerization of ε-caprolactam to the presence of water in the polymerization mixture has been studied. Polymerizations were initiated with 1 mol% sodium salt of ε-caprolactam, magnesium di(ε-caprolactamate) and/or ε-caprolactam magnesium bromide and were carried out at water concentration 0-1 mol% and in the temperature range of 190-230 °C. The influence of water content in the polymerization mixture on the polymerization rate and polymerization degree was evaluated. The studied initiators exhibited different sensitivity to the water added in the polymerization mixture and the role of water in the course of anionic polymerization of ε-caprolactam is discussed. Magnesium initiators are exceptional, they are capable to eliminate retardation effect of water on studied polymerization.     

Controlled polymerization of styrene in the presence of Blatter’s radicals

Russian Chemical Bulletin - Controlled polymerization of styrene (both self-initiated and initiated with azobisisobutyronitrile) in the presence of Blatter’s radical at 125 °C was...     

Ring-opening polymerization of l-lactide in the presence of α-hydroxy-γ-butyrolactone

Among the polymer families, aliphatic polyesters stand out from this category thanks to their degradable and biocompatible properties. In particular, the γ-lactones differ from other lactones by yielding polyesters that can be depolymerized back to the monomer and offer the advantage of counting various biobased monomers. As an example, α-hydroxy-γ-butyrolactone (HBL) is a hydroxy-functionalized monomer that can be obtained by a biological synthetic route from glucose. In this article, the ring-opening copolymerization (ROCP) of HBL and l -lactide (LLA) using t-BuP₄ as catalyst is investigated. The copolymerizations were conducted within a temperature range of 5–100°C, affording monomer conversions exceeding 80%. The characterization of the copolyesters revealed a branched structure consisting of different HBL patterns, including cyclic, linear, and branched motives. Performing a kinetic study of the copolymerization at room temperature provided a deeper understanding of the mechanism. By modulating the reaction parameters, copolymers of low molar masses with an HBL content of up to 33% were synthesized. High molar mass LLA/HBL-based copolyesters, with $$ up to 290,000 g/mol, were synthesized by a straightforward chain coupling reaction with a diisocyanate.     

Anionic polymerization of ϵ-caprolactam—LX. Ionization and solvation changes in the initial stage of the anionic polymerization of lactams in tetrahydrofuran

Interactions between potassium salts of lactams and N-acyllactam propagation centres in the initial stage of the anionic polymerization of lactams were studied by measuring changes in the electric conductivity and in the i.r. spectrum in the range of carbonyl vibration bands of these compounds and of the corresponding derivatives of open-chain alkylamides in tetrahydrofuran. The gradual rise in conductivity and u.v. absorption around 300 nm observed with these systems can be attributed to the formation of 3-oxoimide and 3-oxoamide structures by the condensation of imides.     

Characterization of a heavy oil–propane system in the presence or absence of asphaltene precipitation

When a light hydrocarbon solvent is injected into a heavy oil reservoir under a sufficiently high reservoir pressure, asphaltene precipitation occurs so that the heavy oil is in situ deasphalted during a hydrocarbon solvent-based heavy oil recovery process. The physicochemical properties of this in situ deasphalted heavy oil are rather different from those of the original crude oil in the heavy oil reservoir. In this paper, a heavy oil sample is saturated with a typical light hydrocarbon solvent (i.e., propane) under different saturation pressures in a see-through windowed high-pressure saturation cell. The heavy oil–propane system is characterized by measuring and comparing several important physicochemical properties of the propane-saturated heavy oil samples under different saturation pressures and the flashed-off heavy oil samples, such as the solubility, oil-swelling factor, density, viscosity, asphaltene content, hydrogen and carbon aromaticities. When the heavy oil is saturated with propane at P ≤ 780 kPa and T = 20.8 °C, there is no observable asphaltene precipitation and deposition under a microscope camera. The respective properties of the propane-saturated heavy oil samples taken from the upper and lower parts of the saturation cell are measured and found to be essentially the same within the experimental errors so that the entire system is considered to be almost homogeneous. If the saturation pressure is increased to P = 850 kPa, strong asphaltene precipitation occurs and some large asphaltene particles are deposited onto the bottom of the saturation cell. In this case, the heavy oil is deasphalted and the flashed-off heavy oil has lower density, viscosity, asphaltene content, hydrogen and carbon aromaticities than those of the original heavy crude oil.     

Controlled radical polymerization of alkyl acrylates in the presence of the tri-n-butylborane–p-quinone system

Russian Chemical Bulletin - The reactivities of different p-quinones in the radical polymerization of methyl and tert-butyl acrylates were studied. The inhibitory effect of p-quinones decreases...     

Main kinetic features of ethylene polymerization reactions with heterogeneous Ziegler–Natta catalysts in the light of a multicenter reaction mechanism

A previously developed kinetic scheme for ethylene polymerization reactions with heterogeneous Ziegler–Natta catalysts (see Y. V. Kissin, R. I. Mink, & T. E. Nowlin, J Polym Sci Part A: Polym Chem 1999, 37, 4255 and Y. V. Kissin, R. I. Mink, T. E. Nowlin, & A. J. Brandolini, J Polym Sci Part A: Polym Chem 1999, 37, 4273, 4281) states that the catalysts have several types of active centers that have different activities and different stabilities, produce different types of polymer materials, and respond differently to reaction conditions. Each type of center produces a single polymer component (Flory component), a material with a uniform structure (copolymer composition, isotacticity, etc.) and a narrow molecular weight distribution (weight-average molecular weight/number-average molecular weight = 2.0). This article examines several previously known features of ethylene polymerization and copolymerization reactions on the basis of this mechanism. The discussed subjects include temperature and cocatalyst effects on the polymerization kinetics and molecular weight distribution of polymers and reaction parameter effects (temperature, ethylene and hydrogen partial pressures, and α-olefin and cocatalyst concentrations) on the molecular weights of Flory components. The results show that the formulation of the multicenter kinetic scheme and the development of kinetic tools necessary for the application of this scheme significantly expand our understanding of the working of heterogeneous polymerization catalysts and provide additional means for their control. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1681–1695, 2001     

COS hydrolysis in the presence of oxygen： Experiment and modeling

A mathematical model of COS hydrolysis on Al2O3, with fouling of catalyst, has been developed. Kinetic studies were carried out in a fixed bed reactor under atmospheric pressure and low temperature （40-70℃）. The effects of the COS inlet concentration, temperature, and relative humidity were analyzed. Experimental results of breakthrough curves were used to obtain kinetic parameters, which accounted for effects of S deposition on the inner-face of the catalyst. The model described the experimental breakthrough curves satisfactorily and well explained the performance of COS hydrolysis in the presence of oxygen. The exothermic heat of adsorption and activation energy, assuming Arrhenius type of temperature dependence of the equilibrium constant, were determined. Activation energy of COS hydrolysis and H2S oxidation were 35.9 kJ/mol, 19.6 kJ/mol; adsorption heat of H2O and H2S on Al2O3 were 45.1 and 60.1 kJ/mol respectively. Deactivation coefficient （α） was used to quantify the behavior of COS hydrolysis at different operating conditions. The effect of relative humidity on α is significant in the relative humidity range under study. Experimental data accorded well with model data in the studied range.     

Specific features of oxidation of ferrocenylacetic acid with molecular oxygen in the absence and in the presence of Brønsted acids

Comparative analysis of the specific features of autooxidation of ferrocenylacetic acid (FcCH₂COOH) in organic solvents at 30–50°C in the absence and in the presence of trifluoroacetic acid (processes 1 and 2 respectively) was carried out. It was shown that both reactions proceed as a sequence of two macrostages, the molecular and the chain radical oxidation of the metal complex. Introduction of acid (HX) in the reaction mixture leads to a significant increase in the rate of the process, in the amount of oxygen per one mole of metal complex absorbed by the reaction mixture, and to the change in the yields of main reaction products like hydroxymethylferrocene, formylferrocene, ferrocenylpyruvic acid, and CO₂. On the basis of results of the investigation performed, the kinetic and thermodynamic analysis of primary reactions of the process probable mechanisms of both macrostages in both processes were suggested. The significant effect of approach and orientation on the rate of the molecular oxidation of complex as the bifunctional reagent was noted. An assumption was made that the acid takes place in the molecular oxidation of FcCH₂COOH according to two alternative mechanisms differing by the way of its coordination with O₂ and the metal complex in the prereactional intermediates. The oxidative transformation of these intermediates leads to the generation of radicals of different nature, Fc^+·CH₂C(O)OO^· and HO₂^· which initiate the chain radical oxidation of the metal complex.     

Direct synthesis of carbonyl compounds from THP ethers with IBX in the presence of β-cyclodextrin in water

Water, an environmentally friendly reaction medium, has been utilized for the oxidative deprotection of tetrahydropyranyl ethers 1 with IBX at room temperature in the presence of β-cyclodextrin to give the corresponding carbonyl compounds 2.     

A rationale of the Baeyer-Villiger oxidation of cyclohexanone to ε-caprolactone with hydrogen peroxide: unprecedented evidence for a radical mechanism controlling reactivity

We demonstrate, for the first time, in the Baeyer-Villiger oxidation of cyclohexanone with aqueous hydrogen peroxide under conditions aimed at obtaining ε-caprolactone, that a thermally activated radical reaction leads to the concurrent formation of adipic acid, even when a stoichiometric amount of the oxidant is used. In fact, ε-caprolactone is the primary reaction product, but it is more reactive than cyclohexanone, and quickly undergoes consecutive transformations. When titanium silicalite-1 (TS-1) is used as a catalyst, the high concentration of hydroxy radicals within its pores accelerates the reaction rates, and the consecutive formation of adipic acid (and of lighter diacids as well) becomes largely kinetically preferred. The proper choice of the solvent, which also may act as a radical scavenger, both without catalyst and with TS-1, is a powerful tool for controlling the rates of the various reactions involved.