Influence of the double bond position in combustion chemistry of methyl butene isomers: A shock tube and laser absorption study

Shock tube experiments have been carried out on 2-methyl-1-butene (2M1B), 2-methyl-2-butene (2M2B), and 3-methyl-1-butene (3M1B)—the three isomers of methyl butene compound. Carbon monoxide (CO) time-histories and ignition delay times are obtained behind reflected shockwaves over the temperature range of 1350-1630 K and pressures of 8.3-10.5 atm with stoichiometric mixtures of 0.075% fuel in O₂/Ar. Comparative ignition study reveals that 3M1B ignites significantly faster than the other two isomers, while 2M1B dissociates earlier but ignites later than 2M2B. Possible mechanisms for this behavior are discussed with ignition delay time sensitivity and reaction path analysis. In addition, time-resolved CO measurements are compared with three different reaction mechanisms from the literature. Sensitivity analyses have been carried out to identify important reactions that need attention to accurately predict the chemistry of these isomers. Further investigation into the rates of unimolecular fuel decomposition reactions and C₃H₃ + O₂ = CH₂CO + HCO reaction are suggested based on the current investigation.     

Shock Tube Measurements of Ignition Delay Times for the Butanol Isomers Using the Constrained‐Reaction‐Volume Strategy

Ignition delay times of sec‐, iso‐, and tert‐butanol were measured behind reflected shock waves using both conventional operation and a new constrained‐reaction‐volume (CRV) strategy. This CRV filling method constrains the volume of reactive gases, thereby producing near‐constant‐pressure test conditions for reflected shock measurements. The initial reflected shock conditions cover temperatures ranging from 828 to 1095 K, pressures near 20 atm and an equivalence ratio of 1.0 in air mixtures. Additional data were also collected at 30 atm and at φ = 0.5 for iso‐butanol/O₂/N₂ mixtures. At 20 atm and φ = 1.0, the ignition delay time increases for the isomers in the following order: n‐butanol, iso‐butanol and sec‐butanol, and tert‐butanol. Modeling of all collected data using the Vasu and Sarathy (Energy Fuel 2013, 27, 7072–7080) mechanism showed overall good agreement with the experimental data.     

High‐Temperature Study of 2‐Methyl Furan and 2‐Methyl Tetrahydrofuran Combustion

The ignition behavior of methyl furan (2‐MF) and methyl tetrahydrofuran (2‐MTHF) is investigated using the shock tube technique. Experiments are carried out using homogeneous gaseous mixtures of fuel, oxygen, and argon with equivalence ratios, ?, of 0.5, 1.0, and 2.0 at average pressures of 3 and 12 atm over a temperature range of 1060–1300 K. In addition to ignition delay time measurements, fuel concentration time histories during ignition and pyrolysis of 2‐MTHF are obtained by means of laser absorption spectroscopy using a He–Ne laser at a fixed wavelength of 3.39 µm. With respect to ignition delay times, it is observed that under similar conditions of equivalence ratio and argon/oxygen ratio (D), 2‐MTHF has longer ignition delay times than 2‐MF at 3 atm. In addition, 2‐MTHF has longer ignition delay times than 2‐MF at higher temperatures for the case of 12 atm and under the same conditions of ? and D. The higher reactivity of 2‐MF, as indicated by shorter ignition delay times, is attributed to differences in chemical structure, whereby weaker C–H bond sites are more readily susceptible to radical attack than in 2‐MTHF. It is observed that ignition delay times of 2‐MTHF decrease with increasing equivalence ratio at 12 atm for fixed argon/oxygen ratio. Ignition delay times are compared with model predictions using recent chemical kinetic models of both fuels, showing that both models generally predict shorter ignition delay times than measured. The relatively higher absorption cross section of 2‐MTHF at 3.39 µm allows for its concentration time histories to be determined and compared to model predictions. In line with the observed discrepancy in ignition predictions, predicted 2‐MTHF concentration profiles are such that the fuel is shown to be more rapidly consumed than observed in the experiments. The study advances understanding of the combustion chemistry of these cyclic ethers that are potential alternative fuels.     

Oxidation of small unsaturated methyl and ethyl esters

The ignition delay times were measured behind reflected shock waves for temperatures from 1280 to 1930 K, pressures from of 7–9.65 atm, fuel concentrations of 0.4, 0.5, and 1%, and equivalence ratios equal to 0.25, 1.0, and 2.0 in the cases of four unsaturated esters: methyl crotonate, methyl acrylate, ethyl crotonate, and ethyl acrylate. Ignition delay times were measured using chemiluminescence emission from OH at 306 nm and piezoelectric pressure measurements made at the shock tube sidewall. No important difference of reactivity was observed between methyl and ethyl unsaturated esters, methyl and ethyl crotonate having the same reactivity as methyl butanoate. The reactivity of acrylates is greater than that of crotonates especially at the lowest investigated temperatures. Detailed mechanisms for the combustion of the four studied unsaturated esters have been automatically generated using the version of EXGAS software recently improved to take into account this class of oxygenated reactants. These mechanisms have been validated through satisfactory comparison of simulated and experimental results. The main reaction pathways have been derived from flow rate and sensitivity analyses. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 204–218, 2011     

A shock tube study of cyclopentane and cyclohexane ignition at elevated pressures

Ignition delay times for cyclopentane/air and cyclohexane/air mixtures were measured in a shock tube at temperatures of 847–1379 K, pressures of 11–61 atm, and equivalence ratios of ? = 1.0, 0.5, and 0.25. Ignition times were determined using electronically excited OH emission monitored through the shock tube endwall and piezoelectric pressure measurements made in the shock tube sidewall. The dependence of ignition time on pressure, temperature, and equivalence ratio is quantified and correlations for ignition time formulated. Measured ignition times are compared to kinetic modeling predictions from four recently published mechanisms. The data presented provide a database for the validation of cycloalkane kinetic mechanisms at the elevated pressures found in practical combustion engines. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 624–634, 2008     

Preliminary observations on the high temperature oxidation of ethyl tert-butyl ether

The high temperature oxidation of ethyl tert-butyl ether (ETBE) with oxygen in argon diluent has been studied in reflected shock waves over the temperature range 1160 to 1830 K, with pressures of 3.5 bar and with varying equivalence ratios from 0.3 to 2.4. Measurements of the ignition delay times, characterized by chemiluminescence and pressure rise, show that the rate of oxidation is very similar to that of methyl tert-butyl ether.     

Shock‐tube spectroscopic water measurements and detailed kinetics modeling of 1‐pentene and 3‐methyl‐1‐butene

To understand the effects of the chemical structure of two C₅ alkene isomers on their combustion properties, and to highlight the major chemical reactions occurring during their high‐temperature oxidation, water time histories were measured behind reflected shock waves for the oxidation of 1‐pentene (C₅H₁₀‐1) and 3‐methyl‐1‐butene (3M1B) in 99.5% Ar. The experiments were carried out at three different equivalence ratios (φ = 0.5, 1.0, and 2.0) at pressures and temperatures ranging from 1.29 to 1.47 atm and 1 331 to 1 877 K, respectively. The H₂O quantification extends the database for 1‐pentene and provides new insights for 3M1B. These unique results were used to validate and to develop a new detailed kinetics model. Numerical predictions are presented, and the new model was able to capture the results with suitable accuracy, with 3M1B being notably more reactive than C₅H₁₀‐1. Sensitivity and rate‐of‐production analyses were performed to help explain the results. Under the present conditions, the reactivity is rapidly initiated by molecular dissociation of a fraction of the pentene isomers. The initiation phase then induces H‐atom abstraction by active radicals (H, OH, O, HO₂, and CH₃) to first produce alkenyl C₅H₉ radicals (or an alkyl radical and an alkenyl radical by breaking a C─C bond) and subsequent, smaller fragments. The difference in terms of reactivity between the isomers is essentially due to the fact that 3M1B has one particularly weak tertiary allylic C─H bond, which allows for fast H‐atom abstraction compared with 1‐pentene.     

Autoignition of a Lean Propane-Air Mixture at High Pressures

Ignition delay time behind a reflected shock wave is measured for a lean propane-air mixture with an equivalence ratio of ϕ = 0.5 in wide temperature and pressure ranges (T = 880–1500 K, P = 2–500 atm). Ignition-delay activation energy data obtained in this study are compared with earlier data. A detailed kinetic model is constructed for hydrocarbon ignition, which includes ignition mechanisms for low, high, and intermediate (1000– 1200 K) temperatures. Each of the mechanisms is analyzed. The effect of pressure on the mechanism of autoignition is demonstrated.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 344–353.Original Russian Text Copyright © 2005 by Zhukov, Sechenov, Starikovskii.     

Thermal ignition of acetonitrile. Experimental results and kinetic modeling

Ignition delay times of acetonitrile (CH₃CN) in mixtures containing acetonitrile and oxygen diluted in argon were studied behind reflected shock waves. The temperature range covered was 1420–1750 K at overall concentrations behind the reflected shock wave ranging from 2 to 4×10⁻⁵ mol/cm³. Over this temperature and concentration range the ignition delay times varied by approximately one order of magnitude, ranging from ca. 100 μs to slightly above 1 ms. From a total of some 70 tests the following correlation for the ignition delay times was derived: t_ign=9.77×10⁻¹² exp(41.7×10³/RT)×{[CH₃CN]^0.12[O₂]^−0.76[Ar]^0.34} s, where concentrations are expressed in units of mol/cm³ and R is expressed in units of cal/(K mol). The ignition delay times were modeled by a reaction scheme containing 36 species and 111 elementary reactions. Good agreement between measured and calculated ignition delay times was obtained. A least-squares analysis of 60 computed ignition delay times from six different groups of initial conditions gave the following temperature and concentration dependence: E=46.2×10³ cal/mol, β=0.43, β=−1.18, and β_Ar=0.18. The ignition process is initiated by H-atom ejection from acetonitrile. The addition of oxygen atoms to the system from the dissociation of molecular oxygen and from the reaction CH₃CN+O₂ → HO₂·+CH₂CN·is negligible. In view of the relatively high concentration of methyl radicals obtained in the reaction CH₃CN+H → CH₃+HCN, the branching step CH₃+O₂ → CH₃O+O plays a more important role than the parallel step H+O₂→ OH+O. A discussion of the mechanism in view of the sensitivity analysis is presented. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 839–849, 1997     

Cationic para‐phenyl‐substituted α‐diimine nickel catalyzed ethylene and 4‐methyl‐1‐pentene (co)polymerizations via living/controlled chain‐walking

Upon activation with diethylaluminium chloride (Et₂AlCl), a series of phenyl‐substituted α‐diimine nickel precatalysts conducted 4‐methyl‐1‐pentene (4MP) and ethylene (E) (co)polymerizations via controlled chain‐walking to generate branched amorphous polymers with high molecular weight and narrow molecular weight distribution (M_w/M_n < 1.6). The obtained poly(4MP)s were amorphous elastomers with glass transition temperature (T_g) of ?10 ~ ?24 °C, which are higher than that of E‐4MP copolymer ( ? 63.0 °C). At room temperature (25 °C), 4MP polymerization proceeds in a living manner. The microstructures of the produced poly(4MP)s indicated the 2,1‐ and 1,2‐insertion followed by chain‐walking, the latter being predominant. The NMR analyses of the polymers showed that the obtained poly(4MP) possessed methyl, isobutyl, 2,4‐dimethylpentyl and 2‐methylhexyl groups, while the isobutyl and 2,4‐dimethylalkyl branches derived from 4MP were observed in the E‐4MP copolymer. The branch structures and the insertion‐type of monomer were depended on the polymerization temperature, and the content of methyl branch increased with an increase in the polymerization temperature.     

High-temperature ignition of propane with MTBE as an additive: Shock tube experiments and modeling

Ignition of propane has been studied in a shock tube and by computational modeling to determine the effect of methyl tert-butyl ether (MTBE) as a fuel additive. MTBE and isobutene were added in amounts up to 25% of the fuel to propane-oxygen-argon mixtures in shock tube experiments covering a range of temperatures between 1450 and 1800 K. Ignition delays were measured from chemiluminescence at 432 nm due to excited CH radicals. The temperature dependence of the ignition rates was analyzed to yield Arrhenius parameters of E_a ca. 40 kcal/mol and A ca. 10⁹ s^?1 for the overall propane reaction and E_a ca. 34 kcal/mol and A ca. 10^8.3 s^?1 for the overall propane/MTBE reaction. Reactions involving MTBE and its decomposition products were combined with an established propane mechanism in a numerical model to describe the kinetic interaction of this additive with a typical hydrocarbon fuel. The experiments and the kinetic model both show that MTBE and isobutene retard propane ignition with nearly equal efficiency. The kinetic model demonstrates that isobutene kinetics are responsible for inhibition by both MTBE and isobutene, and the specific elementary reactions that produce this behavior are identified. © 1994 John Wiley & Sons, Inc.     

Shock tube investigation of methyl tert butyl ether and methyl tetrahydrofuran high-temperature kinetics

The autoignition and pyrolysis of two C5 ethers, methyl tert butyl ether (MTBE) and 2-methyltetrahydrofuran (2-MTHF), are investigated using the shock tube reactor. The experiments are carried out at pressures of 3.5 and 12 atm at temperatures above 1000 K with argon as a diluent gas. By means of direct laser absorption, carbon monoxide time histories and associated chemical kinetic timescales are also determined. It is observed that the competition between ignition and pyrolysis times depends on the temperature and equivalence ratio of the ignition mixture, such that there is a temperature above which pyrolysis predominates oxidative kinetics. This crossover temperature shifts toward higher temperatures for reactive systems with a fixed fuel concentration but higher oxygen content. The resulting experimental observations are also compared with predictions of existing chemical kinetic models from the literature. The results point to differences in chemical reactivity, such that in pyrolysis conditions, the reactivity of the cyclic ether, 2-MTHF, is generally higher than that of the aliphatic ether, MTBE. While agreement between experimental observations and model predictions is observed under certain conditions, significant variance between observations and predictions is observed under other conditions. With respect to prediction of the pyrolysis time used to capture the global kinetics of pyrolysis, it is observed that the relation of this time to the time needed to attain 90% of the equilibrium CO concentration varies greatly with the result that the models used in this work generally predict a faster initial formation of CO but a much slower approach to the equilibrium concentration. This is thought to arise from the slow transformation of intermediate CH₂O and CH₂CO to CO. The chemical kinetic models considered in this work are therefore not capable of predicting the CO time histories during pyrolysis.     

十氢萘/空气混合物高温着火延迟的激波管测量

在激波管上进行了气相十氢萘/空气混合物的着火延迟测量, 着火温度为950-1395 K, 着火压力为1.82×10⁵-16.56×10⁵ Pa, 化学计量比分别为0.5、1.0 和2.0. 在侧窗处利用反射激波压力和CH^*发射光来测出着火延迟时间. 系统研究了着火温度、着火压力和化学计量比对十氢萘着火延迟时间的影响. 实验结果显示着火温度和着火压力的升高均会缩短着火延迟时间. 首次在相对高和低压的条件下观察到了化学计量比对十氢萘着火延迟的影响是完全相反的. 当压力为15.15×10⁵ Pa时, 富油混合物呈现出最短的着火延迟时间, 而贫油混合物的着火延迟时间却是最长的. 相反, 当压力为2.02×10⁵ Pa时, 富油混合物的着火延迟时间最长. 着火延迟数据与已有的动力学机理的预测值进行对比, 结果显示机理在所有的实验条件下均很好地预测了实验着火延时趋势. 为了探明化学计量比对着火延迟时间影响的本质, 对高、低压条件下的着火延时进行了敏感度分析.结果显示, 压力为2.02×10⁵ Pa时, 控制着火延迟的关键反应为H+O₂=OH+O, 而涉及十氢萘及其相应自由基的反应在15.15×10⁵ Pa时对着火延迟起主要作用.     

正十一烷/空气在宽温度范围下着火延迟的激波管研究

在加热激波管上测量了气相正十一烷/空气混合物的着火延迟时间,着火温度为宽温度范围731-1399 K,着火压力在2.02 × 10⁵和10.10 × 10⁵ Pa附近,化学计量比分别为0.5、1.0和2.0。通过监测管侧壁观测点处的反射激波压力和OH^*发射光测出着火延迟时间。实验结果显示：在910 K以上,着火延迟时间随着火温度的降低而变长,从910到780 K,着火延迟时间随着火温度的降低而变短（显示出了负温度系数效应）,在780 K以下,着火延迟时间随着火温度的降低再次变长。在所研究的压力下,着火压力的增加使着火时间变短。化学计量比对着火延迟的影响在着火压力为2.02 × 10⁵和10.10 × 10⁵ Pa时是不同的,与在高温区相比,着火延迟在低温区对化学计量比非常敏感。在整个温度范围内,当前实验结果和LLNL（LawrenceLivermore National Laboratory）机理的预测值表现出了很好的一致性。现在的正十一烷/空气的着火数据和先前实验测量的正庚烷/空气、正癸烷/空气和正十二烷/空气的着火延迟时间相比较显示了着火延迟时间随着直链烷碳原子数的增加而减小。敏感度分析显示,高、低温条件下影响正十一烷着火延迟过程的反应是显著不同的。在高温条件下起最大促进作用的反应是H + O₂=O+OH,然而在低温条件下,起最大促进作用的反应是过氧十一烷基（C₁₁H₂₃O₂）的异构化反应。本文研究首次提供了正十一烷/空气的激波管着火延迟时间。     

Measurements of Propanal Ignition Delay Times and Species Time Histories Using Shock Tube and Laser Absorption

Propanal is an aldehyde intermediate formed during the hydrocarbon combustion process. Potentially, the use of oxygenated biofuels reduces greenhouse gas emissions; however, it also results in increased toxic aldehyde by‐products, mainly formaldehyde, acetaldehyde, acrolein, and propanal. These aldehydes are carcinogenic, and therefore it is important to understand their formation and destruction pathways in combustion systems. In this work, ignition delay times were measured behind reflected shock waves for stoichiometric (Φ = 1) mixtures of propanal (CH₃CH₂CHO) and oxygen (O₂) in argon bath gas at temperatures of 1129 K < T < 1696 K and pressures around 1 and 6 atm. Measurements were conducted using the kinetics shock tube facility at the University of Central Florida. Current results were compared to available data in the literature as well as to the predictions of three propanal combustion kinetic models: Politecnico di Milano (POLIMI), National University of Ireland at Galway, and McGill mechanisms. In addition, a continuous wave‐distributed feedback interband cascade laser centered at 3403.4 nm was used for measuring methane (CH₄) and propanal time histories behind the reflected shock waves during propanal pyrolysis. Concentration time histories were obtained at temperatures between 1192 and 1388 K near 1 atm. Sensitivity analysis was carried for both ignition delay time and pyrolysis measurements to reveal the important reactions that were crucial to predicting the current experimental results. Adjustments to the POLIMI mechanism were adopted to better match the experimental data. Further research was suggested for the H abstraction reaction rates of propanal. In addition to extending the temperature and pressure region of literature ignition delay times, we provide the first high‐temperature species concentration time histories during propanal pyrolysis.     

Reaction kinetics and thermochemistry of the chemically activated and stabilized primary ethyl radical of methyl ethyl sulfide,CH3SCH2CH2•, with O2 to CH3SCH2CH2OO•

Oxidation of methyl ethyl sulfide (CH₃SCH₂CH₃, methylthioethane, MES) under atmospheric and combustion conditions is initiated by hydroxyl radicals, MES radicals, generated after loss of a H atom via OH abstraction, will further react with O₂ to form chemically activated and stabilized peroxyl radical adducts. The kinetics of the chemically activated reaction between the CH₃SCH₂CH₂• radical and molecular oxygen are analyzed using quantum Rice-Ramsperger-Kassel theory for k(E) with master equation analysis and a modified strong-collision approach to account for further reactions and collisional deactivation. Thermodynamic properties of reactants, products, and transition states are determined by the B3LYP/6-31+G(2d,p), M062X/6-311+G(2d,p), ωB97XD/6-311+G(2d,p) density functional theory, and CBS-QB3, G3MP2B3, and G4 composite methods. The reaction of CH₃SCH₂CH₂• with O₂ forms an energized peroxy adduct CH₃SCH₂CH₂OO• with a calculated well depth of 34.1 kcal mol⁻¹ at the CBS-QB3 level of theory. Thermochemical properties of reactants, transition states, and products obtained under CBS-QB3 level are used for calculation of kinetic parameters. Reaction enthalpies are compared between the methods. The temperature and pressure-dependent rate coefficients for both the chemically activated reactions of the energized adduct and the thermally activated reactions of the stabilized adducts are presented. Stabilization and isomerization of the CH₃SCH₂CH₂OO• adduct are important under high pressure and low temperature. At higher temperatures and atmospheric pressure, the chemically activated peroxy adduct reacts to new products before stabilization. Addition of the peroxyl oxygen radical to the sulfur atom followed by sulfur-oxygen double bond formation and elimination of the methyl radical to form S(= O)CCO• + CH₃ (branching) is a potentially important new pathway for other alkyl-sulfide peroxy radical systems under thermal or combustion conditions.     

戊酸甲酯高温点火的激波管研究

戊酸甲酯是生物柴油和长链脂类燃烧过程中的中间产物之一。迄今为止,文献中还没有戊酸甲酯点火延迟的实验结果,因此对其点火特性的研究是必要的。在本文工作中,于反射激波后测量了戊酸甲酯/空气和戊酸甲酯/4%氧气/氩气的点火延迟时间。实验条件为:戊酸甲酯/空气点火温度1050–1350 K,点火压力1.5 × 10⁵和16 × 10⁵ Pa,当量比0.5、1和2;戊酸甲酯/4%氧气/氩气点火温度1210–1410 K,点火压力3.5 × 10⁵和7 × 10⁵ Pa,当量比0.75和1.25。点火延迟时间由在距离激波管端面15毫米处的测量点测到的反射激波到达信号和CH自由基信号所决定。所得实验结果显示：对于戊酸甲酯/空气和戊酸甲酯/4%氧气/氩气,温度或压力的增加都一定会使它们的点火延迟时间变短,但对于戊酸甲酯/空气,当量比对其点火延迟时间的影响在高低压下却是不同的(16 × 10⁵ Pa: τ_ign = 5.43 × 10⁻⁶Ф^−0.411exp(1.73 × 10²/RT),1.5 × 10⁵ Pa: τ_ign = 7.58 × 10⁻⁷Ф^0.193exp(2.11 × 10²/RT)。当压力为3.5 × 10⁵–7 × 10⁵ Pa时,还获得了戊酸甲酯/4%氧气/氩气点火延迟时间随点火条件的变化关系：τ_ign = 2.80 × 10⁻⁵(10⁻⁵P)^{−0.446±0.032}Ф^0.246±0.044exp((1.88 ± 0.03) × 10²/RT)。这些关系式反映了点火延迟时间对温度、压力和当量比的依赖关系,且有助于将实验数据归一到特定条件下进行比较。在本文实验条件下,由于戊酸甲酯/空气的燃料浓度远大于戊酸甲酯/4%氧气/氩气的燃料浓度,所测戊酸甲酯/空气的点火延迟时间远短于戊酸甲酯/4%氧气/氩气的点火延迟时间。通过对戊酸甲酯和其它长链脂类的点火特性比较,发现在相对低温时(空气中1200 K以下,氩气中1280 K以下),戊酸甲酯的点火延迟时间要长于其它长链脂类的点火延迟时间。已有的两个戊酸甲酯化学动力学机理都不能很好地预测本文实验结果,对戊酸甲酯机理的进一步完善是需要的。敏感度分析结果表明,支链反应H + O₂ = O + OH对戊酸甲酯的高温点火起着最强的促进作用。据我们所知,本文首次报道了戊酸甲酯的高温点火延迟实验数据,研究结果对了解戊酸甲酯的点火特性非常重要,并且为完善戊酸甲酯的化学动力学机理提供了实验依据。     

Solubility of polystyrene in selectively deuterated methyl acetate

Cloud point measurements were made for binary systems of polystyrene (PS) + methyl acetate (MA) and polystyrene (PS) + selectively deuterated MA: CD₃COOCH₃ and CH₃COOCD₃ with three PS samples of M_w = 4.0 × 10⁵, 2.0 × 10⁶, and 13.2 × 10⁶. All systems are characterized by the phase diagrams with upper and lower critical temperature. H/D isotope effects on miscibility for both selectively deuterated acetates are very large and appeared to be independent of the site of deuterium substitution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47:2140–2143, 2009     

Synthesis of poly(methyl methacrylate) via ARGET ATRP and study of the effect of solvents and temperatures on its polymerization kinetics

This investigation reports the synthesis of poly(methyl methacrylate) via activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) and studies the effect of solvents and temperature on its polymerization kinetics. ARGET ATRP of methyl methacrylate (MMA) was carried out in different solvents and at different temperatures using CuBr₂ as catalyst in combination with N,N,N′,N″,N″‐pentamethyldiethylenetriamine as a ligand. Methyl 2‐chloro propionate was used as ATRP initiator and ascorbic acid was used as a reducing agent in the ARGET ATRP of MMA. The conversion was measured gravimetrically. The semilogarithmic plot of monomer conversion versus time was found to be linear, indicating that the polymerization follows first‐order kinetics. The linear polymerization kinetic plot also indicates the controlled nature of the polymerization. N,N‐Dimethylformamide (DMF), tetrahydrofuran (THF), toluene, and methyl ethyl ketone were used as solvents to study the effect on the polymerization kinetics. The effect of temperature on the kinetics of the polymerization was also studied at various temperatures. It has been observed that polymerization followed first‐order kinetics in every case. The rate of polymerization was found to be highest (k_app = 6.94 × 10⁻³ min⁻¹) at a fixed temperature when DMF was used as solvent. Activation energies for ARGET ATRP of MMA were also calculated using the Arrhenius equation.     

Shock tube measurements of branched alkane ignition times and OH concentration time histories

Ignition times and hydroxyl (OH) radical concentration time histories were measured behind reflected shock waves during the oxidation of three branched alkanes: iso‐butane (2‐methylpropane), iso‐pentane (2‐methylbutane), and iso‐octane (2,2,4‐trimethylpentane). Initial reflected shock conditions ranged from 1177 to 2009 K and 1.10 to 12.58 atm with dilute fuel/O₂/Ar mixtures varying in fuel concentration from 100 ppm to 1.25% and in equivalence ratio from 0.25 to 2. Ignition times were measured using endwall CH emission and OH concentrations were measured using narrow‐linewidth ring‐dye laser absorption of the R₁(5) line of the OH A‐X (0,0) band at 306.7 nm. The ignition times and OH concentration time histories were compared to modeled predictions of seven branched alkane oxidation mechanisms currently available in the literature and the implications of these comparisons are discussed. These data provide a unique database for the validation of detailed hydrocarbon oxidation mechanisms of propulsion related fuels. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 67–78 2004