Temperature‐dependent kinetics for the ozonolysis of selected chlorinated alkenes in the gas phase

The ozonolysis of olefinic species is an important tropospheric process impacting on climate and human health. However, few studies have investigated these reactions as a function of temperature and even less information is available upon the effects of alkene heteroatomic substitution on the Arrhenius parameters. The electron‐withdrawing capacity of substituents about the olefinic bond strongly influences the rate of alkene ozonolysis. To understand better the effect of these substitutions, the temperature‐dependence of a series of ozone–chloroalkene reactions is investigated. Experiments were conducted in the EXTreme RAnge (EXTRA) chamber, over the range of 292–409 K and 760 Torr. The experimentally determined rate coefficients were fitted using an Arrhenius‐type analysis to yield the following activation energies: 30.80 ± 0.79, 23.18 ± 0.59, 65.2 ± 2.8, 116.9 ± 5.6, 29.5 ± 1.8, and 18.67 ± 0.96 kJ mol^?1 and preexponential A‐factors 1.22^+0.39_?0.29×10^?15, 9.3^+6.7_?5.4×10^?16, 1.6^+2.5_?1.0×10^?10, 6⁺²²_?3.9×10^?4, 1.7^+1.6_?0.8×10^?14, and 4.2^+1.9_?1.3×10^?15 cm³ molecule^?1 s^?1 for cis‐1,2‐dichloroethene, trans‐1,2‐dichloroethene, trichloroethene, tetrachloroethene, 2‐chloropropene, and 3‐chloro‐1‐butene, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 120–129, 2011     

Temperature‐dependent feature sensitivity analysis for combustion modeling

Sensitivity analysis is one of the most widely used tools in kinetic modeling. Typically, it is performed by perturbing the A‐factors of the individual reaction rate coefficients and monitoring the effect of these perturbations on the observables of interest. However, the sensitivity coefficients obtained in this manner do not contain direct information on possible temperature‐dependent effects. Yet, in many combustion processes, especially in premixed flames, the system undergoes substantial temperature changes, and the relative importance of individual reaction rates may vary significantly within the flame. An extension of conventional sensitivity analysis developed in the present work provides the means of identifying the temperatures at which individual reaction rate coefficients are most important as a function of input parameters and specific experimental conditions. The obtained information is demonstrated to be of critical relevance in optimizing complex reaction schemes against multiple experimental targets. Applications of the presented approach are not limited to sensitivities with respect to reaction rate coefficients; the method can be used for any temperature‐dependent property of interest (such as binary diffusion coefficients). This application is also demonstrated in this paper. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 282–295, 2005     

Temperature‐dependent conformational analysis of cyclononane: An ab initio study

Quantum chemical methods were used for the theoretical determination of the conformational population for the relevant conformers of cyclononane, i.e., TBC, TCB, TCC, and M4 (or C1), which have been previously investigated experimentally through detailed examination of the nuclear magnetic resonance (NMR) spectrum. Our best Gibbs free energy result, evaluated with MP4(SDTQ)/6‐31G(d,p)//MP2/6‐31G(d,p) energy differences and MP2/6‐31G(d,p) thermal corrections, lead to a temperature‐dependent population in excellent agreement with the experimental results based on the analysis of the low temperature ¹³C NMR spectrum. The nice agreement with experiment is achieved using MP2 harmonic frequencies for the evaluation of vibration partition functions within the standard statistic thermodynamics formalism. Theoretical temperature‐dependent infrared (IR) and ¹³C NMR spectra were simulated and compared with experimental data, which confirmed the ab initio conformational population reported here. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Temperature‐dependent desorption of surfactants in LLDPE blend films

The temperature‐dependent desorption behavior of surfactants in linear low‐density polyethylene (LLDPE) blend films was studied with Fourier transform infrared spectroscopy at 25, 40, and 50 °C. The LLDPE/low‐density polyethylene blend was 70/30. Three different specimens (labeled II, III, and IV) were prepared with various compositions of the surfactant, sorbitan palmitate (SPAN‐40), and the migration controller, poly(ethylene acrylic acid) (EAA). The calculated diffusion coefficients of SPAN‐40 in specimens II, III, and IV at 25, 40, and 50 °C varied from 9.6 × 10⁻¹² to 17.4 × 10⁻¹² cm²/s, from 5.5 × 10⁻¹² to 11.0 × 10⁻¹² cm²/s, and from 3.1 × 10⁻¹² to 5.8 × 10⁻¹² cm²/s, respectively. In addition, the activation energies of specimens II, III, and IV measured between 25 and 50 °C were 18.74, 19.42, and 20.14, respectively. Hence, the desorption rate of the surfactant increased with the temperature and decreased with an addition of EAA, but the activation energy increased with EAA. The diffusion kinetics, analyzed with a plot of the integrated intensity ratio as a function of time, log(I_t/I_∞) versus log t, at 25, 40, and 50 °C obeyed Fickian diffusion behavior. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 218–227, 2001     

Development of a new flow reactor for kinetic studies. Application to the ozonolysis of a series of alkenes

A new flow reactor has been developed to study ozonolysis reactions at ambient pressure and room temperature (297 ± 2 K). The reaction kinetics of O(3) with 4-methyl-1-pentene (4M1P), 2-methyl-2-pentene (2M2P), 2,4,4-trimethyl-1-pentene (tM1P), 2,4,4-trimethyl-2-pentene (tM2P) and α-pinene have been investigated under pseudo-first-order conditions. Absolute measurements of the rate coefficients have been carried out by recording O(3) consumption in excess of organic compound. Alkene concentrations have been determined by sampling adsorbent cartridges that were thermodesorbed and analyzed by gas-chromatography coupled to flame ionization detection. Complementary experimental data have been obtained using a 250 L Teflon smog chamber. The following ozonolysis rate coefficients can be proposed (in cm(3) molecule(-1) s(-1)): k(4M1P) = (8.23 ± 0.50) × 10(-18), k(2M2P) = (4.54 ± 0.96) × 10(-16), k(tM1P) = (1.48 ± 0.11) × 10(-17), k(tM2P) = (1.25 ± 0.10) × 10(-16), and k(α-pinene) = (1.29 ± 0.16) × 10(-16), in very good agreement with literature values. The products of tM2P ozonolysis have been investigated, and branching ratios of (21.4 ± 2.8)% and (73.9 ± 7.3)% have been determined for acetone and 2,2-dimethyl-propanal, respectively. Additionally, a new nonoxidized intermediate, 2-methyl-1-propene, has been identified and quantified. A topological SAR analysis was also performed to strengthen the consistency of the kinetic data obtained with this new flow reactor.     

Pyridine is an organocatalyst for the reductive ozonolysis of alkenes

Whereas the cleavage of alkenes by ozone typically generates peroxide intermediates that must be decomposed in an accompanying step, ozonolysis in the presence of pyridine directly generates ketones or aldehydes through a process that neither consumes pyridine nor generates any detectable peroxides. The reaction is hypothesized to involve nucleophile-promoted fragmentation of carbonyl oxides via formation of zwitterionic peroxyacetals.     

Temperature‐dependent rate coefficients and mechanism for the gas‐phase reaction of chlorine atoms with acetone

The rate coefficient for the gas‐phase reaction of chlorine atoms with acetone was determined as a function of temperature (273–363 K) and pressure (0.002–700 Torr) using complementary absolute and relative rate methods. Absolute rate measurements were performed at the low‐pressure regime (～2 mTorr), employing the very low pressure reactor coupled with quadrupole mass spectrometry (VLPR/QMS) technique. The absolute rate coefficient was given by the Arrhenius expression k(T) = (1.68 ± 0.27) × 10^?11 exp[?(608 ± 16)/T] cm³ molecule^?1 s^?1 and k(298 K) = (2.17 ± 0.19) × 10^?12 cm³ molecule^?1 s^?1. The quoted uncertainties are the 2σ (95% level of confidence), including estimated systematic uncertainties. The hydrogen abstraction pathway leading to HCl was the predominant pathway, whereas the reaction channel of acetyl chloride formation (CH₃C(O)Cl) was determined to be less than 0.1%. In addition, relative rate measurements were performed by employing a static thermostated photochemical reactor coupled with FTIR spectroscopy (TPCR/FTIR) technique. The reactions of Cl atoms with CHF₂CH₂OH (3) and ClCH₂CH₂Cl (4) were used as reference reactions with k₃(T) = (2.61 ± 0.49) × 10^?11 exp[?(662 ± 60)/T] and k₄(T) = (4.93 ± 0.96) × 10^?11 exp[?(1087 ± 68)/T] cm³ molecule^?1 s^?1, respectively. The relative rate coefficients were independent of pressure over the range 30–700 Torr, and the temperature dependence was given by the expression k(T) = (3.43 ± 0.75) × 10^?11 exp[?(830 ± 68)/T] cm³ molecule^?1 s^?1 and k(298 K) = (2.18 ± 0.03) × 10^?12 cm³ molecule^?1 s^?1. The quoted errors limits (2σ) are at the 95% level of confidence and do not include systematic uncertainties. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 724–734, 2010     

Temperature‐ and pressure‐dependent study of 35Cl NQR frequency and spin lattice relaxation time in 2,3‐dichloroanisole

The temperature and pressure dependence of ³⁵Cl NQR frequency and spin lattice relaxation time (T₁) were investigated in 2,3‐dichloroanisole. Two NQR signals were observed throughout the temperature and pressure range studied. T₁ were measured in the temperature range from 77 to 300 K and from atmospheric pressure to 5 kbar. Relaxation was found to be due to the torsional motion of the molecule and also reorientation of motion of the CH₃ group. T₁ versus temperature data were analyzed on the basis of Woessner and Gutowsky model, and the activation energy for the reorientation of the CH₃ group was estimated. The temperature dependence of the average torsional lifetimes of the molecules and the transition probabilities were also obtained. NQR frequency shows a nonlinear behavior with pressure, indicating both dynamic and static effects of pressure. The pressure coefficients were observed to be positive for both the lines. A thermodynamic analysis of the data was carried out to determine the constant volume temperature coefficients of the NQR frequency. The variation of spin lattice time with pressure was very small, showing that the relaxation is mainly due to the torsional motions of the molecules. Copyright © 2010 John Wiley & Sons, Ltd.     

Temperature‐dependent polymer–polymer interactions in polystyrene–polyethylene blends

The effect of the temperature on the interaction between the components of an immiscible polystyrene–polyethylene blend has been analyzed with different techniques. Lap‐shear‐strength data and morphological observations indicate an enhanced interaction between the polymeric phases at elevated temperatures, at which dispersive forces are known to predominate. This raises the degree of compatibility of the polymeric components. Rheological measurements also justify the concept of increased adhesion between the components of the blend when it is processed at very high temperatures. Differential scanning calorimetry analysis lends support to an improved homogeneity of the blend at an elevated temperature; this is again consistent with an improved interaction between the blend phases. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2545–2557, 2004     

Mechanistic and kinetic study on the ozonolysis of 2,4-hexadienedial

The formation and unimolecular reactions of primary ozonides and carbonyl oxides arising from the O₃-initiated reactions of 2,4-hexadienedial (HDE) have been investigated using the density functional theory and ab initio method. The activation energies of O₃ cycloaddition to the >C=C< and >C=O bonds of HDE for the formation primary ozonides (POZ1 and POZ2) are 4.79 and 21.37 kcal mol^?1, respectively, implying that the initial O₃ to the >C=C< bond is favorable pathway. Cleavage of POZ1 to form carbonyl oxides occurs with a barrier of 12.19–21.35 kcal mol^?1, and the decomposition energies range from ?1.09 to ?15.75 kcal mol^?1. The CHOCHOO radical, the hydroxyl radical (OH) formation via H-migration is more favorable than the dioxirane formation via rearrangement. However, the CHOCH=CHCHOO radical, the dioxirane formation via rearrangement is more favorable than OH formation. Using the transition state theory, the rate constants of formation of POZ1 and POZ2 are 1.49 × 10^?19 and 6.03 × 10^?25 cm³ molecule^?1 s^?1 at 300 K, respectively. This study shows that the hyperconjugative effect makes O₃ addition to >C=C< and >C=O bonds of HDE more difficult than to >C=C< bond of ethylene and isoprene and to >C=O bond of formaldehyde. The largest rate constants of OH formation and dioxirane formation in the unimolecular reactions of carbonyl oxides are 6.13 × 10^?4 and 7.93 × 10^?1 s^?1 at 300 K, respectively. The dioxirane is main product in the unimolecular reaction of the carbonyl oxides arising from the O₃-initiated reaction of HDE.     

High reactivity of hexafluoro acetone toward criegee intermediates in the gas‐phase ozonolysis of simple alkenes

Hexafluoro acetone CF₃COCF₃ has been shown to react rapidly with the CH₂OO, CH₃CHOO, and (CH₃)₂COO intermediates that are formed in the ozonolysis of C₂H₄, trans‐2‐C₄H₈, and 2,3‐dimethyl‐2‐butene, respectively, and to form products tentatively assigned to the corresponding secondary ozonides. Relative rate method applied to the C₂H₄ ozonolysis has indicated that CF₃COCF₃ reacts ∼13 times faster than CH₃CHO. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 261–269, 1999     

Temperature‐dependent phase‐segregation behavior and antifouling performance of UV‐curable methacrylated PDMS/PEG coatings

Controllable phase segregation adjustment for immiscible polymer blends has always been tough, which hinders the development of amphiphilic antifouling coatings from more accessible blends. Herein, methacrylated poly(dimethylsiloxane) (PDMS‐MA) was synthesized and mixed with poly(ethylene glycol)methylether methacrylate (PEG‐MA). It was interestingly discovered that these PDMS‐MA/PEG‐MA blends displayed upper critical solution temperatures (UCST) due to thermo‐induced conformational change of PEG‐MA and the UCST changed with PDMS‐MA/PEG‐MA mass ratios. Micro‐/nano‐phase segregation, nanophase segregation, or homogenous morphology were therefore achieved. These PDMS‐MA/PEG‐MA blends with different mass ratios were UV‐cured under varying temperatures to fabricate coatings. Their surface morphology and wettability are readily adjusted by phase segregation. For the first time, highly hydrophilic surface was achieved for coatings with microphase segregation because of the exposure of PEG‐rich domains, which exhibited an enhanced protein resistance against bovine serum albumin (BSA). Anti‐bacterial performance (Shewanella loihica) was also observed for these PDMS/PEG coatings. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1612–1623     

Temperature‐dependent kinetics study of the gas‐phase reactions of atomic chlorine with acetone, 2‐butanone,and 3‐pentanone

A laser flash photolysis–resonance fluorescence technique has been employed to study the kinetics of the reactions of atomic chlorine with acetone (CH₃C(O)CH₃; k₁), 2‐butanone (C₂H₅C(O)CH₃; k₂), and 3‐pentanone (C₂H₅C(O)C₂H₅; k₃) as a function of temperature (210–440 K) and pressure (30–300 Torr N₂). No significant pressure dependence is observed for any of the reactions studied. Arrhenius expressions (units are 10^?11 cm³ molecule^?1 s^?1) obtained from the data are k₁(T) = (1.53 ± 0.19) exp[(?594 ± 33)/T], k₂(T) = (2.77 ± 0.33) exp[(+76 ± 33)/T], and k₃(T) = (5.66 ± 0.41) exp[(+87 ± 22)/T], where uncertainties are 2σ and represent precision only. The accuracy of reported rate coefficients is estimated to be ±15% over the entire range of pressure and temperature investigated. The room temperature rate coefficients reported in this study are in good agreement with a majority of literature values. However, the activation energies reported in this study are in poor agreement with the literature values, particularly for 2‐butanone and 3‐pentanone. Possible explanations for discrepancies in published kinetic parameters are proposed, and the potential role of Cl + ketone reactions in atmospheric chemistry is discussed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 259–267, 2008     

Temperature‐dependent rate coefficient measurements for the reaction of bromine atoms with a series of aldehydes

Relative rate coefficient data have been obtained for the reactions Br + RCHO → RCO + HBr for a series of aldehydes: HCHO, reaction (1); CH₃CHO, reaction (2); CH₃CH₂CHO, reaction (3); CH₃CH₂CH₂CHO, reaction (4). Measurements were made over the temperature range 240–300 K in an environmental chamber/FTIR spectrometer system, using standard relative rate techniques. All measured rate coefficient ratios were found to be independent of temperature over the range studied (k₂/k₁ = 3.60 ± 0.29, k₃/k₁ = 6.65 ± 0.53, k₄/k₁ = 8.62 ± 0.69, and k₃/k₂ = 1.80 ± 0.14), implying that the activation barriers for all four reactions are essentially identical with the A‐factors increasing with the size of the aldehyde. Relative rate coefficients for k₁ and k₂ agree well with currently recommended data at room temperature, but inconsistencies on the order of 20% arise at lower temperatures. The entire set of relative rate coefficient measurements is put on an absolute scale using a combination of currently recommended values for k₁ and k₂. The following expressions (all in units of cm³ molecule⁻¹ s⁻¹) are obtained: k₁ = (0.79 ± 0.10) × 10⁻¹¹ exp(−580 ± 200/T), k₂ = (2.7 ± 0.4) × 10⁻¹¹ exp(−567 ± 200/T), k₃ = (5.75 ± 0.75) × 10⁻¹¹ exp(−610 ± 200/T), k₄ = (5.75 ± 0.75) × 10⁻¹¹ exp(−540 ± 200/T), where uncertainties quoted for the A‐factor reflect the uncertainty in the room temperature value. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 460–465, 2000     

Temperature‐dependent Changes of the Crystal Structure of Li2B4O7

The crystal structure of Li₂B₄O₇ was studied by single crystal X‐ray diffraction whilst the substance was cooled down from room temperature to ?150 °C. The title compound crystallizes in the tetragonal, non‐centrosymmetric space group I 4₁cd (no. 110), a = 9.475(5) Å (r.t.), c = 10.283(6) Å (r.t.), R values for seven different data sets vary from 2.6 to 2.9 %. Low‐temperature single crystal examinations were combined with low‐temperature powder X‐ray diffraction experiments (?189 – +27 °C). The results are discussed in comparison with data earlier obtained at high temperatures (20 – 500 °C). No phase transitions or abrupt changes of the crystal structure were observed. The coordination sphere of the lithium ions is that of a distorted tetrahedron and remains almost unchanged, although the coordination number of the lithium ions decreases slightly with rising temperature, similarly to what was found for LiB₃O₅. An expected rigidity of the boron‐oxygen groups was confirmed. The thermal deformations of the [B₄O₇]^2? framework occur according to the hinge mechanism. This indicates that the LiO₄ chains change their winding on cooling, which leads to deformations along c.     

Temperature‐sensitive polyzwitterionic gels

An abrupt change in the polyzwitterionic swelling ratio as a function of the temperature, sodium chloride concentration and chemical crosslinking density is established. These results are reasonably explained by the model presuming zwitterionic cluster formation in the segments between the chemical junction points. The zwitter‐ionic clusters, produced at low chemical crosslinking density only, act as temperature‐ and salt concentration‐dependent physical junction points. An irreversible temperature‐stimulated swelling‐shrinking behaviour of the polyzwitter‐ionic hydrogels (swelling ratio‐temperature hysteresis loop) at low chemical cross‐linking density is also observed and analysed.     

Formation of secondary ozonides in the gas-phase ozonolysis of simple alkenes

Secondary propene ozonide and isobutene ozonide were formed in the gas-phase ozonolysis of ethene with added acetaldehyde and acetone, respectively. Combined with the formation of hydroperoxymethyl formate and methoxymethyl hydroperoxide in the ethene-ozone reaction system in the presence of HCOOH and CH₃OH, respectively, formation of the secondary ozonides reveals a close similarity between the gas-phase and the liquid-phase ozonolysis of alkenes.     

Temperature‐dependent self‐assembly and rheological behavior of a thermoreversible pmma–PnBA–PMMA triblock copolymer gel

Self‐assembly and mechanical properties of triblock copolymers in a mid‐block selective solvent are of interest in many applications. Herein, we report physical assembly of an ABA triblock copolymer, [PMMA–Pn BA–PMMA] in two different mid‐block selective solvents, n‐butanol and 2‐ethyl‐1‐hexanol. Gel formation resulting from end‐block associations and the corresponding changes in mechanical properties have been investigated over a temperature range of ?80 °C to 60 °C, from near the solvent melting points to above the gelation temperature. Shear‐rheometry, thermal analysis, and small‐angle neutron scattering data reveal formation and transition of structure in these systems from a liquid state to a gel state to a percolated cluster network with decrease in temperature. The aggregated PMMA end‐blocks display a glass transition temperature. Our results provide new understanding into the structural changes of a self‐assembled triblock copolymer gel over a large length scale and wide temperature range. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 877–887