Quasiliving Carbocationic Poiymerization. III. Quasiliving Polymerization of lsobutylene

The polymerization of isobutylene has been investigated by the use of the steady, slow, continuous monomer addition technique in the presence of a variety of initiating systems, i.e., “H₂O”/TiCl₄, “H₂O”/AlCl₃, C₆H₅C(CH₃)₂Cl/TiCl₄, p-ClCH₂ C₆(CH₃)₄* CH₂Cl/AlCl₃ at -50°C. Quasiliving polymerizations have been obtained with the “H₂O” and C₆H₅(CH₃)₂Cl/TiC1₄ systems in 60/40 v/v n-hexane/methylene chloride solvent mixtures with very slow monomer input. After a brief “flash” polymerization, the M _n of PIB increased linearly with the cumulative amount of monomer added (consumed); however, the number of polymer molecules formed also increased, indicating the presence of chain transfer to monomer. With the “H₂O”/TiCl₄ initiating system, M _n,max was 56,000 and M _w /M _n < 2.0. By the use of the C₆H₅C(CH₃)₂CL/TiCl₄ initiating system, quasiliving polymerization has been achieved and chain transfer could virtually be eliminated.     

A SACM study of the cross-combination ratio of rate constants

An analysis of the cross-combination ratio of the rate constants in terms of the statistical adiabatic channel model allows to factorize into two contributions: one due to the motion along the reaction coordinates and another due to the reaction transitional modes. for the CH₃/CCl₃, CH₃/C₂H₃, CH₃/C₃H₅, CH₃/C₂H₅ and C₂H₅/C₃H₅ radical pairs were calculated.     

The pyrolysis of acetaldehyde in the presence of nitric oxide

The kinetics of the acetaldehyde pyrolysis have been studied at temperatures from 450° to 525°C, at an acetaldehyde pressure of 176 torr and at 0 to 40 torr of added nitric oxide. The following products were identified and their rates of formation measured: CH₄, H₂, CO, CO₂, C₂H₄, C₂H₆, H₂O, C₃H₆, C₂H₅CHO, CH₃COCH₃, CH₃COOCH?CH₂, N₂, N₂O, HCN, CH₃NCO, and C₂H₅NCO. Acetaldehyde vapor was found to react with nitric oxide slowly in the dark at room temperature, the products being H₂O, CH₃COOCH₃, CO, CO₂, N₂, NO₂, HCN, CH₃NO₂, and CH₃ONO₂. The rates of formation of N₂ and C₂H₅NCO depend on how long the CH₃CHO-NO mixture is kept at room temperature before pyrolysis; the rates of formation of the other products depend only slightly on the mixing period. The pyrolysis of “clean” CH₃CHO–NO mixtures (i.e., the results extrapolated to zero mixing time, which are independent of products formed in the cold reaction) are interpreted as follows: (1) There are two chain carriers, CH₃ and CH₂CHO, their concentrations being interdependent and influenced by NO in different ways: the CH₃ radical is both generated and removed by reactions directly involving NO, whereas CH₂CHO is generated only indirectly from CH₃ but is also removed by direct reaction with NO. (2) An important mode of initiation by NO is its addition to the carbonyl group with the formation of which is converted into ; this splits off OH with the formation of CH₃NCO or CH₃ + OCN. (3) Important modes of termination are The steady-state equations derived from the mechanism are shown to give a good fit to the experimental rate versus [NO] curves and, in particular, explain why there is enhancement of rate by NO at higher CH₃CHO pressures and, at lower CH₃CHO pressures, inhibition at low [NO] followed by enhancement at higher [NO]. The cold reaction is explained in terms of chain-propagating and chain-branching steps resulting from the addition of several NO molecules to CH₃CHO and the CH₃CO radical. In the “unclean” reaction it is found that the rates of N₂ and C₂N₅NCO formation are increased by CH₃NO₂, CH₃ONO, and CH₃ONO₂ formed during the cold reaction. A mechanism is proposed, involving the participation of α-nitrosoethyl nitrite, CH₃CH(NO)ONO. It is suggested that there are two modes of behavior in pyrolyses in the presence of NO: (1) In the paraffins, ethers, and ketones, the effects are attributed to the addition of NO to a radical with the formation of an oxime-like compound. (2) In the aldehydes and alkenes, where there is a hydrogen atom attached to a double-bonded carbon atom, the behavior is explained in terms of addition of NO to the double bond followed by the formation of an oxime-like species.     

The use of transition-state theory to extrapolate rate coefficients for reactions of O atoms with alkanes

Conventional transition-state theory is used for extrapolating rate coefficients for reactions of O atoms with alkanes to temperatures above the range of experimental data. Expressions are developed for estimating structural properties of the activated complex necessary for calculating enthalpies and entropies of activation. Particular attention is given to the problem of the effect of the O atom adduct on the internal rotations in the activated complex. Differences between primary, secondary, and tertiary attack are discussed, and the validity of representing the activated complexes of all O + alkane reactions by a fixed set of vibrational frequencies and other internal modes is evaluated. Experimental data for reactions of O atoms with 15 different alkanes (CH₄, C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, C₆H₁₄, C₇H₁₆, C₈H₁₈, i–C₄H₁₀, (CH₃)₄C, (CH₃)₂CHCH(CH₃)₂, (CH₃)₃CC(CH₃)₃, c–C₅H₁₀, c–C₆H₁₂, c–C₇H₁₄) are reviewed. The following approximate expressions for ΔS^?(298) and E(298), the entropy and energy of activation, respectively, are consistent with the experimental data and with the calculations: where n_C = number of carbon atoms in the alkane and n_H = the number of “equivalent” H atoms. Using the conventional transition state theory expression, k(298) = 10^15.06 exp(ΔS^?/R) exp(–E(298)/298R) L mol^?1s^?1, one then obtains: These expressions agree with experimental values within a factor approximately 2 for alkanes larger than C₃H₈.     

A shock-tube study of the kinetics of reaction of hydroxyl radicals with H2, CO,CH4, CF3H,C2H4, and C2H6

Concentration-time profiles have been measured for hydroxyl radicals generated by the shock-tube decomposition of hydrogen peroxide in the presence of a variety of additives. At temperatures close to 1300°K the rate constants for the reaction are found to be in the ratio 0.18:0.19:0.59:1.00:2.33:2.88 for the additives CO:CF₃H:H₂:CH₄:C₂H₄:C₂H₆, respectively.     

Quantum chemical studies of propene,ethylene, acetylene and dihydrogen reactivity in the insertion reaction into the titanium-alkyl bond

Using the ab initio method of SCF MO LCAO

1 SCF MO LCAO: Self-consistent field molecular orbital linear combination of atomic orbitals.

in a valency-splitted basis of the Gaussian functions we have studied the addition of various monomers (C₃H₈, C₂H₄, C₂H₂) and dihydrogen to the titanium-alkyl bond in the complex H₂TiCH₃. The structure of transition states in the insertion reaction, heats of π-complex formation and activation energies for the insertion of the coordinated monomers have been calculated. The calculation results show that the reactivity decreases in the order C₂H₂ > C₂H₄ > C₃H₈ > H₂. According to the results obtained, the energy of the π^*-antibonding orbital of monomers can serve as an index of relative reactivity in the insertion reaction into the metal-alkyl bond.     

The electronic effects of substituents containing phosphorus

Dissociation constants are reported for p-phosphorophenols, p-RC₆H₄OH, in aqueous alcohol (1:1 by volume), and the nucleophilic constants ^– of the R are found to be as follows: (C₆H₅)₂P 0.26, (C₆H₅)P(O) 0.68, (C₆H₅)₂P(S) 0. 63, and (C₆H₅)₂(CH₃)P⁺ 1.28.See [1–3] for previous communications in this series.     

Kinetic Parameters for Direct Atomic Substitution Reactions

Experimental data (the rate constants and activation energies) for seven reactions of direct substitution of one atom for another D + CH₃R CH₂DR + H, D + NH₃ DNH₂ + H, D + H₂O HOD + H, F + CH₃X CH₃F + X (X = F, Cl, Br, and I) involving atoms D and F and molecules C₂H₆, H₂O, NH₃, CH₃F, CH₃Cl, CH₃Br, and CH₃I are analyzed using the parabolic model of a bimolecular radical reaction. The activation energies for the thermally neutral analogs of these substitution reactions are calculated. Atomic substitution involving deuterium atoms has a lower activation energy of a thermally neutral reaction than radical abstraction or substitution.     

Kinetics of fluorine atom reactions using resonance absorption spectrometry in the far vacuum ultraviolet reactions F + HCl,CH4, CHCl3 CHCl2F,and CHClF2

Atomic resonance absorption spectrometry with a nonreversed fluorine resonance lamp (～95 nm) has been used to study the kinetics of elementary reactions of ground state F²P_J atoms in a discharge-flow system. The following rate constants (in cm³/molec·sec)

1 All rate constants are given with 1.5 σ.

were determined at 298° K: The reaction F ₂P_J + HCl(1) was found to give J-excited Cl ₂P_1/2 atoms with a product branching ratio [Cl ₂P_1/2]/[Cl ₂P_3/2] = 0.10.     

A spectroscopic determination of the methyl radical recombination rate constant in shock waves

The reactions CH₃ +

and CD₃ +

have been studied in shoch waves at 1200–1500 K and densities of 2 × 10^?6 ?2 × 10^?4 mol cm^?3 using UV absorption near 216 nm. The rate constants at the highest densities: k_H = (1.7 ± 0.6) × 10^?11 cm³ s^?1 and k_D = (2.2 ± 0.9) × 10^?11 cm³ s^?1 are close to the second order limit. At the lowest densities the rates are lower by a factor of 5. The experimental results agree well with theoretical predictions based on the statistical adiabatic channel model but differ from those of conventional RRKM calculations. A direct observation of the equilibrium C₂H₆ ? 2CH₃ favours the “high” value for ΔH⁰₀ (87.76 kcal/mol).     

High-temperature pyrolysis of acetaldehyde

High-temperature (>1000°K) pyrolysis of acetaldehyde (～1% in an atmosphere of pure nitrogen) was examined in a turbulent flow reactor which permits accurate determination of the spatial distribution of the stable species. Results show that the products in order of decreasing importance are CO, CH₄, H₂, C₂H₆, and C₂H₄. Rates of formation were consistent with the Rice–Herzfeld mechanism by including reactions to explain C₂H₄ formation and the possible presence of ketene. A steady-state treatment of the complete mechanism indicates that the overall reaction order decreases from \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{3}{2} $\end{document} to 1, which is supported by the new experimental data. Using earlier low-temperature results, the rate constant for the reaction CH₃CHO → CH₃ + CHO (1) was found as k₁=10^15.85±0.21 exp (?81,775±1000/RT) sec^?1. Also, data for the ratio of rate constants for reactions CH₃CHO + CH₃ → CH₄ + CH₃CO (4) and 2CH₃ → C₂H₆(6) were fitted to the empirical expression k₄/k₆^1/2=10^?13.89±0.03T^6.1 exp(?1720±70/RT) (cm³/mole·sec)^1/2 and causes for the curvature are discussed. The noncatalytic effect of oxygen on acetaldehyde pyrolysis at high temperature is explained.     

Kinetics of the “a” and “b” band emissions of mercury excimers with added gases

The kinetics of the “a” and “b” band emissions arising from the ¹Σ ← ³O_u and ¹Σ ← ³l_u transitions of the diatomic mercury molecule at λ_max ～ 4850 Å and 3350 Å, respectively, have been studied at low concentrations of mercury in the presence of N₂, C₂H₆, C₃H₈, and N₂O. Rate constant values have been obtained for the following reactions of the excimer molecule: Hg₂(³l_u) + N₂ → Hg₂(³O_u) + N₂ and Hg₂(³O_u) + RH → Hg₂(¹Σ) + RH, where RH = C₂H₆ or C₃H₈. From a consideration of the detailed kinetics of band emissions, it was also possible to derive rate constants for the quenching reactions of Hg(³P₀) atoms. These values are in reasonable agreement with those obtained previously from monitoring atom concentrations directly by 4047 Å absorbiometry.     

Beiträge zur Chemie des Phosphors. 72. Über die Alkyl-cyclomonocarba-phosphane (PR)4CH2, R = CH3, C2H5, t-C4H9

Contributions to the Chemistry of Phosphorus. 72. About the Alkyl Cyclomonocarba Phosphanes (PR)₄CH₂, R = CH₃, C₂H₅, t-C₄H₉ The alkyl-substituted cyclomonocarbaphosphanes (PR)₄CH₂ (R = CH₃ 1 , C₂H₅ 2 , t-C₄H₉ 3 ) are obtained in very good yield by the reaction of the corresponding dipotassium alkylphosphides K₂(PR)_n (n = 2, 3, 4) with methylene chloride. Besides, small amounts of the homocyclic rings characteristic for the given substituent and of the five-membered cyclodicarbaphosphanes (PR)₃(CH₂)₂ with isolated CH₂ groups are formed. For the alkylcyclomonocarbaphosphanes 1 and 2 , configuration isomers could be identified for the first time. The “all-trans” forms are always predominant; the relative amounts of the other isomers decrease strongly with increasing number of cis relationships between the substituents at adjacent phosphorus atoms. The ³¹P n.m.r. parameters for three of the all together six isomers of 1 distinguishable by n.m.r. spectrometry and for the “all-trans” isomers of 2 and 3 are reported and discussed. A definite separation is possible between substituent and configuration influence on the chemical shifts as well as on the coupling constants.     

Ethylene–propylene copolymerization initiated with solubilized Ziegler–Natta macromolecular complexes. I. Determination of kinetic parameters

Copolymerization of ethylene with propylene (E–P) was initiated with soluble polystyrene –butadiene–Li/TiCl₄ complexes in toluene leading to vinylic-olefinic based block copolymers. The activity of the system was measured at a constant ratio r = Li/Ti for different feed compositions. From measurements of the amount of copolymers produced, a direct determination of the efficiency of the catalytic system was made. This efficiency was found to be close to that obtained for homopolymerizations of C₂H₄ and C₃H₆ initiated with the same catalytic complex (? 80% with respect to the concentration of “carbon-titanium” bonds). Both the measured values of the efficiency and the determination of the molar masses of the polyolefinic block are consistent with a living character of the system involved in the E–P copolymerization. In such conditions well-defined linear [styrene]-b-[ethylene-co-propylene] copolymers were obtained. Furthermore, ¹³C NMR analyses allowed determination of the comonomer reactivity ratios, the values of which indicate an E–P random copolymerization. From both these values and those of the absolute rate constants of propagation determined for the homopolymerization of C₂H₄ and C₃H₆ initiated with the same catalytic system, the absolute rate constants of cross-propagation were deduced.     

Relative kinetics of the radical addition of benzyl bromide to unsaturated compounds

The relative rate constants of the addition of the C₆H₅CH₂ radical to unsaturated compounds CH₂=CHX (X = C₄H₉, SiMe₃, CF₃, CO₂Me, CN) were determined under the conditions of initiation by the Fe(CO)₅ + DMF system or by benzoyl peroxide. Depending on the values of the relative addition rate constants, the monomers can be arranged into the following series (X): CF₃C₄H₉32Me5 + DMF system, the addition stage proceeds by a free radical mechanism.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 2017–2022, September, 1992.     

Ethylene polymerization with novel bridged tri- and tetranuclear titanocene/MAO systems

Two benzene centered tri- and tetracyclopentadienyl ligands C₆H₃(CH₂C₅H₅)₃-1,3,5 (1) and C₆H₂(CH₂C₅H₅)₄-1,2,4,5 (2) and their titanium complexes C₆H₃[CH₂C₅H₄Ti(C₅H₅)Cl₂]₃-1,3,5 (3), C₆H₃[CH₂C₅H₄Ti(C₅H₄CH₃)Cl₂]₃-1,3,5 (4), as well as C₆H₂[CH₂C₅H₄Ti(C₅H₅)Cl₂]₄-1,2,4,5 (5) were synthesized and characterized by mass and ¹H NMR spectra. In the presence of methylaluminoxane (MAO), 3, 4 and 5 are efficient catalysts for ethylene polymerization in toluene. The influence of the polymerization conditions such as catalyst concentration, MAO/Ti molar ratio, polymerization time and temperature were investigated in detail. 3, 4 and 5 produce linear polyethylene (PE) with broad molecular weight distributions (MWD) and a little lower molecular weight.     

Wellenmechanische Absolutrechnungen an Molekülen und Atomsystemen mit der SCF?MO?LC(LCGO) Methode. V. Bindungsbeteiligung der Inneren Elektronen des C-Atoms

Using the results of ab initio calculations, by comparison of the “1s orbital energies” of the C atom in the compounds C₆H₆, C₅H, C₃H₆ (cyclopropane), C₂H₄ as well as at the C atom itself the bond electrons were found to have a significant influence on the inner electrons. The reason for this is pointed out and an explanation is given. The connection between the bonding and this “1s orbital energy” change as well as the importance of this result for quantum-chemical “models” is discussed.     

Multiple stage pentaquadrupole mass spectrometry for generation and characterization of gas-phase ionic species. The case of the PyC2H 5 +· isomers

Eleven isomers with the PyC₂H ₅ ^+· composition, which include three conventional (1–3) and eight distonic radical cations (4–11), have been generated and in most cases successfully characterized in the gas phase via tandem-in-space multiple-stage pentaquadrupole MS² and MS³ experiments. The three conventional radical cations, that is, the ionized ethylpyridines C₂H₅-C₅H₄N^+· (1–3), were generated via direct 70-eV electron ionization of the neutrals, whereas sequences of chemical ionization and collision-induced dissociation (CID) or mass-selected ion-molecule reactions were used to generate the distonic ions H₂C^·?C₅H₄N⁺?CH₃ (4–6), CH₃?C₅H₄N⁺?CH ₂ ^· (7–9), C₅H₅N⁺?CH₂CH ₂ ^· (10), and C₅H₅N⁺?CH^·?CH₃ (11). Unique features of the low-energy (15-eV) CID and ion-molecule reaction chemistry with the diradical oxygen molecule of the isomers were used for their structural characterization. All the ion-molecule reaction products of a mass-selected ion, each associated with its corresponding CID fragments, were collected in a single three-dimensional mass spectrum. Ab initio calculations at the ROMP2/6–31G(d, p)//6–31G(d, p)+ZPE level of theory were performed to estimate the energetics involved in interconversions within the PyC₂H₅ ^+· system, which provided theoretical support for facile 4?7 interconversion evidenced in both CID and ion-molecule reaction experiments. The ab initio spin densities for the a-distonic ions 4–9 and 11 were found to be largely on the methylene or methyne formal radical sites, which thus ruled out substantial odd-spin derealization throughout the neighboring pyridine ring. However, only 8 and 9 (and 10) react extensively with oxygen by radical coupling, hence high spin densities on the radical site of the distonic ions do not necessarily lead to radical coupling reaction with oxygen. The very typical “spatially separated” ab initio charge and spin densities of 4–11 were used to classify them as distonic ions, whereas 1–3 show, as expected, “localized” electronic structures characteristic of conventional radical ions.     

Flash photolysis of biacetyl in gas phase. Rate constants of reactions between methyl and acetyl radicals

The flash photolysis of biacetyl produces CO, C₂H₆, and CH₃COCH₃ as main products, and in small amounts CO₂, C₂H₄, and CH₃CHO. The rate constants of reactions (2) and (3) of thermally equilibrated radicals were calculated from the amounts of products: .