Triethylaluminum Research Articles

Radiolysis of poly(acetaldehyde‐co‐chloral): A positive E‐beam resist

AbstractAcetaldehyde and chloral were copolymerized using triethyl aluminum catalyst. The copolymer (ACC) obtained with equimolar monomer feed is not alternating in structure as it was once thought to be; it is comprised of two fractions differing in MW and composition. ACC has good thermal stability which is further improved by endcapping. Radiolysis in vacuo caused depolymerization with a G(M) value (number of monomers produced per 100 eV) of about 4000 to 80% completion. The G(S) value for chain scission is 1.9. These processes are effectively inhibited by benzoquinone. Oxygen markedly increases G(M) to ca. 18,000 and > 97% completion. Addition of tetrabutyl ammonium salt or tetramethyl urea has no effect on the depolymerization, whereas the addition of di‐t‐butyl‐p‐cresol causes an induction period after which normal unzipping ensues. Even UV photolysis of ACC in the presence of oxygen produces monomer with a quantum yield of 1.7, but very little photolysis occurs in the absence of oxygen. Gamma radiolysis sensitized by (C6H5)2IPF6 has G(M) value of 32,700. These results are very similar to the radiolysis and photolysis of the homopolymer of monochloroacetaldehyde and reinforce the mechanisms proposed for them. The E‐beam sensitivity of ACC is about 3 × 10−6 C cm−2.

Propylene polymerization in a semibatch slurry reactor over supported TiCl4/MgCl2/ethyl benzoate/triethyl aluminum catalyst. II. A kinetic study based on a multisite model

AbstractIn propylene polymerization over TiCl4/MgCl2/ethyl benzoate (EB)/triethyl aluminum (TEA) catalysts, experimental evidence strongly suggests that active sites have differing propagation and termination rate constants. Although the chemical structure of these sites may be quite similar, their location on the support may affect their polymerization activity, and this results in a distribution of the propagation and deactivation rate constants. To model this type of system, we developed a kinetic model accounting for multiple active sites. The model was fitted to simulated polymerization data to investigate the validity of mathematical approximations used in the derivation of the model equation. Using experimental data, the adequacy of the model was tested, and the statistical inference of parameter estimation was also discussed. The effects of experimental operating variables and additives on the kinetic model parameters revealed an important insight into the fundamentals of this system. The optimum productivity commonly observed has been shown to be the result of differing rates of increase of both propagation and termination rates with Al/Ti ratio and temperature. Kinetic evidence also suggests that the additive selectively poisons atactic‐specific sites.

Propylene polymerization in a semibatch slurry reactor over supported TiCl4/MgCl2/ethyl benzoate/triethyl aluminum catalyst. I. Catalytic behavior

AbstractHigh activity TiCl4/MgCl2/ethyl benzoate (EB)/triethyl aluminum (TEA) catalysts for the polymerization of propylene were synthesized and characterized for particle size distribution and crystallinity. Polymerization was carried out in a semibatch, constant pressure slurry reactor. A correction for interfacial mass transfer was found to be necessary to relate the monomer feed rate to the instantaneous rate of polymerization. Without such a correction serious misinterpretation of rate data could result. Optimum productivity was observed with respect to the Al/Ti ratio. Similar behavior was observed with polymerization temperature. Isotacticity increased with polymerization tamperature and decreased with Al/Ti ratio. The addition of a small amount of 2,2,6,6‐tetramethylpiperidine increased the percentage of isotactic polypropylene to 98% without significantly affecting productivity.

Investigation of AlC bond reactivity in a bidentate ligand system: structure and reactivity studies of [Al(8-quinolinol)(C 2H 5) 2] 2

The reaction of triethyl aluminum, Al 2(C 2H 5) 6 with 8-quinolinol yields the dimeric dialkyl aluminum complex [Al(8-quinolinol)(C 2H 5) 2] 2. The X-ray crystal structure, monoclinic, P2 1/ c, a=18.132(3), b=9.784(5), c=15.191(2) Å, β=112.06(1)°, V= 2497.6(22) Å 3, Z=4, shows that the complex dimerizes through the oxygen atoms, forming a four membered ▪ ring. The 8-quinolinol moiety functions as a bidentate ligand and the coordination environment about the aluminum center is a distorted trigonal-bipyramid. The 1H NMR spectrum indicates that the complex undergoes a conformational rearrangement in solution, removing the equivalence of the alkyl protons. This complex is reactive in both the solid state and solution to air and moisture.

Particle size distribution of polypropylene produced in continuous polymerisation

AbstractA theoretical relationship has been developed between the particle size of polyolefin powders and that of the Ziegler‐Natta catalyst from which they are derived. This has been extended to examine how the yield on catalyst and the residence time distribution in a continuous stirred tank reactor affect the particle size distribution. Experimental confirmation of these relationships has been obtained using TiCl3 catalyst of near‐spherical morphology prepared by low‐temperature reduction of titanium tetrachloride with triethyl aluminium in solution.

27Al NMR spectroscopy of triethylaluminium. A direct method to the determination of the proportion of monomer in solution

The sole 27Al NMR signal of triethylaluminum (TEA) is shifted significantly to lower field with: (1) decreasing concentration; (2) increasing temperature; and (3) increasing polarity of the solvent; that is, in each case with an increase in the amount of the monomeric form. 27Al NMR chemical shifts of Al 2Et 6 and AlEt 3 are estimated as 153 ± 2 and 265 ± 10 ppm, respectively. By use of these and observed values, thermodynamic data K d, Δ H d and Δ S d were calculated for the dissociation of Al 2Et 6. The dependence of the monomer—dimer equilibria on the concentration of TEA in the solvents used indicated the participation of an “intermolecular” process in the exchange of bridging and terminal ethyl groups not only in aromatic solvents but also, in contrast to previous reports, in aliphatic hydrocarbons.

Substrate temperature dependence of GaAs, GaInAs, and GaAlAs growth rates in metalorganic molecular beam epitaxy

The substrate temperature (Ts) dependence (350–700 °C) of GaAs and Ga1−y InyAs growth rates was investigated in metalorganic molecular beam epitaxy (MOMBE), using triethylgallium (TEG), trimethylindium (TMI), and solid arsenic (As4) sources. For GaAs growth, four distinct Ts dependent regions are observed, including a weak desorption process (500–650 °C) characteristic of MOMBE, preceding atomic Ga desorption (Ts >650 °C). When adding a TMI flux to grow Ga1−yInyAs, this desorption process was much enhanced up to 550 °C, and then decreased above 550 °C when the In desorption phenomenon takes place. Correlatively, the In alloy composition peaks at 550 °C. The same dependence was observed in Ga1−yInyAs growth using solid In and TEG sources. However, in Ga1−xAlxAs growth using solid Al or triethylaluminum (TEA) and TEG sources, the weak desorption observed in GaAs MOMBE was strongly minimized. From these results, possible growth mechanisms are discussed.

Time-resolved spectroscopic studies of the ultraviolet-laser photolysis of Al alkyls for film growth

Time-resolved optical emission spectroscopy, with a resolution of ∼10 ns, was used to investigate the formation of excited photofragments during KrF laser-irradiation of trimethylaluminum (TMA) and triethylaluminum (TEA). The gases were introduced into a vacuum chamber as pulsed molecular beams expanding from a free-jet nozzle. The time-dependence of the fluorescence intensity was measured at various positions, corresponding to different gas pressures P, along the molecular beam. In the case of TMA, the primary peaks observed were the Al 4s 2S→3p 2P atomic transition and the CH A 2Δ→X 2Π (0,0) band. The CH intensity ICH following a laser pulse decreased exponentially with a 1/e decay time τCH ranging from ∼530 ns, in agreement with the radiative lifetime of CH 2Δ(v=0), in the low pressure region of the molecular beam, to ∼150 ns at high pressures. The decrease in τCH with increasing PTMA was due to collisional quenching. The decay of the Al emission intensity IAl was nonexponential since the radiative lifetime of the Al 2S state, 6.8 ns, was less than the laser pulse width, ∼15 ns. The rise times of IAl and ICH, on the other hand, were both <10 ns indicating that CH, like Al, is formed photolytically rather than through subsequent collisions involving photofragments. Substituting TEA for TMA suppressed the CH signal while a new molecular band due to AlH [the (0,0) band of the A 1Π→X 1Σ+ transition] was observed in addition to the atomic Al 2S→2P transition. The rise time of IAlH was also <10 ns indicating that it too was formed photolytically. τAlH was ∼80 ns in agreement with the published AlH radiative lifetime. The significance of these results on the mechanisms of TMA and TEA photodecomposition and C incorporation in Al films grown by KrF-laser photolysis is discussed.

ChemInform Abstract: 2,3‐Dimethyl‐1‐ethyl‐1,2,3‐aluminadicarbadodecaborane: A Versatile Carbollyl Transfer Reagent.

AbstractThe o‐dicarborane (I) is converted to the title compound (IV) by reaction with triethyl aluminum (II) and subsequent heating.

ChemInform Abstract: Reactions of Organo‐Aluminum Compounds with Peresters.

AbstractThe reaction of triethyl aluminum (Ia) with the peresters (II) gives the intermediates (III) ‐ (VI), according to the reaction products formed after hydrolysis and the ESR data obtained in the presence of 2‐methyl‐2‐nitrosopropane.

Ethylation of Pyrazines Using Alkylmetals, Such as Triethylaluminum, Diethylzinc, and Triethylborane

Ethylation of Pyrazines Using Alkylmetals, Such as Triethylaluminum, Diethylzinc, and Triethylborane

Excimer Laser Irradiation Effect on Metalorganic Molecular Beam Deposition of Al and Alas : Prospects for Laser-Assisted Epitaxial Growth of Gaalas

ABSTRACTTriisobutylaluminum (TIBA) was used as an aluminum source for metalorganic molecular beam epitaxy (MOMBE). The optical absorption coefficient for TIBA was found to be larger than both tri ethyl aluminum and triethylgallium. TIBA was introduced into a laser-induced MOMBE system and selective deposition of Al and AlAs was carried out. Al metal was deposited on the area where the ArF excimer laser was irradiated and no deposition was observed without the excimer laser irradiation at a substrate temperature of 350 C. Furthermore, a laser large enhancement of the growth rate of AlAs was observed at 350 C.

Free‐radical polymerization of methyl methacrylate and p‐fluorostyrene in the presence of the Mn(acac)3–AlEt3 catalyst system

AbstractMethyl methacrylate and p‐fluorostyrene were polymerized with manganese (III) acetylacetonate–aluminum triethyl catalyst at 60°C in a benzene medium. Maximum activity was found at Al/Mn ratio of 4. Maximum percent conversion of polymer was obtained when the aging time of the catalyst was 10 min. The rate of polymerization was first order with respect to monomer. The rate of polymerization with respect to catalyst and cocatalyst were found to be 0.5 and 1.5, respectively. The overall energy of activation for the polymerization of methyl methacrylate and p‐fluorostyrene were found to be 52.6 and 57.0 kJ/mole, respectively. A free‐radical mechanism is postulated.

Low resistivity Al-doped ZnS grown by MOVPE

Low resistivity Al-doped ZnS layers have been grown by low pressure MOVPE using an adduct of diethylzinc-diethylsulfide (DEZn-DES) and H 2S as source materials and triethylaluminum (TEAl) as a dopant. The lowest resistivity achieved in this study is 3 × 10 −2 Ω cm for layers grown at a temperature of 350°C and at a TEAl transport rate ratio of [TEAl] [DEZn-DES] = 4 × 10 −3 .

The influence of growth chemistry on the MOVPE growth of GaAs and Al xGa 1− xAs layers and heterostructures

A comparison study was carried out on the influence of the growth chemistry on the properties of Al x Ga 1− x As and GaAs layers and quantum well structures. Triethylgallium, triethylaluminum, trimethylgallium, and trimethylaluminum were used in a various combinations during MOVPE growth of Al x Ga 1− x As. Substantial reductions in the carbon incorporation can be achieved using the ethyl based growth chemistry. The observed change in the carbon incorporation with growth chemistry indicates a change in the decomposition kinetics and mechanisms between the various growth precursors. While triethylgallium can be directly substituted for trimethylgallium in the growth of Al x Ga 1− x As, the use of triethyl aluminum requires particular care. Narrow quantum well structures were demonstrated using both ethyl and methyl based precursors.

Preparation of GaAs and Ga1-xAlxAs Multi-Layer Structures by Metalorganic Molecular Beam Epitaxy

Metalorganic molecular beam epitaxial (MOMBE) growth of GaAs and (GaAl)As using triethylgallium (TEG) and triethylaluminum (TEA) has been studied. N-GaAs/p-GaAs multi-layer structures were prepared by applying an alternating ionization voltage to hydrogen. Single-crystal Ga1-xAlxAs ternary alloy with good surface mophology was successfully grown by introducing TEA as an Al source. The epitaxial layers typically showed p-type conduction with a carrier concentration of more than 1018 cm-3, this being due to residual carbon. A (GaAl)As/GaAs multiquantum well (MQW) heterostructure was fabricated by switching TEA and it was observed that the photoluminescence peak energies from the MQW structures were shifted to the higher energy position. Furthermore, selective growth of GaAs and (GaAl)As on a partly SiO2 masked GaAs substrate was investigated. In the MOMBE growth of (GaAl)As, polycrystalline film was deposited on the SiO2 masked region, while no deposition took place in the growth of GaAs.

Superlattice structures grown by metalorganic MBE

The metalorganic molecular beam epitaxial (MOMBE) growth of GaAs and (GaAl)As using triethylgallium (TEG) and triethylaluminum (TEA) has been studied. GaAs/GaAlAs multi quantum well (MQW) heterostructures were fabricated and it was found that the photoluminescence peak energy at room temperature agreed with calculated values. Furthermore, a new technique to grow a nipi superlattice structure was proposed and as a trial growth a n-GaAs/n +-GaAs multilayer was prepared by applying an alternating ionization voltage to hydrogen.

Supported catalyst for olefin polymerization. The role of the third component

Polymerization of propylene was carried out using a magnesium supported titanium catalyst in combination with triethylaluminium(TEA) and a p-substituted benzoate or a phenylcarbinol as the third component in n-heptane under atmospheric pressure. p-Substituted benzoates produced excellent improvement in isotacticity (95–98%) and there was a linear relationship between isotacticity and Hammett's σ value for the p-substituents. On the other hand, phenylcarbinols (which react with TEA to form hemialkoxides) also increased isotacticity. It is considered that the complexes of TEA with the benzoates are the components which give very high isotacticity ( ≧ 95%) rather than the reduction products of the benzoates with TEA and that the dissociation of the hemialkoxides is essential for isotacticity, as observed in the case of the phenylcarbinols.

Electron spin resonance of divalent titanium ions doped into a magnesium chloride host lattice

Magnesium chloride crystals homogeneously doped with titanium ions can be prepared by crystal growth from the melt. The electronic spectrum taken along the c-axis indicates that the titanium ions are six coordinate and divalent. The x band electron spin resonance consists of a series of sharp lines and the nuclear hyperfine due to 47Ti and 49Ti can be observed. The peaks are assigned to a forbidden M s = 2 double quantum transition and orientation studies indicate that the environment is trigonally distorted. These measurements make it possible to interpret the powder spectrum. The powder along with an aluminium alkyl is a catalyst for the polymerization of ethene and a comparison is made between the powder ESR and ESR signals observed in the polymerization of ethene using a conventional Ziegler-Natta catalyst of titanium tetrachloride, magnesium chloride and aluminium triethyl.

Diffusivity and Thermal Cracking Rate of Metalorganic Gases by Chromatography

Metalorganic gases such as trimethylaluminum (TMA), trimethylgallium (TMG), triethylaluminum (TEA), and triethylgallium (TEG) are often used as metal sources of chemical vapor deposition for producing epitaxial thin films of or . Film growth kinetics are governed by thermal cracking of those gases in a thermal boundary layer which is expected to develop on the heated substrate and also by diffusion of those gases from bulk stream into the boundary layer. Since there has been poor understanding on physicochemical properties of these gases, such as rate of thermal cracking reaction and molecular diffusion, the present work is aimed to determine these properties by means of a chromatographic technique (pulse‐response analysis) developed in the field of chemical engineering. Method of moment was used to analyze chromatographic elution curves and measurements at different temperature ranges provided diffusivities (293–428 K) and thermal cracking rate coefficients (454–580 K) of the four gases in hydrogen stream.