Kinetics of the polymerization of isoprene with isopropoxyneodymium dichloride/triethylaluminium binary lanthanide catalyst system

The kinetics of the polymerization of isoprene with the heterogeneous rare earth catalyst system isopropoxyneodymium dichloride/triethylaluminium (Nd(OPri)Cl-2-AlEt(3)) was examined in a specially designed dilatometer. The rate of polymerization is expressed as R(p) approximate to -d[M]/dt = k'(p)[Nd](1.40)[M]. The main kinetical parameters such as the concentration of active propagating chain, the efficiency of lanthanide catalyst used (ELCU), the absolute rate constant of propagation as well as the average life time of growing chains, were determined at 30 degrees C, 40 degrees C, 45 degrees C and 50 degrees C.

Structure and luminescent properties of three new silver lanthanide molybdates

Three new compounds AgLnMo(2)O(8) (Ln = Eu, Gd, Tb) crystallize with a tetragonal scheelite-type structure characterized by MoO4 tetrahedra. The IR spectra show three absorption bands, which correspond respectively to the nu(1), nu(2), and nu(3) modes of the tetrahedral-MoO42- groups. The emission of AgGdMo2O8 shows the band of the MoO42- groups around 600 nm wavelength with very weak intensity. Both AgEuMo2O8 and AgTbMo2O8 emit intensely, and the concentration quenchings of both Eu3+ and Tb3+ luminescences are very weak. For all compounds, Ag+ luminescence is not observed. (C) 1996 Academic Press, Inc.

Copolymerization of styrene with butadiene and isoprene using a rare earth catalyst

In the copolymerization of styrene-butadiene and styrene-isoprene, a novel rare earth catalyst system (CF3CO2)(3)Ln/R(3-n)AlH(n)/(CH3)(3)CCH2Br (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; R = Me-, Et-, i-Bu-, and Oct-; n = 0 and 1) has been studied. The 1, 4 unit contents in the copolymers obtained are found to range from 64.4 to 99.6% with St contents of 5.2 to 59.9%, and intrinsic viscosities of 0.1 to 0.5 dl g(-1) measured by i.r., H-1 n.m.r. and C-13 n.m.r. spectra. From the calculated data of linked ratios, a change in the microstructure is induced by the styrene unit, probably adjacent to the butadiene or isoprene unit. An interesting result is that the ratios of styrene unit linked with 1, 2 or 3,4 units in the copolymers are far higher than in copolymers obtained with the nickel catalyst. The experimental results are discussed in terms of rare earth pi-allyl coordination and back-biting mechanism.

PREPARATION STRUCTURE AND PHYSICAL-PROPERTIES OF NEW SILVER LANTHANIDE MOLYBDENUM OXIDES [AGLNMO(2)O(8)(LN=LA-ND AND SM)]

We present the synthesis of AgLnMo(2)O(8) compounds with Ln = La-Nd and Sm. These compounds represent a scheelite-type structure characterized by MoO4- tetrahedrons. IR spectra show five absorption peaks in the region of 1000-400cm(-1), around 800cm(-1) and 400cm(-1), which correspond to the modes of the tetrahedral MoO42- groups. All of AgLnMo(2)O(8) (Ln = La-Nd and Sm) oxides are dielectric materials at room temperature. The temperature dependence of the magnetic susceptibility ofAgLnMo(2)O(8) (Ln = Ce-Nd and Sm) shows Curie-Weiss law behavior from 100K to 300K. This indicates that both Ce and Pr exist in +3 oxidation state in AgLnMo(2)O(8). For AgLaMo2O8, diamagnetic properties are found as expected.

STEREOCHEMICAL CONTROL IN PROPYLENE POLYMERIZATION WITH A ASYMMETRICALLY SUBSTITUTED TITANOCENE/METHYLALUMINOXANE CATALYST

A new mono-substituted titanocene, (eta(5)-cyclopentadienyl) [eta(5)-(1-(4-methoxyphenyl) cyclohexyl) cyclopentadienyl] dichlorotitanium (I), has been prepared via a novel modified synthesis, and its X-ray crystal structure has been determined. It crystallizes in the orthorhombic space group P2(1)2(1)2(1) with cell constants a=0.968 0(5) nm, b=1.284 6(5) nm, c=1.694 4(6) nm, Z=4, R=0.066. The I/methylaluminoxane (MAO) catalyst system produces at different polymerization temperatures either an isotactic or a syndiotactic polypropylene, both of which have the combined influence of enantiomorphic-site control and chain-end control, or an atactic polypropylene controlled by Bernoullian propagation mechanism.

DSC AND C-13 NMR-STUDIES OF ETHYLENE-PROPENE COPOLYMERS PREPARED BY A HIGHLY-ACTIVE AND STEREOSPECIFIC CATALYST

Ethylene-propene copolymers (EPR) were synthesized at different feed compositions using a highly active and isospecific MgCl2-supported Ti-based catalyst. The thermal behavior of EPR was studied by differential scanning calorimetry, the heterogeneity by f

UNSTEADY DIFFUSION KINETICS OF ZIEGLER-NATTA HETEROGENEOUS CATALYST POLYMERIZATION .4. PREDICTION OF EXPERIMENTAL RESULTS OF PROPYLENE ETHYLENE 1-HEXADECENE TERPOLYMERIZATION

The prediction, based on unsteady diffusion kinetics, of the enhancement of reactivity and incorporation of 1-hexadecene in its copolymerization with propylene on adding a small amount of ethylene (increase from 5,2 mol-% to 10,8 mol-% when 2% of ethylene was added, and to 16,1 mol-% when 5% was added) was verified in the terpolymerization of propylene/1-hexadecene/ethylene on a commercial Solvay-type delta-TiCl3 catalyst. The catalyst efficiency was thus also increased. These augmentations originate from the increase in diffusion coefficient of 1-hexadecene at the catalyst surface when the PP crystallinity decreases on introduction of ethylene. Calculation based on unsteady diffusion kinetics showed that the order of diffusion coefficients ethylene > propylene > 1-hexadecene is reversed as the monomer concentration increases when the monomers are not at their equilibrium concentration. Sequence distribution as determined by means of C-13 NMR revealed a tendency of blocky structure rather than a Bernoullian one. The terpolymer compositions obtained by means of an IR method developed in this work conform rather well with the NMR results. Results in this work not only support the unsteady diffusion kinetics but also provide a new route to prepare olefinic copolymer rubbers with heterogeneous titanium catalysts.

COMPARISON OF THE SULFURIZATION OF COMOK/AL2O3 CATALYST WITH H2S AND CS2

Only H2S consumption and H2O formation was found in the sulfurization of CoMoK/Al2O3 water gas shift catalyst with H2S/H-2. but CO2 was formed first, then CH4, H2O and H2S appeared in the later part of TPS with CS2/H-2. Carbon deposition on the catalyst during the sulfurization with CS2/H-2 caused a lower activity than the catalyst sulfurized with H2S but could be removed in the run of WGS reaction.

STRUCTURE INVESTIGATION OF TI(OBU)4-ALET3 CATALYST BEFORE AND AFTER HEAT-TREATMENT

The catalyst structure of Ti(OBu)4-AlEt3 at different Al/Ti ratios before and after heat aging has been investigated from the data of UV, GC-MS, ESR and C-13 NMR spectra. The complex compounds formed by HTiEt2 and AlEt2(OBu) exist mainly in the catalyst solution, and no -OBu ligands linking with Ti atoms can be found at an Al/Ti ratio of four before heat aging. Many kinds of catalytic species with different size are formed after heat aging the catalyst at 110-degrees-C for 2 h. Dehydrogenation, accompanied by the valence change from Ti3+ to Ti2+, is observed during the aging process of the catalyst.

ELECTROCHEMICAL-BEHAVIOR OF N-METHYL-N'-HEXADECYLVIOLOGEN MONOLAYERS ON SILVER ELECTRODES - EFFECTS OF COUNTERIONS

N-Methyl-N'-hexadecylviologen (C16MV) has been the subject of several electrochemical and spectroelectrochemical studies which characterized the species present in various redox states for C16MV monolayers on silver electrode surfaces. Both self-assembled monolayers (SA) and Langmuir-Blodgett (LB) transferred systems have been studied. These indicated inconsistencies regarding the presence or absence of splitting of the first reduction peak in its cyclic voltammogram (CV). The present study demonstrates the important influence of the specific anionic species present in the supporting electrolyte. Splitting may or may not take place, depending on the size and relative strength of the adsorption of specific anions contributed by the supporting electrolyte. Small, strongly adsorbing anions such as iodide produced peak splitting in the CV of C16MV monolayers; bulky but weakly adsorbing anions such as perchlorate may disrupt the ordered structure of monolayers but produce no splitting. Ancillary data provided by surface enhanced Raman spectroscopy (SERS) was consistent with the electrochemical measurements.

THE ACTIVE OXYGEN ON THE LI/LA2O3 CATALYST SURFACE AND ITS CATALYTIC BEHAVIOR IN THE OXIDATIVE COUPLING OF METHANE

The coupling selectivity was greatly enhanced by adding Li to La2O3, compared with the single La2O3. The O2- species was found on the Li/La2O3 but not on the single La2O3. In low-temperature desorption, ethane desorbed from the Li/La2O3 but was not detected with the single La2O3. It is considered that the addition of Li gave rise to some basic sites which are favorable for the coupling reaction.