Silane bridged polymerized metallocene catalyst for ethylene polymerization

The polymerized metallocene catalyst 4 was prepared by the co-polymerization of ansa-zirconocene complex [CH3Si(2)]ZrCl2 (3) containing vinyl substituted silane bridge with styrene in the presence of radical initiator. Catalyst 4 was found to display high ethylene polymerization activity of 2.28 x 10(6) g PE/(mol . h) with a viscosity average molecular weight (M-eta) value of 61.6 x 10(3) using methylalumoxane (MAO) as a co-catalyst. The ethylene polymerization has been investigated under different conditions.

Self-immobilized catalysts for ethylene polymerization: neutral, single-component salicylaldiminato phenyl nickel(II) complexes bearing allyl substituents

A new family of self-immobilized ethylene polymerization catalysts, derived from neutral, single-component salicylaldiminato phenyl nickel complexes, is described.

Thermally crosslinkable poly(phenylene sulfide)/poly (ether sulfone)/polymerization of monomer reactant-polyimide blends

The effects of thermally crosslinkable polymerization of monomer reactant-polyimide (POI) on the miscibility, morphology, and crystallization of partially miscible poly(ether sulfone) (PES)/poly(phenylene sulfide) (PPS) blends were investigated with differential scanning calorimetry and scanning electron microscopy. The addition of POI led to a significant reduction in the size of PPS particles, and the interfacial tension between PPS and crosslinked POI was smaller than that between PES and crosslinked POI. During melt blending, crosslinking and grafting reactions of POI with PES and PPS homopolymers were detected; however, the reaction activity of POI with PPS was much higher than that with PES. The crosslinking and grafting reactions were developed further when blends were annealed at higher temperatures. Moreover, POI was an effective nucleation agent of the crystallization of PPS, but crosslinking and grafting hindered the crystallization of PPS. The final effect of POI on the crystallinity of the PPS phase was determined by competition between the two contradictory factors. The crosslinking and grafting reactions between the two components was controlled by the dosage of POI in the blends, the premixing sequence of POI with the two components, the annealing time, and the temperature.

Polymerized unsymmetrical iron post-metallocene catalyst for ethylene polymerization

The unsymmetrical allyl containing post-metallocene complex [ArN = C( Me)] [(ArN)-N-' = C(Me)]C5H3NFeCl2 [Ar = 2,6(i- Pr)(2)C6H3, Ar' = 4-allyl-2,6-(i-Pr)(2)C6H3] (3) has been prepared and characterized. Complex (3) can be co-polymerized with styrene in the presence of radical initiator to produce polymerized post-metallocene catalyst which exhibits high activity for ethylene polymerization (2.5 x 10(6) g PE/mol Fe.h).

Synthesis, structure and ring-opening polymerization of phenolphthalein macrocyclic polyarylates

Phenolphthalein based polyarylate macrocyclic oligomers were selectively synthesized by an interfacial polycondensation reaction of o-phthaloyl dichloride with phenolphthalein. The high selectivity benefits from the role of phenolphthalein as a color indicator, an efficient phase transfer catalyst, acid a preferred conformation of the starting materials as indicated by analyzing a single-crystal X-ray structure of an analogous macrocycle. The melt ROP of phenolphthalein polyarylate cyclic dimer was studied using nucleophilic initiators, The molecular weight of the resulting polymers builds up very rapidly at the very early stage of polymerization but decreases with time. During the ROP of cyclic dimer, analogous macrocycles with higher degree of polymerization (n greater than or equal to 3) and linear oligomers were produced by backbiting reaction especially at later stage of polymerization. Conversion of cyclic dimer is very fast at the earlier stage of polymerization and then increases slowly with time as analyzed by gel permeation chromatography. However, the total amount of cyclic oligomers in the ROP system increases with time at the later stage of polymerization because of the formation of larger macrocycles. The resulting polymers are amorphous. Glass transition temperatures (T(g)s) of these polymers are influenced by the polymerization time, type of initiator, and initiator concentration.

Enzymatic and kinetic properties of selenium-containing catalytic antibody with cGPX activity

Three selenium-containing catalytic antibodies mHB4, mHB5 and mHB7 which acted as mimics of cytosolic glutathione peroxidase(cGPX), were prepared by chemically introducing selenium into monoclonal antibodies HB4, HB5 and HB7. HB4. HB5 and HB7 were raised against a GSH derivative GSH-S-DNP dibenzyl ester, The cGPX activity of mHB4, mHB5, mHB7 were 170, 1 867, 32 U/mu mol, respectively. The cGPX activity of mHB5 was 0, 32 fold of natural rabbit liver cGPX and 1. 51 fold of m4A4. About two atoms of selenium existed in each of mHB5 molecule determined by inductively-coupled plasma/mass spectroscopy (ICP-MS), The optimal activity of mHB5 was at between pH 8. 4 and 8, 8, The reaction catalyzed by mHB5 involved a Ping-Pong mechanism. At pH 7. 0 and 37 degreesC, the apparent second-order rate constants for reaction of mHB5 with H2O2 and t-ROOH were as followed: k(+1) (H2O2) = 9. 71 x 10(6) L/(mol min), k(+1)(t-ROOH) = 5. 99 x 10(5) L/(mol.min). Rate accelerations (k(cat)/K-m/k(uncat)) 9. 8 x 10(6) and 3.7 x 10(5) fold those of the uncatalytic reaction were observed.

Monte Carlo simulation of pulsed-laser polymerization in emulsion

The pulsed-laser polymerization in emulsions has been simulated by the Monte Carlo method. Our simulation shows that the best measure of the propagation rate coefficients K-p is the peak maximum of molecular weight distribution for microemulsions when the droplets are small. However, the inflection point at the low-molecular-weight side of the peaks provides the best measure of K-p of bigger droplets. (C) 2000 Elsevier Science Ltd. All rights reserved.

Active components and mechanism of isobutane alkylation with butenes in the catalytic system of HPAs plus AcOH

The catalytic active phase (CAP) of a novel liquid catalyst for isobutane alkylation with butenes was investigated, the composition of the CAP was analysized, The components of the catalytic active phase were separated and examined by the methods of FTIR, UV and NMR etc., On the basis of these results, a reaction mechanism based on the formation of protonated heteropolyacid as an intial stage in the isobutane alkylation with butenes was postulated, which is in agreement with the experimental results.

Novel macrocyclic precursors of poly{aryl ether ketone (sulfone)} containing hexafluoroisopropylidene units: Synthesis, characterization, and polymerization

Cyclic oligomers containing hexafluoroiso-propylidene(HFIP) units were prepared in excellent yields by a nucleophilic aromatic substitution reaction of 4,4(7)- (hexafluoroisopropylidene) diphenol with difluoro-monomers in the presence of anhydrous potassium carbonate under pseudo high dilution conditions. A combination of GPC, MALDI-TOF MS and NMR analysis confirmed the structure of the cyclic oligomers. All macrocyclic oligomers are crystalline and undergo facile melt polymerization to give high molecular weight fluorinated polyethers.

X-ray crystal structure and molecular mechanics calculations of (2,6-iso-dipropyl-phenylamide) dimethyl (tetra-methylcyclopenta-dienyl) silane titanium dichloride

Crystal and molecular structure of (2.6-dipropylphenylamide) dimethyl (tetra-methyl cyclopentadienyl) silane titanium dichloride (I) was fully characterized by X-ray diffraction. The crystal is obtained from a mixture of ether/hexane as orthorhombic. with a = 12.658 (3) Angstrom. b = 16.62 (3) Angstrom. c = 11.760 (2) Angstrom. V = 2474.2 (9) Angstrom(3). Z = 4, space group Pnma. R = 0.0399; Componud I compose of the pi-bounded ring with its dimethylsilyl-dipropyl phenyl amido group and the two terminal chloride atoms coordinated to central metal to form a so-called constrained geometry catalyst (CGC) structure. The result of molecular mechanics (MM) calculations on compound I shows that bond lengths and bond angles from the MM calculation are comparable to the data obtained from the X-ray diffraction study. The relation of the structure of CGCs and their catalytic activity by MM calculations is also discussed.

A study on the catalytic behaviors of concentrated heteropolyacid solution - I. A novel catalyst for isobutane alkylation with butene

The catalytic behaviors of a novel liquid acid catalyst (composed of heteropolyacid and acetic acid) for alkylation of isobutane with butene was investigated. As a solvent acetic acid had a synergistic effect. It enhanced the acid strength of HPA and its stability. The conditions for the formation of the catalytically active phase were studied systematically. The content of crystal water of HPA and the quantity of solvent affect the formation of active phase and the catalytic activity. Catalytically active phase consists of HPA, acetic acid and hydrocarbon produced from the reaction, as well as traces of water from the crystal water of HPA. This catalyst system is comparable to the sulfuric acid in catalytic activity.

Study on a novel polyimide precursor prepared by a modified polymerization of monomeric reactants (MPMR) procedure

A novel polyimide precursor based on the dimethyl ester of 3,3',4,4'-biphenyltetracarboxylic acid, 4,4'-methylene dianiline and the monomethyl ester of 5-norbornene-2,3-dicarboxylic acid (BPDE/MDA/NE) was prepared by a modified polymerization of monomeric reactants (PMR) approach (MPMR). The composition of the precursor was quantitatively characterized by means of FTIR, HPLC and GC. The fractions of imide, amic ester and amic acid units in the precursor, typically prepared by refluxing in 1,4-dioxane for 2 h, were 33.7, 30.8 and 1.1 mol-%, respectively. The portion of free MDA was 3.34 wt.-% as determined by HPLC.

Synthesis and free-radical ring opening polymerization of macrocyclic aryl thioether ether ketone (sulfone) oligomers

Two kinds of novel macrocyclic aryl thioether ether oligomers were synthesized by nucleophilic condensation reaction in high yields under pseudo-high-dilution condition. A combination of H-1 NMR, GPC and MALDI-TOF MS analyses unambiguously confirmed the cyclic nature and their distributions, Macrocyclic thioether ether ketone oligomers can undergo facile melt ring opening polymerization(ROP) initiated by thiyl radical to give a high molecular weight polymer.

Study of the catalytic behaviors of concentrated heteropolyacid solution. I. A novel catalyst for isobutane alkylation with butenes

A novel liquid acid catalyst, composed of heteropolyacid and acetic acid for the alkylation of isobutane with butenes is reported. The conditions for the formation of catalytic active phase as well as its catalytic behaviors in alkylation of isobutane with butenes have been studied. It was found that acetic acid, as a solvent, exerts a synergistic effect on the acid strength of heteropolyacid, and the contents of crystal water in HPAs have influence over the formation of active phase and the catalytic activity. This novel catalyst is comparable to the sulfuric acid in catalytic activity.