scholarly journals Molecular weight control in organochromium olefin polymerization catalysis by hemilabile ligand–metal interactions

2016 ◽  
Vol 12 ◽  
pp. 1372-1379 ◽  
Author(s):  
Stefan Mark ◽  
Hubert Wadepohl ◽  
Markus Enders
Keyword(s):  
Ethylene Polymerization ◽  
Weight Control ◽  
Transfer Reactions ◽  
High Catalytic Activity ◽  
Co Catalyst ◽  
Metal Centers ◽  
Molecular Weights ◽  
Metal Interactions ◽  
Polymerization Catalysis ◽  
Very High

A series of Cr(III) complexes based on quinoline-cyclopentadienyl ligands with additional hemilabile side arms were prepared and used as single-site catalyst precursors for ethylene polymerization. The additional donor functions interact with the metal centers only after activation with the co-catalyst. Evidence for this comes from DFT-calculations and from the differing behavior of the complexes in ethylene polymerization. All complexes investigated show very high catalytic activity and the additional side arm minimizes chain-transfer reactions, leading to increase of molecular weights of the resulting polymers.

scholarly journals Inducible overexpression and secretion of int-1 protein.

1989 ◽  
Vol 9 (8) ◽  
pp. 3377-3384 ◽  
Author(s):  
J Papkoff
Keyword(s):  
Molecular Weight ◽  
Cho Cells ◽  
Secretory Pathway ◽  
Mammary Tissue ◽  
Neural Tubes ◽  
Molecular Weights ◽  
Activation Of Transcription ◽  
Mouse Mammary Tumor ◽  
Tumor Virus ◽  
Very High

The int-1 proto-oncogene is a target for insertional activation of transcription by mouse mammary tumor virus in many murine mammary tumors. Whereas no expression of int-1 is seen in normal mammary tissue, int-1 RNA can be detected in normal mice in the neural tubes of midgestation embryos and in postmeiotic spermatocytes from adult testes. I report here the results of a study in which several different antibodies against synthetic peptides were produced and used to characterize the processing and secretion of int-1 protein. CHO cells were transfected with an inducible int-1 expression vector that was subsequently amplified to generate cell lines expressing very high levels of int-1 protein. Immunoprecipitation of [35S]cysteine-labeled cell lysates from these CHO cells yielded large amounts of four immature forms of int-1 glycoprotein (molecular weights of 36,000, 38,000, 40,000, and 42,000). A significant fraction of these int-1 species formed disulfide-linked multimers. Pulse-chase and glycosidase digestion studies demonstrated that some of the immature species of int-1 protein move through the secretory pathway and are processed to a mature heterogeneous glycoprotein with a molecular weight of about 44,000. Suramin treatment of the CHO cells during pulse-chase experiments increased the amount of 44,000-molecular-weight int-1 protein in the culture medium.

Simultaneous Control of 1,4-cis Selectivity and Molecular Weight of Polymer in Polymerization of Butadiene with Co(acac)3/MAO Catalyst

2005 ◽  
Vol 78 (1) ◽  
pp. 143-154 ◽  
Author(s):  
Kiyoshi Endo ◽  
Naoyoshi Hatakeyama
Keyword(s):  
Molecular Weight ◽  
Reaction Time ◽  
Active Site ◽  
Weight Control ◽  
Catalyst Preparation ◽  
Polymerization Rate ◽  
Polymerization Time ◽  
Molecular Weights ◽  
Molecular Weight Control ◽  
Simultaneous Control

Abstract Simultaneous control of 1,4-cis selective polymerization and molecular weight of polymer in the polymerization of butadiene (BD) with Co(acac)3/MAO catalyst was investigated. The polymerization of BD with the Co(acac)3/MAO catalyst strongly depended on catalyst preparation, and the polymerization rate of BD with Co(acac)3 activated by MAO in the presence of BD was faster than that with previous reported results that the Co(acac)3 activated by MAO in the absence of BD. From a kinetic study, linear relation between ln[BD]0/[BD]t and polymerization time and no induction period for the polymerization were observed in the polymerization of BD with Co(acac)3 activated by MAO in the presence of BD. This indicates that the active site for the polymerization kept constant throughout polymerization. The molecular weights of the polymers increased linearly with polymer yields, and the line passed through the original point. The Mw/Mn of the polymers kept constant during reaction time. The polymerization of BD performed at 0 °C in the Co(acac)3/MAO catalyst gave high molecular weight 1,4-cis poly(BD) (1,4-cis content > 95) and narrow polydispersity (Mw/Mn=1.36). On the basis of these results, it is clear that simultaneous 1,4-cis selective and molecular weight control is possible in the polymerization of BD with the Co(acac)3/MAO catalyst.

Molecular Weight and Chain-Length of Natural and Synthetic Rubber

1934 ◽  
Vol 7 (1) ◽  
pp. 34-39 ◽  
Author(s):  
A. J. Wildschut
Keyword(s):  
Chain Length ◽  
Freezing Point ◽  
Specific Viscosity ◽  
Molecular Weights ◽  
Gutta Percha ◽  
Synthetic Rubber ◽  
The Subject ◽  
Molecular Substances ◽  
Very High

Abstract The determination of the chain-length of high molecular substances, as, e.g., rubber and gutta-percha, has lately been the subject of many investigations, though as yet the problem has not been definitely solved. The ordinary methods—measurements of the raising of the boiling point and of the depression of the freezing point—can be used only for molecular weights of some thousands, and there always remains a large gap between these compounds and the far greater natural ones. To bridge over this gap Staudinger has developed a supposition according to which it is possible to determine very high molecular weights by means of a viscosimetric method. This method depends on the known fact that for dilute solutions, in which the molecules do not hinder each other (so-called sol-solutions), the specific viscosity is proportional to the length of the molecule. For homologs we have:

Vitamin E Protection of the Liver from Paracetamol in the Rat

1974 ◽  
Vol 47 (5) ◽  
pp. 449-459 ◽  
Author(s):  
B. E. Walker ◽  
J. Kelleher ◽  
M. F. Dixon ◽  
M. S. Losowsky
Keyword(s):  
Vitamin E ◽  
Enzyme Activities ◽  
Weight Control ◽  
Treated Group ◽  
Hepatic Necrosis ◽  
Control Group ◽  
Serum Enzyme ◽  
Vitamin E Deficiency ◽  
Body Weight Control ◽  
Very High

1. Control, vitamin E-deficient, vitamin E-supplemented (deficient with added ‘normal’ intake) and vitamin E-treated rats were given paracetamol at a dose of 25.5 mmol (4 g)/kg body weight. Control rats were also given paracetamol with or without simultaneous vitamin E. 2. Plasma aspartate aminotransferase and alanine aminotransferase activities increased to very high values (mean 2842 and 1241 i.u./l respectively) in the control group, and even higher (mean 8220 and 2320 i.u./l respectively) in the vitamin E-deficient group. 3. In the vitamin E-supplemented group the rises in activity were similar but rather less than in the control group (mean 2417 and 815 i.u./l) and in the vitamin E-treated group only very small rises (mean 177 and 98 i.u./l) were seen. 4. Histological evidence of hepatic necrosis correlated closely with plasma enzyme activities. 5. It appears that paracetamol-induced hepatic necrosis is potentiated in vitamin E deficiency and reduced by prior treatment with α-tocopherol. 6. Vitamin E administered simultaneously with paracetamol at 12.8 or 19.2 mmol/kg also greatly reduced the expected rise in serum enzyme activities. 7. These observations may shed some light on the mechanism of paracetamol-induced hepatic necrosis, and may form a basis for preventing or reducing this lesion in man.

A Novel Single-Site Catalyst for Olefin Polymerization

2010 ◽  
Vol 657 ◽  
pp. 83-87
Author(s):  
Sriram Venkataramani ◽  
Tharanikkarasu Kannan
Keyword(s):  
Ethylene Polymerization ◽  
Titanium Tetrachloride ◽  
Olefin Polymerization ◽  
Single Site ◽  
Turnover Frequency ◽  
Reaction Conditions ◽  
Co Catalyst ◽  
Infra Red ◽  
Turn Over Frequency ◽  
Turn Over

A novel single-site catalyst was prepared from N-pheneyldiethanolamine and titanium tetrachloride and characterized using spectroscopic methods such as Nuclear Magnetic Resonance (NMR) spectroscopy and Infra Red (IR) spectroscopy. It was prepared insitu and used to polymerize ethylene along with methylaluminoxane (MAO) as co-catalyst. The turnover frequency for ethylene polymerization was found to be 350 g and 550g polymer/mol catalyst/h for 1 bar and at 2 bar respectively. As the turn over frequency at the studied reaction conditions is good, the present N-pheneyldiethanolamine-based catalyst is a good single-site catalyst for olefin polymerization

Ethylene Polymerization Catalysis by Vanadium-Based Systems Bearing Sulfur-Bridged Calixarenes

2011 ◽  
Vol 30 (21) ◽  
pp. 5620-5624 ◽  
Author(s):  
Carl Redshaw ◽  
Lucy Clowes ◽  
David L. Hughes ◽  
Mark R. J. Elsegood ◽  
Takehiko Yamato
Keyword(s):  
Ethylene Polymerization ◽  
Polymerization Catalysis
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