Substituent Effects on the Stereospecificity of Propylene Polymerization by Novel Asymmetric Bridged Zirconocenes. A Mechanistic Discussion

2000 ◽  
Vol 33 (5) ◽  
pp. 1546-1552 ◽  
Author(s):  
Emma J. Thomas ◽  
James C. W. Chien ◽  
Marvin D. Rausch
Keyword(s):  
Substituent Effects ◽  
Propylene Polymerization

Substituent Effects on Propylene Polymerization in Cyclic Bis(phenoxyaldimine) Titanium Catalysts

2020 ◽  
Vol 53 (24) ◽  
pp. 10803-10812
Author(s):  
Xiangxiang Zhao ◽  
Hao Li ◽  
Yiming Liu ◽  
Yuguo Ma
Keyword(s):  
Substituent Effects ◽  
Propylene Polymerization ◽  
Titanium Catalysts

scholarly journals Substituent Effects of Phenyl Group on Silylene Bridge in Stereospecific Polymerization of Propylene with C1-Symmetric Ansa-Silylene(fluorenyl)(amido) Dimethyl Titanium Complexes

Polymers ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1075 ◽  
Author(s):  
Huajin Wang ◽  
Yanqing Li ◽  
Zhengguo Cai
Keyword(s):  
Substituent Effects ◽  
Phenyl Group ◽  
Propylene Polymerization ◽  
Element Analysis ◽  
Type Method ◽  
Titanium Complex ◽  
X Ray ◽  
Batch Type ◽  
Constrained Geometry ◽  
Stereospecific Polymerization

A C1-symmetric (methylphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (1) and (diphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (2) were synthesized and characterized by 1H NMR, element analysis, and X-ray crystal analysis. The coordination mode of the fluorenyl ligand to the titanium metal is an η3 manner in each complex. These complexes were applied for propylene polymerization using dried modified methyaluminoxane (dMMAO) as a cocatalyst under different propylene pressures in a semi batch-type method. The catalytic activity was strongly dependent on the structure of the complex and the propylene pressure, where complex 1 exhibited the highest activity (600 kg mol−1·h−1) under a propylene pressure of 8.0 atm to produce high molecular weight polypropylene. The polypropylenes obtained were syndiotactic-rich with an rr value of 0.50, indicating that the silylene bridge was not efficient for the isospecificity of a constrained geometry catalyst (CGC). The mechanical properties of the resulting polymers depended on their microstructure.

Substituent effects and solvents

1992 ◽  
Vol 89 ◽  
pp. 1567-1571
Author(s):  
O Pytela ◽  
M Ludwig
Keyword(s):  
Substituent Effects

Modification of Si/Mg Composite Supported Ziegler- Natta Ti-based Catalysts for Propylene Polymerization Using the Third Metal Elements

2019 ◽  
Vol 35 (3) ◽  
pp. 265-279
Author(s):  
WEI ZHU ◽  
◽  
ZHOU TIAN ◽  
PINGKAI JIANG ◽  
BOPING LIU ◽  
...  
Keyword(s):  
Propylene Polymerization ◽  
Metal Elements ◽  
The Third

Substituent Effects on the Thermal Decomposition of Phosphate Esters on Ferrous Surfaces

2019 ◽  
Author(s):  
James Ewen ◽  
Carlos Ayestaran Latorre ◽  
Arash Khajeh ◽  
Joshua Moore ◽  
Joseph Remias ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Film Formation ◽  
Substituent Effects ◽  
Vapour Phase ◽  
Industrial Applications ◽  
Phosphate Esters ◽  
Antiwear Additives ◽  
Formation Mechanisms ◽  
Phosphate Ester ◽  
Wide Range

<p>Phosphate esters have a wide range of industrial applications, for example in tribology where they are used as vapour phase lubricants and antiwear additives. To rationally design phosphate esters with improved tribological performance, an atomic-level understanding of their film formation mechanisms is required. One important aspect is the thermal decomposition of phosphate esters on steel surfaces, since this initiates film formation. In this study, ReaxFF molecular dynamics simulations are used to study the thermal decomposition of phosphate esters with different substituents on several ferrous surfaces. On Fe<sub>3</sub>O<sub>4</sub>(001) and α-Fe(110), chemisorption interactions between the phosphate esters and the surfaces occur even at room temperature, and the number of molecule-surface bonds increases as the temperature is increased from 300 to 1000 K. Conversely, on hydroxylated, amorphous Fe<sub>3</sub>O<sub>4</sub>, most of the molecules are physisorbed, even at high temperature. Thermal decomposition rates were much higher on Fe<sub>3</sub>O<sub>4</sub>(001) and particularly α-Fe(110) compared to hydroxylated, amorphous Fe<sub>3</sub>O<sub>4</sub>. This suggests that water passivates ferrous surfaces and inhibits phosphate ester chemisorption, decomposition, and ultimately film formation. On Fe<sub>3</sub>O<sub>4</sub>(001), thermal decomposition proceeds mainly through C-O cleavage (to form surface alkyl and aryl groups) and C-H cleavage (to form surface hydroxyls). The onset temperature for C-O cleavage on Fe<sub>3</sub>O<sub>4</sub>(001) increases in the order: tertiary alkyl < secondary alkyl < primary linear alkyl ≈ primary branched alkyl < aryl. This order is in agreement with experimental observations for the thermal stability of antiwear additives with similar substituents. The results highlight surface and substituent effects on the thermal decomposition of phosphate esters which should be helpful for the design of new molecules with improved performance.</p>

Chemistry of Unsymmetrical C1-Substituted Oxabenzonorbornadienes

2021 ◽  
Vol 17 ◽  
Author(s):  
Austin Pounder ◽  
Angel Ho ◽  
Matthew Macleod ◽  
William Tam
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Substituent Effects ◽  
Face Selectivity ◽  
Transition Metal Catalyzed ◽  
Catalyzed Reactions ◽  
Metal Catalyzed ◽  
Synthetic Intermediate

: Oxabenzonorbornadiene (OBD) is a useful synthetic intermediate which can be readily activated by transition metal complexes with great face selectivity due to its dual-faced nature and intrinsic angle strain on the alkene. To date, the understanding of transition-metal catalyzed reactions of OBD itself has burgeoned; however, this has not been the case for unsymmetrical OBDs. Throughout the development of these reactions, the nature of C1-substituent has proven to have a profound effect on both the reactivity and selectivity of the outcome of the reaction. Upon substitution, different modes of reactivity arise, contributing to the possibility of multiple stereo-, regio-, and in extreme cases, constitutional isomers which can provide unique means of constructing a variety of synthetically useful cyclic frameworks. To maximize selectivity, an understanding of bridgehead substituent effects is crucial. To that end, this review outlines hitherto reported examples of bridgehead substituent effects on the chemistry of unsymmetrical C1-substituted OBDs.

Influence of solvents on transmission of substituent effects by the oxygen and sulfur bridges

1974 ◽  
Vol 39 (7) ◽  
pp. 1862-1868 ◽  
Author(s):  
A. Perjéssy ◽  
G. Melikian ◽  
P. Hrnčiar ◽  
M. Lácová
Keyword(s):  
Substituent Effects ◽  
Influence Of Solvents

Substituent effects in 1,3-indanediones

1982 ◽  
Vol 47 (5) ◽  
pp. 1486-1493 ◽  
Author(s):  
Alexander Perjéssy
Keyword(s):  
Substituent Effects ◽  
Empirical Equations ◽  
Substituent Constants ◽  
Complex Structural

The carbonyl stretching frequencies correlate well with substituent constants in a series of 166 1,3-indanediones using improved and extended Seth-Paul-Van Duyse equation. Transmissive factors and group electronegativities have been used to find empirical equations for calculation of substituent constants of more complex structural fragments.

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