Analysis of the molecular weight distribution (MWD) in polymerization processes : contribution of different families of active sites to the MWD of polyethylene prepared using supported transition metal catalysts

1998 ◽  
Vol 199 (3) ◽  
pp. 415-421 ◽  
Author(s):  
Giuseppe Maschio ◽  
Cosimo Bruni ◽  
Luigi De Tullio ◽  
Francesco Ciardelli
Keyword(s):  
Molecular Weight ◽  
Transition Metal ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Active Sites ◽  
Metal Catalysts ◽  
Transition Metal Catalysts

scholarly journals The Effect of Iron Impurities on Transition Metal Catalysts for the Oxygen Evolution Reaction in Alkaline Environment: Activity Mediators or Active Sites?

2020 ◽  
Author(s):  
Ioannis Spanos ◽  
Justus Masa ◽  
Aleksandar Zeradjanin ◽  
Robert Schlögl
Keyword(s):  
Transition Metal ◽  
Oxygen Evolution ◽  
Oxygen Evolution Reaction ◽  
Active Sites ◽  
Water Electrolysis ◽  
Metal Catalysts ◽  
Transition Metal Catalysts ◽  
Alkaline Water Electrolysis ◽  
Co Catalysts ◽  
Model Transition

AbstractThere is an ongoing debate on elucidating the actual role of Fe impurities in alkaline water electrolysis, acting either as reactivity mediators or as co-catalysts through synergistic interaction with the main catalyst material. This perspective summarizes the most prominent oxygen evolution reaction (OER) mechanisms mostly for Ni-based oxides as model transition metal catalysts and highlights the effect of Fe incorporation on the catalyst surface in the form of impurities originating from the electrolyte or co-precipitated in the catalyst lattice, in modulating the OER reaction kinetics, mechanism and stability. Graphic Abstract

Metathetical Degradation and Depolymerization of Unsaturated Polymers

1997 ◽  
Vol 70 (3) ◽  
pp. 519-529 ◽  
Author(s):  
J. C. Marmo ◽  
K. B. Wagener
Keyword(s):  
Molecular Weight ◽  
Transition Metal ◽  
Catalytic System ◽  
Lewis Acid ◽  
Catalyst System ◽  
Metal Catalysts ◽  
Transition Metal Catalysts ◽  
Side Reactions

Abstract The employment of transition metal catalysts has been a viable route in the degradation and depolymerization of unsaturated polymers. Initially, unsaturated polymers were degraded with a catalytic system containing a transition metal and a Lewis acid cocatalyst (WCl6/SnBu4). Degradation chemistry was effective in reducing the molecular weight of the polymer, however, the classical catalyst system induces side reactions which generates ill-defined products. These side reactions were obviated by using a preformed alkylidene without a Lewis acid cocatalyst, and perfectly difunctional telechelics were synthesized.

Article

1998 ◽  
Vol 76 (4) ◽  
pp. 371-381 ◽  
Author(s):  
Ian Manners
Keyword(s):  
Molecular Weight ◽  
Transition Metal ◽  
High Molecular Weight ◽  
Ring Opening ◽  
Ring Opening Polymerization ◽  
Metal Catalysts ◽  
Transition Metal Catalysts ◽  
Organometallic Polymer ◽  
Wide Range ◽  
Initial Discovery

Ring-opening polymerization (ROP) of strained ring-tilted metallocenophanes can be achieved thermally, via anionic or cationic initiation, or by the use of transition-metal catalysts and provides access to a wide range of high molecular weight (Mw = 105-106, Mn > 105) poly(metallocenes). These materials possess a variety of interesting properties and many are very easy to prepare. This article provides an overview of our work, giving background to and an account of the initial discovery, and discusses work on the synthesis and properties of new poly(metallocenes) and related materials with particular emphasis on recent research directions.Key words: metallocene, ring-opening polymerization, ferrocenophane, organometallic polymer.

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