Olefins polymerization reactions

Oxalamidinate anions represent the most simple type of bis(amidinate) ligands in which two amidinate units are directly connected via a central C-C bond. Oxalamidinate complexes of d-transition metals have recently received increasing attention for their efficient catalytic activity in olefin polymerization reactions. Almost all the oxalamidinate ligands have been synthesized by deprotonation of the corresponding oxalic amidines [pathway (a) in Scheme 190]. More recently, it was found that carbodiimides, RN = C=NR, can be reductively coupled with metallic lithium into the oxalamidinate dianions [(RN)2C-C(NR)2] [route (c)J which are clearly useful for the preparation of dinuclear oxalamidinate complexes. The lithium complex obtained this way from N,N -di(p-tolyl)carbodiimide was crystallized from pyridine/pentane and... 

The use of organic halide to reactivate a decayed catalyst has been known for other catalytic processes involving transition metal catalysts, especially in olefin polymerization reactions (18-21). 

Despite their importance in olefin polymerization reactions, little attention has been paid to the nature of the adsorbed oxygen species on supported chromium oxide systems. 

The use of B(CgF5)3 and related compounds as co-catalysts for olefin polymerization reactions in so-called single site catalyst systems is probably the most well known application of this family of compounds and one that is utilized on a significant scale worldwide. This story has been well documented in the literature and will not be dealt with here. There are, however, several other applications for B(C6F5)3 and its derivatives that have been explored in some detail or are undergoing development, and this section will highlight these less appreciated applications. 

Early mechanistic studies concerning organolanthanide-catalyzed olefin polymerization reactions showed that insertion of the unsaturated hydrocarbon into the lanthanide-carbon cr-bond is a key step. It was first demonstrated for the... 

Olefin Polymerization Reactions Catalyzed by Lanthanide Amidinates... 

A solvent dependence of the activity was demonstrated earlier,(refs. 3-10 and was also observed in the present study. This may be due to catalyst solubility. The butene concentration as a function of time closely followed the general empirical relationship ln(monomer)t A exp(-Bt) + C. We ascribe no mechanistic interpretation to this observation, but note, however, that similar formulae have been derived from models of olefin polymerization reaction mechanisms. 

Carbosilane dendrimers containing titanium and zirconium complexes on their periphery have been prepared and used in olefin polymerization reactions.Generally, the best synthetic route to these materials involves the synthesis of generations of suitably functionalized dendrimers to which the metal is added in the final step giving products such as 276. Routes involving the incorporation of pre-metallated building blocks gave only low yields of the desired dendrimers. 

SCHEME 7.2 Olefin polymerization reaction schemes (a) conventional Cossee-Arhnan reaction sequence (b) counteranion displaced reaction sequence (c) stereodifferentiation reaction sequence. P and P represent polymer chains of length n and n + 1, respectively. 

Keywords Activation ansa-Zirconocene catalysts Constrained-geometiy catalysts ethene/propene rubbers Isotactic polypropylene Linear low-density polyethylene Molar-mass distribution Olefin polymerization Reaction... 

These observations are specific to ethylene polymerization reactions. Other a-olefin polymerization reactions do not exhibit this type of behavior. In some cases, opposite behavior is observed. For example, propylene polymerization activity with the same catalysts increases in the presence of hydrogen but decreases when higher a-olefins are introduced into the reaction medium. 

Due to the widespread usa of alumimrm alkyls in olefin polymerization reactions (e.g., as water scavenger or for catalyst alkylation), it is often difficult to assess the influence of changes in the reaction conditions on a specific observance in the copolymetization behavior. The choice of an appropriate aluminum compound is cmcial for a satisfartory incorporation of polar monomers into polyolefins. MAO, often used for catalyst activation, is not always able to proted the catalyst from deactivation.This can be attributed to insufficient com-plexation " and a nonuniform composition of the commerdal MAO solutions. The contained trimethylalumi-num (TMA) can also lead to increased chain transfer from the catalyst to the present aluminum compoimds. Hence, isobutyl modified MAO, for example, exhibits better protective characteristics. Therefore, and due to the difficult examination of MAO containing reaction mixtures, the addition of further well-defined aluminum compounds like TMA, triethy-laluminum (TEAL), tri-n-butylaluminum (TNBA), TIBA, and tri-/i-octylaluminum (TOA) has been examined. 

The synthesis of a dicationic alkyl-olefin complex of Rh(iii) 339 allowed to study the effects of ligand geometry upon olefin insertion/alkyl migration, within a catalytic olefin polymerization reaction. ... 

Scheme 19 Olefin polymerization reactions discussed in this section...

The olefin polymerization reaction is exothermic and the reactor design depends on the olefin content of feed gas. For polygasoline production the olefin content is usually in the range 50-60% and a tube-cooled reactor is used. Temperature control is important because phosphate esters can form at temperatures below about 150°C, while at temperatures above about 230 C, thermal cracking or gum forming reactions are likely. In both cases the catalyst loses activity (Table 6.4). 

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