Catalysts cocatalysts

Runa) Catalyst Cocatalyst Temp. Product yields (%)f)... 

A variety of initiators have been used for cationic polymerization. The most useful type of initiation involves the use of a Lewis acid in combination with small concentrations of water or some other proton source. The two components of the initiating system form a catalyst-cocatalyst complex which donates a proton to monomer... 

The catalyst component consists of halides of IV-VIII group elements having transition valence and the cocatalysts are organometallic compounds like alkyls, aryls and hydrides of group I-IV metals. Although there are hundreds of such catalyst cocatalyst systems listed in table below. Systems based on the organoaluminium compounds such as triethyl aluminium (AlEt3) or diethyl aluminium chloride... 

BF3 + H2O Lewis acid Lewis base catalyst cocatalyst... 

The rate of initiation (Ri) for typical cationic reactions is proportional to the concentration of the monomer [M] and the concentration of the catalyst-cocatalyst complex [C] as follows ... 

Entry Catalyst Cocatalyst [O] Additive Temp. Time (°C) (h) 51 (%) 52 (%) Refs. 

J. Kress, M. Wesolek, J.-P. Le Ny, and J. A. Osborn, Molecular Complexes for Efficient Metathesis of Olefins. The Oxo-Ligand as a Catalyst-Cocatalyst Bridge and the Nature of the Active Species, J. Chem. Soc., Chem. Comm. 1981, 1039-1040. 

Description Polypropylene with a melt flowrate ranging from 0.1 to 1,200 can be produced with the Borstar PP process. Currently, Ziegler Natta catalysts are used, but there is a potential to use single-site catalysts latter. When producing homopolymers and random copolymers, the process consists of a loop reactor and a gas-phase reactor in series. One or two gas-phase reactors are combined with this arrangement when heterophasic copolymers are produced. Propylene, catalyst, cocatalyst, donor, hydrogen, and comonomer... 

Titanium tetrachloride is probably one of the most extensively studied Lewis acid and some attempts at answering the questions posed alxjve can be made. The theory of cocatalysis was firmly establiriied by Polanyi s schcml and later in Plesch s laboratory with the system i )butene-titanium tetrachloride °. If one wants to draw any conclusion concerning the possible generalisation of this theory, the details of the reactions among catalyst, cocatalyst and monomer must be understood. This is by no means simple. Given the overall reactions ... 

The polymerisation of benzene through repeated nucleophilic substitutions on the rings was studied by Kovacic et al. using ferric chloride as catalyst and water as cocatalyst. This system is of course outeide the realm of cationic polymerisation throu the double bcmd of an olefin, but illustrates well the role of water in Friedel-Crafts polycondensations. The authors showed that the rate of this reaction went throu a maximum at a catalyst/cocatalyst ratio of one and attributed this observation to the high activity of ferric chloride monohydrate ... 

Eastham and collaborators carried out a thorough study of the isomerisation and polymerisation of butenes by the BF3-CH3OH pair They found that the initial rate of isomerisation of butene-2 was proportional to the concentration of both the catalyst-cocatalyst complex and the free catalyst. We think that these findings are... 

Fig. 12. Variation of electrical conductivity and polymer molecular weight in the polymerisation of isobutene by A1Q3—CjHjOH in ethyl chloride at —78.5 °C, as a function of the catalyst/cocatalyst ratio. (Taken from Ref.

Note The reactions were carried out in toluene at 30 °C for 24 h ([M]o = 0.50 M [catalyst] = [cocatalyst] = 10 mM). Practically no or very little polymers were formed with Nb or Ta catalysts. "Values of Mw were measured by gel permeation chromatography. The reaction was carried out in CCI4. 

Catalyst Cocatalyst Polymerization Process Polymerization Parameters Industrial Requirements... 

Patent Application (Priority) Company Catalyst Cocatalyst Pro- cess Polymer MWD > Remarks ... 

Patent Application (Priority) Company Catalyst Cocatalyst... 

The cationic polymerization of several para-substi-tuted a-methylstyrenes initiated by various Friedel-Crafts catalyst-cocatalyst combinations has been studied for the effects of catalyst type, monomer substituent and reaction solvent polarity on polymer structure and properties. By using solvent mixtures, the tacticity of the resulting polymers could be varied over a wide range, the syndiotactic form being favored in the more polar mixtures. 

Table II. Effect of Variations in Catalyst-Cocatalyst Combinations on MWD for the Polymerization of Monomers with Different p-Substitutes...

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