Polymerisation of ethene

Polymers can be formed from compounds containing a c=c double bond. Alkenes, such as ethene, can undergo addition polymerisation to form a polymer. A polymer is a compound consisting of very long chain molecules built up from smaller molecular units, called monomers. The polymerisation of ethene, to form poly(ethene), is a free radical addition reaction. 

Write the free radical mechanism for the polymerisation of ethene. 

Group 4 metallocene complexes were reported by Wilkinson in early 1953 [4], a few months before Ziegler s seminal discovery that mixtures of TiCl4 and AlEt3 catalysed the polymerisation of ethene. It was not long before the new compounds were tested as potential ethene polymerisation catalysts, not least because these... 

Grubbs group [31, 32] developed another type of Ni-based catalyst. This neutral Ni-catalyst, based on salicylaldimine ligands, is active in ethene polymerisation without any co-activator and originated from the Shell higher olefin process (SHOP). Shortly thereafter another active neutral P,0-chelated nickel catalysts for polymerisation of ethene in emulsion was developed by Soula et al. [33, 34, 35]. The historical development of single site catalysts is represented in Fig. 1. 

Two examples of manufacturing processes that use very high pressures are the Haber process and the polymerisation of ethene. 

The high pressure gas phase polymerisation of ethene to form Polythene involves a free radical mechanism. Thus, when ethylene is heated under great pressure in the presence of a suitable catalyst a large number of molecules of ethene combine together to form a much smaller number of molecules of... 

Scheme 6.1 The polymerisation of ethene (ethylene) (a) a single monomer molecule, (h) double hond opening and (c) monomer hnkage to form the polymer chain...

The reaction of [Cp TaCl2(TI -C4H6)] with methylmagnesium iodide afforded SS [Cp TaMe2(Tl -C4H6)] which was shown to be an active catalyst for the polymerisation of ethene. 

Niobium diene complexes [Cp Nb(Ti -diene)Cl2] (diene = buta-1,3-diene, isoprene, 2,3-dimethylbuta-1,3-diene) and [Cp Nb( n -2,3-dimethylbuta-l,3-diene)2] in the presence of a large excess of methylaluminoxane were found to be active catalysts for the polymerisation of ethene to give polyethylene with extremely narrow polydispersities357. 

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