Polymerisation metallocene-catalysed

The second aspect, predicting reaction dynamics, including the quantum behaviour of protons, still has some way to go There are really two separate problems the simulation of a slow activated event, and the quantum-dynamical aspects of a reactive transition. Only fast reactions, occurring on the pico- to nanosecond time scale, can be probed by direct simulation an interesting example is the simulation by ab initio MD of metallocene-catalysed ethylene polymerisation by Meier et al. [93]. 

Mention has already been made in this chapter of metallocene-catalysed polyethylene (see also Chapter 2). Such metallocene catalysts are transition metal compounds, usually zirconium or titanium. Incorporated into a cyclopentadiene-based structure. During the late 1990s several systems were developed where the new catalysts could be employed in existing polymerisation processes for producing LLDPE-type polymers. These include high pressure autoclave and... 

Report 88 Plasticisers - Selection, Applications and Implications, A.S. Wilson. Report 115 Metallocene-Catalysed Polymerisation, W. Kaminsky, University of Hamburg. 

Report 115 Metallocene-Catalysed Polymerisation, W. Kaminsky, University of Hamburg. 

The LCB in metallocene-catalysed ethene polymerisation is considered to occur via a copolymerisation reaction where a vinyl-terminated polyethene chain is reinserted into a growing chain. Thus, the choice of the catalyst used will be extremely crucial. When the prerequisites of LCB are fulfilled, the process conditions will then be even more important [44, 60]. 

Nenov N, Koch M, Klapper M, Mullen K (2002) PEO-functionalized polystyrene as polymeric support in metallocene catalysed olefin polymerisation. Polym Bull 47 391-398... 

Functionalised PO as block and graft copolymers used as compatibilisers or to increase interactions with other materials are prepared by free radical grafting (the simplest method), metallocene-catalysed copolymerisation of olefins with functional monomers, or anionic polymerisation (silane-containing PO). They are also produced by controlled/living polymerisation techniques such as nitroxide-mediated controlled radical polymerisation, atom transfer radical polymerisation (ATRP), and reversible addition-fragmentation chain transfer (RAFT). 

Fig. 9.53 Kinetic model for polymerization including deactivation. (From E Ochoteco, M. Vecino, M. Montes, J.C de la Cal, Kinetics and properties in metallocene catalysed propene polymerisations, Chem. Eng. Sci. 56 (2001) 4169-4179. Copyright 2001 Elsevier).

In this chapter we will discuss a few topics in the area of alkene polymerisations catalysed by homogeneous complexes of early and late transition metals (ETM, LTM). One of the main research themes for the ETM catalysts has been the polymerisation of propene, while industries have also paid a lot of attention to metallocenes giving LLDPE (linear low-density polyethylene, for thinner plastic bags). In less than a decade a completely new family of catalysts has been developed which enables one to synthesise regioselective and stereoselective polymers of a wide variety of monomers. These new catalysts are starting to find application on industrial scale, but as yet only reports on commercialisation of (branched) polyethylene and polystyrene have appeared. 

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... 

This model would explain the inability of metallocene-alkylaluminium halide systems to promote the polymerisation of propylene and higher a-olefins [94] it is obvious that there is insufficient capability of the more weakly coordinating a-olefins to form reactive, olefin-separated ion pairs by displacement of an aluminate anion from the metal centre. At any rate, the limitation of homogeneous catalysts to the polymerisation of only ethylene was a crucial obstacle to progress in this field for many years. This impediment was fortunately overcome, however, by a series of serendipitous observations [90-95, 100,101,103] that led, around the 1980s, to the discovery by Kaminsky, Sinn et al. [90, 91,94,95,100,101] that metallocenes are activated for catalysing the polymerisation of propylene and other a-olefins (without a, a-disubstituted olefins) by methylaluminoxane [30],... 

However, another factor that determines the properties of metallocene-based catalysts for catalysing olefin polymerisation has to be taken into consideration - the already mentioned agostic interaction of one of the 7-hydrogen atoms of the metal-bound alkyl chain with the metal centre of the metallocene-based catalyst [343,344],... 

In contrast to heterogeneous Ziegler-Natta catalysts, homogeneous catalysts based on biscyclopentadienyl derivatives of group 4 transition metals, which contain cationic metallocene species of formally d° 14-electronic structure, hardly promote the polymerisation of conjugated dienes, since the diene can act as a donor of four electrons rather than of two electrons as in monoolefin polymerisation (let us recall that the polymerisation of conjugated dienes is catalysed by half-sandwich metallocene-based catalysts). However, it has been reported [162] that statistical copolymers of ethylene and butadiene were obtained with the Cp2ZrCl2— [Al(Me)0]x catalyst. 

PFT also involves in situ co-polymerisation of olefins catalysed directly from nanotubes pre-treated by a methylaluminoxane (MAO) or highly active metallocene-based complexes e.g. Cp2ZrCl2). This approach destroys nanotube bundles and results in homogeneously coated CNTs. 

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