Polymerisation coordination

J. C. W. Chien, Coordination Polymerisation, Academic Press, Inc., New York, 1975. 

Coordinative polymerisation with 52 soluble transition metal catalysts (72)... 

Aspects of mechanism of coordination polymerisation of conjugated dienes... 

The high-density polyethylene is linear and can be manufactured by (i) coordination polymerisation of monomer by triethyl aluminium and tritanium chloride, (ii) polymerisation with supported Metal Oxide Catalysts. Such as chromium or molybdenum oxides supported over alumina-silica bases. 

Polymerisation reaction, particularly of olefins and dienes catalysed by organometallic compounds fall under the category of coordination polymerisation, or Ziegler-Natta polymerisation. 

In coordination polymerisation, the catalyst-monomer complex forms a heterogeneous system in which the metal ion is in the solid phase and the carbanion of the alkyl group is in the solvent phase. The monomer is inserted in between the metal ion and the carbanion and the Polymer chain formed is pushed out from the solid catalyst surface. Because of this coordination polymerisation is also known as insertion polymerisation. 

As said in the introduction there are many more polymers than can be discussed within the limits of this chapter, but we want to add just one example of a group of high-value polymers that is made using the same principles of coordination polymerisation as shown above for the commodity polymers. We mentioned metallocene catalysts that can be used to copolymerise ethene and norbomene to give Topas type products. 

Conjugated dienes, 11 Conjugation, 11, 368 Conrotation, 345 Coordination polymerisation, 322 Copolymerisation, 322 Cope reaction, 268 Cope rearrangement, 354 Cracking, 112, 305 Cram s rule, 235 Cross-linking, 323... 

In all the low pressure PE processes the polymer is formed through coordination polymerisation. Three basic catalyst types are used chromium oxide, Ziegler-Natta and single-site catalysts. The catalyst type together with the process defines the basic structure and properties of the polyethylene produced. Apart from the MWD and comonomer distribution that a certain catalyst produces in polymerisation in one reactor, two or more cascaded reactors with different polymerisation conditions increase the freedom to tailor... 

Principles of Coordination Polymerisation. Edited by Witold Kuran Copyright 2001 by John Wiley Sons Ltd ISBNs 0-470-84141-9 (Hardback) 0-470-84583-X (Electronic)... 

What is coordination polymerisation and what are its most characteristic features ... 

Which groups of monomers undergo coordination polymerisation ... 

Explain why coordination polymerisation revolutionised the plastics and rubber industries. 

Coordination polymerisation was first proposed in 1956 for the unusual, at that time, low-pressure polymerisation of ethylene and polymerisation of propylene with the transition metal catalysts discovered by Ziegler in 1953 [1], and for the ferric chloride catalysed ring-opening polymerisation of propylene oxide to crystalline polymer reported by Pruitt et al. in a Dow patent [2]. 

Polymerisation carried out in the presence of a coordination catalyst is referred to as coordination polymerisation , when each polymerisation step involves the complexation of the monomer before its enchainment at the active site of the catalyst. The active site in each coordination catalyst comprises the metal atom (Mt), surrounded with ligands, one of which (X) forms a covalent active bond (Mt X) with this metal atom. This implies that the growing polymer chain is covalently bound to the metal atom. A characteristic feature of coordination polymerisation is the mutual activation of the reacting bonds of both the monomer (M) and the active site (Mt-X) through the complexation of the monomer with the metal atom at this site, which results in the cleavage of these bonds in the concerted reaction. 

Thus, monomer enchainment into the metal-bound polymer chain is preceded by, and activated by, the coordination of the monomer with the metal atom. It must be noted in this connection that only monomers capable of forming labile complexes with the active site of the catalyst may undergo coordination polymerisation. 

Coordination polymerisation via re complexes comprises polymerisation and copolymerisation processes with transition metal-based catalysts of unsaturated hydrocarbon monomers such as olefins [11-19], vinylaromatic monomers such as styrene [13, 20, 21], conjugated dienes [22-29], cycloolefins [30-39] and alkynes [39-45]. The coordination polymerisation of olefins concerns mostly ethylene, propylene and higher a-olefins [46], although polymerisation of cumulated diolefins (allenes) [47, 48], isomerisation 2, co-polymerisation of a-olefins [49], isomerisation 1,2-polymerisation of /i-olcfins [50, 51] and cyclopolymerisation of non-conjugated a, eo-diolefins [52, 53] are also included among coordination polymerisations involving re complex formation. 

The same group of coordination polymerisations in which alkene undergoes re complex formation with the metal atom includes the copolymerisation of ethylene, a-olefins, cycloolefins and styrene with carbon monoxide in the presence of transition metal-based catalysts [54-58], In this case, however, the carbon monoxide comonomer is complexed with the transition metal via the carbon atom. Coordination bond formation involves the overlapping of the carbon monoxide weakly antibonding and localised mostly at the carbon atom a orbital (electron pair at the carbon atom) with the unoccupied hybridised metal orbitals and the overlapping of the filled metal dz orbitals with the carbon monoxide re -antibonding orbital (re-donor re bond) [59], The carbon monoxide coordination with the transition metal is shown in Figure 2.2. 

Polymerisations and copolymerisations of heterounsaturated and heterocyclic monomers in the presence of coordination catalysts constitute a distinct group of coordination polymerisation processes. Considering the nature of the coordination bond of the a type between the monomer heteroatom (beyond carbon monoxide [60]) and the metal atom, the complexes formed differ essentially from the re complexes of unsaturated hydrocarbon monomers with transition metals. 

Coordination polymerisation of heterocyclic monomers comprises polymerisation and copolymerisation processes of such monomers as oxacyclic monomers, especially epoxides [2,61-71], thiacyclic monomers like episulphides [72-76], azacyclic monomers [77,78] and phosphacyclic monomers [79]. Monomers with an exocyclic oxygen atom, such as cyclic esters like lactones [80-90] and lactide [90-92], cyclic acid anhydrides [93-98], cyclic carbonates [99,100] and related monomers, belong to oxacyclic monomers undergoing coordination polymerisation or copolymerisation. 

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