Conjugated diene polymerisation monomer coordination

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. 

It is clear that each polymerisation step involves the insertion of the coordinated conjugated diene into the active metal-carbon a bond, becoming a n bond owing to this insertion, which by subsequent monomer coordination reverts to a a bond. 

Figure 5.3 Schematic presentation of the formation of a ciy-1,4 diad (isotactic in the case of the terminally monosubstututed dienes) versus a 1,2 diad (syndiotactic) in the polymerisation of conjugated dienes. The last inserted monomeric unit (as an r 3-allylic ligand) is below the plane, the incoming coordinating monomer is above the plane and the transition metal atom is on the plane...

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