Isospecificity and Syndiospecificity of the Propagation

The origin of the stereoregulation in conjugated diene coordination polymerisation was recognised by Porri et al. [7,41] who explained the different modes of formation of the isotactic and the syndiotactic polymers in the presence of various transition metal-based catalysts. 

Note that the Mt ()j3-butenyl) species, anti or syn, constitute a chiral centre, irrespective of the substituents. The chirality of such species is connected with the presence of two asymmetric carbon atoms, C2 and C3, in the butenyl group. In the case of the polymerisation of 1,3-butadiene, the enantiomorphic 

Mt ( -butenyl) active species can be presented for anti and syn forms as follows  

The different orientation of the monomer in systems with Ziegler-Natta catalysts based on Ti or Nd and Co or Ni precursors has been suggested [41] to be determined by the presence in the isospecific catalysts (Ti- and Nd-based ones) of anionic ligands bound to the transition metal and the absence of any anionic ligand in the syndiospecific catalysts (Co- and Ni-based ones). In the 

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