Mechanistic-Kinetic Aspects of Polymerisation

In the second step, the actual insertion of coordinating butadiene occurs into the Pd-Oj1 C4H7) bond it involves the migration of the allylic group to the coordinated monomer. The insertion results in the formation of an 3-butenyl group [164,165]. 

The propagation reaction in conjugated diene polymerisation occurs by an analogous insertion, which has been demonstrated by 1H NMR analysis of the polymerisation of partially deuterated butadiene (CD2=CH—CH=CD2) with a simple re-crotyl derivative of nickel, [Ni(/73-C4DgH)I]2 [166], 

As regards chain termination reactions, several processes can bring about termination of the growing macromolecule. These processes have been studied mostly for the polymerisation of butadiene or isoprene with Ziegler-Natta 

Reaction with hydrogen gives rise to the terminated polymer chain and to the Mt-H species, which reforms a new / 3-allyl group on reaction with the monomer [7]  

Spontaneous transfer reactions in conjugated diene polymerisation systems are more complex than those in monoalkene polymerisation systems. Two types of chain termination reaction can occur in principle in polymerisation systems containing conjugated diene. The first type, mononuclear termination, consists in a hydrogen abstraction from the growing chain with the formation of an Mt H bond [scheme (7)] which reforms an Mt [ /3-(All)] bond on reaction with the monomer  

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