Conjugated diene polymerisations

Porri, L. and Giarrusso, A., Conjugated Diene Polymerisation , in Comprehensive Polymer Science, Pergamon Press, Oxford, Vol. 4, pp. 53-108. 

It is interesting that the presence of the alumina-silica carrier in the catalyst is sufficient enough for the activation of the titanocene for the polymerisation, similarly like the presence of methylaluminoxane in the titanocene homogeneous polymerisation system CpTiCl3 alone does not exhibit catalytic activity in conjugated diene polymerisation. 

The activity and stereospecificity of rc-allylic catalysts for conjugated diene polymerisation depend both on the kind of metal and on the nature of the ligand attached to this metal. For instance, Cr(All)3 [137] and Co(f/3-C8Hi3)(C4H6)-CS2 [103] catalysts yield 1,2-polybutadiene, while Cr (A11)2C1 [120], Cr(All)2I [134] and U(A11)3C1 [147] catalysts produce cis-1,4-polybutadiene, but an Nd(All)3.DOX catalyst gives trans-1,4-polybutadiene [146] and a Co(fj3-C4H7)3—I2 catalyst yields eb-c/.v-l, 4/1,2-poly butadiene [137,145] (Table 5.5). 

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],... 

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 ... 

As regards the kinetics of conjugated diene polymerisation in terms of the dependence of the rate of polymerisation on the monomer and catalyst concentrations, most studies show that the polymerisation rate is first order with respect to both the monomer and the catalyst concentration. For instance, the rate of polymerisation of isoprene with the TiCU AlEt3 (1 1) catalyst, leading to a cA-1,4-polymer, is represented by [177]... 

For conjugated diene polymerisations in systems with various 71-allylic catalysts, a first-order dependence of the polymerisation rate on the monomer concentration has been observed in principle. However, the order with respect to the catalyst reflects the different degrees of association of the 71-allylic complexes of transition metals under polymerisation conditions a first-order dependence was found for systems with [Ni(f/3-All)OCOCF3]2 and Ni(z/3-All)X LA catalysts [126,176,179], whereas an order of 0.5 was found for systems with [Pd(z 3-C4H7)C1]2 and [Ni(fj3-All)X]2 catalysts [124,126,180]. 

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