Polycentrism of Catalytic Systems in Polymerisation Processes

A key problem of the catalytic polymerisation theory is known to be that of the AC structure. Experimental studies and theoretical developments in the ionic and ionic-coordination polymerisation of unsaturated compounds revealed a considerable amount of new information about the nature of AC, for example [50-53]. The most important concept is the polycentrism of cataljnic systems as this problem is currently becoming much more important [49]. Researches have advanced from single examples of active centre types, in some catalytic systems, to an awareness of the fact that in some rare cases, the catalytic system can be considered to include only one type of active centre. 

There are several references to the confirmation of several types of AC existing on the surface of heterogeneous catalytic systems and having different stereospecificity [54-56]. Such a conclusion has been made from the study of polymerisation kinetic 

Heterogeneous catalytic systems, microheterogeneous and especially homogeneous catalysts do not provide clear evidence for several types of AC. However, the majority of theses assuming polycentrism of heterogeneous catalysts are applicable for these cases too, as they provide the same reasons for several types of AC to appear [57]. 

Revealing several types of AC, obtaining the functions of their distribution on kinetic inhomogeneity and stereospecificity, determining the number and kinetic parameters for each type of active centre, for specific polymerisation systems, will provide opportunities for more advanced theoretical understanding of ionic and ionic-coordination polymerisation mechanisms. In addition, this approach allows optimisation of the polymerisation processes to synthesise polymers with tailored molecular characteristics (microstructure, MW, MWD, and so on). 

The present generalised understanding of the phenomena of the existence of several types of AC is provided in [49], revealing general regularities and specific peculiarities of the polycentrism in ionic and ionic-coordination polymerisation of unsaturated compounds. 

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