Propagation structural irregularities

Defect groups or structural irregularities need not impair polymer properties, they are simply units That differ from those described by the generalised formula 1 f Initiating radicals arc formed from those Initiator- or transfer agent-derived radicals that add monomer so as to form propagating radicals (see 3.1). 

Because of the very high reactivity of the cationic propagating species—in particular, with ethylenic monomers—the polymerization systems that are commonly used in industry often entail side reactions and frequent structural irregularities in the polymers formed. 

The high reactivity of carbocationic species can be also responsible for rearrangement reactions during the propagation step of certain monomers. For instance, in the polymerization of 3-methylbut-l-ene, structural irregularities could be formed ... 

The rearrangement is due to a higher stability of the tertiary carbonium ion compared to that of the secondary carbonium ion formed after a propagation step. The frequency of these structural irregularities closely depends on the experimental conditions of the polymerization. Such a rearrangement is also observed in the cationic polymerization of 3-pinene ... 

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