Polymerisation by Carbenium Salts or Esters Preparated in situ

The major drawback concerning the use of these stable carbenium salts as initiators for the polymerisation of vinylic monomers, is of course their inabflity to attack certain olefins such as isobutene. The search for alternative catalysts within this famfly has resulted in the remarkable success obtained by Plesch already quoted. Hopefully more such new initiators will become avaflable after this breakthrough. 

Although initial expectations of finding among these systems the first living cationic polymerisation have been proved too optimistic by subsequent more rigorous work, the investigation of the polymerisation of 3-vinyl-N-ethylcarbazole appears to be much more promising in this respect. 

Polymerisation by Carbenium Salts or Esters Preparedl in Situ 

In 1960, Olah and coworkers reported a study on the polymerisation of olefins by various carbenium salts prepared at low temperature just before the addition of the monomer. AUcyl tetrafluoroborates in particular were drown to be fairly active initiators, but the molecular weight of the products were low. The above salts are not stable under normal conditions, but can be hailed in an inert atomsphere at low temperature and their reactivity is such that they can attack alij atic olefins such as butene and isdrutene. However, the very instability of these initiators is an obvious stumbling block inst fundamental studies. 

Kennedy and collaborators have studied the polymerisation of olefinic monomers induced by catalytic combinations consistir of mixtures of organic chlorides and aluminium alkyls. Although the authors claimed that these mixtures gave rise to carbenium salts capable of initiating viiq l polymermtion, we believe that the process leading to active species does not necessarily imply the formation of transient carbenium ions derived from the catalyst pair. For this reason, these systems are not discussed in this section but rather in Chapter IV together with other aluminium halide initiated polymerisations. 

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