Pseudo‐cationic polymerisation after 24 years

It is shown that the theory of pseudo‐cationic polymerisation is now well established. This is because it can account for old and new observations, including the living polymerisations initiated by Giusti's syncatalytic system (I2 + HI); and because attempts at disproving it have been unsuccessful. The theory's essential part is that in certain cationoid polymerisations the propagating species is an ester (which may be stabilised or activated), and that the propagation step involves the insertion of the monomer into a polarised covalent bond. It is made clear that the pseudo‐cationic theory is merely a generalisation of reaction mechanisms which are well known and uncontroversial in conventional organic chemistry. Ten experimental facts are analysed to show the relevance and plausibility of the pseudo‐cationic theory. The two main versions of the “ions‐at‐any‐price” rival theories, namely the “large concentration of invisible ions” view and the “minute concentration of conventional carbenium ions” view are both shown to be incompatible with all the facts. It is emphasised that many industrial cationoid oligomerisations and polymerisations are pseudo‐cationic.