Polymerisation by Acylium Salts and Acyl Esters

The above equflibrium would obviously lie strongly to the lefthand side. The presence of small amounts of water would kill the carbenium ions formed in the initiation reaction and no polymerisation would thus occur in a wet stem. As for the limited yields following rapid initial polymerisation, the authors postulated that the polymer might from a complex with the catalyst and so remove it from the above equflibrium. A firm conclusion on the real nature of the initiation process would however require further fundamental work on this system. 

The preparation, characterisation and reactivity of acylium ions and acyl complexes and esters have been extensively investigated, partfcularly in the last two decades. Their use as initiators in the cationic polymerisation of alkenyl monomers is however a more recent extension of these studies, except for some old exploratory work. 

Three main routes are available for obtaining these ecies  

While the first two allow the isolation of the reaction products, the third does not. When a Lewis acid is mixed with an acyl halide, a donor-acceptor complex RCOX. .. MtX , or full ionisation by halide ion transfer, to give RCO MtX +i, or both, take place. The extent of ionisation depends mostly on the nature and strength of the Lewis acid used Thus, for example, acetyl halides react with stannic chloride and titanium tetrachloride to give mostly the coordination complex while with antimony pentachloride, pen-tafluoride and boron fluoride they give the conesponding acylium salts. Many of these 

The acylation capacity of these species is well documented. 

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