Physical Means of Initiation

Electrdysis of moncaner sdulions in the presence of supporting electrolytes can produce cation radicals which will promote cationic polymerisation. Unfortunately, the contribution of this technique to a better understanding of the fundamentals of initiation and propagation has been disappointingly meagre, as wiU be shown in Chap. Vll. 

The photolytic excitation of charge-transfer complexes is another recent addition to the available physical expedients to promote cationic polymerisation. The cation radicals generated by the photolysis have been characterised in some systems. More recent still is the use of ultraviolet radiation to induce the photolysis of substances whose photoproducts are initiators of cationic polymerisation. These processes will be discussed in Chap. Vin. 

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Several classes of compounds initiate cationic polymerizations of alkenes, including protonic acids, Lewis acids (usually in combination with a cation or proton source), stable carbenium ions, oxidizing reagents, and other strong electrophiles. This section attempts to explain the mechanism of initiation with quantitative information when available physical means of initiation (electric current, y-rays, field ionization and emission, nuclear chemical initiation) will not be discussed. 

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