Electro Initiation of Polymerization
These polymerizations, sometime also called electrolytic polymerizations, are carried out in an electrical field. The field is applied to initiate chain growth. Passage of an electrical current through solutions of monomers in suitable solvents can produce initiating species. Majority of these species, however, are free-radical in nature [78–80]. Early studies on initiation of cationic polymerizations of styrene, isobutyl vinyl ether, and N vinylcarbazole were carried out by dissolving AgClO4 in pure monomers or in nitrobenzene. Electric current was then passed through them at room temperature [81, 82]. Rubbery polymers formed as well as some copolymers, suggesting a cationic path of the polymerization. A mechanism was suggested based on anodic oxidation of the monomer:
Where, M is monomer. Later, however, it was concluded that the polymerization sare due to formation of cation-radicals as the initiating species [83]. Further studies of the phenomenon led to a proposed mechanism of initiation [84] of styrene polymerization in acetonitrile solution. Controlled potential electrolysis at the anode, with the aid of a salt like tetrabutylammonium fluoroborate, is a result of direct anodic oxidation. Electrons are transferred at the anode. This is accompanied by formations of radical cations:
In the above initiation the monomer itself is the initiator and the anode can be regarded as the “co-initiator.” If a supporting electrolyte is first oxidized to a radical, indirect cationic polymerization can result. The radical in a subsequent step oxidizes the monomer to a first initiating entity, the cation-radical [85]. Such an indirect initiation was also suggested for electro polymerization of isobutyl vinyl ether in the presence of BF4 supporting electrolyte [85]:
