Polymerization of complexes with Lewis acids

Molecular orbital calculations support this. Polymerizations can also be carried out with less than stoichiometric ratios of the Lewis acids to the monomers. As an illustration, coupling of an acrylic or a methacrylic monomer with a Lewis acid can be shown as follows  

The increased reactivity toward polymerization by some monomers, even in the presence of less than equimolar amounts of Lewis acids, was suggested to be due to one of two possibilities. It may be due to greater reactivity of the portion of the monomer that complexes toward the growing chain end. It may also be due to formation of new complexes between an uncomplexed monomer and a complexed one 

The picture is more complicated when the Lewis acids are used in combinations with donor-acceptor monomers. The donor-acceptor complexes are believed to form first and then react with Lewis acids according to the following scheme  

A structure of methyl methacrylate and styrene complexed with SnCU was shown to be as follows  

In formations of ternary complexes, the acceptor vinyl compound must have a double bond conjugated to a cyano or to a carbonyl group. Such acceptors are acrylonitrile, methacrylonitrile, acrylic and methacrylic esters and acids, methyl vinyl ketone, acrylamide, etc. Donor monomers are styrene, a-methyl styrene, butadiene, 2-3-dimethyl butadiene, isoprene, chloroprene, etc. 

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