NONRADICAL ADDITION POLYMERIZATION

Another type of nonradical addition polymerization is coordinate or complex catalyst polymerization. This approach stems from the pioneering work of Ziegler and co-workers [11] and Natta [12]. The polymerization is carried out with a suspension of a reaction between a metal alkyl (usually Al, Zn, and Mg) and a transition metal halide (V, Zr, and Ti). 

The addition of certain substances suppresses the polymerization of monomers. These substances act by reacting with the initiating and propagating radicals and converting them to either nonradical species or radicals of reactivity too low to undergo propagation. Such polymerization suppressors are classified according to their effectiveness. Inhibitors stop every radical, and polymerization is completely halted until they are consumed. Retarders are less efficient and stop only a portion of the radicals. In this case, polymerization occurs,... 

Some substances retard or suppress free-radical polymerization by reacting with primary radicals or macroradicals to yield nonradical products or radicals thal are loo stable to add further monomer. Some inhibitors and retarders are chain transfer agents others act by addition processes. 

Another interesting difference in polymerization behavior between methacrylic acid and acrylic acid is the remarkable observation that the reducing agent sodium bisulfite will cause the initiation of the polymerization of methacrylic acid while it does not initiate the polymerization of acrylic acid. It has been suggested that sodium bisulfite and methacrylic acid form a redox couple whereas acrylic acid and sodium bisulfite undergo some sort of addition reaction to form nonradical products [51]. 

Certain substances, when added to the polymerization system, may react with the initiating and propagating radicals converting them either to nonradical species or to less reactive radicals to undergo propagation. Such additives are classified according to their effectiveness ... 

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