Activated monomer mechanism description

With the continual discovery of new reactions leading to the formation of polymers, and with the increased understanding of the mechanisms of those reactions, it is natural that certain definitions of descriptive terms will change with time. The term polycondensation is used here to denote those polymerization reactions which proceed by a propagation mechanism in which an active polymerization site disappears every time one monomer equivalent reacts. This may be illustrated for one propagation step in polyesterification by... 

The propagation of the ensuing polymerization was then described as an insertion of a monomer into the C-Na bond yielding another carbon-sodium bond - a description that differs only slightly from our present formulation. Not surprisingly, it was superfluous to postulate a termination step in this mechanism the polymer still possessed the active C-Na bond. Indeed, polymerization was resumed when fresh monomer was added to the reactor7. ... 

Another heterogeneous process of wide technological importance is emulsion polymerization. It differs from suspension polymerization in that the droplet size is much smaller, typically 0.05 to 5pm in diameter and the initiator is soluble in the aqueous phase rather than the monomer. The droplet particles are held in a stable colloidal suspension with the aid of surface-active agents (emulsifiers) and rapid agitation of the system produces a true emulsion. The mechanism of polymerization is thought to be quite complex and even now is not completely understood. However, the description of emulsion polymerization that is given below is consistent with the widely held views of the probable mechanism. 

---