Dispersion Polymerization

Abstract

The term ‘dispersion polymerization’ can be considered a misnomer. The terms bulk, solution, suspension, emulsion, miniemulsion, and microemulsion all evoke mental images of how these polymerizations are carried out and are at least superficially correct if not conceptually. Generally, these refer to the initial state of the system prior to polymerization while some also describe the final state after the monomer has been converted to polymer (i.e., bulk, solution, and suspension). On the other hand, the three types of emulsions are considered to result in polymer colloids or latexes (although sometimes referred to as ‘emulsion polymers’). Dispersion polymerization, as defined here, however, does not begin with a ‘dispersion’ of monomer in another liquid phase but rather a homogeneous solution as in solution polymerization. The end product, however, can be called a dispersion since stable polymer particles result which are indeed ‘dispersed’ in a continuous liquid phase. Some would say it is more akin to precipitation polymerization which has a similar initial state (i.e., homogeneous) but results in a ‘bulk’ polymer that, through polymerization, has precipitated and separated en masse from the inert liquid phase. Others would contend that it is more like an emulsion polymerization except for the absence of the initial emulsion; although this may on the surface sound absurd, the mechanisms involved in the polymerization indeed have significant similarities and much of the current knowledge of the mechanisms of dispersion polymerization has derived from that in emulsion polymerizations, an area where a great deal of fundamental research has been conducted and continues to be conducted. How the two types of polymerization came together historically is described below.