Handbook of Solvents - George Wypych - ChemTech - Ventech!

13.2 Solvent effects on free radical polymerization 777
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13.2 SOLVENT EFFECTS ON FREE RADICAL POLYMERIZATION
Michelle L. Coote and Thomas P. Davis
Centre for Advanced Macromolecular Design, School of Chemical
Engineering & Industrial Chemistry, The University of New South Wales,
Sydney, Australia
13.2.1 INTRODUCTION
Free radical polymerization is one of the most useful and lucrative fields of chemistry ever
discovered - recent years have seen a tremendous increase in research into this area once
considered a mature technological field. Free radical synthetic polymer chemistry is tolerant
of diverse functionality and can be performed in a wide range of media. Emulsion and
suspension polymerizations have been established as important industrial processes for
many years. More recently, the ‘green’ synthesis of polymers has diversified from aqueous
media to supercritical fluids and the fluorous biphase. An enduring feature of the research
literature on free radical polymerization has been studies into specific solvent effects. In
many cases the influence of solvent is small, however, it is becoming increasingly evident
that solvent effects can be used to assist in controlling the polymerization reaction, both at
the macroscopic and at the molecular levels. The purpose of this chapter is to give a brief introduction
to the types of specific solvent effect that can be achieved in both free radical
homo- and co-polymerizations.
13.2.2 HOMOPOLYMERIZATION
Free radical polymerization can be conveniently codified according to the classical chain
reaction steps of initiation, propagation, transfer and termination. In cases where a significant
solvent effect is operative then the effect is normally exerted in all of these steps. However,
for the purpose of facilitating discussion this chapter is broken down into these
specific reaction steps.
13.2.2.1 Initiation
Solvent effects on the initiation reaction are primarily on the rate of decomposition of initiator
molecules into radicals and in the efficiency factor, f, for polymerization. However, in
some instances the solvent plays a significant role in the initiation process, for example, in