Chemistry Reference
In-Depth Information
CHAPTER
8
Free-Radical Polymerization
Mathematics is all well and good but Nature keeps dragging us
around by the nose.
—Albert Einstein, to Hermann Weyl (1923)
8.1
Scope
We turn our attention now to chain-growth polymerizations. The reader should
recall that the features that distinguish chain-growth and step-growth polymeriza-
tions were summarized in Section 7.2. The present chapter is devoted to the basic
principles of chain polymerizations in which the active centers are free radicals.
Chain-growth reactions with active centers having ionic character are reviewed in
Chapter 11.
Free-radical polymerization is the most widely used process for polymer syn-
thesis. It is much less sensitive to the effects of adventitious impurities than ionic
chain-growth reactions. Free-radical polymerizations are usually much faster than
those in step-growth syntheses, which use different monomers in any case.
Chapter 10 covers emulsion polymerization, which is a special technique of free-
radical chain-growth polymerizations. Copolymerizations are considered sepa-
rately in Chapter 9. This chapter focuses on the polymerization reactions in which
only one monomer is involved.
8.2
Polymerizability of Monomers
A monomer must have a functionality greater than or equal to 2 in order for poly-
mers to be produced from its reactions (Section 1.3). This functionability can be
derived from (1) opening of a double bond, (2) opening of a ring, or (3) coreac-
tive functional groups
[1]
. We considered the fundamentals of the reactions of
monomers of type (3) in Chapter 7. This chapter is concerned with free-radical
reactions of monomers of type (1).
The most important functional groups that participate in chain-growth polymer-
izations are the carbon
carbon double bond in alkenes and the carbon
oxygen
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