Chemistry Reference
In-Depth Information
CHAPTER
12
Polymer Reaction
Engineering
To define it rudely, but not inaptly, engineering is the art of doing that well
with one dollar which any bungler can do after a fashion.
—Arthur M. Wellington, The Economic Theory of Railway Location
12.1
Scope
Engineering of polymerization reactions requires a detailed knowledge of the phe-
nomena that take place in the polymer reactor. This entails a model of the poly-
merization kinetics and the heat and mass transfer features of the particular
polymerization and process. Polymerization reactions are usually complex and a
certain degree of mathematical sophistication is required for effective modeling.
Excursions into the details of particular reactions or modeling techniques are
beyond the scope of this introductory text and this chapter is therefore limited to
a review of the special considerations that apply in the case of various polymeri-
zations and processes. Most of the following discussions are necessarily qualita-
tive, for space reasons.
12.2
Step-Growth Polymerizations
There are some fundamental differences in the engineering of step-growth and
chain-growth polymerizations because of basic distinctions in the mechanisms of
these reactions. A propagation reaction (Section 8.3.2) in a kinetic chain sequence
must be fast or the series of monomer additions will not be long enough to pro-
duce high-molecular-weight polymers before the intervention of termination or
transfer reactions. This is not generally true for step-growth polymerizations
where only an addition reaction is involved and the growth of macromolecules
can occur in a series of starts and stops.
In step-growth polymerizations, overall costs of monomers, solvent recovery,
and preparing the polymer for further processing usually dictate a preference for
reactions that are slow at room temperature. (The reasons behind this generaliza-
tion are summarized in Section 7.3.1.) The ratio of rates of macromolecular
