TABLE OF CONTENTS Polymer reaction engineering is a specialized but important branch of chemical reaction engineering. The odds strongly favor the involvement of chemical engineers with polymers at some point in their career. The kinetics of polymerization reactions can be treated using the basic concepts of Chapters 1 5, but the chemistry and mathematics are more complicated than in the examples given there. The number of chemical species participating in a polymerization is potentially infinite, and the mathematical description of a batch polymerization requires an infinite set of differential equations. Analytical and numerical solutions are more difficult than for the small sets of equations dealt with thus far. Polymerizations also present some interesting mechanical problems in reactor design. Viscosity increases dramatically with molecular weight, and a polymer solution is typically 10 2 10 6 times more viscous than an ordinary liquid. Molecular diffusivities in polymer solutions are lowered by similar factors. Laminar flow is the rule, pressure drops are high, agitation is difficult, and heat and mass transfer limitations can be very severe. The polymer reaction engineer sometimes confronts these problems head on, but most often seeks to avoid them through clever reactor design.
Polymerization reactions are classified as being either chain growth or step growth. In chain-growth polymerization, a small molecule reacts with a growing polymer chain to form an incrementally longer chain:
| (13.1) |  |
where M represents the small molecule that is called the monomer and P l denotes a polymer chain consisting of
