Although the overall chemistry of a polymerization might be obvious in terms of monomers used and polymer produced, this knowledge does not ensure that the details of the chemistry are understood. Polymerizations, especially chain polymerizations, can have a number of intermediate steps that lead to the final result. These intermediate steps or mechanism need to be known if the polymerization itself is to be fully understood. The kinetics associated with polymerization are the principal manifestation of the mechanism underlying the overall chemical process. If a specific polymerization mechanism is proposed then the kinetic equations that ensue from the mechanism should lead to relations for the progress through the polymerization of observables such as the rate of monomer consumption and molecular weight build-up that are in agreement with experiment. If it is desired to have control over the polymerization process in the sense of being able to manipulate results such as molecular weight and its distribution, rate of polymerization, or composition in copolymerizations, then it is highly desirable to have a successful mechanistic and kinetic formulation of the process that expresses the effects of the possible variables.

Step polymerization

The description of the kinetics of step polymerization is greatly simplified if it is realized that the reactivities of the as yet unreacted end groups (carboxyl, amine, etc.) are not sensitive to the length of the chain to which they are attached.