Measuring the Kinetics of Chain Growth Polymerization

Two pieces of kinetic information are essential with respect to applying chemical initiators in radical polymerization the decomposition rate coefficient fed defined as the loss in initiator concentration with time and the efficiency of initiation/, which refers to the fraction of primary radicals that actually start chain growth. As initiator decomposition rates are mostly deduced from independent experiments, by monitoring initiator decay in (inert) solution, it is recommended to select the solvent as close as possible to the monomer system of interest. The solvent material in which the fed measurements have been performed needs to be stated when efficiencies/are presented. For use with ethene polymerization, fed from experiments in solution of heptane should be well suited. 

Polymerization occurs to almost complete yield with no termination or transfer, but with two species of different activity. An example of such a reaction is the anionic polymerization of styrene, in which both the free anion and the ion pair are active species. However, these polymerizations proceed so rapidly that they can no longer be followed with the normal kinetic techniques. Kinetic measurements are therefore carried out by accelerated flow techniques (Figure 18-5). A turbulent current must prevail in this flow tube (Reynolds number over 10,000), since the chains would show growth times of differing duration with a laminar current. In a flow tube, the effective polymerization time t depends on the volume Vq of the flow tube (distance between the mixing jets) and on the volume V of the total liquid flowing through in the time t ... 

---