The kinetics of the polymerization of isoprene on sodium surfaces

The kinetics of the polymerization of isoprene liquid and vapour occurring on sodium surfaces have been investigated at 60 and 25° C. In the case of the liquid phase polymerization diffusion of monomer to the catalytic surface is shown to be the rate-controlling factor, except when the sodium surface is in the form of a sphere of sufficiently small dimensions. The kinetics of the polymerization in presence of toluene are consistent with the view that polymeric chains are initiated by formation of free radicles on the sodium surface, the subsequent propagation occurring while the polymer is still attached to the sodium: termination occurs exclusively by interaction with toluene. In absence of toluene an alternative termination reaction, leading to cross linking and requiring 4.6 kcal. more activation energy than the process involving toluene, comes into play.