AbstractPlots of the degree of polymerization vs. temperature may show maxima in systems polymerizing under equilibrium conditions. It is shown that an equation correlating the temperature at which the maximum occurs with the thermodynamic constants of the polymerizing system, which was previously developed for the autoinitiated polymerization of sulfur can also be applied to the most general case of polymerization subject to external initiation. It is pointed out that such maxima are to be expected when the enthalpies of initiation and propagation are positive, and when the former greatly exceeds the latter.