The n-butyllithium-initiated living anionic polymerization of MesP=CPh2 (Mes = 2,4,6-trimethylphenyl) was studied at a variety of temperatures (T = 296.3, 301.8, 307.4, 313.0, 318.6, and 324.2 K) with a fixed monomer-to-initiator ratio (50: 1). The consumption of monomer and formation of polymer Bu-n[MesP-CPh2](n)Li was monitored by P-31 NMR spectroscopy, and the conversion data obtained were analyzed using first-order kinetics. Up to 50% conversion, the plot of In [M]0[M] vs time was linear, and apparent propagation rate constants (k(p)) were extracted (kp = 21-150 L mol(-1) h(-1), T = 296-324 K). These rate constants were used to construct an Arrhenius plot, and the apparent activation energy for the propagation of P=C bonds was estimated (E-a = 14.0 +/- 0.9 kcal mol(-1)).