CRITICALLY EVALUATED RATE COEFFICIENTS FOR FREE-RADICAL POLYMERIZATION .1. PROPAGATION RATE COEFFICIENT FOR STYRENE

Pulsed-laser polymerization (PLP) in conjugation with molecular weight distribution (MWD) measurement has emerged as the method of choice fo r determining the propagation rate coefficient k(p) in free-radical po lymerizations. Detailed guidelines for using this technique (including essential internal consistency checks) and reporting the results ther efrom are given by the authors, members of the IUPAC Working Party on Modeling of kinetics and processes of polymerization. The results for PLP-MWD k(p) measurements from many laboratories for bulk free-radical polymerization of styrene at low conversions and ambient pressure are collated, and are in excellent agreement. They are therefore recommen ded as constituting a benchmark data set, one that is best fitted by k (p) = 10(7.630) L . mol(-1) . s(-1) exp (-32.51 kJ . mol(-1) / R . T) (the confidence ellipsoid for the Arrhenius parameters is also given). These benchmark data are also used to evaluate the merits of several other methods for determining k(p); it is found that appropriately cal ibrated electron paramagnetic resonance spectroscopy appears to yield reliable values of k(p) for styrene.