Triphenylbismuthonium 1,2,3,4-tetraphenylcyclopentadienylide in 1,4-dioxan initiated radical polymerization of methyl acrylate to similar to30% conversion without gelation because of autoacceleration. The polymer had a viscosity-average molecular weight of 200,000. The kinetic expression was R(p)alpha[I](0.3)[M](.1.16), that is, the system followed nonideal kinetics because of primary radical termination and degradative chain-transfer reactions. The values of k(2) (P)k(t) and the energy of activation were computed as 3.12 x 10(-5) Lmol(-1)s(-1) and 28 kJ/mol, respectively. The ylide dissociated to form a phenyl radical, which brought about polymerization of methyl acrylate. (C) 2004 Wiley Periodicals, Inc.