This study examined the use of a new tetrafunctional peroxide initiator in the bulk free-radical polymerization of methyl methacrylate. The objective was to investigate the effect of using a multifunctional initiator through an examination of the rates of polymerization and the polymer properties. The molecular weights and radii of gyration were obtained with a size exclusion chromatograph equipped with an online multi-angle laser light scattering detector. The performance of the tetrafunctional initiator was compared to that of a monofunctional counterpart [tent-butylperoxy 2-ethylhexyl carbonate (TBEC)]. The results showed that the new tetrafunctional peroxide initiator produced a faster rate of polymerization than TBEC at an equivalent concentration but also generated a polymer of a lower molecular weight. This trend was the opposite of what was observed in a previous study with styrene. When TBEC was used at a concentration four times that of the new tetrafunctional peroxide initiator, both produced equal rates of polymerization and similar molecular weights. The degree of branching was also investigated with radius-of-gyration plots. (C) 2004 Wiley Periodicals, Inc.