Initiation in the free radical polymerization of dicyclohexyl fumarate (DCHF), isopropyl phenyl fumarate (iPPF) and isopropyl benzyl fumarate (iPBF), and the copolymerization of DCHF with tert-butyl vinyl ether (E), initiated by di-tert-butyl peroxalate, has been investigated at 60 î The rate coefficient for addition of the tert-butoxy radical to the fumarates is of the order 105 M-1 s-1 with differences between the different fumarates being at most a factor of about two. A significant amount of monomer addition to the primary propagating radical in the case of DCHF occurred despite competition with trapping, indicating that the first propagation step is orders of magnitude faster than the propagation step for macroradicals. In the copolymerization system DCHF/E, second-generation carbon-centered radicals containing two fumarate units were formed, whereas the corresponding species in the homopolymerization of E was not observed. This is consistent with the fact that E does not undergo homopolymerization.