We present here a H-1 NMR spectroscopy study of the kinetics of the ROMP macroinitiation of poly(exo-N-phenyl-2.3-norbornene dicarboximide) with various dioxepine derivatives and Grubbs first generation ruthenium initiators. We have recently demonstrated that this so-called "sacrificial block copolymer" approach yields hydroxy-functionalized ROMP polymers with high end-group functionality. This study shows that the substituents on the dioxepine are important for functionalization efficiency, in the order phenyl > isopropyl > methyl. Addition of triphenylphosphine to the ruthenium carbene initiator resulted in lower k(i)/k(p) (rate of initiation/rate of propagation) values for the macroinitiation than in the absence of triphenylphosphine. We demonstrate that the value of k(i)/k(p) for macroinitiations can be estimated for new sacrificial monomers by analyzing one or two functionalization reactions. This provides an easy tool for the rapid screening and evaluation of new sacrificial monomers.