The synthesis of polystyrene (PS) macromonomers functionalised with a norbornene (Nbe) unit and their living ring-opening metathesis polymerisation (ROMP) to produce comb graft co-polymers is described. Macromonomers comprising of one PS chain per Nbe unit and two PS chains per Nbe unit have been synthesised with a variety of chain lengths of PS. These macromonomers have been subjected to ROMP initiated with three different catalysts and the effect of catalyst along with the effect of solvent, concentration and time on the extent and rate of macromonomer polymerisation have been studied. Molecular weight analysis of the comb graft co-polymers by triple-detection size-exclusion chromatography (SEC) with light scattering has greatly improved the ease and accuracy of interpretation of results.