The "3(rd) generation Grubbs" initiator (H2IMeS)(3-bromopyridine)(2)(Cl)(2)Ru=CHPh (1) accomplishes the synthesis of ABC triblock copolymers via living ring-opening metathesis polymerisation (ROMP) of norbornene derivatives. Complete initiation and an outstanding tolerance of functional groups are provided, which is proven by a combined study by, means. of matrix-assisted laser desorption/ionisation mass spectrometry, gel permeation chromatography and NMR spectroscopy on an ABC triblock cooligomer.