A series of fluorinated homopolymers and block co-polymers has been synthesised using the four-coordinate molybdenum ring-opening metathesis polymerisation (ROMP) initiators [Mo(=CHR)(=NAr)(OR')2], where R = CMe(2)Ph, Ar = 2,6-C6H3-Pr-2(i) and R' = CMe(3) or CMe(CF3)(2).