We describe a facile, one-pot, two-step polymerization towards synthesizing block co-polymers bearing reactive isocyanate functional groups. Reversible addition fragmentation chain transfer (RAFT) polymerization is used to mediate the co-polymerization of isocyanate-bearing monomers dimethyl meta-isopropenyl benzyl isocyanate (TMI) and 2-isocyanatoethyl methacrylate (ICEMA) with styrene and methyl methacrylate (MMA), respectively. ICEMA was incorporated into the polymer at a faster rate than TMI and its unhindered isocyanate group was found to be more reactive than the hindered isocyanate group of TMI. Both the TMI/styrene and the MMA/ICEMA systems maintain the reactivity of the isocyanate functionality, which was exploited by attaching representative hydroxyl-bearing small and large molecules as well as solid substrates to the block co-polymers. Thus, we demonstrate the versatility of the block co-polymer system as a basis for forming branched polymers or as grafts for a solid substrate. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2771-2782, 2011