A new methodology has been developed for preparing alpha-functional polymers in a one-pot simultaneous polymerization/isocyanate "click" reaction. Our original synthetic strategy is based on the preparation of a carbonyl-azide chain transfer agent (CTA) precursor that undergoes the Curtius rearrangement in situ during reversible addition-fragmentation chain transfer (RAFT) polymerization yielding well-controlled alpha-isocyanate modified polymers. This strategy overcomes numerous difficulties associated with the synthesis of a polymerization mediator bearing an isocyanate at the R group and with the handling of such a reactive functionality. This new carbonyl-azide CTA can control the polymerization of a wide range of monomers, including (meth)acrylates, acrylamides, and styrenes (M-n = 2-30 kDa; D = 1.16-1.38). We also show that this carbonyl-azide CTA can be used as a universal platform for the synthesis of alpha-end-functionalized polymers in a one-pot RAFT polymerization/isocyanate "click" procedure.