The utilization of blocked isocyanates for efficient post-polymerization functionalization of different polymers is presented. For this purpose, well-defined polymers obtained by the RAFT polymerization procedure are modified by conversion of the end groups to blocked isocyanates. Furthermore, α,ω-carboxy-terminated polystyrene and poly(phenylene ethynylene) are functionalized with blocked isocyanates. The utilization of these end groups could be shown by functionalization with anthracene moieties. The blocked isocyanates offer improved stability of functional polymers compared to isocyanate functionalized polymers. Their handling is much easier and it is possible to precipitate these polymers in methanol. On the other hand, an efficient reaction with an amine or an alcohol at 130 °C could be demonstrated. Thus, the versatility of this approach is shown, which offers a wide range of possibilities for potential applications, e.g., as soft segments in polyurethanes or for further functionalization towards tailor-made polymers.