A new way to obtain functionalized polymers by 3,3′-sigmatropic Claisen rearrangement has been developed and identified. The process was identified for three polyamides and three allyl-derivatives with different functional groups and rigidity. The Claisen rearrangement process seems to be independent of the polymeric structure, and it is only affected by the allyl functionality. The polymeric structure conditioned the rate of the process. The influence of polymer chain and allyl-derivatives on a cyclodehydration process was also studied. The cyclodehydration reaction is mainly affected by the rigidity of the polymer chain; therefore, it is influenced by the corresponding alkenyl structure. This work demonstrates the great potential of this approach that allows, by a simple and well-known process, the alkene functionalization of the polymeric chain in order to create a great variety of new high-performance materials for the application of these polymers in multiple fields.