RAFT Polymerisation by the Radical Decarboxylation of Carboxylic Acids**

Abstract The controlled grafting of polymers from small‐ and macro‐molecular substrates is an essential process for many advanced polymer applications. This usually requires the pre‐functionalisation of substrates with an appropriate functional group, such as a RAFT agent or ATRP initiator, which requires additional synthetic steps. In this paper, we describe the direct grafting of RAFT polymers from carboxylate containing small molecules and polymers via photochemical radical decarboxylation. This method utilises the innate functional groups present in the substrates, and achieves efficient polymer initiation in a single step with excellent control of molecular weight and dispersity.