Surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization was used to synthesize poly(methyl methacrylate) (PMMA) and poly2-(methacryloyloxy)ethyldimethyl-(3-sulfopropyl)ammoniumhydroxide (PMEDSAH) brushes grafted from reactive polyp-xylylene surfaces. The synthetic approach involved functionalization of substrates via chemical vapor deposition polymerization of an electron-deficient alkynyl-functionalized 2.2paracyclophane derivative. An azide-functionalized RAFT agent was anchored to the resulting poly(p-xylylene-4-methyl propiolate)-co-p-xylylene films via copper-free click-chemistry. Subsequent SI-RAFT polymerization yielded PMMA and PMEDSAH films with narrow dispersity which was further tuned by varying the concentration of a sacrificial RAFT agent in solution. Polymer dispersity was determined by size exclusion chromatography to be in the range of 1.2–1.4 for both polymers. This work provides a novel surface modification strategy to decorate a wide range of different substrates with polymer brushes, thereby eliminating the need for cumbersome modification protocols, which so far had to be established for each substrate material independently. Display omitted •Novel approach for SI-RAFT polymerization strategy applicable to a range of organic and inorganic surfaces.•Vapor-based reactive coatings based on functionalized poly-p-xylylene for SI-RAFT polymerization.•The surface modification strategy can be extended to the synthesis of a variety of polymers.