Grafting polymer brushes through electrochemically mediated surface-initiated atom transfer radical polymerization (SI-eATRP) has well-known advantages including use of low concentrations of catalyst, no need for an inert atmosphere, and opportunities to control polymer composition and architecture. Preparation of materials with tailored properties also requires control of polymer density; this can be achieved by grafting from a substrate with a controlled density of anchor sites. Toward this aim, a sparse monolayer of ethynylphenyl groups, with known density, was immobilized on a carbon substrate via electroreduction of a protected aryldiazonium ion. Poly(N-isopropylacrylamide) (PNIPAM) was grafted from the substrate in a onepot solution comprising azido-derivatized initiator, NIPAM and a Cu catalyst. Electroreduction of Cu(II) to Cu(I) catalyzes both the clicking of initiator to surface ethynylphenyl groups, and SI-eATRP. This novel method is simple and convenient, combining the advantages of SI-eATRP with the key advantage of polymerization from a well-defined layer of anchor sites.