Synthesis of a thiol-reactive telechelic polystyrene and conjugation of cysteine is reported. A dimethylfulvene-protected maleimide-functionalized atom transfer radical polymerization (ATRP) initiator (3) was synthesized, and the thermostability was compared to the analogous furan-protected initiator (1) by thermogravometric analysis (TGA). The former protecting group was stable to a higher temperature than the latter in the bulk phase (143°C vs 125°C) and thus was investigated as an initiator for the ATRP of styrene. Kinetic studies of the polymerization of styrene mediated by copper(I)/N,N,N′, N″,N″-pentamethyldiethylenetriamine (PMDETA) indicated that the reaction proceeded in a controlled manner with high initiator efficiency (92%). Polystyrene with a number-average molecular weight (Mn) of 2530 Da and a narrow polydispersity index (PDI) of 1.15 was then synthesized and subjected to atom transfer radical (ATR) coupling to form the bis-functionalized polymer. Gel permeation chromatography (GPC) and 1H NMR spectroscopy studies indicated that dimerization had occurred and that the end groups were intact. Reactivity of the polymer was demonstrated by an in-situ retro-Diels-Alder and thioether bond formation first with model compound benzyl mercaptan and then with the amino acid N-acetyl-L-cysteine methyl ester. Bis-conjugation was verified by inspection of the 1H NMR spectra and by elemental analysis.