Straightforward Synthesis of Cysteine-Reactive Telechelic Polystyrene

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 ( M n ) 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 1 H 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 1 H NMR spectra and by elemental analysis.