Polymer synthesis. N,N-dimethylacrylamide (DMA) was distilled under reduced pressure to remove the inhibitor. tertButyl Dithiobenzoate (t-BDB) was synthesized by a one-step process as described in reference 7. Polymerization reactions were carried out on a Schlenck line. To prepare P(DMA-co-NAS) with a target composition of 60 mol % NAS groups, NAS (2.46 g, 14.5 mmol), DMA (0.96 g, 9.7 mmol), AMBN (16 mg, 0.09 mmol), t-BDB (54 mg, 0.26 mmol) were added into 45 mL of anhydrous DMF. The solution was degassed with three freeze-pump-thaw cycles and heated with continuous stirring at 60 °C for 16 h. Then the solution was cooled and precipitated in 400 mL diethyl ether. The collected solid was redissolved in 1,4-dioxane and precipitated in diethyl ether and then dried under reduced pressure to remove residual solvent. The yield of polymer was 87%.

Synthesis of tert-Butyl Dithiobenzoate (tBDB). S-(Thiobenzoyl)thioglycolic acid (10.6 g, 0.05 mol) was dissolved in dilute alkaline solution containing 2 equiv of NaOH (4.0 g, 0.1 mol in 400 mL of H₂O). Then, tert-butylmercaptan (4.95 g, 0.055 mol) was added under stirring at room temperature. The mixture was stirred for a period of 15 h. Afterward, tert-butyl dithiobenzoate, which separated out as a heavy, dark, pink oil, was extracted with ether (1 × 600 mL, 1 × 300 mL). The organic extracts were washed with 0.1 N aqueous NaOH (3 × 300 mL) and water (3 × 300 mL), then dried over MgSO4, filtered, and evaporated. Then the product was left overnight under vacuum (0.01 mmHg, 40 °C) to eliminate the residual tert-butylmercaptan (bp = 63 °C). The yield of tert-butyl dithiobenzoate (t-BDB), which remained as a dark pink oil after purification, was 90%.

参考文献：

1. Polymer-Based Elemental Tags for Sensitive Bioassays, Chem. Int. Ed. 2007, 46, 6111.
2. Controlled Free-Radical Polymerization of n-Butyl Acrylate by Reversible Addition-Fragmentation Chain Transfer in the Presence of tert-Butyl Dithiobenzoate. A Kinetic Study, Macromolecules 2004, 37, 6329.