Surface-initiated atom transfer radical polymerization.

(A) Surface functionalization with APTES and installation of bromide initiator: Unless otherwise stated, steps were performed under ambient conditions. Glass slides (Nexterion Glass B, Schott AG, Mainz, Germany) were immersed in a 10% solution of 3-aminopropyltriethoxysilane (APTES) (Gelest, Inc.; Morrisville, PA) in ethanol overnight, and subsequently rinsed with fresh ethanol and then with deionized water. Chips were spun dry at 150 rcf for 5 min and then cured in an oven at 110°C for 2 h. Next, the chips were cooled to room temperature then placed in a dichloromethane solution containing 1% α-bromoisobutyryl bromide (BIB) and 1% triethylamine (TEA) (Sigma Aldrich; St. Louis, MO) for 45 min, followed by rinsing in fresh dichloromethane, then ethanol, and then in deionized water. The chips were spun dry 150 rcf for 5 min and then stored under ambient conditions. (B) Preparation of polymerization solution: Degassed polymerization solutions were prepared as described in Table S1 and then transferred into an inert (Ar environment) glovebox. (C) Surface-initiated atom-transfer radical polymerization: In an Ar environment, sodium ascorbate (Sigma Aldrich; St. Louis, MO) was added to the polymerization solution described above and gently stirred for 1 min (specific amount of sodium ascorbate for each monomer is listed in Table S1), at which point the solution changed color from blue to violet. Initiator-functionalized glass slides were then placed in this solution for polymerization (without stirring). After allowing polymerization to proceed for the desired time points (Table S1), slides were rinsed three times with deionized water, then centrifuged at 150 rcf for 6 min and allowed to dry under ambient conditions. The thickness of polymer brushes was determined by reflective-mode ellipsometry, as described below.