Poly(ethylene glycol) brushes grafted to silicon substrates by click chemistry: influence of PEG chain length, concentration in the grafting solution and reaction time

Abstract

The grafting of poly(ethylene glycol) (PEG) brushes to silicon substrates by the copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition, also coined as click chemistry, was studied in detail. First, the grafting kinetics of an alkyne-functionalized dimethylchlorosilane SAM from a toluene solution or in the vapor phase was monitored by water contact angle measurements. α-Methoxy-ω-azido-PEGs with M_w of 5, 20, and 50 kDa were then grafted to the alkyne functionalized SAMs via click chemistry in THF using Cu(PPh₃)₃Br/DIPEA as the catalytic system. The influence of polymer concentration in the grafting solution (Φ = 0.01–50 wt%) and reaction time (t = 0–72 h) on the thickness, morphology and wetting properties of the PEG brushes was investigated by ellipsometry, scanning probe microscopy and water contact angle measurements. PEG brushes up to 6 nm thick with homogeneous surface coverage and morphology as well as surface roughness on a nanometric scale were thus obtained using mild and robust grafting conditions.