Effect of Segmental Adsorption on the Tethering of End-Functionalized Polymer Chains

Abstract

A comparison study was conducted of tethering in a poor solvent, in which segmental adsorption as well as tethering occurred, and tethering in good solvent, in which, for the conditions used, only tethering, and no adsorption, occurred. Monodisperse, amine end-functionalized polystyrene was tethered to the surface of silicate glass by chemical reaction with epoxide reactive sites thereon. The tethering process was monitored in real time by means of a procedure that enabled differentiation between chains held to the surface of the substrate by segmental adsorption alone and chains tethered to it by chemical bonds. The differences between tethering in the absence and presence of segmental adsorption were striking; not only was the kinetics of tethering changed, but also the number of chains tethered per unit surface area was larger (not smaller) and saturation was reached earlier when segmental adsorption occurred.

Salt-Induced Control of the Grafting Density in Poly(ethylene glycol) Brush Layers by a Grafting-to Approach

“…49 Meticulous investigations regarding polymer grafting kinetics by Penn and coworkers for different polymer systems encountered a third regime where thermal fluctuations create openings large enough to accommodate new coils, and a mushroom to brush conformational change occurs. 19,[50][51][52][53][54][55][56][57][58] In the present work, we demonstrate how the grafting density of the PEG brush layer can be systematically tuned by the addition of a salt (Na2SO4) with a strong salting-out effect. The thiolated polymers are directly attached to gold, which is a widely used material in bio-interface science.…”

Effect of solvent quality on kinetics of tethered layer formation

“…The modest increases in surface attachment density achieved by increasing χ are to be contrasted with the more substantial increases that can be achieved by use of tethering conditions that allow segmental adsorption 15. In a different series of experiments in our laboratory, the surface attachment density of the chains tethered by chemical bonds to the substrate was approximately doubled when a solvent was used in which segmental adsorption occurred simultaneously with tethering.…”

“…The absence of segmental adsorption of the polymers used in this work to the epoxide‐derivatized substrate in each solvent of interest was verified by means of auxiliary experiments of the type described previously 15. In brief, solutions containing mixtures of monodisperse, inert‐ended PEO with M n = 8000 g/mol and monodisperse, inert‐ended PEO with M n = 2000 g/mol were prepared from all three solvents of interest.…”

“…The increase in surface attachment density of tethered chains with time was determined by means of an off‐line, real‐time method in which the depletion of polymer from solution was quantitatively analyzed. The details of the method have been reported in our previous publications 13, 15. In brief, aliquots taken at frequent intervals throughout the tethering process were stabilized against precipitation by addition of a small amount of chlorobenzene, and were then analyzed on a Waters® Size Exclusion Chromatogram (SEC) system equipped with three Styragel columns (HR3, HR1, and HR 0.5) in sequence and a refractive index detector.…”

“…For these systems, we observed three distinct regimes of kinetics,12–14 as shown in Figure 2. We also conducted studies in a poor solvent that specifically allowed segmental adsorption of the polymer to the substrate 15. These studies showed that segmental adsorption is a powerful variable, not only changing the shape of the kinetics profile but also dramatically increasing both tethering rate and tethering density, as shown in Figure 3.…”