Effect of solvent quality on kinetics of tethered layer formation

Abstract

We conducted a study of the effect of solvent quality on the kinetics of formation of a layer of polymer chains tethered to a solid substrate. In these experiments, tethering was accomplished by means of chemical bond formation between reactive sites on the surface and the end-functional groups of the polymer chains in solution. All experimental variables were held constant except for the -parameter between the polymer and solvent. Variation in the -parameter was achieved by use of a series of nonpolar, organic solvents. The distinct three-regime kinetics, typical of tethering reactions run in a good solvent and in the absence of segmental adsorption, was observed over the range of values for the -parameter. As expected, an increase in the -parameter (a decrease in solvent quality) did result in increased tethering density, but, contrary to expectation, no increase in tethering rate was observed.

Evidence that three-regime kinetics is inherent to formation of a polymer brush by a grafting-to approach

“…Excellent reviews are available that detail the graing-to method specically, 2 or provide an overview of the theory and preparation of polymer brushes, 3 or describe the increasingly important mixed brushes, which are brushes composed of two or more chemically different polymer chains. 4 We have been studying polymer brushes for some time, and, in previous publications, [5][6][7][8][9][10] we reported the observation of three-regime kinetics for graing of amine-functionalended polymer chains to a single type of surface, epoxidederivatized amorphous silica. We observed this characteristic three-regime prole for several different types of polymers as well as for different polymer architectures, molecular weights, and types of solvent.…”

Sensing surface PEGylation with microcantilevers

“…Consistent with XPS [ 8 ], ellipsometry [ 8 , 34 ], QCM [ 35 ] and AFM [ 36 ] polymer “grafting to” studies, we find that the adsorption profile of mPEG–SH on Au suggests two-regime kinetics [ 35 ] of layer formation as characterized by an initial phase of fast chain grafting (first regime) followed by a slow approach that plateaus towards saturation (second regime). We did not observe a third kinetic regime characterizing the so-called mushroom-to-brush transition [ 37 – 38 ]. This kind of transition was observed for systems where segmental adsorption of polymer (i.e., non-covalent polymer-surface interaction) [ 35 ] did not occur.…”

Comparison of Tethering of Linear and Four-Arm Poly(ethylene oxide)

“…Tethering Reactions. Linear PEO-NH 2 or four-arm PEO-NH 2 (Polymer Source, Inc., Quebec, Canada) were tethered to the epoxide-derivatized surface of the silica substrate. ,, This involved room temperature exposure (with stirring) of the derivatized substrate to a solution of carefully weighed polymer in toluene (0.80 mg/mL). The solution also contained a known amount of inert-ended PEO of M n = 2000 g/mol and M w / M n = 1.05 (Polymer Source) as internal standard.…”

“…Real-Time Monitoring of Kinetics. The disappearance of the PEO-NH 2 from the solution was monitored by means of a real-time, off-line method made quantitative by the unchanging internal standard in each reaction mixture. ,, Briefly, small aliquots were removed from the stirring reaction mixture at frequent intervals. The silica substrate was removed from each aliquot by filtration, and the solution was analyzed by size exclusion chromatography (SEC) for PEO-NH 2 .…”

“…Test for Segmental Adsorption. Segmental adsorption of PEO to the surface of the substrate was evaluated by a method described previously, ,, which consisted of exposure of the substrate to a solution containing carefully weighed amounts of inert-ended, monodiperse PEO of M n = 2000 and 8000 g/mol. The solution was monitored with SEC, in which the digitized areas of the two peaks were compared over time.…”