Producing High-Density High-Molecular-Weight Polymer Brushes by a “Grafting to” Method from a Concentrated Homopolymer Solution

Abstract

Here, a new procedure and method are presented for the production of highly grafted polymer brushes. Thiol-terminated polyethylene oxide (PEO-SH) of molecular weight (M(w)) 20,000 (20k) is grafted to a gold surface from highly concentrated aqueous solutions of nonthiolated polyethylene oxide homopolymer. The M(w) and volume fraction of the homopolymer solution are varied in order to control the grafting density of the resulting PEO-SH brush. As a result, 20k M(w) PEO-SH brushes with grafting densities up to 0.3 chains/nm(2) are achieved, as determined by ellipsometry. Highly concentrated homopolymer solutions of volume fraction greater than approximately 12% and M(w) greater than approximately 938 produce near-ideal solvent conditions for the 20k M(w) PEO-SH chains; we have found that this facilitates the achievement of higher grafting densities of end-functionalized polymer brushes than would be possible from simple solutions. We propose this as a suitable method for applications where the grafting density of a brush surface must be accurately varied and controlled consistently. The effect of chemisorption time and cleaning procedure on the resulting brush grafting density are also explored.

Mixed poly (ethylene glycol) and oligo (ethylene glycol) layers on gold as nonfouling surfaces created by backfilling

“…The grafting from technique generally gives higher graft density since the limiting factor is diffusion of monomer onto the reactive ends of growing chains, whereas in the case of the grafting to technique the limitation is diffusion of entire polymer chains to the reactive substrate. 10 Several strategies such as cloud point grafting, 11 grafting in homopolymer solutions, 12 grafting from polymeric melts, 13 and underbrush formation by backfilling with shorter molecules 14 have been used to increase the graft density for grafting to techniques. The backfilling approach, unlike the other three strategies that depend on minimization of excluded volume interactions, is a simple method wherein the interchain spaces present in layers of high M W PEG chains are filled with shorter PEG chains that can diffuse to the surface.…”

Mode of lysozyme protein adsorption at end-tethered polyethylene oxide brushes on gold surfaces determined by neutron reflectivity

“…Thiol-terminated PEO brushes were deposited upon these surfaces using the concentrated homopolymer solution procedure described in previous work [38]. These brush surfaces could be determined ex situ using ellipsometry, however due to their extremely low wet volume fraction and inherent complexity of the substrates used it was not possible to determine the presence of a hydrated brush using NR.…”

“…In previous work we demonstrated a novel procedure for producing PEO polymer brushes on relatively smooth gold surfaces (roughness ∼ 2 nm) [38]. We were able to accurately control the grafting of these brushes over the range of grafting at which PEO brushes become protein resistive using a concentrated homopolymer solution.…”

Polymer Brushes by the “Grafting to” Method

“…[14,15] Other options for minimizing the excluded volume interactions, and thereby producing thicker (10-30 nm) grafted layers, are to conduct the grafting from a ''theta'' solvent [16] or from a concentrated polymer solution. [17,18] Synthesis of brushes on flat substrates, [12,[19][20][21] porous structures, [22,23] fibers/textiles, [24][25][26][27][28][29][30][31] and nanoparticles [28,32,33] using the ''grafting to'' procedures has been reported. In addition to synthesis of the uniform grafted layers the ''grafting to'' approach can be readily employed to synthesize patterned anchored polymer layers and brushes with variations in grafting density along a substrate ( Figure 1).…”

“…[48][49][50][51][52][53][54][55] Furthermore, thiol and silane substances can bear other functionalities and thereby can bring different chemical groups to a surface for further chemical modifications. Numerous examples exist for the utilization of thiol [18,[56][57][58][59][60][61][62][63][64] and silane [14,16,20,21,33,41, reactions for polymer brush preparation via the ''grafting to'' method. The modification of the surface with a grafted polymer layer can be done in either a single step or two or more steps.…”