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Grafting Density (grafting + density)

Distribution by Scientific Domains

Polymers and Materials Science	93%

Distribution within Polymers and Materials Science

Polymer Science & Technology General	66%
General & Introductory Materials Science	33%

Selected Abstracts

Quantification of Grafting Densities Achieved via Modular "Grafting-to" Approaches onto Divinylbenzene Microspheres

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
Leena Nebhani
Abstract The surface modification of divinylbenzene (DVB)-based microspheres is performed via a combination of reversible addition fragmentation chain transfer (RAFT) polymerization and rapid hetero-Diels,Alder (HDA) chemistry with the aim of quantifying the grafting densities achieved using this "grafting-to" method. Two variants of the RAFT-HDA concept are employed to achieve the functionalization of the microspheres. In the first approach, the microspheres are functionalized with a highly reactive diene, i.e., cyclopentadiene, and are subsequently reacted with polystyrene chains (number-averaged molecular weight, Mn,=,4200,g,mol,1; polydispersity index, PDI,=,1.12.) that carry a thiocarbonyl moiety functioning as a dienophile. The functionalization of the microspheres is achieved rapidly under ambient conditions, without the aid of an external catalyst. The surface grafting densities obtained are close to 1.2,×,1020 chains per gram of microspheres. In the second approach, the functionalization proceeds via the double bonds inherently available on the microspheres, which are reacted with poly(isobornyl acrylate) chains carrying a highly dienophilic thiocarbonyl functionality; two molecular weights (Mn,=,6000,g,mol,1, PDI,=,1.25; Mn,=,26,000,g,mol,1, PDI,=,1.26) are used. Due to the less reactive nature of the dienes in the second approach, functionalization is carried out at elevated temperatures (T,=,60,°C) yet in the absence of a catalyst. In this case the surface grafting density is close to 7,chains,nm,2 for Mn,=,6000,g,mol,1 and 4,chains,nm,2 for Mn,=,26,000,g,mol,1, or 2.82,×,1019 and 1.38,×,1019,chains g,1, respectively. The characterization of the microspheres at various functionalization stages is performed via elemental analysis for the quantification of the grafting densities and attenuated total reflectance (ATR) IR spectroscopy as well as confocal microscopy for the analysis of the surface chemistry. [source]

A Random Sequential Adsorption Model for Protein Adsorption to Surfaces Functionalized with Poly(ethylene oxide)

ADVANCED MATERIALS, Issue 16 2009
Parag Katira
A random sequential adsorption model for the adsorption of proteins to surfaces functionalized with poly(ethylene oxide)/poly(ethylene glycol) at a range of molecular weights and grafting densities is presented. An excellent fit of the model predictions to experimental results suggests that the random arrangement of polymer chains leading to polymer-free "bald" spots is a critical factor in primary protein adsorption. [source]

Grafting polymer chains bearing an N -succinimidyl activated ester end-group onto primary amine-coated silica particles and application of a simple, one-step approach via nitroxide-mediated controlled/living free-radical polymerization

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2010
Julien Parvole
Abstract In a first part, the alkoxyamine initiator derived from BlocBuilder® based on the nitroxide SG1 and bearing an N -succinimidyl ester function was used to synthesize a variety of well-defined polymers with the activated ester group at the ,-end. The grafting of those polymer chains onto primary-amine functionalized Stöber silica particles was performed in soft conditions at room temperature and was studied as a function of the polymer chain length, the type of solvent, and the concentrations of both polymer and amine. Polymer grafting densities were mainly in the 0.1,0.2 chain nm,2 range. To increase the grafting density in simple experimental conditions, a direct one-step method was then proposed: the primary-amine modified silica, the N -succinimidyl ester functionalized alkoxyamine, and the monomer were all introduced into the reaction medium at once. This technique allowed grafting and chain growth to take place simultaneously at the polymerization temperature (i.e., 120 °C for styrene), in a single step, and produced hybrid particles with very high grafting density, up to 0.9 chain nm,2, and long polymer chains. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 173,185, 2010 [source]

Quantification of Grafting Densities Achieved via Modular "Grafting-to" Approaches onto Divinylbenzene Microspheres

Reactive Imprint Lithography: Combined Topographical Patterning and Chemical Surface Functionalization of Polystyrene- block -poly(tert -butyl acrylate) Films

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2010
Joost Duvigneau
Abstract Here, reactive imprint lithography (RIL) is introduced as a new, one-step lithographic tool for the fabrication of large-area topographically patterned, chemically activated polymer platforms. Films of polystyrene- block -poly(tert -butyl acrylate) (PS- b -PtBA) are imprinted with PDMS master stamps at temperatures above the corresponding glass transition and chemical deprotection temperatures to yield structured films with exposed carboxylic acid and anhydride groups. Faithful pattern transfer is confirmed by AFM analyses. Transmission-mode FTIR spectra shows a conversion of over 95% of the tert -butyl ester groups after RIL at 230,°C for 5 minutes and a significantly reduced conversion to anhydride compared to thermolysis of neat films with free surfaces in air or nitrogen. An enrichment of the surface layer in PS is detected by angle-resolved X-ray photoelectron spectroscopy (XPS). In order to demonstrate application potentials of the activated platforms, a 7,nm,±,1,nm thick NH2 -terminated PEG layer (grafting density of 0.9 chains nm,2) is covalently grafted to RIL-activated substrates. This layer reduces the non-specific adsorption (NSA) of bovine serum albumin by 95% to a residual mass coverage of 9.1,±,2.9,ng cm,2. As shown by these examples, RIL comprises an attractive complementary approach to produce bio-reactive polymer surfaces with topographic patterns in a one-step process. [source]

Grafting polymer chains bearing an N -succinimidyl activated ester end-group onto primary amine-coated silica particles and application of a simple, one-step approach via nitroxide-mediated controlled/living free-radical polymerization

Simultaneous reversible addition fragmentation chain transfer and ring-opening polymerization

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2008
Maude Le Hellaye
Abstract The simultaneous ring-opening polymerization (ROP) of ,-caprolactone (,-CL) and 2-hydroxyethyl methacrylate (HEMA) polymerization via reversible addition fragmentation chain transfer (RAFT) chemistry and the possible access to graft copolymers with degradable and nondegradable segments is investigated. HEMA and ,-CL are reacted in the presence of cyanoisopropyl dithiobenzoate (CPDB) and tin(II) 2-ethylhexanoate (Sn(Oct)2) under typical ROP conditions (T > 100 °C) using toluene as the solvent in order to lead to the graft copolymer PHEMA- g -PCL. Graft copolymer formation is evidenced by a combination of size-exclusion chromatography (SEC) and NMR analyses as well as confirmed by the hydrolysis of the PCL segments of the copolymer. With targeted copolymers containing at least 10% weight of PHEMA and relatively small PHEMA backbones (ca. 5,000,10,000 g mol,1) the copolymer grafting density is higher than 90%. The ratio of free HEMA-PCL homopolymer produced during the "one-step" process was found to depend on the HEMA concentration, as well as the half-life time of the radical initiator used. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3058,3067, 2008 [source]

Switchable thin-film surface prepared via a simple grafting-to method using a polystyrene- b -poly(2-vinylpyridine) copolymer

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2006
Ying Wang
Abstract A polystyrene- b -poly(2-vinylpyridine) block copolymer containing a methylhydridosilane linking group was chemically grafted to an 8-trichlorosilyloctene monolayer via a simple one-step hydrosilylation reaction. The resulting Y-shaped thin film exhibited a low grafting density, which was characteristic of the grafting-to technique. To further reduce the miscibility of the two arms, methyl iodide was reacted with the poly(2-vinylpyridine) block to produce quaternary ammonium groups. The surfaces before and after quaternization were both solvent-switchable when subjected to block-selective solvents. Tensiometry, ellipsometry, attenuated total reflection/Fourier transform infrared, and atomic force microscopy were used to characterize the properties and morphology of both unquaternized and quaternized samples. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5608,5617, 2006 [source]

Formation of Inorganic/Organic Nanocomposites by Nitroxide-Mediated Polymerization in Bulk Using a Bimolecular System

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 10 2004
Julien Parvole
Abstract Summary: A series of organic-inorganic nanoparticles were synthesized by nitroxide-mediated polymerization (NMP) of butyl acrylate initiated by a self-assembled monolayer of an azo initiator. The azo initiator was immobilized on silica particles in the presence of a stable nitroxide radical, SG1 (an acyclic , -phosphonylated nitroxide, N - tert -butyl- N -(1-diethylphosphono-2,2-dimethyl)propyl nitroxide). After preliminary qualitative characterization by X-ray spectroscopy (XPS) and Fourier-transform infrared (FTIR) measurements, the nanoparticles were studied by thermogravimetric analysis (TGA) to determine the polymer grafting density and to permit a comparison with corresponding values of the initiator monolayer. It was demonstrated that the grafting from polymerization exhibits a controlled character with a low polydispersity (,<,1.2) in a large range of molecular weights of the grafted chains (from 4,000 up to 145,000 g,·,mol,1) under the conditions when the stable radical SG1, acting as chain growth moderator tethered to the inorganic core, was used. [source]

Grafted Polymer Chains Interacting with Substrates: Computer Simulations and Scaling

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2008
Radu Descas
Abstract We review scaling methods and computer simulations used in the study of the static and dynamic properties of polymer chains tethered to adsorbing surfaces under good solvent conditions. By varying both the grafting density and the monomer/surface interactions a variety of phases can form. In particular, for attractive interactions between the chains and the surface the classical mushroom-brush transition known for repulsive substrates splits up into an overlap transition and a saturation transition which enclose a region of semidilute surface states. At high grafting densities oversaturation effects and a transition to a brush state can occur. We emphasize the role of the critical adsorption parameters for a correct description and understanding of such polymer adsorption phenomena. [source]

Normal and Lateral Deformation of Lyotropically Ordered Polymer Brush

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2006
Alexey A. Polotsky
Abstract Summary: Planar polymer brush formed by semirigid chains of freely jointed rigid segments and immersed into a solvent is considered. Brush collapse induced by deterioration of the solvent quality and its deformation by external normal or lateral force is studied. It is demonstrated that these three different situations can be described in the framework of the common approach. It is shown that the collapse is accompanied by liquid-crystalline (LC) ordering within the brush. The LC transition can be jump-like (the first order) or continuous, depending on the segment's aspect ratio and grafting density. Transition point is investigated in detail, the corresponding phase diagrams are calculated. It is shown that the phase diagrams of a normally deformed brush have different structures, with a narrow ,leg' in the good solvent region for sparsely grafted brush, with two coexistence regions and a triple point, in addition, for shorter segment length or without these features if the chains are densely grafted. For the laterally deformed brush, phase diagrams have similar structures with a critical point in the good solvent regime. Polymer brush subjected to deformation by normal (top) and lateral (bottom) external force. [source]

Structure of Polymer Brushes in Cylindrical Tubes: A Molecular Dynamics Simulation

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 7 2006
Dimitar I. Dimitrov
Abstract Summary: Molecular dynamics simulations of a coarse-grained bead-spring model of flexible macromolecules tethered with one end to the surface of a cylindrical pore are presented. Chain length N and grafting density , are varied over a wide range and the crossover from "mushroom" to "brush" behavior is studied for three pore diameters. The monomer density profile and the distribution of the free chain ends are computed and compared to the corresponding model of polymer brushes at flat substrates. It is found that there exists a regime of N and , for large enough pore diameter where the brush height in the pore exceeds the brush height on the flat substrate, while for large enough N and , (and small enough pore diameters) the opposite behavior occurs, i.e. the brush is compressed by confinement. These findings are used to discuss the corresponding theories on polymer brushes at concave substrates. Snapshot picture of a brush grafted inside of a cylinder, for , , displaying different chains in distinct colors in order to be able to distinguish them. Top shows a side view of the cylinder, and the lower part a view of the cross-section. Note that the particles forming the cylindrical wall are not displayed. [source]

Surface-initiated nitroxide-mediated polymerization: a tool for hybrid inorganic/organic nanocomposites ,in situ' synthesis

POLYMER INTERNATIONAL, Issue 10 2006
Leïla Ghannam
Abstract Hybrid silica particles comprised of an inorganic core and an organic polymer shell can be synthesized by surface-initiated nitroxide-mediated polymerization (SINMP) in the presence of a grafted alkoxyamine as initiator. The layer of initiator molecules attached or adsorbed to the particles surface is based on a nitroxide group. The synthesis and characterization of these alkoxyamine structures are briefly described. The grafted initiator particles are studied in order to determine the nature of the anchorage sites and the grafting density. With a stable radical or nitroxide as chain-growth moderator tethered to the inorganic core, it was demonstrated that the grafting from or to SINMP exhibits a control character with a very low polydispersity and good agreement between theoretical/experimental molecular weights. A comparative review of different alkoxyamines with a bimolecular system based on a grafted azoic initiator in the presence of an acyclic ,-phosphonylated nitroxide called SG1 is also described. Moreover, original methods for the synthesis of alkoxyamine grafted surface by in situ trapping of carbon radicals and some new developments for colored pigments will be reported. These topics could be one of the directions of the field in the next years. Copyright © 2006 Society of Chemical Industry [source]

Dendrimer-grafted cell adhesion peptide,modified PDMS

BIOTECHNOLOGY PROGRESS, Issue 4 2008
A. S. Mikhail
Abstract Surface concentration of cell adhesion peptides is thought to play a role in the interactions between biomaterials and cells. The high density of functional groups at the periphery of dendrimers has been exploited in various applications, but their full potential for generating surfaces with high functional group concentrations has not yet been realized. Poly(dimethylsiloxane) elastomers were surface modified with both polyethylene oxide (PEO) and generation 3 diaminobutane dendrimers. PEO and the dendrimers were subsequently used as linker molecules for surface grafting of cell adhesion peptides. ATR-FTIR, X-ray photoelectron spectroscopy, and water contact angle results confirmed the successful attachment of the polymer linkers and peptides. Peptide grafting density was quantified by means of 125I radiolabeling. Maximum surface peptide grafting density on dendrimer-modified surfaces was twofold greater than the maximum peptide grafting density achieved via the PEO linker. However, vascular endothelial cell adhesion was significantly greater on surfaces modified with the PEO linker, presumably due to the highly flexible PEO spacer making the peptide more accessible for binding with the cell surface receptors. These results suggest that, although peptide surface density may be important, optimizing surface density may not be sufficient for improving biological interactions. [source]