Formation of polyacrylate brushes on silica surfaces

cited By 52International audienceWe report the formation of polyacrylate (molten state polymers: Tg <room temperature) monolayers attached onto silica surfaces using covalently bonded initiators for radical-chain polymerisation. In a first reaction step, the initiator is self-assembled on the surface. In a subsequent reaction, the initiator is activated and the polymer formed in situ at the surface of the substrate with high grafting density ('grafting from' procedure). Moreover, the use of a living free radical process permits the molecular weight and polydispersity of the polymer chains to be controlled, and thus the polymer monolayer thickness also. We have also made a preliminary qualitative characterisation by X-ray spectroscopy (XPS) and Fourier transformed infrared (FTIR) measurements. © 2002 Society of Chemical Industry

Block copolymer grafted-silica particles: A core/double shell hybrid inorganic/organic material

cited By 74International audienceHybrid inorganic/organic materials consisting of a poly(n-butyl acrylate)-b-poly(styrene) diblock copolymer anchored to silica particles were synthesized via 'grafting from' technique using a controlled/living free radical polymerization named stable free radical polymerization. XPS and FTIR analysis were used to control the effectiveness of the chemical modification of the silica particles. Thermal characterizations were performed by thermal gravimetric analysis (TGA) and by differential scattering calorimetry (DSC). The TGA permitted the determination of the quantity of grafted polymer and thus the grafting density; DSC was used to study the influence of the silica and blocks of the copolymer on their thermal behaviors. The glass transition temperature of the grafted copolymers was compared to these of free polymers or copolymers homologues. © 2004 Elsevier Ltd. All rights reserved

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

cited By 41International audienceHybrid 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 β-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. © 2006 Society of Chemical Industry

Surface initiated polymerization of poly (butyl acrylate) by nitroxide mediated polymerization: First comparative polymerization of a bimolecular and a unimolecular initiator-grafted silica particles

cited By 40International audienceHybrid silica-particles comprising an inorganic core and an organic polymer shell have been synthesized by nitroxide mediated polymerization of butyl acrylate in the presence of a grafted alkoxyaroine. The layer of initiator molecules attached to the surface of silica is based on an acyclic β-phosphonylated nitroxide alsqreferred to SGL. The synthesis and the characterization by NMR of this aikoxyamine structure are briefly described. Moreover, the grafted initiator particles have been studied by XPS, NMR 29Si CP/ MAS, and TGA in order to determine the nature of the anchorage sites and the grafting density. With this stable radical as chain growth mctderator tethered to the inorganic core, it is demonstrated that the grafting from polymerization exhibits a control character with a: very low polydispersity index (I < 1.1). For the first time, a comparative study with a btmo-lecular System based on a grafted azoic initiator in presence of SG1 is also described, A different kinetic behavior has been demonstrated and interpreted in terms of variation of the initial [monamer]/[imtiator] ratio. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Choose sides: Differential polymer adhesion

cited By 18International audienceAFM-based single molecule desorption measurements were performed on surface end-grafted poly(acrylic acid) monolayers as a function of the pH of the aqueous buffer to study the adhesion properties of polymers that bridge two surfaces. These properties were found to depend on the adhesion forces of both surfaces in a differential manner, which is explained with a simple model in analogy to the Bell-Evans formalism used in dynamic force spectroscopy. The measured interaction forces between the poly(acrylic acid) chains and silicon nitride AFM tips depend on the grafting density of the polymer monolayers as well as on the contour length of the polymer chains. This study demonstrates that the stability of polymer bridges is determined by the adhesion strengths on both surfaces, which can be tuned by using pH-dependent polyelectrolyte monolayers. © 2007 American Chemical Society

Initiator-Grafted Silica Particles for Controlled Free Radical Polymerization: Influence of the Initiator Structure on the Grafting Density

cited By 63International audienceA series of organic-inorganic hybrid particles were synthesized by a self-assembled layer of different initiators, immobilized on silica particles and used for controlled radical polymerization. We use three different initiator systems for atom-transfer radical polymerization (ATRP), unimolecular nitroxide mediated polymerization (NMP), and bimolecular NMP, for the development of the hybrid inorganic/organic particles. After preliminary qualitative characterization by X-ray spectroscopy (XPS) and Fourier-transformed infrared (FT-IR) measurements, the hybrid nanoparticles were studied by thermogravimetric analysis (TGA) to determine and discuss the initiator graft density in terms of steric hindrance

AFM-based single molecule force spectroscopy of end-grafted poly(acrylic acid) monolayers

cited By 45International audienceAFM-based single molecule force spectroscopy has been applied to study the detachment of poly(acrylic acid) (PAA) chains preadsorbed onto a silicon nitride tip surface at varied pH. In particular, monolayers of end-grafted chains prepared by nitroxide-mediated polymerization initiated from silica substrates were brought into close contact with the silicon nitride tip of an AFM. The detachment of PAA chains from the tip surface is reflected by a set of constant-force plateaus in the AFM force spectra. From those, comprehensive information about the molecular length distribution of surface-grafted polymers, about their conformation, and about their interaction with the tip as a function of pH is deduced. At neutral pH, the plateau-length distribution well reproduces the molecular weight distribution of the grafted polymers as obtained by GPC. At high pH, increasing electrostatic repulsion between PAA and the tip surface reduces the strength of adsorption, which is manifested in a decrease of average plateau lengths and measured detachment forces. At low pH, complex force spectra and a bimodal distribution of apparent molecular lengths are obtained, reflecting the poor solubility of protonated PAA chains in water as well as polymer-substrate interactions. © 2006 American Chemical Society

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.

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