Synthesis Of Polymer Brushes Research Articles

The Kinetics of Polymer Brush Growth in the Frame of the Reaction Diffusion Front Formalism

We studied the properties of a reaction front that forms in irreversible reaction–diffusion systems with concentration-dependent diffusivities during the synthesis of polymer brushes. A coarse-grained model of the polymerization process during the formation of polymer brushes was designed and investigated for this purpose. In this model, a certain amount of initiator was placed on an impenetrable surface, and the “grafted from” procedure of polymerization was carried out. The system consisted of monomer molecules and growing chains. The obtained brush consisted of linear chains embedded in nodes of a face-centered cubic lattice with excluded volume interactions only. The simulations were carried out for high rafting densities of 0.1, 0.3, and 0.6 and for reaction probabilities of 0.02, 0.002, and 0.0002. Simulations were performed by means of the Monte Carlo method while employing the Dynamic Lattice Liquid model. Some universal behavior was found, i.e., irrespective of reaction rate and grafting density, the width of the reaction front as well as the height of the front show for long times the same scaling with respect to time. During the formation of the polymer layer despite the observed difference in dispersion of chain lengths for different grafting densities and reaction rates at a given layer height, the quality of the polymer layer does not seem to depend on these parameters.

Synthesis of Polymer Brushes and Removable Surface Nanostructures on Tannic Acid Coatings

Polymer brushes refer to polymer chains that are end-grafted to surfaces or interfaces at high grafting density. Polymer brushes are able to make surface self-assembly or surface coassembly with free block copolymer (BCP) chains, and surface nanostructures with different morphologies are formed on the surfaces. The formation of the surface nanostructures endows materials with new surface properties. To develop a simple and versatile approach to the synthesis of polymer brushes and surface nanostructures, the synthesis of polymer brushes and surface nanostructures on tannic acid (TA) coatings was investigated in this research. TA molecules were coated on the surfaces of amino-modified silica particles (SiO2-NH2) through noncovalent bonds. Quaternized poly(2-(dimethylamino)ethyl methacrylate)-block-polystyrene (qPDMAEMA-b-PS) chains were anchored onto the TA coatings through electrostatic interaction between qPDMAEMA blocks and TA coatings, and PS brushes are formed on the particle surfaces. Thermo gravimetric analysis demonstrates the grafting of the BCP chains on the TA coatings, and the calculation results indicate that the PS chains on the silica particles are in the polymer brush regime. PS brushes on TA coatings are able to make surface coassembly with free BCP chains, and surface nanostructures with different sizes and morphologies are produced on TA coatings. The grafting density of PS blocks and BCP concentration both exert significant influences on the formation of the surface nanostructures. The surface nanostructures can be removed from the particle surfaces in the aqueous solution of sodium chloride. This research provides a simple and versatile method for the fabrication of polymer brushes and removable surface nanostructures on any solid substrates, which have specific interactions with TA molecules.

Synthesis of end group-functionalized PGMA-peptide brush platforms for specific cell attachment by interface-mediated dissociative electron transfer reversible addition-fragmentation chain transfer radical (DET-RAFT) polymerization

Polymer brush synthesis is a powerful approach to fabricate functional bio-interfaces. To enhance the control over brush synthesis and end groups, we have synthesized poly(glycidyl methacrylate) PGMA brushes with carboxylic acid end functional groups by interface-mediated dissociative electron transfer reversible addition-fragmentation chain transfer radical (DET-RAFT) polymerization on titanium surfaces. This method does not require the use of metals and occurs under mild conditions. The brushes obtained were analyzed comprehensively in order to understand how to control cell attachment behavior. The PGMA brushes synthesized by DET-RAFT polymerization were characterized by X-ray photoelectron spectroscopy (XPS), grazing angle Fourier transform infrared (GA-FTIR) spectroscopy, water contact angle measurements and variable angle spectroscopic ellipsometry. The terminal carboxylic acid functional groups were covalently conjugated with arginine-glycine-aspartic acid (RGD) and arginine-alanine-aspartic acid (RAD, negative control) peptides in one step. RGD selective attachment of NIH 3T3 fibroblasts was observed exclusively on PGMA-RGD brushes. Thus, a new versatile strategy has been validated to obtain functional biointerfaces for selective cell attachment in the absence of any metallic catalyst.

Synthesis of Polymer Brushes by Surface-Initiated Controlled/Living Free Radical Polymerization Techniques

The surface modifications are necessary to alter the inherent surface physical/chemical properties of materials in terms of adhesion, wettability, friction, biocompatibility etc. for using in textile, electronic and biomedical industries. Surface modifications are usually made by grafting of polymer brushes to the solid substrates. The grafting process allows controlling and manipulation of surface properties without changing the chemical structure of polymers. Besides their chemical structures, grafting density of polymer brushes and average distance between the polymer chains attached to the surface are also important parameters, affecting the intended use of the grafted materials. Synthesis of functional polymer brushes is generally carried out by one of surface-initiated controlled/living free radical polymerization techniques, namely Atom Transfer Radical Polymerization (ATRP), Nitroxide-Mediated Polymerization (NMP), Photoiniferter-Mediated Polymerization (PIMP) and Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT). This review reports the strategies of these techniques for generating polymer brushes and summarizes the application of polymer brushes in multiple fields.

Comparison of Long-Term Stability of Initiating Monolayers in Surface-Initiated Controlled Radical Polymerizations.

The reproducibility of polymer brush synthesis via surface-initiated controlled radical polymerization is interrogated. Experiments compare the stability of initiating monolayers for surface-initiated (SI) reversible addition-fragmentation chain transfer polymerization (SI-RAFT) and SI atom transfer radical polymerization (SI-ATRP). Initiator-functionalized substrates are stored under various conditions and grafting densities of the resulting polymer brush films are determined via in situ ellipsometry. Decomposition of one of the examined SI-RAFT initiators results in limited reproducibility for polymer brush surface modification. In contrast, initiators for SI-ATRP show excellent stability and reproducibility. While both techniques bring inherent benefits and limitations, the described findings will help scientists choose the most efficient technique for their goals in chemical and topographical surface modification.

Surface-Initiated Photoinduced ATRP: Mechanism, Oxygen Tolerance, and Temporal Control during the Synthesis of Polymer Brushes

Surface-initiated, photoinduced atom transfer radical polymerization (SI-photoATRP) enables the controlled and rapid synthesis of compositionally diverse polymer brushes over large areas by employing very small reaction volumes under ambient conditions and without the need for prior deoxygenation of monomer mixtures. The concentration of copper species and the type and content of amine-based ligands determine the mechanism of SI-photoATRP, regulate the kinetics of polymer-brush growth, and govern the tolerance of this polymer-grafting method toward oxygen. Despite mechanistic analogies with the corresponding solution processes, the intrinsic, highly confined nature of SI-photoATRP leads to significant differences from polymerizations within homogeneous systems. This is especially important to attain controlled/living polymerization and temporal control over polymer-brush growth by using UV light as a trigger.

Chemical Surface Modification of Polymeric Biomaterials for Biomedical Applications.

This review focuses on the attachment of polymer brushes to polymeric biomaterial substrates by chemical surface modification methods for biomedical applications. In the first part of this paper, a general introduction to the synthesis of polymer brushes is given. Thereafter, a comprehensive overview of recent work on the chemical surface modification of polymeric biomaterials, with a focus on "grafting-to," "grafting-from," and "grafting-through" strategies, is provided. Finally, some representative cutting-edge biomedical applications of modified polymeric biomaterials, mainly including antifouling materials and biocompatible materials, are highlighted. On the basis of this literature study, a perspective on future trends in this field is provided.

Preparation of poly(N-isopropylacrylamide) by interface-mediated dissociative electron transfer reversible addition–fragmentation chain transfer (IMDET-RAFT) polymerization technique

N-isopropylacrylamide was successfully polymerized on silicon disc surfaces at room temperature by interface-mediated dissociative electron transfer reversible addition–fragmentation chain transfer (IMDET-RAFT) polymerization. The IMDET-RAFT technique was used for the first time to synthesize polymer brushes with a new mechanism using inorganic sulfides without using metal at room temperature. The polymerization was well controlled and the PNIPAAm brushes were successfully grown on silicon disc surfaces. The presence of sulfur atoms at the chain end was demonstrated by XPS experiments to demonstrate the controlled nature of the polymerization. Polymer brushes synthesized by IMDET-RAFT technique have high grafting density and grafting density was found to be 0.76 chain/nm2. This study is thought to be an important alternative to the new generation controlled/living polymerization, especially for RAFT polymerization techniques used in polymer brush synthesis. PNIPAAm brushes synthesized with IMDET-RAFT technique are an important starting point for future studies in terms of the synthesis of polymer brushes with IMDET-RAFT technique using a wide range of monomers both at ambient temperature and metal free. It is believed that this technique has the potential to be used in the future, especially in the preparation of temperature sensitive surfaces, bio-application studies and many surface modifications. In this study, application of silicon disc surfaces IMDET-RAFT polymerization was used for the first time to afford preparation of well-defined poly (NIPAAm) brushes at ambient temperature.

A photo-selective chain-end modification of polyacrylate-iodide and its application in patterned polymer brush synthesis

A photo-selective chain-end modification of polyacrylate-iodide (polymer-I) was developed. The method was used to generate chain-end patterned polymer brushes.

Photo-Controlled Organocatalyzed Living Radical Polymerization and Its Application to Polymer Brush Synthesis on Surface

Photo-Controlled Organocatalyzed Living Radical Polymerization and Its Application to Polymer Brush Synthesis on Surface

Polymer brush synthesis on surface modified carbon nanotubes via in situ emulsion polymerization

In situ emulsion polymerization was employed for synthesizing carbon nanotube (CNT) composites in a colloidal system with poly(styrene) or PS to form nanostructured brush. CNTs were initially functionalized with oleic acid, followed by silanization with (3-aminopropyl) triethoxysilane to impart cross-linking properties. Styrene monomers were efficiently grafted to surface modified CNT via emulsion polymerization with variable CNT concentrations. FTIR analyses of the functionalized CNT and PS/CNT composites confirmed the bond formation and effectiveness of the developed experimental method. X-ray photoelectron spectroscopy confirmed the presence of the desired bonds and the composition of the composites. Structural properties of the composites characterized by TEM confirmed excellent deagglomeration and dispersion of CNTs in PS/CNT composite. Thermal characteristics from TGA and DSC data showed enhanced properties for the nanocomposites as a function of the CNT content. BET measurements indicated significant improvements in surface area and pore volume with enhancements in gas sorption for the polymer nanocomposites.

Review on Polymer Brush Synthesis Via Controlled Radical Polymerization Technique

Review on Polymer Brush Synthesis Via Controlled Radical Polymerization Technique

Towards controlled polymer brushes via a self-assembly-assisted-grafting-to approach.

Precise synthesis of polymer brushes to modify the surface of nanoparticles and nanodevices for targeted applications has been one of the major focuses in the community for decades. Here we report a self-assembly-assisted-grafting-to approach to synthesize polymer brushes on flat substrates. In this method, polymers are pre-assembled into two-dimensional polymer single crystals (PSCs) with functional groups on the surface. Chemically coupling the PSCs onto solid substrates leads to the formation of polymer brushes. Exquisite control of the chain folding in PSCs allows us to obtain polymer brushes with well-defined grafting density, tethering points and brush conformation. Extremely high grafting density (2.12 chains per nm2) has been achieved in the synthesized single-tethered polymer brushes. Moreover, polymer loop brushes have been successfully obtained using oddly folded PSCs from telechelic chains. Our approach combines some of the important advantages of conventional ‘grafting-to' and ‘grafting-from' methods, and is promising for tailored synthesis of polymer brushes.

Stable Poly(methacrylic acid) Brush Decorated Silica Nano-Particles by ARGET ATRP for Bioconjugation

The synthesis of polymer brush decorated silica nano-particles is demonstrated by activator regeneration by electron transfer atom transfer radical polymerization (ARGET ATRP) grafting of poly(tert-butyl methacrylate). ATRP initiator decorated silica nano-particles were obtained using a novel trimethylsiloxane derivatised ATRP initiator obtained by click chemistry. Comparison of de-grafted polymers with polymer obtained from a sacrificial initiator demonstrated good agreement up to 55% monomer conversion. Subsequent mild deprotection of the tert-butyl ester groups using phosphoric acid yielded highly colloidal and pH stable hydrophilic nano-particles comprising approximately 50% methacrylic acid groups. The successful bio-conjugation was achieved by immobilization of Horseradish Peroxidase to the polymer brush decorated nano-particles and the enzyme activity demonstrated in a conversion of o-phenylene diamine dihydrochloride assay.

Methods of controlled radical polymerization for the synthesis of polymer brushes

Methods for the synthesis of polymer (molecular) brushes via various controlled-radical-polymerization approaches are considered, and their properties are analyzed. Special attention is paid to atomtransfer radical polymerization, which is most frequently used for these purposes. The potential of the synthesis of molecular brushes with various chemical structures, including amphiphilic brushes, is demonstrated in many examples.

Polymer Brushes: Promises and Challenges

Surface-tethered polymers, or "polymer brushes", are emerging as key elements in the context of regulating the surface characteristics of materials. Their properties, such as biocompatibility, antifouling, colloidal stability, wettability, and corrosion resistance, play a vital role in ascertaining their potential applications. The availability of straightforward procedures for polymer brush synthesis, which are applicable to a wide range of monomers and are adaptable to a range of substrates, is a clear advantage over other surface-modification strategies. Herein, the important advancements that are pertinent to the fabrication of polymer brushes are outlined. Furthermore, an exhaustive up-to-date overview of the developments in different application domains, including smart drug-delivery systems, biosensing, antifouling, stimuli-responsive surfaces, and ion-conducting membranes, that benefit from the developments in the field of polymer brushes, is presented.

Rapid, simple, and cost-effective treatments to achieve long-term hydrophilic PDMS surfaces

This paper describes rapid, simple, and cost-effective treatments for producing biocompatible and long-term hydrophilic polydimethylsiloxane (PDMS) surfaces identified in an experimental study investigating 39 treatments in all. The wetting of the surfaces was monitored during six months. Changes in surface morphology and chemical composition were also analyzed. Some of the treatments are presented here for the first time, while for earlier presented treatments the selection of investigated parameters was wider and the observation period for the surface wetting longer. The PDMS surfaces were modified by surface activation, physisorption, and synthesis of both “grafting to” and “grafting from” polymer brushes. In surface activation, the PDMS sample was exposed to oxygen plasma, with several combinations of exposure time and RF power. In the physisorption and synthesis of polymer brushes, three commercially available and biocompatible chemicals were used: 2-hydroxyethyl methacrylate (HEMA), polyethylene glycol (PEG), and polyvinylpyrrolidone (PVP). Thirty-three of the 39 treatments rendered the PDMS hydrophilic, and in 12 cases the hydrophilicity lasted at least six months. Seven of these long-term hydrophilic coatings supported a contact angle of 30° or less. Three of the long-lasting hydrophilic coatings required only minutes to prepare.

Surface-Initiated Group Transfer Polymerization Mediated by Rare Earth Metal Catalysts

We present the first example of a surface-initiated group transfer polymerization (SI-GTP) mediated by rare earth metal catalysts for polymer brush synthesis. The experimentally facile method allows rapid grafting of polymer brushes with a thickness of >150 nm in <5 min at room temperature. We show the preparation of common poly(methacrylate) brushes and demonstrate that SI-GTP is a versatile route for the preparation of novel polymer brushes. The method gives access to both thermoresponsive and proton-conducting brush layers.

The induction of thrombus generation on nanostructured neutral polymer brush surfaces

Surface induced thrombus generation is a major clinical concern associated with vascular medical devices and implants. Here, we show that high graft density hydrophilic non-charged poly (N,N-dimethylacrylamide) (PDMA) brushes prevent the initiation of blood coagulation on synthetic surfaces. Using a multi-faceted analysis approach, we have identified that PDMA brushes greater than 0.27 chains/nm 2 graft density showed this highly desired property. Non-specific protein adsorption is greatly reduced on high density brushes compared to bare surface as evident from isothermal titration calorimetry, gel electrophoresis, and proteomic analyses. We have identified approximately 129 proteins of various types on bare and PDMA brush coated surfaces at a range of surface concentrations. Thromboelastography, platelet activation, and aggregation analyses show that only high graft density brushes are neutral to blood coagulation. Since the polymer brush synthesis can be adapted to most currently used biomedical materials, these results have significant impact in the design of highly hemocompatible surfaces.

Synthesis of surface‐initiated polymer brushes using macro‐initiators

AbstractThe synthesis of polymer brushes using surface‐adsorbed macro‐initiators is briefly reviewed, with particular emphasis being placed on the combination of atom transfer radical polymerisation with polyelectrolytic macro‐initiators. The latter contain 2‐bromoester initiator groups and can be readily prepared with either cationic or anionic character from (co)polymer precursors. Such macro‐initiators offer convenient functionalisation of a wide range of colloidal and planar charged surfaces such as silica, mica, alumina or tin(IV) oxide, since electrostatic adsorption occurs rapidly from aqueous solution at room temperature. A wide range of hydrophilic methacrylic polymer brushes have been grown from these macro‐initiators, offering potential applications in surface lubricity and tribology, tuneable surface (de)wetting and cell detachment. In some cases surface degrafting can occur if thicker polymer brushes are targeted. However, this problem can be circumvented if pairs of oppositely charged polyelectrolytic macro‐initiators are used to build up ionically crosslinked multilayers via layer‐by‐layer self‐assembly. This facile approach to surface functionalisation appears to be steadily growing in popularity and has now been adopted by a number of research groups in several countries. Copyright © 2009 Society of Chemical Industry