Controlled grafting of well-defined epoxide polymers on hydrogen-terminated silicon substrates by surface-initiated ATRP at ambient temperature

Facile Preparation of Epoxide-Functionalized Surfaces via Photocurable Copolymer Coatings and Subsequent Immobilization of Iminodiacetic Acids

Herein, we report a simple coat/cure preparation of epoxide-functionalized surfaces using a photocurable copolymer technology. The photocurable copolymer, poly(glycidyl methacrylate- co-butyl acrylate- co-4-benzoylphenyl methacrylate) (GBB), was synthesized by single electron transfer-living radical polymerization (SET-LRP). The epoxide content in the copolymer was tuned by controlling the content of glycidyl methacrylate. Three copolymers, GBB(1), GBB(2), and GBB(3), with epoxide contents of 22, 63, and 91 mol %, respectively, were cast onto polypropylene films and photocured by UV-light exposure. Subsequently, iminodiacetic acids (IDA) were immobilized onto the GBB-coated materials via a ring-opening reaction. The IDA-functionalized coatings GBB(1)-IDA, GBB(2)-IDA, and GBB(3)-IDA presented IDA contents of 1.47 ± 0.08, 18.67 ± 1.46, and 49.05 ± 2.88 nmol/cm², respectively, which increased as the epoxide content increased. The IDA-functionalized GBB coatings exhibited metal chelating capability toward transition metal ions (e.g., iron and copper). The reported photocurable copolymer technology offers a facile and tunable preparation of epoxide-functionalized surfaces, with potential extended applications in biopatterning, active packaging, and nanotechnology.

Dual-Gated Microparticles for Switchable Antibody Release

We pioneer the design of dual-gated microparticles, both responsive to changes in temperature and pH, for stimuli-responsive chromatography targeted at the efficient separation of antibodies. Dual-gated microspheres were synthesized by introducing RAFT-based thiol-terminal block copolymers of poly(N-isopropylacrylamide-b-4-vinylpyridine) (P(NIPAM-b-4VP, 4800 ≤ M_n/Da ≤ 10 000, featuring block length ratios of 29:7, 29:15, and 29:30, respectively) by thiol-epoxy driven ligation to the surface of poly(glycidyl methacrylate) (PGMA) microparticles (10-12 μm), whereby the 4-vinylpyridine units within the lateral chain enable protein binding. The switchable protein release abilities of the resulting microparticle resins are demonstrated by adsorption of immunoglobulins at 40 °C and pH 8 and their release at 5 °C or pH 3, respectively. We demonstrate that P(NIPAM₂₉-b-4VP₃₀)-grafted PGMA particles show a maximum adsorption capacity for immunoglobulins of 18.9 mg mL^-1 settled resin at 40 °C/pH 8, whereas the adsorption capacity decreased to 7.5 mg mL^-1 settled resin at 5 °C while retaining the pH value, allowing the unloading of the chromatographic column by a facile temperature switch. Critically, regeneration of the dual-gated microspheres became possible by lowering the pH to 3.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Surface-Initiated ARGET ATRP of Poly(Glycidyl Methacrylate) from Carbon Nanotubes via Bioinspired Catechol Chemistry for Efficient Adsorption of Uranium Ions

Surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) integrated with mussel-inspired polydopamine (PDA) chemistry was, for the first time, employed for controlled grafting of poly(glycidyl methacrylate) (PGMA) brushes from carbon nanotubes (CNTs). The strategy initially involved deposition of a PDA layer by spontaneous self-polymerization, which is a benign and nonsurface specific way for anchoring 2-bromoisobutyryl bromide to form initiators on the CNTs. Dense and uniform PGMA brushes were then grown via ARGET ATRP using low concentration of Cu catalyst in different solvents. With abundant highly reactive epoxy groups, the PGMA-grafted CNTs could serve as a versatile platform for further modification or functionalization. Ethylenediamine ligands were facilely introduced, imparting the functionalized CNTs with record-high adsorption ability toward uranium ions among CNTs composites. The integrated strategy combining surface-initiated ARGET ATRP technique and PDA chemistry would provide new opportunities for surface engineering of nanomaterials for advanced applications.

Tuning the growth, crosslinking, and gating effect of disulfide-containing PGMAs on the surfaces of mesoporous silica nanoparticles for redox/pH dual-controlled cargo release

PGMA brushes grown on MSN surfaces via SI-ATRP could be cross-linked by cystamine or through a KI/H₂O₂ (30%) assisted disulfide bond exchange to realize gating effects for redox/pH dual-controlled cargo release.

Uptake of Fe(iii), Ag(i), Ni(ii) and Cu(ii) by salicylic acid-type chelating resin prepared via surface-initiated atom transfer radical polymerization

With chloromethylated PS being the base material, a new type of ASA/PGMA/PS resin with high capacity was prepared by grafting GMA on the surface of the resin via surface-initiated atom transfer radical polymerization and followed by the derivatization with 5-ASA.

Design of enzyme-immobilized polymer brush-grafted magnetic nanoparticles for efficient nematicidal activity

Parasitic nematodes adversely affect agricultural industry and global health. An efficient and reusable nematicidal platform is developed by immobilization enzyme on the surface of magnetic NPs.

Adsorption of sterically stabilized latex particles at liquid surfaces: effects of steric stabilizer surface coverage, particle size, and chain length on particle wettability

A series of five near-monodisperse sterically stabilized polystyrene (PS) latexes were synthesized using three well-defined poly(glycerol monomethacrylate) (PGMA) macromonomers with mean degrees of polymerization (DP) of 30, 50, or 70. The surface coverage and grafting density of the PGMA chains on the particle surface were determined using XPS and (1)H NMR spectroscopy, respectively. The wettability of individual latex particles adsorbed at the air-water and n-dodecane-water interfaces was studied using both the gel trapping technique and the film calliper method. The particle equilibrium contact angle at both interfaces is relatively insensitive to the mean DP of the PGMA stabilizer chains. For a fixed stabilizer DP of 30, particle contact angles were only weakly dependent on the particle size. The results are consistent with a model of compact hydrated layers of PGMA stabilizer chains at the particle surface over a wide range of grafting densities. Our approach could be utilized for studying the adsorption behavior of a broader range of sterically stabilized inorganic and polymeric particles of practical importance.

Peptide immobilisation on porous silicon surface for metal ions detection

In this work, a Glycyl-Histidyl-Glycyl-Histidine (GlyHisGlyHis) peptide is covalently anchored to the porous silicon PSi surface using a multi-step reaction scheme compatible with the mild conditions required for preserving the probe activity. In a first step, alkene precursors are grafted onto the hydrogenated PSi surface using the hydrosilylation route, allowing for the formation of a carboxyl-terminated monolayer which is activated by reaction with N-hydroxysuccinimide in the presence of a peptide-coupling carbodiimide N-ethyl-N'-(3-dimethylaminopropyl)-carbodiimide and subsequently reacted with the amino linker of the peptide to form a covalent amide bond. Infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy are used to investigate the different steps of functionalization.The property of peptides to form stable complexes with metal ions is exploited to achieve metal-ion recognition by the peptide-modified PSi-based biosensor. An electrochemical study of the GlyHisGlyHis-modified PSi electrode is achieved in the presence of copper ions. The recorded cyclic voltammograms show a quasi-irreversible process corresponding to the Cu(II)/Cu(I) couple. The kinetic factors (the heterogeneous rate constant and the transfer coefficient) and the stability constant of the complex formed on the porous silicon surface are determined. These results demonstrate the potential role of peptides grafted on porous silicon in developing strategies for simple and fast detection of metal ions in solution.

Functionalization of regenerated cellulose membrane via surface initiated atom transfer radical polymerization for boron removal from aqueous solution

In this study, an adsorptive membrane was prepared for efficient boron removal. Poly(glycidyl methacrylate) was grafted on the surfaces of the regenerated cellulose (RC) membrane via surface-initiated atom transfer radical polymerization, and N-methylglucamine was used to further react with epoxide rings to introduce polyhydroxyl functional groups, which served as the major binding sites for boron. The pristine and modified membranes were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), dynamic water contact angle measurement, and scanning electron microscopy. It was shown that the designed functional groups were successfully grafted onto the RC membrane, and surface modification contributed to higher boron binding capability. The optimal pH range for boron adsorption was 4-8. Under a neutral pH condition, the maximum adsorption capacity of the modified membrane was determined to be 0.75 mmol/g, which was comparable with those of commercial resins. Studies of electrolyte influence indicated the formation of inner-sphere surface complexes on the membrane surface. The ATR-FTIR and XPS analyses showed that secondary alcohol and tertiary amine groups were mainly involved in boron adsorption, and tetrahedral boron complexes were found on the membrane surface.

Direct photochemical functionalization of Si(111) with undecenol

Direct UV photochemical functionalization of H-terminated Si(111) with bifunctional 10-undecen-1-ol was achieved with selective attachment via its vinyl end, resulting in the formation of a compact monolayer with free terminal alcohol groups. This is due to the faster radical propagation mechanism in hydrosilylation with alkene compared to the nucleophilic attack mechanism of alcohol, which is impeded by intermolecular hydrogen bonding present at room temperature. Evidence from X-ray photoelectron spectroscopy, infrared spectroscopy, and resistance to fluoride etching shows that Si-C is the interfacial bond, and atomic force microscopy shows the presence of a smooth, uniform monolayer conforming to the atomic terraces of the Si(111) surface. The application of such a hydroxyl-terminated monolayer was demonstrated by tethering a bromoinitiator through surface esterification and thereafter subjecting the surface to the surface-initiated atom-transfer radical polymerization of butyl methacrylate. The poly(butyl methacrylate) brushes formed were found to be smooth (R(a) < 0.3 nm) and uniform even for a thin film of 4.0 nm.

Tris(hydroxymethyl)aminomethane-functionalized silica particles and their application for hydrophilic interaction chromatography

A new method is presented for synthesizing a highly hydrophilic silica-based material for use in hydrophilic interaction chromatography. Porous silica particles used as a starting substrate were modified with 3-bromopropyl trichlorosilane and grafted with glycidyl methacrylate by controlled ("living") atom transfer radical polymerization in order to introduce an oxirane-carrying reactive tentacle layer on the silica surface. The grafted material was thereafter subject to an oxirane ring opening reaction with tris(hydroxy-methyl)aminomethane in dimethylformamide to yield a polymer-bound equivalent of the well known and highly hydrophilic "TRIS" buffering substance. Chemical characterization was done by diffuse reflectance FT-IR, X-ray photoelectron spectroscopy, elemental analysis, and (1)H NMR. Porosity and surface area examination was done with Brunauer-Emmett-Teller. Chromatographic application of the material was evaluated by separations of nucleic bases, small organic acids, and common nucleotides under mixed hydrophilic interaction chromatography and weak anion exchange conditions.

Room temperature, aqueous post-polymerization modification of glycidyl methacrylate-containing polymer brushes prepared via surface-initiated atom transfer radical polymerization

This manuscript reports on the post-polymerization modification of poly(glycidyl methacrylate) (PGMA) and PGMA-co-poly(2-(diethylamino)ethyl methacrylate) (PGMA(x)-co-PDEAEMA(y)) (co)polymer brushes prepared via surface-initiated atom transfer radical polymerization (SI-ATRP). The aim of this study was to evaluate the ability of tertiary amine groups incorporated in the polymer brush to accelerate the ring-opening of the epoxide groups by primary amines and to facilitate the aqueous, room temperature post-polymerization modification of the brushes. Using Fourier transform infrared (FTIR) spectroscopy to monitor the ring-opening reaction of the epoxide groups, it was found that the incorporation of 2-(diethylamino)ethyl methacrylate (DEAEMA) groups in the PGMA brushes significantly accelerated the rate of the post-polymerization modification reaction with several model amines. The rate enhancement was dependent on the fraction of DEAEMA units incorporated in the copolymer brush. For example, whereas 24 h was necessary to obtain a conversion of approximately 40% for PGMA brushes immersed in a 1 M propylamine solution in water, the same conversion was reached, in identical reaction conditions, after 8 and 2 h with copolymer brushes containing 10 mol % and 25 mol % of DEAEMA along the copolymer chains, respectively. In a final series of proof-of-concept experiments, the feasibility of the glycidyl methacrylate containing brushes to act as substrates for protein immobilization was studied. Using FTIR spectroscopy and quartz crystal microbalance with dissipation (QCM-D) experiments, it could be demonstrated that the incorporation of DEAEMA units not only enhanced the rate of the protein immobilization reaction, but also resulted in higher protein binding capacities as compared to a PGMA homopolymer brush. These features make PGMA(x)-co-PDEAEMA(y) brushes very attractive candidates for the development of protein microarrays, among others.

Fabrication of thermoresponsive polymer gradients for study of cell adhesion and detachment

A poly(N-isopropylacrylamide) (PNIPAAm) gradient covalently anchored on a silicon substrate with a linear variation of thickness was fabricated by continuous injection of the reaction mixture (NIPAAm, CuBr and its ligand, methanol, and water) into a glass chamber containing a silicon wafer, whose surface had been homogeneously immobilized with bromoisobutyryl bromide (BIBB). Because of the good control of the surface-initiated atom transfer radical polymerization (SI-ATRP) technique, the thickness of the PNIPAAm brushes was linearly proportional to the polymerization time. As a result, the gradient length and sharpness could be easily controlled by the experimental parameters such as the polymerization time and the injection rate. The as-prepared PNIPAAm gradients were characterized by ellipsometry, water contact angle, and atom force microscopy to detect their alteration of the thickness, surface wettability, and morphology, confirming the gradient structure. X-ray photoelectron spectroscopy confirmed the surface composition of the PNIPAAm. In vitro culture of HepG2 cells was implemented on the gradient surfaces, revealing that the cells could adhere at 37 degrees C and could be detached at 24 degrees C when the gradient thickness was in the range of 20-45 nm. The work thus develops a method to fabricate the stable gradient surface with better quality control, and clarifies in a facile manner the appropriate thickness of the PNIPAAm brushes in terms of cell adhesion and detachment.

Construction of a comb-like glycosylated membrane surface by a combination of UV-induced graft polymerization and surface-initiated ATRP

Carbohydrate residues are found on the extracellular side of the cell membrane. They form a protective coating on the outer surface of the cell and are involved in intercellular recognition. Synthetic carbohydrate-based polymers, so-called glycopolymers, are emerging as important well-defined tools for investigating carbohydrate-based biological processes and for simulating various functions of carbohydrates. In this work, the surface of a polypropylene microporous membrane (PPMM) was modified with comb-like glycopolymer brushes by a combination of UV-induced graft polymerization and surface-initiated atom-transfer radical polymerization (ATRP). 2-Hydroxyethyl methacrylate (HEMA) was first grafted to the PPMM surface under UV irradiation in the presence of benzophenone and ferric chloride. ATRP initiator was then coupled to the hydroxyl groups of poly(HEMA) brushes. Surface-initiated ATRP of a glycomonomer, D-gluconamidoethyl methacrylate, was followed at ambient temperature in aqueous solvent. Water had a significant acceleration effect on the ATRP process; however, loss of control over the polymerization process was also observed. The addition of CuBr2 to the ATRP system largely increased the controllability at the cost of the polymerization rate. The grafting of HEMA, the coupling of ATRP initiator to the hydroxyl groups, and the surface-initiated ATRP were confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.

Detailed Structural Examinations of Covalently Immobilized Gold Nanoparticles onto Hydrogen-Terminated Silicon Surfaces

The modification of flat semiconductor surfaces with nanoscale materials has been the subject of considerable interest. This paper provides detailed structural examinations of gold nanoparticles covalently immobilized onto hydrogen-terminated silicon surfaces by a convenient thermal hydrosilylation to form Si-C bonds. Gold nanoparticles stabilized by omega-alkene-1-thiols with different alkyl chain lengths (C3, C6, and C11), with average diameters of 2-3 nm and a narrow size distribution were used. The thermal hydrosilylation reactions of these nanoparticles with hydrogen-terminated Si(111) surfaces were carried out in toluene at various conditions under N2. The obtained modified surfaces were observed by high-resolution scanning electron microscopy (HR-SEM). The obtained images indicate considerable changes in morphology with reaction time, reaction temperature, as well as the length of the stabilizing omega-alkene-1-thiol molecules. These surfaces are stable and can be stored under ambient conditions for several weeks without measurable decomposition. It was also found that the aggregation of immobilized particles on a silicon surface occurred at high temperature (> 100 degrees C). Precise XPS measurements of modified surfaces were carried out by using a Au-S ligand-exchange technique. The spectrum clearly showed the existence of Si-C bonds. Cross-sectional HR-TEM images also directly indicate that the particles were covalently attached to the silicon surface through Si-C bonds.