Universal surface-initiated polymerization of antifouling zwitterionic brushes using a mussel-mimetic peptide initiator

We report a universal method for the surface-initated polymerization (SIP) of an antifouling polymer brush on various classes of surfaces, including noble metals, metal oxides, and inert polymers. Inspired by the versatility of mussel adhesive proteins, we synthesized a novel bifunctional tripeptide bromide (BrYKY) that combines atom-transfer radical polymerization (ATRP) initiating alkyl bromide with l-3,4-dihydroxyphenylalanine (DOPA) and lysine. The simple dip-coating of substrates with variable wetting properties and compositions, including Teflon, in a BrYKY solution at pH 8.5 led to the formation of a thin film of cross-linked BrYKY. Subsequently, we showed that the BrYKY layer initiated the ATRP of a zwitterionic monomer, sulfobetaine methacrylate (SBMA), on all substrates, resulting in high-density antifouling pSBMA brushes. Both BrYKY deposition and pSBMA grafting were unambiguously confirmed by ellipsometry, X-ray photoelectron spectroscopy, and goniometry. All substrates that were coated with BrYKY/pSBMA dramatically reduced bacterial adhesion for 24 h and also resisted mammalian cell adhesion for at least 4 months, demonstrating the long-term stability of the BrYKY anchoring and antifouling properties of pSBMA. The use of BrYKY as a primer and polymerization initiator has the potential to be widely employed in surface-grafted polymer brush modifications for biomedical and other applications.     

Reversible pH-controlled switching of poly(methacrylic acid) grafts for functional biointerfaces

Responsive polymeric brushes of poly(methacrylic acid) (PMAA) were grafted from silicon surfaces using controlled surface-initiated atom-transfer radical polymerization (SI-ATRP). The growth kinetics of PMAA was investigated with respect to the composition of the ATRP medium by grafting the polymer in mixtures of water and methanol with different ratios. The dissociation behavior of the polymer layers was characterized by FTIR titration after incubating the polymer-grafted substrates in PBS buffer solutions with different pH values. PMAA layers show a strong pH-dependent behavior with an effective pK(a) of the bulk polymer brush of 6.5 ± 0.2, which is independent of the polymer brush thickness and methanol content of the ATRP grafting medium. The pH-induced swelling and collapse of the grafted polymer layers were quantified in real time by in situ ellipsometry in liquid environment. Switching between polymer conformations at pH values of 4 and 8 is rapid and reversible, and it is characterized by swelling factors (maximum thickness/minimum thickness) that increase with decreasing the methanol content of the SI-ATRP medium.     

Facile surface immobilization of ATRP initiators on colloidal polymers for grafting brushes and application to colloidal crystals

Bromo-initiators for atom transfer radical polymerization (ATRP) were successfully immobilized on the surfaces of cross-linked poly(methyl methacrylate) (PMMA) spheres by soap-free emulsion polymerization using CBr(4) as the chain transfer agent. Subsequent surface-initiated ATRP (SI-ATRP) afforded a layer of PMMA brushes covalently attached to the sphere surfaces. Colloidal crystal films of these monodisperse spheres were then studied to identify the relationship between variation in particle diameter and the optical properties. The particle diameters were controlled by varying the feed monomer proportions in soap-free emulsion polymerization and the thickness of the grafted brush layer. It was found that the particle diameter could successfully be controlled to obtain crystal films that produce a variety of brilliant colors in the visible region. The results of this study can provide useful information for facile preparation of surface-immobilized ATRP initiators on colloidal polymers and can be employed for grafting polymer brushes.     

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

Controlled grafting of well-defined epoxide polymer brushes on the hydrogen-terminated Si(100) substrates (Si-H substrates) was carried out via the surface-initiated atom-transfer radical polymerization (ATRP) at room temperature. Thus, glycidyl methacrylate (GMA) polymer brushes were prepared by ATRP from the alpha-bromoester functionalized Si-H surface. Kinetic studies revealed a linear increase in GMA polymer (PGMA) film thickness with reaction time, indicating that chain growth from the surface was a controlled "living" process. The graft polymerization proceeded more rapidly in the dimethylformamide/water (DMF/H(2)O) mixed solvent medium than in DMF, leading to much thicker PGMA growth on the silicon surface in the former medium. The chemical composition of the GMA graft-polymerized silicon (Si-g-PGMA) surfaces were characterized by X-ray photoelectron spectroscopy (XPS). The fact that the epoxide functional groups of the grafted PGMA were preserved quantitatively was revealed in the reaction with ethylenediamine. The "living" character of the PGMA chain end was further ascertained by the subsequent growth of a poly(pentafluorostyrene) (PFS) block from the Si-g-PGMA surface, using the PGMA brushes as the macroinitiators.     

结构规整的高密度两亲性接枝聚合物刷的合成及其自组装研究

大分子单体通过两种可控聚合方法, 即开环易位聚合(ROMP)和原子转移自由基聚合(ATRP)的联用, 合成一种新型两亲性接枝聚合物刷. 具有高环张力的降冰片烯单侧链大分子单体norbornene-graft-poly(ε-caprolactone)/Br (PCL- NBE-Br)首先进行ROMP反应, 生成聚合物主链, 每个单体单元上含有一条PCL链和一个溴官能团; 然后用含溴的ROMP聚合物poly(norbornene)-graft-poly(ε-caprolactone)/Br (PCL-PNBE-Br)作为大分子引发剂引发单体2-(dimethyl- amino)ethyl methacrylate)的ATRP反应, 生成结构明确的高密度两亲性接枝聚合物刷poly(norbornene)-graft-poly(ε- caprolactone)/poly(2-(dimethylamino)ethyl methacrylate) (PCL-PNBE-PDMAEMA), 其主链每个单体单元上均含有一条疏水性PCL接枝链和一条亲水性PDMAEMA接枝链. 最后, 研究此类高密度两亲性接枝聚合物刷的自组装行为, 用动态激光光散射(DLS)研究其在混合溶剂(THF/H2O)中的胶束行为, 考察胶束溶液的浓度以及不同长度的亲水性接枝链对胶束尺寸的影响; 利用透射电镜(TEM)观察胶束为球形, 具有类似线团或草莓状的形态.     

Unprecedented covalently attached ATRP initiator onto OH-functionalized mica surfaces

Mica substrates were activated by a plasma method leading to OH-functionalized surfaces to which an atom transfer radical polymerization (ATRP) radical initiator was covalently bound using standard siloxane protocols. The unprecedented covalently immobilized initiator underwent radical polymerization with tert-butyl acrylate, yielding for the first time end-grafted polymer brushes that are covalently linked to mica. The initiator grafting on the mica substrate was confirmed by time-of-flight secondary ion mass spectrometry (TOF-SIMS), while the change in the water contact angle of the OH-activated mica surface was used to follow the change in surface coverage of the initiator on the surface. The polymer brush and initiator film thicknesses relative to the virgin mica were confirmed by atomic force microscopy (AFM). This was done by comparing the atomic step-height difference between a protected area of freshly cleaved mica and a zone exposed to plasma activation, initiator immobilization, and then ATRP.     

Stereoregulation of thermoresponsive polymer brushes by surface-initiated living radical polymerization and the effect of tacticity on surface wettability

In this study, stereocontrolled poly(N-isopropylacrylamide) (PIPAAm) brushes were grafted from surfaces by atom transfer radical polymerization (ATRP) in the presence of a Lewis acid, and the effect of PIPAAm brush tacticity on the thermoresponsive wettabiliy was investigated. PIPAAm grafted by ATRP in the presence of Y(OTf)(3) showed high isotacticity, while the control brush polymerized in the absence of Y(OTf)(3) was clearly atactic. The isotacticity and molecular weight of PIPAAm brushes were controlled by polymerization conditions. The wettability of isotactic PIPAAm-grafted surfaces decreased slightly below 10 °C, although the phase transition temperature of atactic surface was 30 °C, and the bulk isotactic polymer was water-insoluble between 5 and 45 °C.     

NHS-ester functionalized poly(PEGMA) brushes on silicon surface for covalent protein immobilization

Poly(PEGMA) homopolymer brushes were developed by atom transfer radical polymerization (ATRP) on the initiator-modified silicon surface (Si-initiator). Through covalent binding, protein immobilization on the poly(PEGMA) films was enabled by further NHS-ester functionalization of the poly(PEGMA) chain ends. The formation of polymer brushes was confirmed by assessing the surface composition (XPS) and morphology (atomic force microscopy (AFM), scanning electronic microscopy (SEM)) of the modified silicon wafer. The binding performance of the NHS-ester functionalized surfaces with two proteins horseradish peroxidase (HRP) and chicken immunoglobulin (IgG) was monitored by direct observation. These results suggest that this method which incorporates the properties of polymer brush onto the binding surfaces may be a good strategy suitable for covalent protein immobilization.     

Grafting acrylic polymers from flat nickel and copper surfaces by surface-initiated atom transfer radical polymerization

Acrylic polymers, including poly(methyl methacrylate), poly(2,2,2-trifluoroethyl methacrylate), poly( N,N'-dimethyaminoethyl methacrylate), and poly(2-hydroxyethyl methacrylate) were grafted from flat nickel and copper surfaces through surface-initiated atom transfer radical polymerization (ATRP). For the nickel system, there was a linear relationship between polymer layer thickness and monomer conversion or molecular weight of "free" polymers. The thickness of the polymer brush films was greater than 80 nm after 6 h of reaction time. The grafting density was estimated to be 0.40 chains/nm2. The "living" chain ends of grafted polymers were still active and initiated the growth of a second block of polymer. Block copolymer brushes with different block sequences were successfully prepared. The experimental surface chemical compositions as measured by X-ray photoelectron spectroscopy agreed very well with their theoretical values. Water contact angle measurements further confirmed the successful grafting of polymers from nickel and copper surfaces. The surface morphologies of all samples were studied by atomic force microscopy. This study provided a novel approach to prepare stable functional polymer coatings on reactive metal surfaces.     

Carbohydrate‐Responsive Surface Adhesion Based on the Dynamic Covalent Chemistry of Phenylboronic Acid‐ and Catechol‐Containing Polymer Brushes

A glue, based on dynamic covalent chemistry, with a strong adhesion (2.38 kg cm^?2), water resistance and carbohydrate responsive reversibility is presented. Using surface initiated atom transfer radical polymerization (SI‐ATRP), glass and silicon surfaces were coated with copolymers functionalized with phenylboronic acids and catechols. In combination with microcontact printing (μCP) these polymer brushes give access to a carbohydrate responsive “supramolecular Velcro”.     

Polymer brushes via surface-initiated polymerizations

Polymer brushes produced by controlled surface-initiated polymerization provide a route to surfaces coated with well-defined thin polymer films that are covalently bound to the substrate. All of the major controlled polymerization techniques have been applied to the synthesis of polymer brushes and examples of each are presented here. Many examples of brush synthesis in the literature have used the living atom transfer radical polymerization (ATRP) system, and in this tutorial review a particular focus is given to examples of this technique.     

Site-specific dense immobilization of antibody fragments on polymer brushes supported by silicone nanofilaments

For site-specific dense immobilization of antibodies on a solid support, we prepared phosphorylcholine copolymer brushes on silicone nanofilaments. The nanofilaments were prepared on a silicon wafer by treatment with trichloromethylsilane (MeSiCl 3). To generate Si-OH groups on the nanofilaments, O 2 plasma was irradiated on the surface. Initiators for atom transfer radical polymerization (ATRP) were then coupled on the filaments. Phosphorylcholine copolymer brushes were prepared by a "grafting from" process, and pyridyl disulfide groups were introduced into the polymer chains. F(ab') fragments were then specifically immobilized onto these surfaces via a thiol-disulfide interchange reaction. The amount of antibodies immobilized on the nanofilament-supported copolymer brushes was approximately 65 times greater than that on smooth wafer-supported copolymer brushes.     

Synthesis and characterization of surface-initiated polymer brush prepared by reverse atom transfer radical polymerization

Surface-initiated reverse atom transfer radical polymerization (reverse ATRP) technique was used to synthesize well-controlled nanostructure of polymer brushes from silicon wafer. Kinetic studies revealed a linear increase in polymer film thickness with reaction time, indicating that chain growth from surface was a controlled process with a “living” characteristic. This technique provides a simple and efficient approach to create various nanostructures of polymer brushes potentially used for designing nanodevices. Analysis of the polymer brush layers was conducted using ellipsometry, XPS, AFM and contact angle measurements, respectively.     

High capacity, charge-selective protein uptake by polyelectrolyte brushes

Surface plasmon resonance was used to measure binding of proteins from solution to poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes end-grafted from gold surfaces by atom transfer radical polymerization (ATRP). PDMAEMA brushes were prepared with a variety of grafting densities and degrees of polymerization. These brushes displayed charge selective protein uptake. The extent of uptake for net negatively charged bovine serum albumin (BSA) scaled linearly with the surface mass concentration of grafted PDMAEMA, regardless of grafting density. BSA was bound at a constant ratio of 120 DMAEMA monomer units per protein molecule for all brushes examined. The equivalent three-dimensional concentration of BSA bound in the brush (i.e., the bound BSA surface excess concentration divided by the brush thickness) decreased monotonically with decreasing grafting density. The concentration of BSA bound within brushes prepared at higher grafting densities was comparable with the aqueous protein solubility limit. BSA desorption from the brush required changes in solution pH and/or ionic strength to eliminate its net electrostatic attraction to PDMAEMA. Net positively charged lysozyme was completely rejected by the PDMAEMA brushes.     

To patterned binary polymer brushes via capillary force lithography and surface-initiated polymerization

An effective approach is described for the synthesis of binary patterned polymer brushes using a combination of capillary force lithography and surface-initiated polymerization. First, the approach calls for an ultrathin polystyrene (PS) mask to be deposited, in a pattern, over a surface to which a layer of polymerization initiator has already been anchored. Next, surface-initiated atom transfer radical polymerization (ATRP) is performed. This can graft the initial polymer brush onto those areas of the surface unprotected by the PS mask. After grafting is complete, the PS mask is removed and a second brush is synthesized on the newly exposed areas.     

Qualitative degradation of the pesticide coumaphos in solution,controlled aerosol,and solid phases on quaternary ammonium fluoride polymer brushes

With the growing demand for measurements of organophosphate (OP) pesticide use in agriculture along with the potential threat of OP‐based chemical warfare agents, there is a need for new devices or surfaces that can quickly degrade OPs into less toxic substances in a variety of environments. Using surface‐initiated atom transfer radical polymerization and post‐polymerization synthesis, we prepared a series of quaternary ammonium fluoride‐based polymer brushes designed to absorb and degrade OPs. Specifically, a polymer brush was formed using 2‐dimethylamino‐ethyl methacrylate (DMAEMA) as monomer, which, following post‐polymerization quaternization of the tertiary amine with alkylating agents and fluoride ion exchange, afforded the OP‐reactive polymer surfaces. Poly(DMAEMA) brushes were grown to thicknesses of ~100 nm on silicon wafers and glass slides and characterized by ellipsometry, atomic force microscopy, and Raman spectroscopy. Quaternization and subsequent ion exchange of the brushes were characterized by Raman spectroscopy and X‐ray photoelectron spectroscopy, respectively. The interaction of the brushes with OPs was evaluated using the OP‐based pesticide coumaphos, through the presence of the highly fluorescent degradation product chlorferon; analyzed qualitatively via fluorescence microscopy; and confirmed via nuclear magnetic resonance and mass spectrometry. We found that the fluoride form of the brush reliably degraded coumaphos deposited via controlled solution‐based applications and aerosol applications (electrohydrodynamic jetting) and from microcontact printing of the dried solid directly onto the brush. No degradation was seen for coumaphos deposited on poly(DMAEMA) or the iodide form of the quaternized brush. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and morphological study of thick benzyl methacrylate-styrene diblock copolymer brushes

We demonstrate, for the first time, the synthesis of model poly(benzyl methacrylate) [P(BnMA)] brushes of very high thickness (>300 nm) on silicon wafer. P(BnMA) brush is also synthesized from the surface of silica nanoparticles, from a covalently anchored initiator monolayer, using ambient temperature ATRP. The kinetic studies and block copolymerization from the surface anchored P(BnMA)-Br macroinitiator showed that the polymerization was controlled in nature. AFM, ellipsometry, and water contact angle were used for the characterization of the polymer brush. The grafting density of the P(BnMA) brush, formed by immersion in a dilute monomer solution, was relatively less (～11% less) in comparison to that obtained by immersion in neat monomer under similar conditions. The P(BnMA)-Br macroinitiator brushes were used to synthesize P(BnMA-b-S) diblock copolymer brushes by the ATRP of styrene at 95 °C. The P(BnMA-b-S) brushes showed stimulus response to a selective solvent and various nanopatterns were observed according to the composition of the block copolymer.     

A combinatorial approach to study solvent-induced self-assembly of mixed poly(methyl methacrylate)/polystyrene brushes on planar silica substrates: effect of relative grafting density

This article reports the study of the effect of relative grafting densities of two polymer chains on solvent-induced self-assembly of mixed poly(methyl methacrylate) (PMMA)/polystyrene (PS) brushes through a combinatorial approach. Gradient-mixed PMMA/PS brushes were synthesized from a gradient-mixed initiator-terminated monolayer by combining atom transfer radical polymerization (ATRP) and nitroxide mediated radical polymerization (NMRP) in a two-step process. The gradient-mixed initiator-terminated monolayer was fabricated by first formation of a gradient in density of an ATRP initiator through vapor diffusion followed by backfilling of an NMRP-initiator-terminated trichlorosilane. After treatment of a gradient-mixed brush whose PS Mn was slightly lower than that of PMMA with glacial acetic acid, a selective solvent for PMMA, relatively ordered nanodomains were observed in the region where the ratio of PS to PMMA grafting density (number of polymer chains/nm2) was in the range from 0.67 to 2.17 and the overall grafting density was approximately 0.85 polymer chains/nm2. Contact angle hysteresis were high (> or =40 degrees ) in this region and XPS studies confirmed that the PMMA chains were enriched at the outermost layer. The nanodomains are speculated to be of a micellar structure with PS chains forming the core shielded by PMMA chains.     

Polymer brushes on multiwalled carbon nanotubes by activators regenerated by electron transfer for atom transfer radical polymerization

The synthesis and characterization of multiwalled carbon nanotube (MWCNT) polymer brushes produced by activators regenerated by electron transfer (ARGET) in atom‐transfer radical polymerization (ATRP) was discussed. The polymer brushes were synthesized by esterification of the MWCNT carboxylic acid groups with hydroxyethyl‐2‐bromoisobutyrate and subsequently used in ARGET ATRP. This created a well defined living polymer brush carbon nanotube of comparatively low polydispersity and a polymer layer 10 nm thick. As, ARGET ATRP uses only minute concentrations of copper (II) catalyst, and is less sensitive to air compared to other living polymerization techniques, this process is a more industry‐compatible route for the commercialization of such materials. The structural and chemical properties were explored by a range of techniques including high resolution transmission electron microscopy, gel permeation chromatography, elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. In addition, the polymer brush nanotubes were explored for their potential use in films and as fillers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Nanomechanical properties of polymer brushes by colloidal AFM probes

Nanomechanical properties of end grafted polymer layers were studied by AFM based, colloidal probe compression measurements. Zwitterionic poly(sulfobetaine methacrylate) (PSBMA) brush was grafted from planar Si surface and poly(methyl methacrylate) (PMAA) brush was grown on colloidal probe by surface initiated atom transfer radical polymerization. PMAA brush was further modified with adhesion promoting arginyl-glycyl-aspartic acid (RGD) peptide sequences. Force–distance curves were obtained for systems where the polymer brushes were probed on unmodified surfaces or face to each other. For each systems the grafting density of the polymer brush was determined applying a ‘box’ like polymer brush model based on the theory by de Gennes. ‘Average’ grafting density was calculated in cases when two polymer brushes face each other: RGD functionalized PMAA or PMAA against PSBMA. For our systems the values for the grafting density was between 0.04 and 0.11 nm^?2. Furthermore the measured approach force–distance curves were fitted according to the Hertz model and the apparent Young’s modulus was determined for all measurements being in a range of around 250 kPa at physiological conditions.