Self-assembly of catecholic macroinitiator on various substrates and surface-initiated polymerization

A catechol-containing macroinitiator has been designed for the surface-initiated atom transfer radical polymerization (SI-ATRP) from various substrates at ambient temperature. Temperature-sensitive poly(N-isopropyl acrylamide) (PNIPAM) brushes were successfully grafted from a range of substrates surfaces, including metals and polyimides, via SI-ATRP using the resulting macroinitiator, which were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle measurements, and atomic force microscopy (AFM). Effects of the temperature response behavior of PNIPAM brushes on the water contact angles and the impedance of the modified surfaces were also exhibited. The self-assembled film of macroinitiator and the resulting polymer brushes were both stable to soaking of basic solvents, and the brushes did not show any exfoliation or delamination even after 2 h of ultrasonic test. The advantages of the macroinitiator in strong interactions with surfaces and high stability and convenience make it possible to modify the native materials with polymer brushes in a convenient and nondestructive way. Importantly, the macroinitiator is compatible with microcontact printing, and patterned polymer brushes on Ti plate were demonstrated by microcontact printing of BrDOPAMA and the following SI-ATRP.     

Synthesis and characterization of surface-grafted polyacrylamide brushes and their inhibition of microbial adhesion

A method is presented to prevent microbial adhesion to solid surfaces exploiting the unique properties of polymer brushes. Polyacrylamide (PAAm) brushes were grown from silicon wafers by atom transfer radical polymerization (ATRP) using a three-step reaction procedure consisting of immobilization of a coupling agent gamma-aminopropyltriethoxysilane, anchoring of an ATRP initiator 4-(chloromethyl)benzoyl chloride, and controlled radical polymerization of acrylamide. The surfaces were characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, ellipsometry, and contact-angle measurements. The calculated grafting density pointed to the presence of a dense and homogeneous polymer brush. Initial deposition rates, adhesion after 4 h, and detachment of two bacterial strains (Staphylococcus aureus ATCC 12600 and Streptococcus salivarius GB 24/9) and one yeast strain (Candida albicans GB 1/2) to both PAAm-coated and untreated silicon surfaces were investigated in a parallel plate flow chamber. A high reduction (70-92%) in microbial adhesion to the surface-grafted PAAm brush was observed, as compared with untreated silicon surfaces. Application of the proposed grafting method to silicone rubbers may offer great potential to prevent biomaterials-centered infection of implants.     

Spectroscopic Investigation of Polypeptide Plane Brushes

Fourier transform infrared spectroscopy (FTIR) was used for determination of orientational and conformational characteristics of plane polypeptide brushes with different density of polypeptide chains grafted to modified silicon surface. The determination of grafting density of polypeptide chains in brushes, which depends on chemical structure of spacer groups, was carried out using ultraviolet (UV) spectroscopy. The influence of chemical structure of modifying spacer groups and outer conditions on the characteristics of plane polypeptide brushes was established. The peculiarities of α-helical structure (random coil transfer of polymer chains in brushes under the action of denaturants) were investigated.     

Stimuli-responsive polyelectrolyte polymer brushes prepared via atom-transfer radical polymerization

We present an account of our research into polyelectrolyte polymer brushes that are capable of acting as stimuli-responsive films. We first detail the synthesis of poly(acrylic acid) polymer brushes using ATRP in a "grafting from" strategy. Significantly, we employed a chemical-free deprotection step that should leave the anchoring ester groups intact. We have demonstrated how these polymer assemblies respond to stimuli such as pH and electrolyte concentration. We have used poly(acrylic acid) polymer brushes for the synthesis of metallic nanoparticles and review this work. We have used XPS, ATR-FTIR, and AFM spectroscopy to show the presence of silver and palladium nanoparticles within polymer brushes. Finally, we report the synthesis of AB diblock polyampholyte polymer brushes that represent an extension of polyelectrolyte polymer brushes.     

Internal Architecture of Zwitterionic Polymer Brushes Regulates Nonfouling Properties

In this work, we study how film thickness and chain packing density affect the protein‐resistant properties of polymer brushes in complex media. Polymer brushes based on dual‐functional poly(carboxybetaine acrylamide) (pCB) were prepared via surface‐initiated photoiniferter‐mediated polymerization. By adjusting UV radiation time and solvent polarity, pCB films with different thicknesses can be achieved and characterized using an ellipsometer. The packing density of pCB polymer chains is directly related to the swelling ratio of swollen to collapsed film thicknesses. Results showed that the dry film thickness alone, used often in the literature, is not sufficient to correlate with nonfouling properties and the chain packing density must be considered for the design of nonfouling surface coatings.     

Polymer-modified opal nanopores

The surface of nanopores in opal films, assembled from 205 nm silica spheres, was modified with poly(acrylamide) brushes using surface-initiated atom transfer radical polymerization. The colloidal crystal lattice remained unperturbed by the polymerization. The polymer brush thickness was controlled by polymerization time and was monitored by measuring the flux of redox species across the opal film using cyclic voltammetry. The nanopore size and polymer brush thickness were calculated on the basis of the limiting current change. Polymer brush thickness increased over the course of 26 h of polymerization in a logarithmic manner from 1.3 to 8.5 nm, leading to nanopores as small as 7.5 nm.     

Neutral and charged polymer brushes at solid surfaces

Neutral and charged polymer brushes covalently attached to planar solid surfaces were generated by using self-assembled monolayers of an azo initiator and radical chain polymerization in situ. The brushes were characterized by FTIR-spectroscopy, optical waveguide-spectroscopy and Ellipsometry. Especially the film thicknesses of surface bound polyelectrolyte (PEL) monolayers were measured by optical waveguide spectroscopy (OWS) as a function of the humidity of the environment. The PEL brushes show strong increases in thickness as well as strong decrease of the refractive index of the surface attached layer due to water incorporation caused by the exposure to the humid environment. Additionally the behavior of neutral as well as charged brushes in contact with solvent was investigated by using multiple-angular-scans of ellipsometry in a total internal reflectance setup. The scaling behavior of the brush height as a function of the graft density of the attached polymer molecules was investigated for the neutral brush as well as for the PEL brush system.     

Multicomponent polymer brushes

This article describes a general synthetic route to laterally distinctive multicomponent polymer brushes on gold. The procedure involves repeated surface patterning using microcontact printing (muCP) of initiator-terminated thiols without backfilling with inert thiols and surface-initiated atomic transfer radical polymerization steps. In between brush growth, the remaining initiator moieties are deactivated to avoid reinitiation on existing brushes. Optical and fluorescence microscopy, atomic force microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy have been used to characterize every step of this procedure. We found that brushes can be grown from initiator-modified surfaces that contain bare gold areas and that these areas remain available for further patterning using muCP. To demonstrate the flexibility of this approach, surfaces containing four different polymer brushes in patterns ranging from 2 x 4 microm lines to 20 x 20 microm squares were fabricated. The range of chemical functionalities incorporated includes cationic and anionic polyelectrolytes, as well as thermally responsive polymers.     

Synthesis and characterization of surface‐initiated polymer brushes on silicon substrates by reversible addition fragmentation chain transfer polymerization

Polymer brushes were prepared by using the reversible addition fragmentation chain transfer (RAFT) technique. The silicon substrates (Si (111) surface) were modified with ethyl xanthate groups which were introduced by the treatment of Si (111) surface with sodium ethyl xanthate. The polymer brushes were then prepared under RAFT conditions from the Si (111) wafer. Its “living” characteristics were determined by a series of characterizations including gel permeation chromatography (GPC), ellipsometry, and contact angle measurements. The results showed a well‐defined graft layer consisting of polymer brushes with low‐polydispersity could be prepared directly on Si (111)‐X surface (where X represents an ethyl xanthate groups). The structure of the polymer brushes was characterized and confirmed with the surface sensitive techniques such as X‐ray photoelectron spectroscopy (XPS) and scanning probe microscopy (SPM). Copyright © 2007 John Wiley & Sons, Ltd.     

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.     

Perfluorocarbon thin films and polymer brushes on stainless steel 316 L for the control of interfacial properties

Perfluorocarbon thin films and polymer brushes were formed on stainless steel 316 L (SS316L) to control the surface properties of the metal oxide. Substrates modified with the films were characterized using diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), contact angle analysis, atomic force microscopy (AFM), and cyclic voltammetry (CV). Perfluorooctadecanoic acid (PFOA) was used to form thin films by self-assembly on the surface of SS316L. Polypentafluorostyrene (PFS) polymer brushes were formed by surface-initiated polymerization using SAMs of 16-phosphonohexadecanoic acid (COOH-PA) as the base. PFOA and PFS were effective in significantly reducing the surface energy and thus the interfacial wetting properties of SS316L. The SS316L control exhibited a surface energy of 38 mN/m compared to PFOA and PFS modifications, which had surface energies of 22 and 24 mN/m, respectively. PFOA thin films were more effective in reducing the surface energy of the SS316L compared to PFS polymer brushes. This is attributed to the ordered PFOA film presenting aligned CF(3) terminal groups. However, PFS polymer brushes were more effective in providing corrosion protection. These low-energy surfaces could be used to provide a hydrophobic barrier that inhibits the corrosion of the SS316L metal oxide surface.     

High density cationic polymer brushes from combined “click chemistry” and RAFT‐mediated polymerization

A simple method for preparing cationic poly[(ar‐vinylbenzyl)trimethylammonium chloride)] [poly(VBTAC)] brushes was used by combined technology of “click chemistry” and reversible addition‐fragmentation chain transfer (RAFT) polymerization. Initially, silicon surfaces were modified with RAFT chain transfer agent by using a click reaction involving an azide‐modified silicon wafer and alkyne‐terminated 4‐cyanopentanoic acid dithiobenzoate (CPAD). A series of poly(VBTAC) brushes on silicon surface with different molecular weights, thicknesses, and grafting densities were then synthesized by RAFT‐mediated polymerization from the surface immobilized CPAD. The immobilization of CPAD on the silicon wafer and the subsequent polymer formation were characterized by X‐ray photoelectron spectroscopy, water contact angle measurements, grazing angle‐Fourier transform infrared spectroscopy, atomic force microscopy, and ellipsometry analysis. The addition of free CPAD was required for the formation of well‐defined polymer brushes, which subsequently resulted in the presence of free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface. In addition, by varying the polymerization time, we were able to obtain poly(VBTAC) brushes with grafting density up to 0.78 chains/nm² with homogeneous distributions of apparent needle‐like structures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Surface-confined photopolymerization of pH-responsive acrylamide/acrylate brushes on polymer thin films

Dynamic acrylamide/acrylate polymeric brushes were synthesized at gold-plated quartz crystal surfaces. The crystals were initially coated with polystyrene-type thin films, derivatized with photolabile iniferter groups, and subsequently subjected to photoinitiated polymerization in acrylamide/acrylate monomer feeds. This surface-confined polymerization method enabled direct photocontrol over the polymerization, as followed by increased frequency responses of the crystal oscillations in a quartz crystal microbalance (QCM). The produced polymer layers were also found to be highly sensitive to external acid/base stimuli. Large oscillation frequency shifts were detected when the brushes were exposed to buffer solutions of different pH. The dynamic behavior of the resulting polymeric brushes was evaluated, and the extent of expansion and contraction of the films was monitored by the QCM setup in situ in real time. The resulting responses were rapid, and the effects were fully reversible. Low pH resulted in full contractions of the films, whereas higher pH yielded maximal expansion in order to minimize repulsion around the charged acrylate centers. The surfaces also proved to be very robust because the responsiveness was reproducible over many cycles of repeated expansion and contraction. Using ellipsometry, copolymer layers were estimated to be approximately 220 nm in a collapsed state and approximately 340 nm in the expanded state, effectively increasing the thickness of the film by 55%.     

Novel approach for metallic surface-initiated atom transfer radical polymerization using electrografted initiators based on aryl diazonium salts

This paper reports on the preparation of poly(methyl methacrylate) (PMMA), poly(n-butyl acrylate) (PBA), and polystyrene (PS) brushes at the surface of conducting materials that were modified by the electrochemical reduction of a brominated aryl diazonium salt BF4-, +N2-C6H4-CH(CH3)-Br (D1). The grafted organic species -C6H4-CH(CH3)-Br was found to be very effective in initiating atom transfer radical polymerization (ATRP) of vinyl monomers. This novel approach combining diazonium salts and ATRP allowed PMMA, PBA, and PS brushes to be grown from the surface of iron electrodes. The polymer films were characterized in terms of their chemical structure by infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy. Atomic force microscopy studies indicated that the polymer brushes are densely packed. Contact angle measurements of water drops on PS and PMMA brushes were 88.1 +/- 2.0 and 70.3 +/- 2.1 degrees, respectively, which is consistent with the published wettability data for the corresponding polymer sheets.     

Three‐dimensional Arrangement of Short DNA Oligonucleotides at Surfaces via the Synthesis of DNA‐branched Polyacrylamide Brushes by SI‐ATRP

Short DNA oligonucleotide branches are incorporated into acrylamide brushes via surface initiated atom transfer radical polymerization in an attempt to increase DNA surface density by building three‐dimensional molecular architectures. ATR‐FTIR as well as hybridization studies followed by SPR confirm the incorporation of the DNA sequences into the polymer backbone. MALDI‐TOF analysis further suggests that six acrylamide monomer units are typically separating DNA branches present on a single brushes approximately 26 units long. This new approach offers a promising alternative to SAM‐based nucleic acid and aptamer sensors and could enable the realization of more complex soft materials of controlled architecture capable of both recognition and signaling by including additional optically or electrochemically active moieties.

     

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.     

Au/聚4-乙烯基吡啶-b-聚乙二醇嵌段聚合物刷的合成及其pH响应行为

作为受限高分子体系的一个经典模型,高分子刷在胶体稳定、聚合物链的自组装以及摩擦学等方面具有潜在的应用价值。 本文通过原子转移自由基聚合(ATRP)和点击化学(Click Chemistry)方法在金(Au)基底表面制备了pH响应性聚4-乙烯基吡啶-b-聚乙二醇(P4VP-b-PEG)嵌段聚合物刷。 通过频率-耗散型石英微天平(QCM-D)、X射线光电子能谱(XPS)和原子力显微镜(AFM)等技术手段分别对Au/P4VP-b-PEG聚合物刷经不同pH值溶液处理后的形态变化、表面组成和表面形貌进行了进一步深入研究。 结果表明,用不同pH值溶液处理P4VP-b-PEG嵌段聚合物刷后,该聚合物刷呈现刺激响应规律。 当pH=1.5时,P4VP链段质子化,由于静电排斥作用使P4VP-b-PEG链段呈伸展构象;当pH=11.5时,P4VP链段去质子化,并且由于失去部分结合水,P4VP-b-PEG链段呈塌缩构象。     

Synthesis of patterned polymer brushes from flexible polymeric films

Surface-initiated polymerizations were carried out from polymeric surfaces of commercially important polyester films, poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN). These plastic films were modified prior to polymerization by plasma oxidation, exposing surface hydroxyl groups, in order to immobilise patterned self assembled monolayers (SAMs) of trichlorosilane initiator, through the soft lithographic method of microcontact printing (μCP). Subsequently, polymerizations were initiated from the surface via controlled atom transfer radical polymerization (ATRP), under aqueous conditions, to create patterned brushes of the thermo-responsive polymer poly(N-isopropyl acrylamide) (PNIPAM). By creating patterned, rather than homogeneous brushes characterization was made possible by atomic force microscopy (AFM).     

Surface-initiated PET-RAFT polymerization under metal-free and ambient conditions using enzyme degassing

An open-to-air method for the efficient synthesis of surface-tethered polymer brushes based on photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization is reported. Key to this approach is an enzyme-assisted strategy using glucose oxidase to facilitate the in situ removal of oxygen during the polymerization process. Control experiments in the absence of glucose oxidase confirm the importance of enzymatic deoxygenation for successful polymerization of a variety of acrylamide, methacrylate, and acrylate monomers. In accordance with controlled polymerization kinetics, a linear increase in brush height as a function of irradiation time for a range of light intensities is demonstrated. Importantly, the use of light to mediate growth and the inherent monomer versatility of PET-RAFT allow for the facile fabrication of well-defined polymer brushes under aqueous conditions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 70–76     

Molecular brushes with long polyfluorene backbones and polymethacrylic acid side chains: Luminescent properties and self-organization in solutions

A series of molecular brushes with a polyfluorene (PF) backbone and polymethacrylic acid side chains of varying lengths were prepared by atom transfer radical polymerization. The structure and composition of the synthesized compounds were confirmed by ¹H NMR and IR spectroscopy. Effect of the length of the backbone on spectral and conformational parameters of the macromolecules in solutions was analyzed. The grafting density of side chains was about 90%. Spectral methods have been used to determine the dependence of side chain grafting on the luminescent properties of polymer solutions, including quantum yields. It was shown that an optimal length of polymethacrylic acid side chains provides solubility of the polymer brushes. Solutions of PF-graft-polymethacrylic acid complexes with the model substance curcumin were investigated. It was established that the molecular brushes containing curcumin form monomolecular micelles. Molecular brushes with zinc phthalocyanine, potential systems for photodynamic, and photothermal therapy, were studied.