Synthesis, characterization and application of well-defined environmentally responsive polymer brushes on the surface of colloid particles

Well-defined poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) brushes with high density were synthesized on the surface of polystyrene latex by atom transfer radical polymerization (ATRP) using acetone/water as the solvent and CuCl/CuCl₂/bpy as the catalyst. It was found that the polydispersity of PDMAEMA brushes decreased with the increasing external CuCl₂ concentration. The polymer brushes showed their lower critical solution temperature (LCST) at 31 and 33 °C under pH values of 10.0 and 8.0, respectively. Dynamic light scattering studies demonstrate that PDMAEMA brushes were pH- and salt-responsive. PDMAEMA domains were used as the nanoreactors to generate gold nanoparticles on the surface of colloid particles. TEM results indicate that monodispersed gold nanoparticles were obtained. These gold composite nanoparticles displayed effective catalytic activity in the reduction of 4-nitrophenol by NaBH₄.     

Elastomer polymer brushes on flat surface by bimolecular surface-initiated nitroxide mediated polymerization

The method of formation of well-defined polymer brushes based on the nitroxide mediated polymerization (NMP) of n-butyl acrylate (BA) initiated from a self-assembled mono-layers (SAMs) of an azoic initiator in the presence of a stable nitroxide radical is described. After preliminary qualitative characterization by X-ray photoelectron spectroscopy, the samples were studied by ellipsometry in order to determine the dry film thickness (initiator and polymer) and the grafting density of macromolecular chains. It is demonstrated, that in the presence of stable counter radical SG1, acting as chain growth moderator, the surface initiated NMP exhibits a living/controlled character permitting to control architectural parameters (e.g. degree of polymerization) of elastomer grafted polymer chains. The possibility to use the living control character of this type of polymerization to re-initiate grafted chains in order to increase the thickness of an elastomer thin film with conservation of the brushes regime has been demonstrated.     

Memory effect in polymer brushes containing pendant carbazole groups

Poly(9-(2-(4-vinyl(benzyloxy)ethyl)-9H-carbazole)) (PVBEC) brushes, have been successfully prepared on the silicon surfaces via surface-initiated atom transfer radical polymerization (ATRP). Conductance switching at a voltage of about −2.1 V is observed in the memory device based on the PVBEC brushes. The fabricated device shows the good memory characteristics as the ON/OFF current ratio up to 10⁵, and enduring 10⁶ read cycles under −1 V pulse voltages. Compared with those of the conventional Si/PVBEC/Al device fabricated by spin-coating, the switch voltage is lower and the ON/OFF current ratio is higher in the volatile Si-g-PVBEC/Al memory device.     

Poly(l-lactide) comb polymer brushes on the surface of clay layers

Poly(l-lactide) (PLLA) comb polymers on poly(hydroxyethyl methacrylate) (PHEMA) backbone were prepared on the surface of clay layers by a combination of in situ atom transfer radical polymerization (ATRP) and ring-opening polymerization. An ATRP initiator with a quaternary ammonium salt end group was intercalated into the interlayer spacing of clay. PHEMA polymer brushes on the surface of clay layers were prepared by in situ ATRP. PLLA comb polymers on PHEMA backbone were prepared by ring-opening polymerization. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that with the increase of comb chain length more and more exfoliated structure was created. Aggregation of wormlike comb polymer brushes on the surface of clay layers was observed by TEM. Differential scanning calorimeter (DSC) results indicated that both the melting points and glass transition temperatures of the comb polymer brushes increase with the increase of comb chain length. The equilibrium melting temperature of the comb polymer brush on the surface of clay layers is lower than cleaved polymer. An atomic force microscopy (AFM) image proves the formation of wormlike structure by cleaved comb polymers.     

Synthesis and characterization of TiO2 nanoparticles chemically coated with zwitterionic polymer brushes

This study introduces a synthetic method to graft zwitterionic poly (2-methacryroyloxyethyl phosphoryl choline) brushes onto TiO₂ nanoparticles with thickness of a few nanometers. The grafting of zwitterionic polymer brushes was characterized by electron microscope measurements, zeta-potential analysis, and thermo-gravimetric analysis. The technique we employed to synthesize those hybrid nanoparticles was a modified seeded emulsion polymerization in which the polymerization loci were changed in the stage of radical initiation and chain propagation. We have found that the polymerization loci should be on the surface for achieving the effective grafting of polymer brushes. From the suspension rheology studies, we have observed that the suspension of our hybrid nanoparticles was dominated by the attractive force as well as by packing volume effect. This unique rheological behavior is expected to be useful for understanding the inter-particle interactions in complex formulations.     

Poly(vinylbenzylchloride) beads grafted with polymer brushes carrying hydrazine ligand for reversible enzyme immobilization

Poly(glycidylmethacrylate), p(GMA), brush grafted poly(vinylbenzyl chloride/ethyleneglycol dimethacrylate), p(VBC/EGDMA), beads were prepared by suspension polymerization and the beads were grafted with poly(glycidyl methacrylate), p(GMA), via surface‐initiated atom transfer radical polymerization aiming to construct a material surface with fibrous polymer. The epoxy groups of the fibrous polymer were reacted with hydrazine (HDZ) to create affinity binding site on the support for adsorption of protein. The influence of pH, and initial invertase concentration on the immobilization capacity of the p(VBC/EGDMA‐g‐GMA)‐HDZ beads has been investigated. Maximum invertase immobilization onto hydrazine functionalized beads was found to be 86.7 mg/g at pH 4.0. The experimental equilibrium data obtained invertase adsorption onto p(VBC/EGDMA‐g‐GMA)‐HDZ affinity beads fitted well to the Langmuir isotherm model. It was shown that the relative activity of immobilized invertase was higher than that of the free enzyme over broader pH and temperature ranges. The K_m and V_max values of the immobilized invertase were larger than those of the free enzyme. After inactivation of enzyme, p(VBC/EGDMA‐g‐GMA)‐HDZ beads can be easily regenerated and reloaded with the enzyme for repeated use. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Highly efficient synthesis of cylindrical polymer brushes with various side chains via click grafting-onto approach

Though much attention has been paid to synthesis of cylindrical polymer brushes, it is still not easy to prepare well-defined brushes by a general approach. Herein, well-defined cylindrical polymer brushes with various side chains were synthesized via grafting-onto approach by CuAAC click chemistry. Narrowly dispersed polymer backbones functionalized with azide groups were obtained by post-modification of poly(glycidyl methacrylate) (PGMA) which was prepared by reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerization. The alkyne-terminated side chains, polystyrene, polyacrylates, polymethacrylates and poly(N-alkyl acrylamide)s, were synthesized by RAFT mediated radical polymerization with alkyne-containing chain transfer agents (CTAs). The CuAAC reactions between the backbone and side chain polymers were conducted with an equivalent feed of alkyne-terminated side chains and azide groups under mild conditions. Influences of reaction conditions and chemical composition of polymer side chains on grafting efficiency and molecular weight distribution of the polymer brushes were investigated. It is demonstrated that the side chains of polystyrene, polyacrylates and poly(N-alkyl acylamide)s were grafted at a density above 85% while that of polymethacrylates decreased to ca. 50%. The polymer brushes synthesized under the optimized reaction conditions had well-defined chemical composition and narrow distribution of molecular weight, and their wormlike morphology was visualized by atomic force microscopy (AFM).     

Synthesis of binary mixed homopolymer brushes by combining atom transfer radical polymerization and nitroxide-mediated radical polymerization

This communication describes a novel strategy to synthesize binary mixed homopolymer brushes from mixed self-assembled monolayers (SAMs) on silica substrates by combining atom transfer radical polymerization (ATRP) and nitroxide-mediated radical polymerization (NMRP). Mixed SAMs terminated by ATRP and NMRP initiators were prepared by coadsorption of two corresponding organotrichlorosilanes from toluene solutions. Mixed poly(methyl methacrylate) (PMMA)/polystyrene (PS) brushes were synthesized by ATRP of MMA at 80 °C followed by NMRP of styrene at 115 °C. Corresponding ‘free’ initiators were added into the solutions to control the polymerizations. We have found that the brush thickness increases with molecular weight in a nearly linear fashion. For a series of binary brushes consisting of PMMA of molecular weight of 26,200 and PS of various molecular weights, we have observed a transition in water contact angles with increasing PS molecular weight after CH₂Cl₂ treatment. Moreover, binary mixed polymer brushes with comparable molecular weights for two grafted polymers undergo reorganization in response to environmental changes, exhibiting different wettabilities.     

SiO2表面原位接枝聚环氧丙烷高分子刷的制备及表征

通过“Stober”法制备出单分散球形SiO₂粒子,并采用3-缩水甘油醚氧基丙基三甲氧基硅烷对其表面进行功能化修饰,然后,利用异丙醇铝作为多相催化剂,原位引发环氧丙烷（PO）单体开环聚合,制得了聚环氧丙烷（PPO）高分子刷接枝改性的SiO₂（PPO-g-SiO₂）。研究了单体添加量、反应温度及反应时间等因素对聚环氧丙烷高分子刷接枝量的影响规律。采用红外光谱（FT-IR）、X射线光电子能谱（XPS）、透射电子显微镜（TEM）、扫描电子显微镜（SEM）及热重分析（TGA）等分析方法对制备的PPO-g-SiO₂的化学结构、微观形貌以及接枝量进行了表征。结果显示,当单体添加量为2.38 mol·L^-1,反应温度为80℃,反应时间为24 h时,PPO在SiO₂表面的接枝量可达23.56%（质量分数）;其厚度约为15 nm。     

Gold nanoparticle layers from multi‐step adsorption immobilised on a polymer surface during injection molding

Functional nanoparticles exhibit, e.g., a chemical functionality. For their use, a reliable immobilisation is often required. Here, a method is described, how those nanoparticles can be immobilised on a thermoplastic surface using melt processing. Gold nanoparticles (AuNP) are assembled in a layer on a substrate by adsorption. The degree of coverage can be controlled by repeating the adsorption process. During each adsorption step, the particles were arranged on the surface as chain‐like aggregates with close particle–particle contacts, rather than as isolated particles. The degree of area coverage on the substrate surface was up to 70%. The AuNP layers were transferred onto the surfaces of polycarbonate (PC) sheets by injection molding. The AuNP were partly embedded by the thermoplastic polymer and in this way permanently immobilised on the part surface. The reduction of methyl orange demonstrated the accessibility of the gold surface for small molecules. Furthermore, the fabrication of bactericide surfaces, sensor surfaces, all using AuNP immobilised on a thermoplastic part surface may become possible. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43608.     

Preparation of well-defined environmentally responsive polymer brushes on monolithic surface by two-step atom transfer radical polymerization method for HPLC

Well-defined poly (2-(dimethylamino) ethyl methacrylate) (PDMAEMA) brushes were successfully prepared on the monolithic surface via two-step atom transfer radical polymerization (ATRP). The polymer brushes synthesized by the second-step ATRP were based on the active bromic groups resulting from poly (ethylene glycol dimethacrylate) (pEDMA) monolith which was prepared at room temperature by the first-step ATRP. Element analysis was used to monitor the grafting process at different reaction times. Each step of preparation was characterized by scanning electron microscope, infrared spectrum and mercury intrusion porosimetry. Employment of PDMAEMA grafted monolith as the stationary phase for chromatographic analysis of steroids demonstrated that the PDMAEMA brushes possessed both pH- and salt-responsive properties. Noticeably, it has been found that the chain length of PDMAEMA brushes could influence the retention behavior of steroids due to the controllability of ATRP, which proposed an interesting alternative to modulate retention in HPLC. This is the first application of PDMAEMA brushes grafted monolith by two-step ATRP method for constructing responsive surface in HPLC and it might exploit a new path for widening the monolith application in various fields.     

Effect of miscibility on migration of third component in star‐like co‐continuous and disperse‐within‐disperse mixed brushes

Novel ternary mixed‐brush single crystals were designed with disperse‐within‐disperse and star‐like co‐continuous morphologies based on poly(ethylene glycol) (PEG)‐b‐polystyrene (PS)/PEG‐b‐poly(methyl methacrylate) (PMMA)/PEG‐b‐polyaniline (PANI) and PEG‐b‐PS/PEG‐b‐PMMA/PEG‐b‐(poly(?‐caprolactone) (PCL) or poly(l ‐lactide) (PLLA)) block copolymers, respectively. In the disperse‐within‐disperse ternary mixed brushes, PANI nanorods were dispersed within the matrix (PS)–dispersed (PMMA) amorphous brushes. The flexibility and rigidity of brushes mainly affected the ultimate morphology and arrangement of amorphous coiled brushes in the vicinity of PANI nanorods. In addition, the migration of PCL and PLLA crystallizable brushes was evident into PMMA phases dispersed in the PS matrix, leading to star‐like co‐continuous patterns of PCL and PLLA brushes. This phenomenon was related to the miscibility of crystallizable PCL and PLLA brushes with the PMMA phase. The migration of crystallizable PCL and PLLA brushes increased the size of PMMA domains in the star‐like co‐continuous patterns. Despite the larger osmotic pressure of PLLA brushes, their higher miscibility with PMMA chains reflected the greater PMMA dispersal and wider PLLA star‐like branches. © 2017 Society of Chemical Industry     

Preparation and characterization of dual-responsive spiropyran-based random copolymer brushes via surface-initiated atom transfer radical polymerization

Silica nanoparticles (SiO₂) were grafted with the precursor random copolymer of 1′-(2-acryloxyethyl)-3′,3′-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2′-indoline) (SPMA) and tert-butyl methacrylate (tBMA) by surface-initiated atom transfer radical polymerization (SI-ATRP), and SiO₂-g-P(SPMA-co-methacrylic acid (MAA)) was obtained via chemical hydrolysis of the resulting precursor random copolymer in acidic conditions. From transmission electron microscopy, we observed the spherical morphology of monodispersed silica nanoparticles and core-shell structure of SiO₂-g-P(SPMA-co-MAA). Energy dispersive spectroscopy, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, and the thermogravimetric analysis indicated that the polymer had been successfully grafted onto the surface of silica nanoparticles. The dual-responsive properties were characterized by means of ultraviolet-visible spectrophotometer and dynamic light scattering. The average hydrodynamic diameter of SiO₂-g-P(SPMA-co-MAA) increased from 185.7 to 212.7 nm under ultraviolet light irradiation for 5 min. Also, the particle size of SiO₂-g-P(SPMA-co-MAA) increased with the rising pH value of surrounding condition.     

Grafting of nanospherical PMMA brushes on cross-linked PMMA nanospheres for addition in two-solution bone cements

Poly(methyl methacrylate) (PMMA) brushes were grafted to the surface of cross-linked PMMA nanospheres for use as the polymer phase in the preparation of the two-solution bone cement. PMMA chains grafted on the core of the cross-linked PMMA nanostructures were hypothesized to impart viscosity to the cement mixture, while providing entanglements with the matrix chains formed during cement cure. The first goal of this study was to develop a novel synthetic strategy to decorate the surface of nanoparticles with functional groups that allowed for grafting of PMMA brushes via radical polymerization. The grafting reactions were performed at specific combinations of monomer and initiator to produce a range of molecular weights adequate for the preparation of bone cements. The second goal was to investigate the ability of this novel methodology to produce high graft densities on the core surface from the analysis of the hydrodynamic properties of brushes. The synthetic pathway discussed enabled the synthesis of brushes with high graft densities and molecular weights tuned to provide optimal viscosities for preparation of brush-containing two-solution bone cements.     

Physicochemical behaviour of cationic polyelectrolyte brushes

Water soluble cationic polyelectrolytes, composed of chargeable basic monomers, make up one major subclass of stimuli-responsive polymer brushes. They have displayed potential in bio-sensing, antimicrobial and drug delivery applications, and in micro-electromechanical devices. However optimising these polybasic brushes for such promising practical applications requires the nanoscale structure and interfacial chemistry to be well-understood. Herein we discuss recent theoretical and experimental work concerning the behaviour of cationic polybasic brushes. Particular attention is focussed towards ionisable polybasic brushes whose degree of charge is variable and solution behaviour is dependent on environmental pH, temperature or ionic strength, as well as the specific nature of the dissolved electrolyte or the presence of applied electrical fields. Polybasic brushes are complex systems that behave in ways far beyond extant theoretical predictions. As discussed herein, these brushes exhibit diverse hydrophobicity modulated salt- and pH-responsive behaviour and structures, tuneable interfacial friction, adhesion and wettability, and specific ion effects that follow the Hofmeister series.     

Influence of poly(acrylic acid) grafting density on switchable protein adsorption/desorption of poly(2-methyl-2-oxazoline)/poly(acrylic acid) mixed brushes

Poly(dopamine) is employed as an anchor to obtain a series of poly(acrylic acid) (PAA) and poly(2-methyl-2-oxazoline) (PMOXA) mixed brush coatings by sequential grafting to methods with PAA chains longer than PMOXA chains. Then, the prepared mixed brush coatings are rigorously characterized. The results show that the grafting density of PAA in mixed brushes could be well adjusted by changing the concentration of PAA solution used for the preparation of mixed brush coatings and the amounts of lysozyme adsorbed on PMOXA/PAA mixed brushes increase with increasing the grafting density of PAA chains while the desorption amounts decrease significantly when the grafting density of PAA is higher than one-half of PMOXA chains. When the grafting density of PAA is about one-half of PMOXA chains, the mixed brush could absorb high amounts of lysozyme (898.4 ng cm⁻²), and then more than 90% of adsorbed proteins could be released sharply by changing pH and ionic strength (I). © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48135.     

水介质中表面引发ATRP法合成PMAA聚电解质刷

水介质中以表面引发ATRP法在单分散的二氧化硅微球表面接枝了一层PMMA聚合物刷,然后通过水解得到PMAA聚电解质刷。通过控制ATRP的反应时间得到了不同分子量且分子量分布较窄的聚电解质刷。结果表明,接枝硅烷偶联剂APTES的最佳反应方式为静置反应,对于1 g微球最佳接枝量为4 mL,聚电解质刷的分子量随ATRP反应时间增长而增大。     

Formation of poly(octadecyl acrylate) brushes on a silicon wafer surface

To introduce an ultrahydrophobic polymeric phase onto a silicon wafer, an initiator‐modified silicon wafer was prepared with 2‐bromopropionyl bromide and then surface‐initiated atom transfer radical polymerization of octadecyl acrylate was carried out from the initiator‐grafted silicon wafer using CuBr and N,N,N′,N″‐pentamethyldiethylenetriamine as catalyst precursors. The resultant poly(octadecyl acrylate) [poly(ODA)] brushes were characterized by ellipsometry, X‐ray photoelectron spectroscopy, grazing angle Fourier transform infrared spectroscopy, atomic force microscopy, gel permeation chromatography and water contact angle measurements. Wettability of the poly(ODA) brushes was found to depend on the surface coverage (Γ) and the root mean square roughness. The most hydrophobic surface (Γ = 25.35 mg m^?2 and root mean square roughness 11.9 nm) exhibited a water contact angle of 171.1 ± 0.2°. Copyright © 2011 Society of Chemical Industry     

Highly uniform hole spacing micro brushes based on aligned carbon nanotube arrays

Highly uniform hole spacing micro brushes were fabricated based on aligned carbon nanotube (CNT) arrays synthesized by chemical vapor deposition method with the assistance of anodic aluminum oxide (AAO) template. Different micro brushes from CNT arrays were constructed on silicon, glass, and polyimide substrates, respectively. The micro brushes had highly uniform hole spacing originating from the regularly periodic pore structure of AAO template. The CNT arrays, serving as bristles, were firmly grafted on the substrates. The brushes can easily clean particles with scale of micrometer on the surface of silicon wafer and from the narrow spaces between the electrodes in a series of cleaning experiments. The results show the potential application of the CNT micro brushes as a cleaning tool in microelectronics manufacture field.