Constructing polyamidoamine dendrons from poly(poly(ethylene glycol) monomethacrylate) brushes grafted from planar silicon hydride surfaces for biomedical applications

A facile approach was established to construct polyamidoamine (PAMAM) dendrons from polymer brushes of poly(poly(ethylene glycol) monomethacrylate) (Si-g-P(PEGMA-OH)) grafted from a planar silicon hydride surface. First the Si-g-P(PEGMA-OH) brushes were grown via surface-initiated atom transfer radical polymerization with robust Si–C links on silicon surfaces. The side-chain hydroxyl groups of Si-g-P(PEGMA-OH) were chlorinated with thionyl chloride and further chlorines were substituted with amino groups of ethylenediamine, giving terminal primary amines. Borrowing the solution synthesis approach, we constructed second and third generations of PAMAM dendrons on-chip by surface-initiated alternative growth of two monomers, methyl acrylate and ethylenediamine. Two applications of silicon-based PAMAM dendrons were shown: the dense amino groups were activated via a cross-linker, N-succinimidyl-6-maleimidylhexanoate, to capture a free-thiol-carrying peptide of oxytocin and the third generation of PAMAM dendrons was used as a platform to on-chip synthesize a three amino acid peptide of Arg-Gly-Asp (RGD). The above conclusions were mainly derived from a home-built multiple transmission-reflection infrared spectroscopy, and complemented by X-ray photoelectron spectroscopy, UV–Vis spectroscopy and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry.     

Poly(hydroethyl acrylate) grafted from ZnO nanoparticles via surface-initiated atom transfer radical polymerization

Poly(hydroethyl acrylate) (PHEA) was grafted from ZnO nanoparticles via the copper-mediated surface-initiated atom transfer radical polymerization (SI-ATRP) technique with the bromo-acetamide modified ZnO nanoparticles (BrA-ZnO) as macroinitiators with the catalysts of 1,10-phenanthroline and Cu(I)Br in water. Graft reaction was first order kinetic with respect to the polymerizing time in the low monomer conversion stage, this being typical for ATRP. A percentage of grafting (PG%) of 62.4% was achieved in 12 h, calculated from the elemental analysis results. The product, poly(hydroethyl acrylate) grafted ZnO nanoparticles (PHEA-ZnO) were also characterized with Fourier transform infrared spectroscopy (FT-IR), UV–vis spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).     

Surface-initiated atom transfer radical polymerization from TiO2 nanoparticles

Two kinds of hydrophilic polymers, poly(oxyethylene methacrylate) (POEM) and poly(styrene sulfonic acid) (PSSA), were grafted from TiO₂ nanoparticles via the surface-initiated atom transfer radical polymerization (ATRP) technique. Chlorine modified TiO₂ nanoparticles (TiO₂-Cl), the ATRP initiators, were synthesized by the reaction of -OH in TiO₂ with 2-chloropropionyl chloride (CPC). FT-IR, UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS) clearly showed that the polymer chains were successfully grafted from the surface of TiO₂ nanoparticles. The hydrophilically modified TiO₂ nanoparticles have a better dispersion in alcohol than unmodified nanoparticles, as revealed by transmission electron microscopy (TEM). It was also found that the polymer grafting did not significantly alter the crystalline structure of the TiO₂ nanoparticles according to the X-ray diffraction (XRD) patterns. Grafting amounts were 10% of the weight for both TiO₂-POEM and TiO₂-PSSA nanoparticles, as determined by thermogravimetric analysis (TGA).     

Modification of polysulfone membranes via surface-initiated atom transfer radical polymerization

Hydrophilic poly((poly(ethylene glycol) methyl ether methacrylate) (P(PEGMA)) and poly(glycidylmethacrylate) (PGMA) brushes were grafted from chloromethylated polysulfone (CMPSF) membrane surfaces via surface-initiated atom transfer radical polymerization (ATRP). Prior to ATRP, chloromethylation of PSF was performed beforehand and the obtained CMPSF was prepared into porous membranes by phase inversion process. It was demonstrated that the benzyl chloride groups on the CMPSF membrane surface afforded effective macroinitiators to graft the well-defined polymer brushes. ¹H NMR was employed to confirm the structure of CMPSF. The grafting yield of P(PEGMA) and PGMA was determined by weight gain measurement. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the grafting of P(PEGMA) and PGMA chains. Water contact angle measurements indicated that the introduction of P(PEGMA) and PGMA graft chains promoted remarkably the surface hydrophilicity of PSF membranes. The effects of P(PEGMA) and PGMA immobilization on membrane morphology, permeability and fouling resistance were investigated. It was found that P(PEGMA) and PGMA grafts brought higher pure water flux, improved hydrophilic surface and better anti-protein absorption ability to PSF membranes after modification. And evidently, macromonomer P(PEGMA) brought much better properties to the PSF membranes than PGMA macromonomer.     

Grafting poly(ethylene glycol) monomethacrylate onto Fe3O4 nanoparticles to resist nonspecific protein adsorption

Magnetic nanoparticles grafted with poly(poly(ethylene glycol) monomethacrylate) (P(PEGMA)) were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. In this approach, S-benzyl S′-trimethoxysilylpropyltrithiocarbonate, used as a chain transfer agent for RAFT, was first immobilized onto the magnetic nanoparticle surface, and then PEGMA was grafted onto the surface of magnetic nanoparticle via RAFT polymerization. The results showed that P(PEGMA) chains grew from magnetic nanoparticles by surface-induced RAFT polymerization. The grafted P(PEGMA) chains can decrease the nonspecific adsorption of proteins on the surface of Fe₃O₄ nanoparticles.     

One-step copolymerization modified magnetic nanoparticles via surface chain transfer free radical polymerization

Copolymer brushes growing onto magnetic nanoparticles were prepared by surface chain transfer free radical polymerization. Block copolymer brushes (P(PEGMA)-co-PNIPAAm) consist of poly(ethylene glycol) monomethacrylate (PEGMA) and N-isopropylacrylamide monomer. X-ray photoelectron spectroscopy (XPS) characterized the chemical composition of copolymer. Thermogravimetric analysis (TGA) suggested that the amount of copolymer on magnetic nanoparticles decreased with increasing azodiisobutyronitrile (AIBN). The saturation magnetization decreased significantly with increasing P(PEGMA)-co-PNIPAAm. The thermosensitive point is about 43 °C for magnetic nanoparticles with 33.8% P(PEGMA)-co-PNIPAAm.     

Versatile functionalization of Fe3O4 nanoparticles via RAFT polymerization and click chemistry

Azide-functionalized chain transfer agent (CTA) was synthesized and subsequently employed to mediate the reversible addition fragmentation transfer (RAFT) polymerization of poly(ethylene glycol) monomethacrylate (PEGMA) on the alkyne-functionalized Fe₃O₄ nanoparticles surface together with click chemistry. In a single pot procedure, azide-functionalized CTA, alkyne-functionalized Fe₃O₄ and PEGMA were combined to produce the desired product. Fourier transformed infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) results showed that PEGMA chains were grafted to Fe₃O₄ nanoparticles using RAFT polymerization and click chemistry.     

Synthesis and characterization of TiO2/Ag/polymer ternary nanoparticles via surface-initiated atom transfer radical polymerization

We report on the novel ternary hybrid materials consisting of semiconductor (TiO₂), metal (Ag) and polymer (poly(oxyethylene methacrylate) (POEM)). First, a hydrophilic polymer, i.e. POEM, was grafted from TiO₂ nanoparticles via the surface-initiated atom transfer radical polymerization (ATRP) technique. These TiO₂-POEM brush nanoparticles were used to template the formation of Ag nanoparticles by introduction of a AgCF₃SO₃ precursor and a NaBH₄ aqueous solution for reduction process. Successful grafting of polymeric chains from the surface of TiO₂ nanoparticles and the in situ formation of Ag nanoparticles within the polymeric chains were confirmed using transmission electron microscopy (TEM), UV-vis spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). FT-IR spectroscopy also revealed the specific interaction of Ag nanoparticles with the CO groups of POEM brushes. This study presents a simple route for the in situ synthesis of both metal and polymer confined within the semiconductor, producing ternary hybrid inorganic-organic nanomaterials.     

In situ preparation and fluorescence quenching properties of polythiophene/ZnO nanocrystals hybrids through atom-transfer radical polymerization and hydrolysis

In this paper, a new approach for in situ preparing nanocomposites of conjugated polymers (CPs) and semiconductor nanocrystals was developed. Polythiophene grafted poly(zinc methacrylate) (PTh-g-PZMA) copolymer was synthesized by atom-transfer radical polymerization (ATRP) of zinc methacrylate (ZMA) initiated from the macroinitiator poly(2,5-(3-(bromoisopropyl-carbonyl-oxymethylene) thiophene)) (PTh-Br) with pendant initiator groups. Subsequently, the polythiophene grafted poly(methacrylate)/ZnO (PTh-g-PMA/ZnO) hybrid heterojunction nanocomposites were successfully prepared by in situ hydrolysis of PTh-g-PZMA casting films in alkaline aqueous solution. The structures of PTh-Br, PTh-g-PZMA and PTh-g-PMA/ZnO were confirmed by the proton nuclear magnetic resonance (¹H NMR) spectra, Fourier transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS). The morphologies of PTh-g-PMA/ZnO films prepared for different hydrolysis time were observed in the cross-sections by scanning electron microscope (SEM). The SEM images revealed that ZnO nanocrystals were uniformly dispersed in polymers without any aggregation and the appearances of ZnO nanocrystals changed from nanoparticles to nanorods with the hydrolysis treatment time increasing. The optical properties of these nanocomposites were studied by ultraviolet-visible (UV-vis) absorption and fluorescence spectroscopy. UV-vis absorption spectroscopy showed that the adsorption band of PTh-g-PMA/ZnO hybrids was broader than that of PTh-Br, implying that the existence of ZnO nanocrystals increased the optical absorption region of hybrids. The photoluminescence (PL) spectra of the hybrids showed that fluorescence quenching occurred in PTh-g-PMA/ZnO blends and a maximum of 85% of the fluorescence intensity quenched in the PTh-g-PMA/ZnO obtained from treatment in NaOH aqueous solution for 2 h, which revealed the existence of photo-induced charge transfer between the polythiophene chains and ZnO. These results indicated that the hybrid heterojunction nanocomposites could be promising candidates for photovoltaic applications.     

Preparation and characterization of smart polymer brush-modified magnetic nanoparticles for biomedicine application

This paper investigates synthesis and characterization of smart polymer brush-modified magnetic nanoparticles (SPB-MNPs). Magnetic nanoparticles (MNPs) modified with poly(poly(ethylene glycol) monomethacrylate (poly(PEGMA)) brush were first functioned with activated pyridyldithio. Then, MNPs functioned with pyridyldithio (MNPs-PEG-PDT) were conjugated with 4-diamino-6-mercaptopyrimidine (DMP) to form SPB-MNPs via stimuli-responsive disulfide linkage. Fourier transform infrared spectra (FTIR) was used to monitor the preparation process of MNPs-PEG-PDT. MNPs-PEG-PDT is very highly reactive toward DMP. The disulfide linkage of SPB-MNPs can be cleaved by reduced glutathione (GHS). The concentration of GHS plays an important role in controlling the cleaved efficiency. The optimum concentration of GHS to release DMP is in the millimolar range.     

Surface modification of PVDF membrane via AGET ATRP directly from the membrane surface

This contribution demonstrates a method for PVDF microporous membrane modification via surface-initiated activators generated by electron transfer atom transfer radical polymerization (AGET ATRP) directly from the membrane surface. Three hydrophilic polymers, poly(2-(N,N-dimethylamino) ethyl methacrylate) (PDMAEMA), poly(2-oligo (ethylene glycol) monomethyl ether methacrylate) (POEGMA), and poly(2-hydroxyethyl methacrylate) (PHEMA), were grafted from the PVDF membrane surface in aqueous solution at room temperature. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the successful covalent tethering of the polymer chains onto the PVDF membrane surface. The gravimetry results indicated an approximately linear increase of the graft yields, up to about 330 μg/cm² for DMAEMA and 470 μg/cm² for both HEMA and OEGMA, with the polymerization time. Block copolymer brushes were prepared by chain extension. Water contact angle decreased over 50% for high yields, indicating improved surface hydrophilicity. The effects of the graft polymerization on membrane surface morphology, pore structure and permeability were investigated. It was found that the surface roughness was decreased and the pore size distribution was narrowed. The membrane permeability increased at low graft yields due to the enhanced hydrophilicity and decreased at high graft yields due to the overall reduction of the pore diameters.     

A new hyperbranched star polyether electrolyte with high ionic conductivity

Hyperbranched poly(glycidol) containing hydroxyl groups was firstly synthesized via anionic polymerization and then reacted with 2-bromoisobutyl bromide to form macroinitiator HPG-Br. Finally, a hyperbranched star polymer (HPG-PPEGMA) was successfully prepared by atom transfer radical polymerization (ATRP) of poly(ethylene glycol) methyl ether methacrylate using HPG-Br as macroinitiator. The structures and properties of the obtained polymers were characterized by ¹H NMR, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The ionic conductivity of the polymer electrolytes composed of HPG-PPEGMA and lithium bis(trifluoromethanesulfonimide) (LiTFSI) was investigated via electrochemical impedance spectroscopy. The results showed that the room temperature ionic conductivity of the prepared hyperbranched star polymer electrolytes had a higher ionic conductivity. When [EO]/[Li] was 20, the ionic conductivity of the hyperbranched star polymer electrolyte was up to 1?×?10^?4 Scm^?1 at 30 °C. The onset decomposition temperature of the hyperbranched star polyether could reach 374 °C, indicating that the hyperbranched star polymer had a good thermal stability. The XRD results showed that the structure of the hyperbranched star polymer was beneficial to improve the ionic conductivity due to possessing a low degree of crystallinity.     

Surface modification of zinc oxide nanoparticle by PMAA and its dispersion in aqueous system

Commercial zinc oxide nanoparticles were modified by polymethacrylic acid (PMAA) in aqueous system. The hydroxyl groups of nano-ZnO particle surface can interact with carboxyl groups (COO-) of PMAA and form poly(zinc methacrylate) complex on the surface of nano-ZnO. The formation of poly(zinc methacrylate) complex was testified by Fourier-transform infrared spectra (FT-IR). Thermogravimetric analysis (TGA) indicated that PMAA molecules were absorbed or anchored on the surface of nano-ZnO particle, which facilitated to hinder the aggregation of nano-ZnO particles. Through particle size analysis and transmission electron micrograph (TEM) observation, it was found that PMAA enhanced the dispersibility of nano-ZnO particles in water. The dispersion stabilization of modified ZnO nanoparticles in aqueous system was significantly improved due to the introduction of grafted polymer on the surface of nanoparticles. The modification did not alter the crystalline structure of the ZnO nanoparticles according to the X-ray diffraction patterns.     

Single-ion conductivity enhancement for the composite polymer electrolytes based on Li(PVAOB)/PPEGMA for lithium-ion batteries

In the present work, a series of single-ion conducting composite polymer electrolytes based on lithium polyvinyl alcohol oxalate borate (Li(PVAOB)) and poly(polyethylene glycol methacrylate) (PPEGMA) were produced. PEGMA was polymerized into PPEGMA, and the Li(PVAOB) was prepared from poly (vinyl alcohol) (PVA), oxalic acid, and boric acid. Li(PVAOB) was blended with PPEGMA at different stoichiometric ratios to obtain a single-ion conducting system. All the electrolytes were characterized by Fourier transformation infrared spectroscopy (FT-IR), thermogravimetry analysis (TGA), differential scanning calorimeter (DSC), and scanning electron microscopy (SEM) techniques. These results verified the interaction between host and guest polymers, sufficient thermal stability within the measured conductivity domain, and the homogeneity of the composite electrolytes. The effect of PPEGMA onto the ionic conductivity was investigated using impedance spectroscopy. The Li(PVAOB)-60PPEGMA is the optimum content, and this sample has a maximum ionic conductivity of 3 × 10^?4 S/cm at 100 °C which is approximately five orders of magnitude higher than neat Li(PVAOB). Activation energy (E _a ) of ionic transport decreased from 11.9 to 0.27 kJ/mol, suggesting a much faster ionic mobility for higher PPEGMA-containing samples.     

Solvothermal synthesis and characterization of sandwich-like graphene/ZnO nanocomposites

Graphene-based nanocomposites are emerging as a new class of materials that hold promise for many applications. In this paper, we present a general approach for the preparation of sandwich-like graphene/ZnO nanocomposites in ethylene glycol (EG) medium using graphene oxide as a precursor of graphene and zinc acetylacetonate as a single-source precursor of zinc oxide. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy and thermogravimetry analysis. It was shown that the as-formed ZnO nanoparticles with a diameter of about 5 nm were densely and uniformly deposited on both surfaces of the graphene sheets to form a sandwich-like composite structure and as a result, the restacking of the as-reduced graphene sheets was effectively prevented. The ZnO-coated graphene nanocomposites can be expected to effectively improve the photocatalysis and sensing properties of ZnO and would be promising for practical applications in future nanotechnology.     

Prediction of protein interaction behaviour with PEG-grafted matrices using X-ray photoelectron spectroscopy

Due to the considerable scientific and commercial interest in poly(ethylene glycol) (PEG) grafted solid surfaces for biomedical applications, it is important to characterize the properties and behaviour of these modified surfaces. In this study, we applied a unique method to predict the magnitude of interactive forces exerted between a globular protein and PEG-grafted matrices. Carboxyl functionalized solid matrices were covalently grafted with PEG-amine derivatives at varying PEG surface concentrations and layer thicknesses by controlling the grafting reaction parameters. X-ray photoelectron spectroscopy was used to characterize these PEG-grafted matrices using the standard overlay model. A detailed and systematic correlation between PEG layer thickness and the distance between the grafted PEG chains resulted in valuable information regarding protein interactions with these PEG-grafted matrices. Finally, this predicted interaction behaviour was validated with fluorescent images obtained from fluorescein isothiocyanate-labelled Cytochrome c-conjugated solid matrices using confocal laser scanning microscopy.     

A comparative study for the electrocatalytic oxidation of alcohol on Pt-Au nanoparticle-supported copolymer-grafted graphene oxide composite for fuel cell application

The platinum-gold bimetallic nanoparticles supported poly(cyclotriphosphazene-co-benzidine)-grafted graphene oxide (poly(CP-co-BZ)-g-GO) composite has been prepared for electrochemical performance studies. Cyclic voltammetry and chronoamperometric studies were carried out to check the electrochemical properties of Pt-Au/poly(CP-co-BZ)-g-GO and Pt/poly(CP-co-BZ)-g-GO catalysts for methanol, ethylene glycol and glycerol in alkaline medium. The morphology and crystalline structure of the prepared Pt-Au/poly(CP-co-BZ)-g-GO and Pt/poly(CP-co-BZ)-g-GO and catalysts have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FT-IR). From the electrochemical results, it was concluded that Pt-Au/poly(CP-co-BZ)-g-GO catalyst shows higher catalytic activity and stability compared to Pt/poly(CP-co-BZ)-g-GO catalyst. The catalytic activity of Pt/poly(CP-co-BZ)-g-GO catalyst has been compared with Pt/poly(CP-co-BZ), Pt/GO and Pt/C catalysts. In addition, oxidation current of ethylene glycol is higher than the methanol and glycerol in alkaline medium on the prepared catalyst.     

Preparation of well-defined polymer-silicon wafer hybrids via surface-initiated RAFT-mediated process

A simple method was developed for the immobilization of reversible addition-fragmentation chain-transfer (RAFT) initiators on the silicon surface. Well-defined polymer-silicon hybrids, including the tethered brushes of glycidyl methacrylate (GMA) polymer, poly(ethylene glycol) monomethacrylate (PEGMA) polymer and block copolymer on a silicon wafer, were prepared via surface-initiated RAFT living radical polymerization. The “living” chain ends were used as the macroinitiator for the subsequent synthesis of diblock copolymers.     

Blue shift in the luminescence spectra of MEH-PPV films containing ZnO nanoparticles

Luminescence properties of nanocomposites consisting of ZnO nanoparticles in a conjugated polymer, poly [2-methoxy-5-(2′-ethyl hexyloxy)-phenylene vinylene] (MEH-PPV), were investigated. Photoluminescence measurements reveal a blue shift in the emission spectrum of MEH-PPV upon incorporation of ZnO nanoparticles into the polymer film while the emission is increasingly quenched with increasing ZnO concentration. In contrast, the structure of the polymer and its conjugation length are not affected by the presence of ZnO nanoparticles (up to 16 wt% ZnO) as revealed by Raman spectroscopy. The blue shift and photoluminescence quenching are explained by the separation of photogenerated electron-hole pairs at the MEH-PPV/ZnO interface and the charging of the nanoparticles.     

Preparation and ionic conductivity of composite polymer electrolytes based on hyperbranched star polymer

Hyperbranched star polymer HBPS-(PPEGMA) _x was synthesized by atom transfer radical polymerization (ATRP) using hyperbranched polystyrene (HBPS) as macroinitiator and poly(ethylene glycol) methyl ether methacrylate (PEGMA) as monomer. The structure of the prepared hyperbranched star polymer was characterized by ¹H NMR, ATR-FTIR, and GPC. Polymer electrolytes based on HBPS-(PPEGMA) _x , lithium salt, and/or nano-TiO₂ were prepared. The influences of lithium salt concentration and type, nano-TiO₂ content, and size on ionic conductivity of the obtained polymer electrolytes were investigated. The results showed that the low crystallinity of the prepared polymer electrolyte was caused by the interaction between lithium salt and polymer. The addition of TiO₂ into HBPS-(PPEGMA) _x /LiTFSI improved the ionic conductivity at low temperature. The prepared composite polymer electrolyte showed the highest ionic conductivity of 9?×?10^?5 S cm^?1 at 30 °C when the content of TiO₂ was 15 wt% and the size of TiO₂ was 20 nm.