Preparation and characterization of composites built of poly(N-benzophenoyl methacrylamide-co-N-hydroxyethyl acrylamide) cores and silica raspberry-like shells with dual orthogonal functionality

The design and fabrication of novel poly(N-benzophenoyl methacrylamide-co-N-hydroxyethyl acrylamide)@SiO(2) composites are reported herein. These core-shell composites demonstrate orthogonal functionality, composed of photoreactive cores, containing a benzophenone (BPh) moiety and silica (SiO(2)) shells, enabling the utilization of the free hydroxyl groups via silane-based chemistry. The co-polymer cores, which are 1.28μm in diameter, are first obtained by dispersion polymerization of photoreactive (N-benzophenoyl methacrylamide) (polyBPMA) and N-Hydroxyethyl acrylamide (HEAA). Next, silica seeds with a 42nm diameter are deposited onto the surfaces as a result of the hydrolysis and the condensation of tetraethyl orthosilicate (TEOS) in a basic condition. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), FT-infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), UV-spectrophotometry, X-ray photoelectron spectroscopy (XPS), and ζ-potential measurements were used to characterize the composites. The morphology and surface smoothness of the deposited silica nanoparticles (NPs) were found to strongly depend on a number of parameters such as the pH value of the medium, TEOS concentration, and the temperature.     

Grafting of hyperbranched cyclotriphosphazene polymer onto silica nanoparticle and carbon black surfaces

The surface grafting of hyperbranched cyclotriphosphazene polymer onto silica nanoparticles and carbon black was investigated. The grafting of hyperbranched cyclotriphosphazene polymer onto these surfaces was achieved by the repeated reactions of hexachlorocyclotriphosphazene with hexamethylenediamine from surface amino groups and sodium carboxylate groups, respectively. The percentage of grafting onto silica and carbon black surfaces exceeded 760 and 390%, respectively. However, it proved difficult to achieve the theoretical growth of cyclotriphosphazene polymer from these surfaces because of steric hindrance. The introduction of sulfonic acid groups was successfully achieved by the reaction of terminal chlorophosphazene groups of the hyperbranched polymer‐grafted silica and carbon black with sulfanilic acid. The content of sulfonic acid groups introduced onto silica and carbon black surfaces was 4.98 mmol/g and 5.70 mmol/g, respectively. The sulfonated cyclotriphosphazene polymer‐grafted carbon black was extremely hydrophilic, yielding stable colloidal dispersions in polar solvents. The sulfonated cyclotriphosphazene polymer‐grafted silica and carbon black showed ionic conductivity, with the conductance increasing exponentially with increasing relative humidity and temperature. This study may offer important leads in the application of silica nanoparticles and carbon black in polymeric membranes for fuel cells. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4218–4226, 2008     

Attachment of Polymer Films to Aluminium Surfaces by Photochemically Active Monolayers of Phosphonic Acids

Summary: We describe a simple photochemical process that allows the covalent attachment of a variety of different polymers at room temperature onto aluminium surfaces. The system is based on a photoreactive benzophenone derivative that is bound to aluminium surfaces by a phosphonic acid anchor. The synthesis of the phosphonic acid is described and the immobilization of this compound is studied by X‐ray photoelectron and FT‐IR spectroscopy. After deposition of the polymeric coating, UV light illumination at 365 nm, and solvent extraction of the substrate, polymer monolayers are obtained that are chemically bound to the surface.

Covalent attachment of polymers to the aluminium‐bound benzophenone phosphonic acid.     

Synthesis of UV‐cured acrylic–silica hybrid nanocomposites from dendritic acrylic oligomer and acrylic‐functionalized silica

An acrylic–silica hybrid polymeric nanocomposite, comprising well‐distributed silica nanoparticles in acrylic matrix, has been synthesized at a markedly rapid rate from a dendritic acrylic oligomer (DAO) and an acrylic‐functionalized silica (A‐silica) via UV‐curing. A‐silica was made by functioning colloidal silica nanoparticles with 3‐methacryloxypropyltrimethoxysilane (MATMS) and DAO was formed by reacting 1,5‐diamino‐2‐methylpentane (MPMDA) with trimethylopropane triacrylate (TMPTA). The MATMS has been found either doubly or singly bonded to silica nanoparticles but not triply bonded, and the inclusion of MATMS into the siloxane network structure increases the size of silica nanoparticles. The well distribution of A‐silica and its good compatibility with DAO cause an increase in T_d of the acrylic–silica hybrid material. Silica nanoparticles are too small to cause any significant light scattering, and do not have deleterious effects on transparency. The “hybrid‐on‐polyethylene terephathalate” films exhibited satisfactory hardness and surface roughness because of silica nanoparticles. The preparation as well as the characterization of the constituting species and the final hybrid material are described in detail. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8149–8158, 2008     

Synthesis and characterization of silica‐graft‐polystyrene hybrid nanoparticles: Effect of constraint on the glass‐transition temperature of spherical polymer brushes

The effect of the chain constraint on the glass‐transition temperature of polystyrene (pS) was studied in the context of polymer tethering to curved surfaces. The synthesis and characterization of silica‐graft‐polystyrene (SiO₂‐g‐pS) hybrid nanoparticles is reported. Silica nanoparticles possessing covalently bound pS chains were prepared by the atom transfer radical polymerization of styrene from functionalized colloidal surfaces. These hybrid nanoparticles serve as interesting examples of spherical polymer brushes, as a high density of grafted pS was achieved on the inorganic colloid. The confirmation of a brushlike extension of immobilized chains in a good solvent was obtained with dynamic light scattering in toluene of SiO₂‐g‐pS colloids possessing various molar masses of tethered pS. The solid‐state morphology of SiO₂‐g‐pS ultrathin films was assessed with transmission electron microscopy, and this confirmed that the silica colloids were well‐dispersed in a matrix of the tethered polymer. Differential scanning calorimetry was used to study the effects of tethering and chain immobilization on the glass‐transition temperature of pS. The measured glass‐transition temperature of annealed bulk films of the hybrid nanoparticles was elevated with respect to the value for pure bulk pS. The enhancements ranged from 13 to 2 K for SiO₂‐g‐pS brushes possessing tethered pS with number‐average molecular weights of 5230 and 32,670 g/mol, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2667–2676, 2002     

Photoreactive azido-containing silica nanoparticle/polycation multilayers: durable superhydrophobic coating on cotton fabrics

In this study, we report the functionalization of silica nanoparticles with highly photoreactive phenyl azido groups and their utility as a negatively charged building block for layer-by-layer (LbL) electrostatic assembly to produce a stable silica nanoparticle coating. Azido-terminated silica nanoparticles were prepared by the functionalization of bare silica nanoparticles with 3-aminopropyltrimethoxysilane followed by the reaction with 4-azidobenzoic acid. The azido functionalization was confirmed by FTIR and XPS. Poly(allylamine hydrochloride) was also grafted with phenyl azido groups and used as photoreactive polycations for LbL assembly. For the photoreactive silica nanoparticle/polycation multilayers, UV irradiation can induce the covalent cross-linking within the multilayers as well as the anchoring of the multilayer film onto the organic substrate, through azido photochemical reactions including C-H insertion/abstraction reactions with surrounding molecules and dimerization of azido groups. Our results show that the stability of the silica nanoparticle/polycation multilayer film was greatly improved after UV irradiation. Combined with a fluoroalkylsilane post-treatment, the photoreactive LbL multilayers were used as a coating for superhydrophobic modification of cotton fabrics. Herein the LbL assembly method enables us to tailor the number of the coated silica nanoparticles through the assembly cycles. The superhydrophobicity of cotton fabrics was durable against acids, bases, and organic solvents, as well as repeated machine wash. Because of the unique azido photochemistry, the approach used here to anchor silica nanoparticles is applicable to almost any organic substrate.     

Preparation of Comb‐like Styrene Grafted Silica Nanoparticles

Abstract

Comb‐like polystyrene grafted silica nanoparticles (c‐PS‐SNs) were prepared by the following steps: (a) methacryloxypropyl silica nanoparticles (MPSNs) were used as macromonomer and free radical copolymerized with 4‐vinyl benzyl chloride (VBC) by a solution polymerization method; (b) the product of (A), poly(4‐vinyl benzyl chloride) grafted silica nanoparticle (PVBC‐SN) was separated and then used as a macroinitiator for the surface‐initiated atom transfer radical polymerization (SI‐ATRP) of styrene catalyzed by the complex of Cu(I)Br and 2,2′‐bipyridyl (bipy) in toluene solutions. The structurally well‐defined polymer chains were grown from the nanoparticle surfaces to yield particles composed of a silica core and a well defined, densely grafted outer comb‐like PS layer. A percentage of grafting (PG%) (the weight ratio of the PS grafted with that of the silica charged) of more than 80% was achieved after a polymerizing time of 5?hr.     

UV‐cured polyester‐acrylate nanocomposite films with silane‐grafted silica nanoparticles

UV‐curing technique was employed in this study to prepare polyester‐acrylate nanocomposite films with silane‐grafted silica nanoparticles. Methacryloxypropyl trimethoxysilane was grafted to the surfaces of silica nanoparticles to improve dispersion of silica nanoparticles as well as interfacial adhesion between the resin matrix and silica nanoparticles. The silane‐grafting was confirmed by nuclear magnetic resonance and infrared spectroscopy. The effects of the silane‐grafting on the mechanical and optical properties as well as UV‐curing behavior of the nanocomposite films were investigated. The tensile strength, transmittance, UV‐curing rate, and final chemical conversion of the nanocomposite films were increased by use of the grafted silica nanoparticles as compared to the use of neat silica nanoparticles. Copyright © 2011 John Wiley & Sons, Ltd.     

Silica/Silicone Nanofilament Hybrid Coatings with Almost Perfect Superhydrophobicity

A facile method for the preparation of silica/silicone nanofilament hybrid coatings with almost perfect superhydrophobicity (contact angle=179.8° and sliding angle=1.3°) is presented. The coatings are obtained by dip‐coating of silica nanoparticles, followed by chemical vapor deposition of silicone nanofilaments. Predominant growth of silicone nanofilaments onto aggregated silica nanoparticles generates a two‐tier structure. The effect of silica nanoparticle size on the growth of silicone nanofilaments, along with their anti‐wetting properties and transparency are investigated in detail. Surface roughness and anti‐wetting properties can be simply regulated by controlling the size of silica nanoparticles.     

Suppression of surface pattern formation in spin‐coated polymer films by the addition of polydimethylsiloxane‐grafted silica nanoparticles

Polydimethylsiloxane (PDMS)‐grafted nanoparticles and PDMS were added, respectively, to inhibit the dewetting of polymer films and the formation of surface patterns in spin coating. Uniform and flat films were successfully achieved with the addition of PDMS‐grafted silica nanoparticles or PDMS. Time‐of‐flight secondary ion mass spectrometry depth profiling indicated that PDMS‐grafted silica nanoparticles and PDMS preferentially segregated to the surface. A high concentration of bromine end groups was observed at the interface. The surface layer of PDMS or PDMS‐grafted silica nanoparticles can decrease the surface tension of the polymer solutions and reduce the evaporation rates of the solvents, providing more time for the bromine end groups to anchor themselves at the silicon substrates. Copyright © 2016 John Wiley & Sons, Ltd.     

Comparison of monomethoxy‐, dimethoxy‐, and trimethoxysilane anchor groups for surface‐initiated RAFT polymerization from silica surfaces

The immobilization of reversible addition–fragmentation chain transfer (RAFT) agents on silica for surface‐initiated RAFT polymerizations (SI‐RAFT) via the Z‐group approach was studied systematically in dependence of the functionality of the RAFT‐agent anchor group. Monoalkoxy‐, dialkoxy‐, and trialkoxy silyl ether groups were incorporated into trithiocarbonate‐type RAFT agents and bound to planar silica surfaces as well as to silica nanoparticles. The immobilization efficiency and the structure of the bound RAFT‐agent film varied strongly in dependence of the used solvent (toluene vs. 1,2‐dimethoxyethane) and the anchor group functionality, as evidenced by atomic force microscopy, transmission electron microscopy, dynamic light scattering, and UV/Vis spectroscopy. Surface‐initiated RAFT polymerizations using functionalized silica nanoparticles revealed that grafted oligomers, which often occur in SI‐RAFT, are not formed within the crosslinked structures that originate from the immobilization, and that RAFT‐agent films that show less aggregation during the immobilization are more efficient during SI‐RAFT in terms of polymer grafting density. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 103–113     

Immobilization of RAFT agents on silica nanoparticles utilizing an alternative functional group and subsequent surface‐initiated RAFT polymerization

Silica–polystyrene core‐shell particles were successfully prepared by surface‐mediated reversible addition fragmentation chain transfer (RAFT) polymerization of styrene monomer from the surfaces of the silica‐supported RAFT agents. Initially, macro‐RAFT agents were synthesized by RAFT polymerization of γ‐methacryloxypropyltrimethoxysilane (MPS) in the presence of chain transfer agents (CTAs). Immobilization of CTAs onto the silica surfaces was then performed by reacting silica with macro‐RAFT agents via a silane coupling. Grafting of polymer onto silica forms core‐shell nanostructures and shows a sharp contrast between silica core and polymer shell in the phase composition. The thickness of grafted‐polymer shell and the diameter of core‐shell particles increase with the increasing ratio of monomer to silica. A control experiment was carried out by conventional free radical emulsion copolymerization of MPS‐grafted silica and styrene under comparable conditions. The resulting data provide further insight into the chemical composition of grafted‐polymers that are grown from the silica surface through RAFT process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 467–484, 2009     

Adsorption of Polyelectrolyte-Nanoparticle Systems on Silica: Influence on Interaction Forces

In this work, we have studied the interfacial properties of cationic polyelectrolyte (PE) and silica nanoparticle (NP) systems at macroscopic silica surfaces by means of ellipsometry. The influence of adsorbed layers on the interactions between silica surfaces was also investigated using the bimorph surface force apparatus. Added nanoparticles were observed to strongly swell the interfacial polyelectrolyte layers, an effect partly related to neutralization of charged polyelectrolyte groups. The effect was more pronounced for low charged than for highly charged polyelectrolytes. Overall, the presence of nanoparticles seemed to increase the repulsive interaction measured between silica surfaces. The force measured on approach was long range and quite strongly repulsive. On separation, an attractive bridging interaction was measured for polyelectrolyte-covered surfaces. For the low charged polyelectrolyte used in the study, the force turned repulsive on addition of nanoparticles. For the highly charged polyelectrolyte used, a change from a very strong attraction (involving a jump of the surfaces out of contact) to a very long-range elastic attractive force was observed on adding nanoparticles. The long-range elastic force indicates that polymer chains and nanoparticles form a transient network in the gap between the surfaces. The observed difference in the outward force curves may explain why the addition of nanoparticles appears to improve, e.g., shear-resistance and reflocculation characteristics of polymeric flocculants. Copyright 2000 Academic Press.     

Thermoplastic polyurethane/silica nanocomposite fibers by electrospinning

Thermoplastic polyurethane/silica nanocomposite fibers with good mechanical properties were prepared by electrospinning, using colloidal silica as the source of silica and dimethyl formamide as the solvent. The fiber morphology was examined by field emission scanning electron microscopy. The average fiber diameter is about 0.8 μm with 0–10 wt % silica, and silica nanoparticles were observed on all fiber surfaces. X‐ray photoelectron spectroscopy analysis of Si in combination with transmission electron microscopy observation suggest that silica nanoparticles have a fairly uniform distribution in the fibers rather than enriching on the fiber surfaces. Tensile tests show that the incorporation of silica nanoparticles can bring about a significant reinforcing effect without decreasing the ductility. The reinforcing effect is further confirmed by dynamic mechanical analysis. The thermoplastic polyurethane/silica composite fiber mats can adsorb gold nanoparticles after further treatment with 3‐aminopropyltriethoxysilane, demonstrating that the composite fibers could be used as functional fibers by using the properties of silica nanoparticles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Synthesis of gold–poly(methyl methacrylate) core–shell nanoparticles by surface‐confined atom transfer radical polymerization at elevated temperature

Surface‐confined atom transfer radical polymerization was used to prepare gold nanoparticle–poly(methyl methacrylate) core–shell particles at elevated temperature. First, gold nanoparticles were prepared by the one‐pot borohydride reduction of tetrachloroaurate in the presence of 11‐mercapto‐1‐undecanol (MUD). MUD‐capped gold nanoparticles were then exchanged with 3‐mercaptopropyltrimethoxysilane (MPS) to prepare a self‐assembled monolayer (SAM) of MPS on the gold nanoparticle surfaces and subsequently hydrolyzed with hydrochloric acid. The extent of exchange of MUD with MPS was determined by NMR. The resulting crosslinked silica‐primer layer stabilized the SAM of MPS and was allowed to react with the initiator [(chloromethyl)phenylethyl] trimethoxysilane. Atom transfer radical polymerization was conducted on the Cl‐terminated gold nanoparticles with the CuCl/2,2′‐bipyridyl catalyst system at elevated temperature. The rates of polymerization with the initiator‐modified gold nanoparticles exhibited first‐order kinetics with respect to the monomer, and the number‐average molecular weight of the cleaved graft polymer increased linearly with the monomer conversion. The presence of the polymer on the gold nanoparticle surface was identified by Fourier transform infrared spectroscopy and transmission electron microscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3631–3642, 2005     

Preparation of novel photoreactive polycarbazole‐based microparticles: Reactivity features

Four types of innovative benzophenone (BPh)‐ or aryl azide (ArAz)‐containing photoreactive polycarbazole (polyCbz)‐based microparticles (MPs) were prepared using an oxidative liquid phase polymerization system. Their photochemical reactivity was evaluated by their reaction with highly inert poly(2‐chloro‐paraxylelene) (Parylene C) films. Possible mechanisms for the photochemical reaction of those MPs with Parylene C were discussed. The highly photoreactive BPh was found to react more inside the particle causing internal cross‐linking of MP polyCbz chains, fusion between adjoining particles and deformation of their spherical structure. In contrast, the less reactive but more selective ArAz‐containing MPs were found to react much more with Parylene C. The strong reactivity of such photoreactive MPs toward Parylene C films emphasizes a general method for the functionalization of stable nonfunctional polymeric coatings. This paves the way to simple and solvent‐free functionalization of nonfunctional coatings and materials by light. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Photografting of polymers onto nanosized silica surface initiated by eosin moieties immobilized onto the surface

The photograft polymerization of various vinyl monomers onto nanosized silica surfaces was investigated. It was initiated by eosin moieties introduced onto the silica surface. The preparation of the silica with eosin moieties was achieved by the reaction of eosin with benzyl chloride groups on the silica surface.These were introduced by the reaction of surface silanol groups with 4‐(chloromethyl)phenyltrimethoxysilane in the presence of t‐butyl ammonium bromide as a phase‐transfer catalyst. The photopolymerization of various vinyl monomers, such as styrene, acrylamide, acrylic acid, and acrylonitrile was successfully initiated by eosin moieties on the silica surface in the presence of ascorbic acid as a reducing agent and by oxygen. The corresponding polymers were grafted from the silica surface. The grafting efficiency (percentage of grafted polymer to total polymer formed) in the photoinitiation system was much larger than that in the radical polymerization initiated by surface radicals; these radicals were formed by the thermal decomposition of azo groups introduced onto the silica surface. It was found that the polymer‐grafted silica gave stable dispersions in good solvents of grafted polymer and the wettability of the surfaces can be easily controlled by grafting of polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 600–606, 2005     

Controlled post‐synthesis grafting of thermoresponsive poly(N‐isopropylacrylamide) on mesoporous silica nanoparticles

Ordered mesoporous silica nanoparticles with pore diameter of 5 nm were synthesized by modification of the sol‐gel synthesis method. Post‐synthesis two‐step grafting of thermoresponsive poly(N‐isopropylacrylamide) inside the mesopores of the nanoparticles was carried out by distillation–precipitation polymerization of the methacryloxy‐functionalized mesoporous nanoparticles with N‐isopropylacrylamide monomer. A precise control on the quantity of the grafted polymer was achieved by changing the ratio of monomer to methacryloxy‐functionalized nanoparticles. The polymer‐grafted hybrid nanoparticles obtained were fully characterized by infrared spectroscopy, X‐ray diffraction, dynamic light scattering, transmission electron microscopy, thermal, and gas‐volumetric analyses, which clearly showed presence and thermoresponsive behavior of the polymer inside the mesopores with the preservation of the characteristic mesoporous structure of the nanoparticles. Copyright © 2015 John Wiley & Sons, Ltd.     

A Novel Route to Organic–Inorganic Hybrid Nanomaterials

The in situ formation of functionalized silica nanoparticles is reported. The reactive stabilizers used in the study, [3‐(2‐bromoisobutyryl)propyl]triethoxysilane and [3‐(2‐bromoisobutyryl)propyl]ethoxydimethylsilane, have an atom transfer radical polymerization (ATRP) initiator at the noncondensable end. Condensation with tetraethoxysilane yields silica nanoparticles with a surface‐immobilized initiator. The size of these functionalized silica nanoparticles can be controlled by varying the time of initiator addition and initiator concentration. The silica particle sizes ranged from 10 to 300 nm. With the initiator functionalized silica nanoparticles, ATRP synthesis was performed with styrene, tert‐butyl acrylate, and methyl acrylate to produce organic–inorganic nanomaterials.