Transparent polymer nanocomposites with high refractive index were prepared by grafting polymer chains onto anatase TiO 2 nanoparticles via a combination of phosphate ligand engineering and alkyneazide ''click'' chemistry. Highly crystalline TiO 2 nanoparticles with 5 nm diameter were synthesized by a solvothermal method and used as high refractive index filler. The synthesized phosphate-azide ligand anchors strongly onto the TiO 2 nanoparticle surface and the azide end group allows for attachment of poly(glycidyl methacrylate) (PGMA) polymer chains through an alkyne-azide ''click'' reaction. The refractive index of the composite material increased linearly from 1.5 up to 1.8 by increasing the loading of TiO 2 particles to 30 vol % (60 wt %). UV-vis spectra show that the nanocomposites exhibited a transparency around 90% throughout the visible light range. It was also found that the PGMAgrafted TiO 2 nanoparticles can be well dispersed into a commercial epoxy resin, forming transparent high refractive index TiO 2 -epxoy nanocomposites.

Tuning the dispersion of inorganic nanoparticles within organic matrices is critical to optimizing polymer nanocomposite properties and is intrinsically difficult due to their strong enthalpic incompatibility. Conventional attempts to use polymer brushes to control nanoparticle dispersion are challenged by the need for high graft density to reduce particle core-core attractions and the need for low graft density to reduce the entropic penalty for matrix penetration into the brush. We validated a parametric phase diagram previously reported by Pryamtisyn et al. (Pryamtisyn, V.; Ganesan, V.; Panagiotopoulos, A. Z.; Liu, H.; Kumar, S. K. Modeling the Anisotropic Self-Assembly of Spherical Polymer-Grafted Nanoparticles. J. Chem. Phys.2009, 131, 221102) for predicting dispersion of monomodal-polymer-brush-modified nanoparticles in polymer matrices. The theoretical calculation successfully predicted the experimental observation that the monomodal-poly(dimethyl siloxane) (PDMS)-brush-grafted TiO(2) nanoparticles can only be well dispersed within a small molecular weight silicone matrix. We further extended the parametric phase diagram to analyze the dispersion behavior of bimodal-PDMS-brush-grafted particles, which is also in good agreement with experimental results. Utilizing a bimodal grafted polymer brush design, with densely grafted short brushes to shield particle surfaces and sparsely grafted long brushes that favor the entanglement with matrix chains, we dispersed TiO(2) nanoparticles in high molecular weight commercial silicone matrices and successfully prepared thick (about 5 mm) transparent high-refractive-index TiO(2)/silicone nanocomposites.

Visibly highly transparent indium tin oxide (ITO)/epoxy nanocomposites were prepared by dispersing polyglycidyl methacrylate (PGMA) grafted ITO nanoparticles into a commercial epoxy resin. The oleic acid stabilized, highly crystalline, and near monodisperse ITO nanoparticles were synthesized via a nonaqueous synthetic route with multigram batch quantities. An azido-phosphate ligand was synthesized and used to exchange with oleic acid on the ITO surface. The azide terminal group allows for the grafting of epoxy resin compatible PGMA polymer chains via Cu(I) catalyzed alkyne-azide "click" chemistry. Transmission electron microscopy (TEM) observation shows that PGMA grafted ITO particles were homogeneously dispersed within the epoxy matrix. Optical properties of ITO/epoxy nanocomposites with different ITO concentrations were studied with an ultraviolet-visible-near-infrared (UV-vis-NIR) spectrometer. All the ITO/epoxy nanocomposites show more than 90% optical transparency in the visible light range and absorption of UV light from 300 to 400 nm. In the near-infrared region, ITO/epoxy nanocomposites demonstrate low transmittance and the infrared (IR) transmission cutoff wavelength of the composites shifts toward the lower wavelength with increased ITO concentration. The ITO/epoxy nanocomposites were applied onto both glass and plastic substrates as visibly transparent and UV/IR opaque optical coatings.

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The polymeric functionalization of quantum dots via ligand exchange is a robust method for the preparation of stable fluorescent particles with high quantum yields. For most biological applications of quantum dots, water solubility is a key requirement; to achieve biocompatibility, polymeric ligand systems that can provide water solubility as well as effective anchoring groups are advantageous. In this work, histamine functional polymers bearing poly(ethylene glycol) (PEG) side chains were prepared using RAFT polymerization. A versatile postmodification strategy using activated ester units of Nmethacryloxysuccinimide (NMS) and poly(ethylene glycol) methacrylate in the polymer chain afforded copolymers ranging from 6K to 50K with low polydispersities, along with tailored composition of each monomer along the copolymer chain. By controlling the monomer ratio, PEGMA molecular weight, time, and temperature, the composition could be tuned to study its effect on quantum dot functionalization. Representative oleate-capped CdSe/Cd x Zn 1−x S QDs purified by a recently established gel permeation chromatography (GPC) method were used to test the effectiveness of the histamine-bearing polymers for preparation of water-soluble QDs. Successful ligand exchange of the QDs was characterized by good dispersions in water, lack of aggregation between QDs, and good quantum yields in water. Overall, the synthetic method demonstrates a facile and robust postmodification strategy for the formation of multiply binding, histamine-bearing copolymers, which can be applied to nanomaterials for fundamental investigations and bioimaging/biodistribution studies. ■ INTRODUCTIONIn the past decade, considerable progress has been seen in applications of semiconductor nanocrystals (quantum dots, QDs) in areas such as light-emitting diodes, 1 solar cells, 2 and bioimaging applications. 3,4 Based on the size and choice of material, the emission and absorption wavelengths of quantum dots can be tuned, allowing for narrow emission bands and high quantum yields. 5,6 The right choice of surface functional groups prevents aggregation of the quantum dots, allows for good dispersions in its environment, passivates the quantum dot surface, and maintains high fluorescence quantum yield. 7 This in turn allows for its successful implementation in various high performance applications.Hence, the need for soft functional materials that allow for quantum dots to be well dispersed in a variety of environments and facilitate stability over extended periods of time is essential. In the case of well-represented II−VI, III−V, and IV−VI compound semiconductors, colloidal quantum dots are synthesized with hydrophobic ligands such as oleic acid and trioctylphosphine; these ligands are necessary to manage precursor reactivity and colloidal stability during high-temperature growth but lead to QDs with low solubility in polar solvents. 7 Encapsulation with surfactants, silica shells, or amphiphilic copolymers can yield stable and water-soluble QDs but adds considerably to hy...