Organic/Metallic Nanohybrids Based on Amphiphilic Dumbbell-Shaped Dendrimers
Department of Chemical Engineering, National Chung Hsing University, Taichung 402, Taiwan.ACS Applied Materials & Interfaces (Impact Factor: 6.72). 03/2012; 4(4):1897-908. DOI: 10.1021/am300499k
In this study, we synthesized a series of amphiphilic dumbbell-shaped dendrimers through the addition reactions of a hydrophilic poly(oxyalkylene) with hydrophobic dendrons based on 4-isocyanate-4'-(3,3-dimethyl-2,4-dioxo-azetidine)diphenylmethane with different numbers of branching generations. The addition reaction of azetidine-2,4-diones of dendrons to amines of poly(oxyalkylene) was proceeded by stirring the reactants in dry tetrahydrofuran (THF) under nitrogen at 60 °C. In aqueous media, the dumbbell-shaped dendrimers self-assembled into micelles with their hydrophobic dendrons in the core and their hydrophilic poly(oxyalkylene) segments forming loops in the corona shell. Employing the unique self-assembled micelle structures as templates for subsequent chemical reduction of the Ag(+) ions, we generated new types of organic/metallic [silver nanoparticle (AgNP)] nanohybrid clusters. The long poly(oxyalkylene) loops that extended into the aqueous phase complexed with the Ag(+) ions, providing the suspension with steric stabilization to prevent the AgNPs from collision and flocculation. After reduction, the AgNPs were present in a homogeneous distribution in the round dendrimer micelle-stabilized nanoclusters. The diameter of each AgNP was less than 10 nm; the diameter of each round nanocluster was in the range of 50-200 nm. The encapsulation efficiency of the AgNPs in micelles was about 54-69% for the dumbbell-shaped dendrimer based organic/AgNP nanohybrid.
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ABSTRACT: In this study, we synthesized a dual-functional building intermediate, 4-(3,3-diethyl-2,4-dioxoazetidin-1-yl)benzoyl chloride (DEDA-BC), from readily available starting materials, including 4-isocyanatobenzoyl chloride and p-tolyl isocyanate. In its iterative syntheses of hard segments, we first treated the highly reactive acid chloride of DEDA-BC with the monoamine (aniline) or the diamine (4,4′-methylenedianiline, 4,4′-MDA) to form first-generation azetidien-2,4-dione intermediates. We then reacted these derivatives with 4-aminobenzylamine at the more-selective azetidine-2,4-dione group of DEDA-BC to form the first-generation of benzyl amine extenders. Using this alternating method, we obtained high yields of supramolecular extenders of various chain lengths (n = 1–3) in a systematic manner, without the need for tedious purification steps, under catalyst-free conditions. The mono- and diamine extenders with numbers of repeating units ranging from one to three were synthesized precisely through this new iterative synthetic approach. The molar mass increases between each generation were 365 g mol–1 for the monoamine series and 730 g mol–1 for the diamine series. The three generations of supramolecular extenders possessed the distinctive characteristics of multiple hydrogen bonding moieties and narrow molecular weight distributions. Their gelation phenomena in THF revealed that these amine extenders underwent supramolecular assembly, through intermolecular hydrogen bonding, to form organogels. We used these well-defined extenders with various chain lengths in the preparation of polyurethane (PU) elastomers. Small-angle X-ray scattering revealed well-defined microdomains in the morphologies of the PU elastomers presenting multiply hydrogen-bonded terminal groups. The tensile and thermal properties of the prepared PUs were dependent on the effects of the content of hard segments, the chain length, and the strength of hydrogen bonding.Macromolecules 07/2012; 45(13):5358-5370. DOI:10.1021/ma300815q · 5.80 Impact Factor
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ABSTRACT: Water-soluble fluorescent hyperbranched poly(amido acids) (HBPAAs), based on wholly aliphatic structures were prepared through direct self-condensation of N-(3-aminopropyl) diethano succinate amine (APDESA, AB 2 monomer) in the presence of N,N-dicyclohexylcarbodiimide (DCC) as a condensa-tion agent. The resulting HBPAAs were soluble in water, DMF and THF, and the structure of synthesized AB 2 monomer and polymers was confirmed by IR, 1 H, and 13 C NMR measurements. TEM image indicated that the HBPAAs self-assembled in H 2 O to form a spherical micelle with a diameter ranging from 30 to 50 nm. A significant pH-dependent profile of fluorescent intensity in the pH range from 3 to 10 was observed, wherein pH 4 provided a critical jump as the solution pH was increased. Further increasing the pH to 10 decreased the fluorescence because of partial hydrolysis. Strong fluorescence emission was observed at 395 nm in aqueous media and the fluorescence quantum yields are to 23%. These amphi-philic HBPAAs, with excellent water-solubility, void-rich space, multiple functional peripheries and high blue fluorescence, have potential uses as tracing nanocarriers and molecular-level containers.Polymer 01/2013; 54(2):623. DOI:10.1016/j.polymer.2012.12.013 · 3.56 Impact Factor
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ABSTRACT: Nonlinear optical dendrons with alternating terminal groups of the stearyl group (C18) and chromophore were prepared through a convergent approach. These chromophore-containing dendrons were used as the intercalating agents for montmorillonite via an ion-exchange process. An orderly exfoliated morphology is obtained by mixing the dendritic structure intercalated layered silicates with a polyimide. As a result, optical nonlinearity, i.e. the Pockels effect was observed for these nanocomposites without resorting to the poling process. EO coefficients of 9–22 pm V−1 were achieved despite that relatively low NLO densities were present in the nanocomposites, particularly for the samples comprising the dendrons with alternating moieties. In addition, the hedging effects of the stearyl group on the self-alignment behavior, electro-optical (EO) coefficient and temporal stability of the dendron-intercalated montmorillonite/polyimide nanocomposites were also investigated.04/2013; 4(9):2747-2759. DOI:10.1039/C3PY00034F
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