Dendronized linear polymers are prepared from dendritic azides and poly(vinylacetylene) using "click chemistry." The Cu(I)-catalyzed Huisgen [2 + 3] cycloaddition is quantitative up to the third generation.
Components that click: A large number of diverse dendrimers (see scheme) was prepared in almost quantitative yield by the click-chemistry transformation described in the title. In some cases filtration or solvent extraction was the only method required for purification in this highly efficient construction of the triazole units of the dendrimers.
Polyether dendritic compounds bearing folate residues on their surface were prepared as model drug carriers with potential tumor cell specificity. Starting from ester-terminated polyether dendrimers, hydrazide groups were easily introduced to the surface of the dendrimers by reaction with hydrazine. Folate residues were then conjugated to the hydrazide chain ends of the dendrimers by direct condensation with folic acid in the presence of a condensing agent or by reaction with an active ester derivative of folic acid. Essentially complete functionalization of the terminal hydrazide groups was achieved for both the first and the second generation dendrimers with four and eight hydrazide groups. For the G-2 dendrimer with 16 hydrazide groups, an average number of only 12.6 folate residues were attached to each dendrimer. The conjugates are soluble in aqueous medium above pH 7.4. In addition, a similar conjugation of the antitumor drug methotrexate to the dendrimer was also investigated. Once optimized, these molecules may form the basis for a novel family of multivalent drug carriers.
Printed electronics provides a promising potential pathway toward the realization of ultralow-cost RFID tags for item-level tracking of consumer goods. Here, we report on our progress in developing materials, processes, and devices for the realization of ultralow-cost printed RFID tags. Using printed nanoparticle patterns that are subsequently sintered at plastic-compatible temperatures, low-resistance interconnects and passive components have been realized. Simultaneously, printed transistors with mobilities >10/sup -1/ cm/sup 2//V-s have been realized using novel pentacene and oligothiophene precursors for pMOS and ZnO nanoparticles for nMOS. AC performance of these devices is adequate for 135-kHz RFID, though significant work remains to be done to achieve 13.56-MHz operation.
Designed to help define new scientific directions related to complex systems in order to create new understanding about the nano world and complicated, multicomponent structures.
Read morePrinted organic electronics is promising for realizing low-cost flexible displays and RFID tags. We describe the state of the art in printed organic electronics, focusing on advanced materials currently being studied to realize devices with enhanced performance, including soluble oligomer semiconductor precursors, printable self-assembled monolayer dielectrics, and printable high-K dielectric precursors. These materials should enable the realization of devices with low operating voltages and carrier mobilities sufficiently high for the demonstration of high-quality displays and RFID tags on plastic.
Read morePorous monolithic polymers have been prepared by photoinitiated polymerization of mixtures consisting of 2-hydroxyethyl methacrylate, ethylene dimethacrylate, UV-sensitive free radical initiator and porogenic solvent within channels of specifically designed microfluidic chips and used as micromixers. Substituting azobisisobutyronitrile with 2,2-dimethoxy-2-phenylacetophenone considerably accelerated the kinetics of the polymerization. Mixtures of cyclohexanol and 1 -dodecanol and of hexane and methanol were used, respectively, to control the porous properties and therefore the mixing efficiency of the device. The performance of the monolithic mixers has been tested by pumping aqueous solutions of two fluorescent dyes at various flow rates and monitoring the point at which the boundary of both streams completely disappears. Best results were achieved with a monolithic mixer containing very large irregular pores.
Read moreA fullerene-containing norbornene derivative is used for ring-opening metathesis polymerization to synthesize living polymers with high fullerene content. Incorporation of fullerene at every repeat of a small monomer allows high fullerene content and short inter-fullerene distances in a soluble polymer. The living nature of the polymerization also allows the synthesis of diblock copolymers, which exhibit micellar aggregation in solution and phase separation with interpenetrating C60-domains in a thin film upon TEM imaging.
Read moreVapor−liquid equilibria for dendritic-polymer solutions were obtained using a classic gravimetric-sorption method; the amount of solvent absorbed by the dendrimer was measured as a function of solvent vapor pressure. Three series of dendrimers, each with the same tertiary amine core structure, but different surface groups, were investigated in a variety of organic solvents in the range 50−75 °C. The dendrimer surface groups were dodecylamines, octadecyl amides, and polyisobutylene. Solvent absorption depends strongly on dendrimer composition and generation number.
Read moreScanning probe lithography (SPL) has recently been shown to be a versatile technique for patterning semiconductor surfaces. The intense electric field emanating from the scanning probe tip can be used for the patterning of carbon- based self-assembled monolayers and thin films, as well as the anodization or field-enhanced oxidation of passivated metal surfaces. We have been investigating the use of monolayers and ultra-thin films made from dendritic polymers as resists for SPL. Dendrimer films have ben prepare by both covalent and ionic binding to the wafer surface. Silicon wafers were treated with dendritic chlorosilanes to afford self-assembled monolayer from the functionalized dendrons. Ionically bound dendrimer films were prepared by treating an aminopropylsilane-modified wafer surface with a dendritic carboxylic acid. These ultra-thin dendrimer films were characterized by atomic force microscopy, contact angle goniometry, and optical ellipsometry. The dendrimer films were shown to be effective resist for SPL, and we have patterned negative tone oxide images onto dendrimer modified wafer surfaces. Pattern transfer can be achieved by a selective wet etch resulting in the formation of positive tone images.
Read morepH-Responsive drug carriers have the potential to provide selective drug release at therapeutic targets including tumors and in acidic intracellular vesicles such as endosomes and lysosomes. We have developed a new approach to the design of acid-sensitive micelles by incorporating hydrophobic acetal groups on the core block of a micelle-forming block copolymer. Hydrolysis of the acetals at mildly acidic pH is designed to reveal polar groups on the core-forming block, thus changing its solubility and disrupting the micelle, triggering drug release. The anticancer drug doxorubicin (DOX) was encapsulated in these pH-sensitive micelles, and the acetal hydrolysis rates and DOX release rates were determined in the pH range of 4.0 to 7.4 and were compared to those of control systems. The micelle disruption was investigated by dynamic light scattering. The in vitro toxicities of the empty and DOX-loaded micelles were determined, and the intracellular fate of the encapsulated DOX was compared to free DOX using fluorescence confocal microscopy.
Read moreThe gradual rigidification of a single dendronized chain upon increasing the size and density of the dendron units attached to it is studied using a Monte Carlo simulation. The dependence of the backbone flexibility on the size and density of the dendrons is used as an input to study the self-assembly of dendronized polymers using a real space, self-consistent field theoretic method. These calculations predict different phases in melts and solutions, ranging from lamellar to gyroid phases, depending upon various physical (temperature, concentration) and architectural (relative volume fraction of the backbone and the dendron units) parameters.
Read moreThe first dendrimer-supported synthesis of oligothiophenes is reported. The dendrimer serves both as a solubilizing group and a "handle" to facilitate the iterative synthesis of the oligothiophenes. The dendrimer-functionalized oligothiophenes with minimal ring substitution were found to have an extended conjugation compared to analogous oligomers having several linear alkyl chain solubilizing substituents.
Read moreAbstract : Collaborative research was conducted by the faculty known as the Lithography Network. This network brings together world class researchers over a broad set of technology areas essential to the success of maskless lithography and non-conventional patterning. The primary faculty by task is listed below: Task 1: Electron Beam Technology for Maskless Lithography, Professor R. Fabian Pease (Coordinator); Task 2: Spatial Light Modulators for Maskless lithography, Professor Olav Solgaard (Coordinator); Professor Andrew Neureuther; Task 3: Maskless Droplet-On-Demand (DoD) Systems. Professor Vivek Subramanian (Coordinator), Professor Jeffrey Bokhor; Task 4: Advanced Materials for Maskless Lithography, Professor C. Grant Willson (Coordinator), Professor Jean Frechet; Task 5: Characterization of Nanoscale Phenomena for Maskless Lithography, Professor Andrew R. Neureuther (Coordinator); Task 6: Data Compression and Path Issues for Maskless Lithography, Professor Avideh Zakhor (Coordinator).
Read moreThe relationship between film morphology and thin film transistor (TFT) performance was investigated for two symmetrical α,ω-substituted sexithiophene derivatives containing thermally removable solubilizing groups. Solution deposition methods such as spin-coating, dip-casting, and inkjet-printing were optimized for solvent and annealing temperatures, and several substrate surface treatments were explored. The resulting thin films were characterized with AFM and the observed semiconductor performance was found to correlate with the morphology of the films, with the most crystalline films exhibiting the highest performance. Devices showed overall mobilities as high as 0.07 cm2/V s with on/off ratios > 108, which are among the highest reported values for oligothiophenes solution cast at room temperature.
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