ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTAn A2 + B3 Approach to Hyperbranched Aliphatic Polyethers Containing Chain End Epoxy SubstituentsTodd Emrick, Han-Ting Chang, and Jean M. J. FréchetView Author Information Department of Chemistry, University of California, Berkeley, California 94720-1460 Cite this: Macromolecules 1999, 32, 19, 6380–6382Publication Date (Web):August 20, 1999Publication History Received3 May 1999Revised27 July 1999Published online20 August 1999Published inissue 1 September 1999https://pubs.acs.org/doi/10.1021/ma990687bhttps://doi.org/10.1021/ma990687brapid-communicationACS PublicationsCopyright © 1999 American Chemical SocietyRequest reuse permissionsArticle Views2010Altmetric-Citations258LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Monomers,Nuclear magnetic resonance spectroscopy,Organic polymers,Polymerization,Polymers Get e-Alerts
pH-Sensitive linkages designed to undergo hydrolysis at mildly acidic pH can trigger the release of therapeutics selectively at targets such as tumor and inflammatory tissues and in the endosomes and lysosomes of cells. Acetals have the potential to be used as linkages for a range of alcohol functionalities, and, by altering their chemical structure, it is possible to tune their hydrolysis rate. The syntheses of four conjugates of model drug molecules with PEO using acetals of varying chemical structure are described herein. Primary and secondary alcohols, as well as syn-1,2-diols, were incorporated in the conjugates. The hydrolysis kinetics were investigated by HPLC, and the conjugates had half-lives ranging from less than 1 min to several days at pH 5.0, with slower hydrolysis at pH 7.4 in all cases. These acetal linkages are therefore promising for use in a variety of drug delivery applications ranging from polymer-drug conjugates to pH-sensitive micelles and nanoparticulate systems.
Nanoscale patterning and electronics fabrication on flexible polymer substrates via direct nanoirnprinting of metal nanoparticles was demonstrated. The metal nanoparticle solution enables a simple one-step metal nanoirnprinting with very low pressure and temperature. Electrical and structural characterizations on flexible substrate during cyclic bending deformations verify the robustness of the nanoimprinted structures to mechanical deformation conditions.
Abstract The divergent dendronization of an ϵ‐caprolactone‐based polymer has been performed to provide access to dendronized polymers with sufficient biocompatibility and degradability for use as drug‐delivery scaffolds. The synthesis was performed through the tin(II) 2‐ethylhexanoate‐catalyzed polymerization of a γ‐functionalized ϵ‐caprolactone monomer, followed by the divergent growth of pendant polyester dendrons at each repeat unit. The resulting dendronized polymers were obtained up to the fourth generation with molecular weights as high as 80,000 Da and with polydispersities between 1.11 and 1.22. The fourth‐generation hydroxyl‐terminated dendronized polymer was degradable under a variety of aqueous conditions. A comparison of the dendronization approach with a procedure involving the ring‐opening polymerization of a second‐generation dendritic macromonomer reveals that the former procedure is best suited for the preparation of this family of dendronized polyesters because it requires shorter reaction times and affords materials with higher degrees of polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3563–3578, 2004
A series of small dendritic structures containing one of two efficient multiphoton absorbing dyes at the periphery and a nile red derivative at the core have been synthesized. These molecules display efficient (>96%) fluorescence resonance energy transfer (FRET) from the periphery to the core on selective excitation of the two-photon absorbing chromophore by either UV (linear absorption) or high-intensity IR (nonlinear absorption) radiation. In addition, a significant increase in core emission is observed on excitation of the peripheral chromophores, compared to direct excitation of the core. This "antenna effect" essentially doubles between increasing dendrimer generations within a series. The combination of the ability of the peripheral chromophores to absorb high-intensity IR radiation, coupled with a very efficient energy transfer process and a significant increase in the fluorescence of the acceptor chromophore, makes these molecules potentially useful for a variety of applications, including optical power limiting and biomedical imaging.
ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTA New Approach to Hyperbranched Polymers by Ring-Opening Polymerization of an AB Monomer: 4-(2-Hydroxyethyl)-ε-caprolactoneMingjun Liu, Nikolay Vladimirov, and Jean M. J. FréchetView Author Information Department of Chemistry, University of California, Berkeley, California 94720-1460 Cite this: Macromolecules 1999, 32, 20, 6881–6884Publication Date (Web):September 15, 1999Publication History Received18 May 1999Revised19 August 1999Published online15 September 1999Published inissue 1 October 1999https://pubs.acs.org/doi/10.1021/ma990785xhttps://doi.org/10.1021/ma990785xrapid-communicationACS PublicationsCopyright © 1999 American Chemical SocietyRequest reuse permissionsArticle Views2019Altmetric-Citations138LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Alcohols,Monomers,Organic polymers,Polymers,Ring-opening polymerization Get e-Alerts
In the area of crosslinked chemical supports, continuous media such as rigid macroporous polymer monoliths have certain advantages. Following an introduction to monolithic porous polymer materials, the various applications of macroporous polymer monoliths are reviewed. The Figure shows an SEM image of a monolith prepared within the confines of a polyimide-coated fused silica capillary.
Photomechanical switching (photoisomerization) of molecules at a surface is found to strongly depend on molecule-molecule interactions and molecule-surface orientation. Scanning tunneling microscopy was used to image photoswitching behavior in the single-molecule limit of tetra-tert-butyl-azobenzene molecules adsorbed onto Au(111) at 30 K. Photoswitching behavior varied strongly with surface molecular island structure, and self-patterned stripes of switching and nonswitching regions were observed having approximately 10 nm pitch. These findings can be summarized into photoswitching selection rules that highlight the important role played by a molecule's nanoscale environment in determining its switching properties.
Self-assembled polyester dendritic bow-ties with various peripheral groups were prepared, and\ntheir association constants were measured by <sup>1</sup>H NMR in CDCl<sub>3</sub>. The two complementary dendrons\nwere prepared by attachment of either a bis(adamantylurea) or a glycinylurea to the focal point of\nthe dendron. The parent self-assembled system with benzylidene acetals on one periphery and\nisopropylidene acetals on the other had an association constant of 520 M<sup>-1</sup>. Upon deprotection of\none dendron, the association constant is increased by more than an order of magnitude as the\nsolubility of the hydroxyl-terminated dendron in CDCl<sub>3</sub> is decreased. In contrast, attachment of\ntri(ethylene oxide) units to the periphery of one dendron lowers the association constant by almost\nan order of magnitude. The causes of these relatively large changes in complex strength are\ndiscussed in terms of solubility, steric effects, competitive hydrogen bonding, and the structure of\nthe dendritic scaffold.
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.
Printed 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.
Dendrimer monolayers have been designed for use as positive resists for scanning probe lithography (SPL). Several new amphiphilic poly(benzyl ether) dendrimers with carboxylic acids at either the focal point or the "periphery" have been prepared. These can form ionically bound dendrimer monolayers that may serve as either positive or negative tone resists for SPL. The amphiphilic dendrimers self-assemble onto (3-aminopropyl)silanized Si(100) wafer surfaces to afford ultrathin films. The dendrimer monolayers were characterized by AFM, ellipsometry, and contact angle goniometry. Patterning a singly charged dendrimer monolayer results in the formation of positive tone holes ∼35 nm in width. Similarly, patterning a multiply charged dendrimer monolayer in a direct-write manner with the scanning probe microscope results in the formation of negative tone oxide features ∼80 nm in width.
High molecular weight poly(p-hydroxystyrene) (PHS) was dendronized in high yield by the divergent grafting of aliphatic polyester dendrons using acetal and ketal protected anhydride derivatives of bis(hydroxymethyl)propionic acid. Relatively low polydispersities (PDI = 1.1-1.3) were maintained throughout the dendronization process. Detailed characterization of a series of these polymers by size exclusion chromatography (SEC) and SEC with multi-angle laser light scattering (SEC-MALLS) clearly shows the effect of dendron steric bulk on the persistence length (ξ) of the polymer main chain in solution. As a result of the fixed degree of polymerization (DP), the main chain rigidification that accompanies lateral dendron growth causes an unusual relationship between Rg,z and molecular weight across a series of generations. The rodlike structure and contour length of the alkylated dendronized polymers was also characterized by scanning force microscopy (SFM) on mica, highly oriented pyrolytic graphite (HOPG), and molybdenum disulfide (MoS2) surfaces. One of the G3 dendronized polymers with an alkylated periphery showed significant physical gelation behavior at concentrations below 1 wt % in several organic solvents, which constitutes additional evidence that the solution phase rigidity of a polymer chain can be enhanced by dendronization.
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.
Porous 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.
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.
.webp){kind=small}