ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFullerene-bound dendrimers: soluble, isolated carbon clustersK. L. Wooley, C. J. Hawker, J. M. J. Frechet, F. Wudl, G. Srdanov, S. Shi, C. Li, and M. KaoCite this: J. Am. Chem. Soc. 1993, 115, 21, 9836–9837Publication Date (Print):October 1, 1993Publication History Published online1 May 2002Published inissue 1 October 1993https://pubs.acs.org/doi/10.1021/ja00074a075https://doi.org/10.1021/ja00074a075research-articleACS PublicationsRequest reuse permissionsArticle Views743Altmetric-Citations159LEARN 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 Get e-Alerts
A family of water-soluble, negative-tone, high-resolution, chemically amplified photoresists based on partially or fully deprotected poly(1,2:5,6-di-O-isopropylidene-3-O-methacryloyl-α-d-glucofuranose) is described. Both the molecular weight of the parent ketal-protected polymer and the extent of its deprotection to a water-soluble polymer containing 3-O-methacryloyl-d-glucopyranose repeat units must be carefully controlled to provide good coating and imaging properties. The two ketal protecting groups of the poly(1,2:5,6-di-O-isopropylidene-α-d-glucofuranose) have different reactivity, and their complete removal requires long reaction times under hydrolytic conditions. The detailed deprotection chemistry of the polymer is readily understood through model studies with the fully and partially protected analogues of the polymer pendant groups: 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose and 1,2-isopropylidene-α-d-glucopyranose. When combined with a water-soluble photochemical precursor of acid such as (4-methoxyphenyl)dimethylsulfonium trifluoromethanesulfonate, films of the deprotected or partially deprotected poly(1,2:5,6-di-O-isopropylidene-3-O-methacryloyl-α-d-glucofuranose) undergo acid-catalyzed cross-linking. The enhanced performance of the partially deprotected polymers over that of poly(3-O-methacryloyl-d-glucopyranose) suggests that the presence of remaining hydrophobic groups that afford water dispersibility rather than full solubility may be key to their performance. Imaged negative-tone features as small as 0.2 μm are obtained with these materials that have sensitivities of ca. 30 mJ/cm2 with wholly aqueous casting and processing.
The porosity and flow characteristics of macroporous polymer monoliths that may be used to prepare separation media, flow-through reactors, catalysts, or supports for solid-phase chemistry can be controlled easily during their preparation. Key variables such as temperature, composition of the pore-forming solvent mixture, and content of cross-linking divinyl monomer allow the tuning of average pore size within a broad range spanning 2 orders of magnitude. The polymerization temperature, through its effects on the kinetics of polymerization, is a particularly effective means of control, allowing the preparation of macroporous polymers with different pore size distributions from a single composition of the polymerization mixture. The choice of pore-forming solvent is also important, larger pores being obtained in a poor solvent due to an earlier onset of phase separation. Increasing the proportion of the cross-linking agent present in the monomer mixture not only affects the composition of the final monoliths but also decreases their average pore size as a result of early formation of highly cross-linked globules with a reduced tendency to coalesce. The synergy of different effects has also been observed under specific polymerization conditions using two monomer pairs, styrene−divinylbenzene and glycidyl methacrylate−ethylene dimethacrylate polymerized in close molds. Mercury intrusion porosimetry measurements, inverse size exclusion chromatography, and back pressure measured at different flow rates with the macroporous monoliths were used for the characterization of the porous properties. A good correlation between pore size and flow resistance that follows the Hagen−Poiseuille equation used previously to describe flow through a straight tube has been found.
Read moreAbstract The enantioselective reaction of diethylzinc (II) with the benzaldehydes (I), yielding the alcohols (III), is catalyzed by polymer‐bound chiral amino alcohols.
Read moreCopolymers containing Ru(bpy)3 and coumarin-2 chromophores prepared using both grafting and copolymerization approaches exhibit Förster-type energy-transfer efficiencies ranging from 70% to above 98%.
Read morePorous monodisperse poly(methacrylic acid-co-ethylene dimethacrylate) and poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) beads, which can be used as a platform for the production of separation media, polymeric reagents, and supports, have been prepared using the staged templated suspension polymerization process. Since the direct polymerization of methacrylic acid, which would lead to beads bearing carboxyl groups in a single step, is not compatible with the preparation technique, poly(tert-butyl methacrylate-co-ethylene dimethacrylate) beads were prepared and then selectively deprotected. In contrast, beads containing aliphatic hydroxyl groups can be prepared directly despite the high solubility of 2-hydroxyethyl methacrylate in water. The degree of functionalization and porous properties of the beads are largely controlled by the monomer composition in the polymerization mixture. One application for the functionalized beads is the preparation of very selective chiral separation media for HPLC of enantiomers.
Read moreAcylation resins in a new monolithic format have been prepared by the functionalization of polyethylene-encased porous poly(chloromethylstyrene-co-divinylbenzene) disks. These disks have been obtained from a monolithic rod prepared by polymerization in a cylindrical glass mold, then cut into a disk format. A free radical azo initiator 4,4'-azobis(4-cyanovaleric acid) attached to available chloromethyl functionalities at the surface of the pores was used to initiate graft polymerization of 4-acetoxystyrene or chloromethylstyrene from the surface. Addition of a small percentage of divinylbenzene to the polymerization mixture leads to the formation of a layer of swellable reactive polymer gel at the surface of the macropores. This both prevents the undesirable increase in flow resistance through the monolith and improves the yield of grafting. The final reaction steps involve formation of an active phenolic moiety grafted to the disks and its reaction with acid anhydride. The use of grafted disks as acylating resin to transform various amines to amides in flow-through operations is demonstrated in a variety of solvents including alcohols. The acylation ability of the depleted disks can easily be recovered, and the disks can be reused many times.
Read moreThe suspension copolymerization of several t-butoxycarbonyl (t-BOC) protected 4-vinyl phenols with divinylbenzene has been studied to produce high porosity 10 μm bead materials with surface areas of 200–300 m2/g for use as separation media. The choice and amount of porogen is critical for the control of porosity and surface area while particle size and size distribution is controlled by other reaction variables. The t-BOC protecting groups of the polymers are easily removed by thermolysis and the deprotected beads are useful in the separation of amines. The relationship between polymer structure and separation ability in h.p.l.c. has been explored and the effect of alkyl substituents located ortho to the phenolic groups is discussed.
Read moreReactive polymers play many roles, from supports for solid-phase synthesis or catalysis to media for separations. Although macroporous polymer beads that provide high reactive capacities and excellent solvent tolerance are well established, approaches to monosized beads with optimized pore structures or multiple chemistries segregated within pores of different sizes have expanded their realm of application. Polymer monoliths containing intricate pore networks can be obtained in any desired shape by a simple molding process and provide unique advantages such as fast kinetics, high reactivity, and high throughput. Applications ranging from immobilized enzyme reactors to fast media for the separation of synthetic or biopolymers are presented.
Read moreADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDendrimer and polystyrene surfactant structure at the air-water interfaceP. M. Saville, J. W. White, C. J. Hawker, K. L. Wooley, and J. M. J. FrechetCite this: J. Phys. Chem. 1993, 97, 2, 293–294Publication Date (Print):January 1, 1993Publication History Published online1 May 2002Published inissue 1 January 1993https://pubs.acs.org/doi/10.1021/j100104a006https://doi.org/10.1021/j100104a006research-articleACS PublicationsRequest reuse permissionsArticle Views337Altmetric-Citations69LEARN 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 options Get e-Alerts
Read moreAbstract A simple molding process carried out within the confines of a chromatographic column has been used for the preparation of macroporous poly(glycidyl methacrylate‐ co ‐ethylene dimethacrylate) and poly(styrene‐ co ‐divinylbenzene) rods. The novel monolithic separation media that are obtained are useful for the HPLC separation of biological and synthetic polymers. The presence of large pores with a diameter of about 1 μm makes the molded rod columns easily permeable to eluents. Therefore, the back pressure of these columns is modest even at high flow rates. In contrast to the conventional HPLC columns packed with beads, all of the mobile phase flows through the continuous monolithic medium. As a result of this total convection, the efficiency of the molded media is almost independent of the flow rate. This improves significantly the separation ability of the rod columns and very fast separations of macromolecules such as peptides, proteins, and synthetic polymers have been demonstrated.
Read moreTo obviate the destructive interaction of highly reactive metallocene catalysts with classical silica-based supports while retaining the advantage of supported catalysts, a noninteracting polystyrene support was developed. Supported catalysts for the polymerization of α-olefins are prepared by treating lightly cross-linked, chloromethylated polystyrene beads consecutively with a secondary amine, an ammonium salt of a weakly coordinating anion, and a neutral dialkylmetallocene. Catalytic sites are distributed homogeneously throughout the support particle, and the polymerization occurs within the bead, in contrast to traditional surface-supported metallocene catalysts. The copolymerization of ethylene and 1-hexene at 40°C affords discrete spherical polyolefin beads with a size (0.3 to 1.4 millimeters) that varies according to the polymerization time.
Read moreADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMolecular self-assembly of liquid crystalline side-chain polymers through intermolecular hydrogen bonding. Polymeric complexes built from a polyacrylate and stilbazolesTakashi Kato, Hideyuki Kihara, Toshiyuki Uryu, Akira Fujishima, and Jean M. J. FrechetCite this: Macromolecules 1992, 25, 25, 6836–6841Publication Date (Print):December 1, 1992Publication History Published online1 May 2002Published inissue 1 December 1992https://pubs.acs.org/doi/10.1021/ma00051a018https://doi.org/10.1021/ma00051a018research-articleACS PublicationsRequest reuse permissionsArticle Views1106Altmetric-Citations174LEARN 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 Get e-Alerts
Read moreADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNew solid-phase catalysts for asymmetric synthesis: cross-linked polymers containing a chiral Schiff base-zinc complexShinichi Itsuno, Yoshiki Sakurai, Koichi Ito, Toshihiro Maruyama, Seiichi Nakahama, and J. M. J. FrechetCite this: J. Org. Chem. 1990, 55, 1, 304–310Publication Date (Print):January 1, 1990Publication History Published online1 May 2002Published inissue 1 January 1990https://pubs.acs.org/doi/10.1021/jo00288a051https://doi.org/10.1021/jo00288a051research-articleACS PublicationsRequest reuse permissionsArticle Views1113Altmetric-Citations152LEARN 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 Get e-Alerts
Read moreAbstract A new type of twin liquid crystalline complex having two terminal mesogenic units and a central flexible spacer has been formed through intermolecular hydrogen bonds between a nonmesogenic aliphatic diacid and mesogenic stilbazoles.
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