Polymers containing coumarin and Ru(BpyMe2)32+ chromophores were synthesized using a grafting approach and also a copolymerization approach. It was found that the solubility of polymers made from Ru-containing monomers was higher than that observed for comparable polymers obtained by grafting of Ru complexes onto bpy-containing prepolymers. The resulting bichromophoric macromolecules exhibited enhanced absorption and luminescence properties compared to the single Ru(BpyMe2)32+ complexes due to a very efficient (>95%) energy transfer between the coumarin donor dyes and the ruthenium chromophores. In addition, a novel system in which two different donor dyes are present together with the Ru complex was synthesized and also found to deliver efficient energy transfer to the ruthenium complexes.
The design of chemically amplified imaging systems based on acid catalyzed thermolytic cleavage of polymer main-chains has been exploited with a variety of structures containing tertiary, allylic, or benzylic ester groups. In all cases, the esters have been designed for their ability to undergo facile thermolytic elimination. This report outlines the preparation, study, and imaging of several polyesters containing thermolytically active moieties. These new acid labile polyesters have been incorporated into two-component imaging materials for which radiation sensitivity is due to the presence of compounds which produce acid upon irradiation. The photogenerated acid is then used to catalyze thermolytic cleavage of the polyester main-chain in a process which does not consume the acid and therefore provides for chemical amplification. Imaging is possible using a variety of radiation sources, from deep-UV to X-rays. The concept of imaging through multiple main-chain cleavage is important as it can lead to self- or dry developing images. In the present study, only partial self-development was observed as one of the diacid liberated by the chain cleavage process was not volatile. A second family of radiation sensitive imaging materials has also been designed based on the catalyzed electrophilic crosslinking of polymers containing aromatic rings. While this new approach is only illustrated here for systems in which crosslinking involves polymer pendant groups, the same design is also applicable to polymer main-chains. This family of crosslinkable, chemically amplified, resist materials shows very high sensitivities of ca. 1mJ/cm2 for exposure in the deep-UV, ca. 1μC/cm2 for E-beam exposure, and ca. 12-15mJ/cm2 for X-ray synchrotron radiation.
The design and preparation of new polyester dendrimer, poly(ethylene oxide) hybrid systems for drug delivery and related therapeutic applications, are described. These systems consist of two covalently attached polyester dendrons, where one dendron provides multiple functional handles for the attachment of therapeutically active moieties, while the other is used for attachment of solubilizing poly(ethylene oxide) chains. By varying the generation of the dendrons and the mass of the poly(ethylene oxide) chains, the molecular weight, architecture, and drug loading can be readily controlled. The "bow-tie" shaped dendritic scaffold was synthesized using both convergent and divergent methods, with orthogonal protecting groups on the periphery of the two dendrons. Poly(ethylene oxide) was then attached to the periphery of one dendron using an efficient coupling procedure. A small library of eight carriers with molecular weights ranging from about 20 kDa to 160 kDa were prepared and characterized by various techniques, confirming their well-defined structures.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolution and solid-state properties of hybrid linear-dendritic block copolymersIvan Gitsov and Jean M. J. FrechetCite this: Macromolecules 1993, 26, 24, 6536–6546Publication Date (Print):November 1, 1993Publication History Published online1 May 2002Published inissue 1 November 1993https://pubs.acs.org/doi/10.1021/ma00076a035https://doi.org/10.1021/ma00076a035research-articleACS PublicationsRequest reuse permissionsArticle Views685Altmetric-Citations161LEARN 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 ISSUEPREVCommunicationNEXTStimuli-Responsive Hybrid Macromolecules: Novel Amphiphilic Star Copolymers With Dendritic Groups at the PeripheryIvan Gitsov and Jean M. J. FréchetView Author Information Baker Laboratory, Department of Chemistry Cornell University Ithaca, New York 14853-1301 Cite this: J. Am. Chem. Soc. 1996, 118, 15, 3785–3786Publication Date (Web):April 17, 1996Publication History Received18 December 1995Published online17 April 1996Published inissue 1 January 1996https://pubs.acs.org/doi/10.1021/ja9542348https://doi.org/10.1021/ja9542348rapid-communicationACS PublicationsCopyright © 1996 American Chemical SocietyRequest reuse permissionsArticle Views1076Altmetric-Citations189LEARN 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:Dendrons,Hydrophilicity,Macromolecules,Micelles,Micellization Get e-Alerts
Read moreThe accelerated synthesis of regular dendritic poly (ether-urethane) macromolecules through growth of two generations in a single synthetic operation has been explored. This procedure requires the use of two AB2 monomers such as 3,5-diisocyanatobenzyl chloride and 3.5-dihydroxybenzyl alcohol that can react pairwise in a one-pot sequential addition procedure. The two monomers are added stepwise to a previously formed first-generation dendrimer to produce a third-generation dendritic molecule without any need for intermediate purification or activation procedures. When 3,5-dihydroxybenzyl alcohol is used as the second monomer, some irregular growth is seen due to the occurrence of a side reaction involving transesterification of the carbamic ester moiety. The side reaction can be avoided if 3,5dihydroxybenzyl alcohol is replaced by methyl 3,5-dihydroxybenzoate.
Read moreAbstract A new approach to resist materials that exhibit chemical amplification is based on systems comprised of three structural units at least one of which is polymeric: (a) an aromatic moiety such as poly(4‐hydroxystyrene), Novolac, or other aromatic compounds which are susceptible to electrophilic aromatic substitution; (b) a latent electrophile which may be polyfunctional and, in the case of this study, is a carbocation precursor; (c) a material which generates strong acid upon irradiation. Exposure of a film containing these three structural components affords a latent image of acid dispersed in the polymer matrix. In a subsequent baking step, the photogenerated acid reacts with the latent electrophile releasing a very reactive carbocationic species which becomes bound to the aromatic moiety. As one of the components of the resist is polymeric and multifunctional, the result is a rapid increase in molecular weight due to branching and crosslinking of the chains. In terms of imaging, this process translates into the formation of a negative image of the mask although under some conditions a positive image may also be produced. The system shows a very high sensitivity and can provide high resolution images devoid of distortion due to the absence of swelling during development.
Read moreADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA new approach to mesophase stabilization through hydrogen bonding molecular interactions in binary mixturesTakashi Kato and Jean M. J. FrechetCite this: J. Am. Chem. Soc. 1989, 111, 22, 8533–8534Publication Date (Print):October 1, 1989Publication History Published online1 May 2002Published inissue 1 October 1989https://pubs.acs.org/doi/10.1021/ja00204a044https://doi.org/10.1021/ja00204a044research-articleACS PublicationsRequest reuse permissionsArticle Views2276Altmetric-Citations601LEARN 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 moreThe preparation and modification of highly functionalized polyether dendrimers containing a versatile diethyl isophthalate terminal group is presented. The convergent synthesis consists of the construction of diester-terminated dendrons containing benzylic bromide functions at the focal point and their subsequent attachment to 4,4'-biphenol cores. Dendrons up to the third generation can be prepared using recrystallization alone as the primary means of purification, allowing the synthesis to be performed on the scale of tens to hundreds of grams. The third and fourth generation bidendron dendrimers (with 32 and 64 terminal ester functionalities, respectively) have been subjected to a variety of surface modification reactions including hydrolysis, ester interchange, and amide−ester interchange, many of which proceed with complete conversion of the functional groups and in high isolated yield. The addition of alcohols such as benzyl alcohol or a first generation 3,5-di(benzyloxy)benzyl alcohol dendron to the dendrimer surface serves to increase the generation number of the dendrimers by one or two in what amounts to a "double convergent growth" approach. The analysis of these structurally precise dendrimers by matrix-assisted laser desorption ionization time of flight is described.
Read moreA variety of strong bases and hydrocarbon-soluble superbases (SB) have been used for the selective metalation of poly(isobutylene-co-p-methylstyrene) at the benzylic p-methyl position. The reaction was monitored by quenching the metalated polymer with chlorotrimethylsilane and measuring the resulting functionalization by 1H NMR spectrometry. A study of different SB's prepared from butyllithium and a heavier alkali metal alkoxide showed the importance of the alkali metal used in the alkoxide. Both the degree of metalation and the selectivity increase with the size of the metal cation (Li+ < Na+ < K+ < Cs+). Best results for the quantitative metalation of all of the benzylic p-methyl groups of the copolymer were obtained using a 2-fold molar excess of the SB derived from s-BuLi and cesium l-(−)-menthoxide in the ratio of 1:3. Ring metalation is estimated to less than 2%, and the polymer backbone is unreactive. Time-dependent metalation reactions carried out between −78 and +65 °C reveal that, regardless of the reaction temperature, maximum metalation takes place in less than 2 min. Other superbases such as [(trimethylsilyl)methyl]potassium or alkali metal amides exhibit negligible reactivities under the reaction conditions used.
Read moreADVERTISEMENT RETURN TO ISSUEPREVArticleStabilization of a liquid-crystalline phase through noncovalent interaction with a polymer side chain [Erratum to document cited in CA111(16):135185v]Takashi Kato and Jean M. J. FrechetCite this: Macromolecules 1990, 23, 1, 360Publication Date (Print):January 1, 1990Publication History Published online1 May 2002Published inissue 1 January 1990https://pubs.acs.org/doi/10.1021/ma00203a065https://doi.org/10.1021/ma00203a065research-articleACS PublicationsRequest reuse permissionsArticle Views171Altmetric-Citations38LEARN 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 moreThe polycondensation of bis-allylic or bis-benzylic diols with dibromomethane under phase transfer catalysis may be used to generate some polyformal polymers and copolymers which depolymerize readily when heated or when subjected to acidolysis. The polymers are best prepared by condensation of diols such as 1,4-dihydroxy-2-cyclohexene or 1,4-dihydroxy-1,2,3,4-tetrahydronaphthalene and CH2Br2 under phase transfer conditions. The polymers which are obtained by this process generally have fairly broad polydispersities and are stable to temperatures higher than 150°C. Under acid catalysis, they decompose below 80°C to afford mainly the aromatic elimination product (benzene or naphthalene), and formaldehyde hydrate. As the polymers absorb very weakly even in the deep-UV (Emax < 300), imaging is possible through formulations incorporating both the polyformals and a small amount of a triarylsulfonium salt or similar photoacid generator. The polyformals can be used as self-developing and chemically amplified imaging systems which operate in the deep-UV and possess good sensitivities due to the catalytic nature of their photoinitiated thermal decomposition.
Read moreAbstract Hydrogen-bonded ferroelectric liquid-crystalline complexes have been obtained by self-assembly of S-(+)-4-(2-methylbutoxy)benzoic acid and trans-4-alkoxy-4'-stilbazoles. Chiral smectic C phases are induced by the formation of the hydrogen bonds between the chiral nonmesogenic benzoic acid and the achiral stilbazoles. The chiral smectic C phase of the complex has been characterized by X-ray measurement. The hydrogen-bonded complex shows stable ferroelectric behavior in electric fields.
Read moreThe synthesis of new poly(siloxysilanes) by polyhydrosilation of AB2, AB4, and AB6 monomers using a solid-supported catalyst is described. Analysis of the polymers by gel permeation chromatography shows weight-average molecular weight values near 5−10 000 amu with polydispersities of ∼2. Addition of fresh monomer to the polymerized material only leads to a slight increase in molecular weight. In all cases, polymerization is accompanied by significant intramolecular cyclization side reaction. These results can be explained by considering factors such as the unequal reactivity of the different oligomeric species and their tendency to form cyclic species, but no clear evidence for a growth-limiting effect arising from steric crowding could be seen. End capping of the terminal silicon hydride groups by hydrosilation with a variety of reagents has been demonstrated, affording a diversity of functionalized poly(siloxysilane) materials.
Read moreAbstract A novel separation medium based on uniform size beads of 4-hydroxystyrene-divinylbenzene can be used for both the size exclusion chromatography of small molecules and their separation by reversed-phase chromatography. The new 5 μm material is prepared by the controlled swelling of monodispersed polystyrene particles, that serve both as porogen and shape template, with a polymerization mixture consisting of the monomers and dibutylphthalate, followed by a suspension polymerization. Removal of the acetoxy groups by hydrolysis with aqueous base leads to the final poly(4-vinylphenol-co-divinylbenzene) monodispersed beads. Polymerization conditions that favor the formation of very small pores were developed to optimize the beads for the SEC separation of small molecules. The SEC calibration curve confirms that the optimized beads contain a large volume of pores suitable for the separation of solutes with a molecular weight of up to about 1000. The ability to separate alkylbenzenes according to their hydrodynamic sizes has been demonstrated using a column packed with this material. In addition, the phenol chemistry used in combination with a hydrophobic crosslinking monomer provides this separation medium with an unusual versatility that allows both reversed phase and normal phase chromatography to be run in the same column after a simple change of the mobile phase.
Read moreA novel convergent approach for the synthesis of dendritic macromolecules is presented and its scope and versatility demonstrated with the synthesis of a series of monodisperse dendritic polyether macromolecules based on 3,5-dihydroxybenzyl alcohol as the monomer unit up to a molecular weight of 40 689.
Read moreEvaluation d'un adhesif a base de lessive residuaire sulfitique, d'une resine alcaline phenol-formaldehyde et d'un catalyseur acide
Read more
.webp){kind=small}