Showing papers by "Virgil Percec published in 2009"

Dendron-Mediated Self-Assembly, Disassembly, and Self-Organization of Complex Systems

Abstract: Dendron-mediated self-assembly, disassembly, and self-organization of complex systems have been investigated. The most ideal building blocks would need to display shape persistence in solution and in the solid state, since only this feature provides access to the use of complementary methods of structural analysis. Most supramolecular dendrimers are chiral even when they are constructed from nonchiral building blocks and are equipped with mechanisms that amplify chirality. This poses additional challenges associated with the understanding of the structural origin of chirality in different supramolecular structures through combinations of structural analysis methods. While many supramolecular structures assembled from dendrimers and dendrons resemble some of the related morphologies generated from block-copolymers, they are much more complex and are not determined by the volume ratio between the dissimilar parts of the molecule.

Single-Electron Transfer and Single-Electron Transfer Degenerative Chain Transfer Living Radical Polymerization

Abstract: The special of Chemical Review informs about studies conducted on single-electron transfer and single-electron transfer degenerative chain transfer living radical polymerization. Researchers have demonstrated that living radical polymerization (LRP) can be significantly effective for the synthesis of tailored polymers. The special issue aims at covering the latest progress in two related polymerization methodologies that rely on single-electron transfer (SET), single-electron transfer degenerative chain transfer living radical polymerization (SET-DTLRP), and single-electron transfer living radical polymerization (SET-LRP). It is demonstrated that SET-DTLRP proceeds through SET initiation and competition of SET activation, deactivation, and degenerative transfer (DT). SET-LRP proceeds exclusively through a SET initiation, activation, and deactivation. It is also revealed that the two techniques have arose from investigations into Cu-catalyzed LRP initiated with sulfonyl halides.

Surface-Dependent Kinetics of Cu(0)-Wire-Catalyzed Single-Electron Transfer Living Radical Polymerization of Methyl Acrylate in DMSO at 25 °C

Abstract: The effect of Cu(0) wire dimensions on the Cu(0) wire/Me6-TREN-catalyzed heterogeneous single-electron transfer living radical polymerization (SET-LRP) of methyl acrylate (MA) initiated with methyl 2-bromopropionate (MBP) in DMSO at 25 °C was analyzed by kinetic experiments. These kinetic results were compared with those of Cu(0) powder/Me6-TREN-catalyzed SET-LRP. Both wire and powder produce perfect SET-LRP with a first-order rate of polymerization in growing species up to 100% conversion. Nevertheless, Cu(0) wire experiments demonstrated SET-LRP with greater perfection, allowing for the accurate determination of the external rate order (vis-a-vis surface area) for heterogeneous Cu(0) catalyst and accurate prediction of kpapp from wire dimension. Cu(0) wire also exhibited a significantly greater control of molecular weight distribution than Cu(0) powder. The combined advantages of easier catalyst preparation, handling, predictability, tunability, simple recovery/recycling, and enhanced control of molecul...

Synthesis of dendritic macromolecules through divergent iterative thio-bromo “Click” chemistry and SET-LRP

Abstract: The development of a novel nucleophilic thio-bromo “Click” reaction, specifically base-mediated thioetherification of thioglycerol with α-bromoesters was reported in an earlier article. The combination of this thio-bromo click reaction with subsequent acylation with 2-bromopropionyl bromide provides an iterative two-step divergent growth approach to the synthesis of a new class of poly(thioglycerol-2- propionate) (PTP) dendrimers. In this article, the addition of a third step, the single-electron transfer living radical polymerization (SET-LRP) of methyl acrylate (MA), was shown to provides access to a three-step “branch” and “grow” divergent approach to dendritic macromolecules wherein poly(methyl acrylate) (PMA) connects the branching subunits. This facile methodology can provide a diversity of dendritic macromolecular topologies and will ultimately provide the means to the development of self-organizable dendritic macromolecules. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3940–3948, 2009

Synthesis of dendrimers through divergent iterative thio-bromo “Click” chemistry

Abstract: The development of a novel nucleophilic thio-bromo “Click” reaction, specifically base-mediated thioetherification of thioglycerol with α-bromoesters, is reported. Combination of this thio-bromo click reaction with subsequent acylation with 2-bromopropionyl bromide provides an iterative two-step divergent growth approach to the synthesis of a new class of poly(thioglycerol-2-propionate) (PTP) dendrimers. This approach is demonstrated in the rapid preparation of four generation (G1–G4) of PTP dendrimers with high-structural fidelity. The isolated G1–G4 bromide-terminated dendrimers can be used directly as dendritic macroinitiators for the synthesis of star-polymers via SET-LRP. Additionally, the intermediate hydroxy-terminated dendrimers are analogs of other water-soluble polyester and polyether dendrimers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3931–3939, 2009

The disproportionation of Cu(I)X mediated by ligand and solvent into Cu(0) and Cu(II)X2 and its implications for SET-LRP

Abstract: Disproportionation of Cu(I)X is the major step in Single-Electron Transfer Living Radical Polymerization (SET-LRP). The disproportionation of Cu(I)X mediated by Me-6-TREN in various solvents was studied through UV-vis spectroscopy and Dynamic Light Scattering (DLS). UV-vis experiments reveal that disproportionation is dependent on both solvent composition and concentration of Me-6-TREN, consistent with a revised equilibrium expression and corroborated by mathematical models. Electrochemistry data do not accurately predict the extent of disproportionation in the presence of Me6-TREN. Exemplified by DMSO, a favored solvent for SET-LRP, LTV-vis spectroscopy shows that under certain conditions disproportionation is four-orders of magnitude greater than the value reported from electrochemistry experiments. Through LTV-vis and DLS analysis, it was demonstrated that DMSO, DMF, DMAC, and NMP, stabilize colloidal Cu(0), while acetone, EtOH, EC, MeOH, PC, and H2O facilitate agglomeration of Cu(0) particles. Additionally, for colloidal Cu(0) stabilizing solvents, the amount of ligand and solvent composition decide the particle size distribution. Therefore, the kinetics of SET-LRP are cooperatively and synergistically determined by the complex interplay of solvent polarity, the extent of disproportionation in the solvent/ligand mixture, and the ability of that mixture to stabilize colloidal Cu(0) or control particle size distribution. The implications of these results for SET-LRP are discussed. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47:5606-5628, 2009

New efficient reaction media for SET‐LRP produced from binary mixtures of organic solvents and H2O

Abstract: SET-LRP is mediated by a combination of solvent and ligand that promotes disproportionation of Cu(I)X into Cu(0) and Cu(II)X 2 . Therefore, the diversity of solvents suitable for SET-LRP is limited. SET-LRP of MA in a library of solvents with different equilibrium constants for disproportionation of Cu(I)X such as DMSO, DMF, DMAC, EC, PC, EtOH, MeOH, methoxyethanol, NMP, acetone and in their binary mixtures with H 2 O was examined. H 2 O exhibits the highest equilibrium constant for disproportionation of Cu(I)X. The apparent rate constant of the polymerization exhibits a linear increase with the addition of H 2 O. This is consistent with higher equilibrium constants for disproportionation generated by addition of H 2 O to organic solvents. Furthermore, with the exception of alcohols and carbonates, the rate constant of polymerization in binary mixtures could be correlated with the Dimroth-Reichardt solvent polarity parameter. This is consistent with the single-electron transfer mechanism proposed for SET-LRP that involves a polar transition state. These experiments demonstrate that the use of binary mixtures of solvents with H 2 O provides a new, simple and efficient method for the elaboration of a large diversity of reaction media that are suitable for SET-LRP even when one of the two solvents does not mediate disproportionation of Cu(I)X.

Self-Assembly of Dendronized Triphenylenes into Helical Pyramidal Columns and Chiral Spheres

Abstract: The synthesis and structural and retrostructural analyses of a library containing 10 triphenylenes functionalized with self-assembling benzyl ether and phenyl propyl ether dendrons are reported. These dendronized triphenylenes adopt a crown rather than discotic conformation. Their crown conformation mediates the self-assembly of the discotic triphenylene unit in helical pyramidal columns and in chiral spheres. The chiral spheres are generated from short segments of helical pyramidal columns that are spherically distorted. Therefore, the chirality of the sphere is determined by a short helical pyramidal column that represents the inner part of the supramolecular sphere. Both the helical pyramidal columns and the chiral spheres represent supramolecular architectures that were self-assembled for the first time from discotic molecules. The helical pyramidal columns self-organize in various hexagonal and rectangular lattices, while the chiral spheres self-organize into cubic and tetragonal periodic arrays and into a quasiperiodic 12-fold liquid quasicrystal. The helical sense of the helical pyramidal columns and of helical spheres is selected by a stereocenter that can be incorporated either in the alkyl groups of the dendron or in the triphenylene part of the dendritic crown via donor-acceptor interactions. The self-assembly process of the dendronized triphenylene donor can be programmed by a new supramolecular "polymer effect" generated by donor-acceptor interactions.

Predicting the structure of supramolecular dendrimers via the analysis of libraries of AB3 and constitutional isomeric AB2 biphenylpropyl ether self-assembling dendrons.

Abstract: The synthesis of 4′-hydroxy-4-biphenylpropionic, 3′,4′-dihydroxy-4-biphenylpropionic, 3′,5′-dihydroxy-4-biphenylpropionic, and 3′,4′,5′-trihydroxy-4-biphenylpropionic methyl esters via three efficient and modular strategies including one based on Ni-catalyzed borylation and sequential cross-coupling is reported. These building blocks were employed in a convergent iterative approach to the synthesis of one library of 3,4,5-trisubstituted and two libraries of constitutional isomeric 3,4- and 3,5-disubstituted biphenylpropyl ether dendrons. Structural and retrostructural analysis of supramolecular dendrimers revealed that biphenylpropyl ether dendrons self-assemble and self-organize into the same periodic lattices and quasi-periodic arrays observed in previously reported libraries, but with larger dimensions, different mechanisms of self-assembly, and improved solubility, thermal, acidic, and oxidative stability. The different mechanisms of self-assembly led to the discovery of two new supramolecular structu...

Self-Assembly of Dendritic Crowns into Chiral Supramolecular Spheres

Abstract: The synthesis and structural and retrostructural analysis of a library of dendronized cyclotriveratrylene containing seven nonchiral and seven chiral self-assembling dendrons is reported. These dendronized cyclotriveratrylenes exhibit a crown conformation that we named dendritic crown. Selected examples of dendritic crowns self-assemble into helical pyramidal columns that self-organize into columnar crystals or into 2-D columnar hexagonal lattices with intracolumnar order. A second group of dendritic crowns self-assembles into helical pyramidal columns and spherical supramolecular dendrimers that self-organize into cubic and tetragonal lattices. A third group of dendritic crowns self-assembles only in spherical supramolecular dendrimers. The helical pyramidal columns and spherical supramolecular dendrimers assembled from dendronized cyclotriveratrylene containing nonchiral dendrons are chiral but racemic while those generated from chiral dendrons exhibit amplified chirality. Structural analysis by a combi...

Cooperative and synergistic solvent effects in SET‐LRP of MA

Abstract: SET-LRP requires a combination of ligand and solvent that mediates the disproportionation of Cu(I)X into Cu(O) activator, and Cu(II) deactivator. The solvent also modulates the kinetics of the reaction. More polar solvents, including mixtures of water and organic solvents enhance the rate of polymerization in accord with the Dimroth-Reichardt parameter. Here, it is demonstrated that a similar effect is observed in binary mixtures of organic solvents, wherein the addition of a more polar solvent to a less polar solvent provides a linear increase in the apparent rate constant of propagation, k . However, this linear relationship does not hold for the entire range of volume fraction for binary mixtures when ethylene carbonate (EC) or MeOH are one of the two components. Results herein, suggest that the kinetics of SET-LRP in these solvent mixtures is cooperatively and synergistically determined by polarity, degree of disproportionation, and also by another parameter related to the ability of the solvent to stabilize colloidal Cu(0) and determine its particle size.

The effect of ligand on the rate of propagation of Cu(0)‐wire catalyzed SET‐LRP of MA in DMSO at 25 °C

Abstract: The effect of initial ligand concentration on the apparent rate constant of propagation of single-electron transfer living radical polymerization (SET-LRP) of MA in DMSO at 25 °C was examined using various lengths of Cu(0) wire as catalyst. It was determined that unlike other parameters such as initiator concentration, solvent concentration, and deactivator concentration, no simple external rate-order for the ligand concentration could be determined. Rather, the response of the rate of SET-LRP to initial ligand concentration is complex and is likely determined by a competition of ligand-dependent extent of disproportionation as well as the role of ligand concentration in the surface mediated activation process. Results suggest that a minimum concentration of ligand is needed to achieve both acceptable reaction rate and reaction control, and therefore, ligand concentration must be considered in designing experimental conditions for SET-LRP.

SET‐LRP of vinyl chloride initiated with CHBr3 in DMSO at 25 °C

Abstract: The development of Cu(0)/TREN/CuBr2-catalyzed SET-LRP of VC initiated with CHBr3 in DMSO at 25 °C is reported. The use of CuBr2 additive allows for the first LRP of low molecular weight VC (target DP = 100), as well as lower Cu powder loading levels, improved Ieff and control in the synthesis of higher molecular VC, targeted degree of polymerization = 350, 700, 1,000, 1,400. 1H NMR and HSQC confirm the bifunctionality of CHBr3 as an initiator and suggest that deleterious side-reactions such as the formation of allylic chlorides occur primarily at the onset of the reaction. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4130–4140, 2009

Dendronized supramolecular polymers self-assembled from dendritic ionic liquids

Abstract: The synthesis, structural, and retrostructural analysis of a library of self-assembling dendrons containing triethyl and tripropyl ammonium, pyridinium and 3-methylimidazolium chloride, tetrafluoroborate, and hexafluorophosphate at their apex are reported. These dendritic ionic liquids self-assemble into supramolecular columns or spheres which self-organize into 2D hexagonal or rectangular and 3D cubic or tetragonal liquid crystalline and crystalline lattices. Structural analysis by X-ray diffraction experiments demonstrated the self-assembly of supramolecular dendrimers containing columnar and spherical nanoscale ionic liquid reactors segregated in their core. Both in the supramolecular columns and spheres the noncovalent interactions mediated by the ionic liquid provide a supramolecular polymer and therefore, these assemblies represent a new class of dendronized supramolecular polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4165–4193, 2009

Elucidating the Structure of the Pm$\bar 3$n Cubic Phase of Supramolecular Dendrimers through the Modification of their Aliphatic to Aromatic Volume Ratio

Abstract: The synthesis, and structural and retrostructural analysis of a library of second-generation conical dendrons that self-assemble into spherical supramolecular dendrimers is reported. This library consists of amphiphilic dendrons with n-alkyl groups containing from 4 to 16 carbon atoms. The dendrons containing 6 to 16 carbon atoms in their n-alkyl groups self-assemble into spherical supramolecular dendrimers that self-organize in a Pm3n cubic lattice. The structural and retrostructural analysis of the Pm3n lattices generated from the supramolecular dendrimers demonstrated that the volume of the aromatic core of the spherical dendrimers is not dependent on the number of carbon atoms from their alkyl groups. This result facilitated the calculation of the average values of the absolute electron density of the aliphatic and aromatic domains of the spherical supramolecular dendrimers. The relative intensity of the higher order diffraction peaks of the Pm3n lattice increases as the volume of the aliphatic part of the sphere mediated by the number of carbon atoms in the «-alkyl groups decreases. This study demonstrates the maximum increase of the relative intensity of the higher order diffraction peaks of the Pm3n lattice generated from non-hollow supramolecular dendrimers.

Proton Transport from Dendritic Helical-Pore-Incorporated Polymersomes

Abstract: The ability to add synthetic channels to polymersome (polymer vesicle) membranes could lead to novel membrane composites with unique selectivity and permeability. Proton transport through two different synthetic pores, self-assembled from either a dendritic dipeptide, (6Nf-3,4-3,5)12G2-CH2-Boc-L-Tyr-L-Ala-OMe, or a dendritic ester, (R)-4Bp-3,4-dm8G1-COOMe, incorporated into polymersome membranes are studied. Polymersomes provide an excellent platform for studying such transport processes due to their robustness and mechanical and chemical stability compared to liposomes. It is found that the incorporated dendritic dipeptide and dendritic ester assemble into stable helical pores in the poly(ethylene oxide)-polybutadiene (PEO-PBD) polymersomes but not in the poly(2-methyloxazoline)-poly(dimethylsiloxane)-poly(2-methyl oxazoline) (PMOX-PDMS-PMOX) polymersomes. The incorporation is confirmed by circular dichroism (CD), changes in purely synthetic mechanical strength (e.g., areal expansion modulus) as assessed by micropipette aspiration, and cryo-TEM. In addition to the structural analyses, a transport measurement shows the incorporated dendritic helical pores allow facile transport of protons across the polymersome membranes after up to one month of storage. This integration of synthetic porous channels with polymersome substrates could provide a valuable tool for studying active transport processes in a composite membrane. These composites will ultimately expand the family of biologically inspired porous-membrane mimics.

Synthesis of poly(2‐methoxyethyl acrylate) by single electron transfer—Degenerative transfer living radical polymerization catalyzed by Na2S2O4 in water

Abstract: Living radical polymerization of 2-methoxyethyl acrylate (MEA) was achieved by single-electron-transfer/degenerative transfer mediated living radical polymerization (SET-DTLRP) in water catalyzed by sodium dithionate. The poly(2-methoxyethyl acrylate) is an amphiphilic polymer with a hydrophobic part (polyethylene chain) and a mildly hydrophilic tail. The plots of number-average molecular weight versus conversion and ln{[M]0/[M]} versus time are linear, indicating a controlled polymerization. This method leads to the preparation of α,ω-di(iodo) poly(2-methoxyethyl acrylate)s (α,ω-di(iodo)PMEA) macroinitiators that can be further functionalized. The molecular weight distributions were determined using a combination of three detectors (TriSEC): right-angle light scattering (RALLS), a differential viscometer (DV) and refractive index (RI). The method studied in this work represents a possible route to prepare well-tailored macromolecules made of 2-methoxyethyl acrylate (biocompatible material) in an environmentally friendly reaction medium. To the best of our knowledge there is no previous report dealing with the synthesis of PMEA by any LRP approach in aqueous medium. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4454–4463, 2009

Synthesis of α,ω‐di(iodo)PVC and of four‐arm star PVC with identical active chain ends by SET‐DTLRP of VC initiated with bifunctional and tetrafunctional initiators

Abstract: Na2S2O4-catalyzed single-electron transfer – degenerative chain transfer-mediated living radical polymerization (SET-DTLRP) of VC initiated with the bifunctional initiators 1,2-bis(iodopropionyloxy)ethane, dimethyl 2,5-diiodohexanedioate, and bis(2-methoxyethyl)-2,5-diiodohexanedioate as well as the tetrafunctional initiator pentaerythritol tetrakis(2-iodopropionate) is reported. This SET-DTLRP was performed in water at ambient temperature in the presence of polyvinyl alcohol and hydroxypropyl methylcellulose surfactants and provides methods for the synthesis of α,ω-di(iodo)PVC with two identical active chain ends and of four-arm star PVC with four identical active chain ends. These difunctional and tetrafunctional derivatives of PVC are also macroinitiators for the synthesis of ABA triblock copolymers and four-arm star block copolymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 635–652, 2009

Synthesis of the four‐arm star‐block copolymer [PVC‐b‐PBA‐CH(CH3)COOCH2]4C by SET‐DTLRP initiated from a tetrafunctional initiator

Abstract: Pentaerythritol tetrakis(2-iodopropionate) was used as a tetrafunctional initiator for the Na2S2O4 catalyzed SET-DTLRP of n-butyl acrylate in water at room temperature. The resulting tetrafunctional poly(n-butyl acrylate) macroinitiator with Mn = 14,864 or Mn = 3627 per arm was used to initiate the SET-DTLRP of vinyl chloride and provide the first examples of four-arm star-block copolymers [PVC-b-PBA-CH(CH3)COOCH2]4C. The Mn of the PVC segment from each arm of the four-arm star-block copolymer varied between 353 and 33,622. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 628–634, 2009

Introduction to frontiers in polymer synthesis.

Abstract: One of the pioneers of the field of Polymer Science made the following statement in the Preface to his book on the history of polymers: “I found out quickly that there is no substitute for reading eVery reference citedssecond-hand citations are incredibly unreliable.”1 In spite of the fact that I agree with this statement, in an interval of less than ten years I accepted for the second time2 the invitation of Josef Michl to edit a Thematic Issue of Chemical Reviews on Polymer Synthesis. The first reason was that the Editors of this journal and the members of their Editorial Board and Editorial Office provide an example of dedication and leadership for the other editors in the field of chemistry, and therefore, it was impossible to turn them down. The second reason is that some of the current electronic sources of information are no more reliable than secondhand citations, and therefore, I feel that comprehensive reviews written by premier practitioners are needed more than ever before. The third reason was that, at this time, the field of polymer synthesis is already accepted as a traditional discipline of chemistry and currently is assuming the leading role of bridging between organic, organometallic, and supramolecular chemistry, catalysis, biology, medicine, and nanotechnology. Therefore, it is very important to read the most recent developments at the Frontiers in Polymer Synthesis described by the inventors of this interdisciplinary field. Since the previous thematic issue was published,1 several landmark discoveries produced by the field of polymer synthesis were recognized as providers of unprecedented impacts in novel functional materials through conducting organic polymers3 and in synthetic methods for organic, medicinal, polymer, and supramolecular chemistry through metathesis reactions.4 These topics were extensively reviewed and will not be discussed again in this thematic issue. The ultimate goal of polymer synthesis is to design, through a complementary and synergistic combination of covalent and supramolecular methods, synthetic polymers that approach the structural complexity and fidelity of biological macromolecules. These synthetic polymers would have to ultimately provide functions on demand with the aid of their precise primary structure. While these synthetic methods are in their early stages of development, traditional but more efficient synthetic methods for polymer synthesis continue to be elaborated. The goal of this Thematic Issue is to highlight with a group of 27 reviews the most recent advances in the development of new synthetic methods and strategies of polymer synthesis and discuss their use in the design of polymers with complex topology and architecture and the self-assembly of complex systems. The current state of the art in polymer synthesis relies on living polymerization methods that were discovered for carbanionic species in 1956.5a,b They were followed by living polymerizations proceeding by carbocations,5c metathesis4 and free radicals.5d,e In the first four reviews, Sawamoto and co-workers, Yamago, Rosen and Percec, and Satoh and Kamigaito discuss advances in novel methodologies for living radical polymerization of olefins, for the elaboration of complex polymer topology and the control of tacticity. Chen and Nozaki and co-workers review the developments of coordination polymerization of polar vinyl monomers by single-site metal catalysts. Aoshima and Kanaoka highlight living cationic polymerization of functional monomers. Kobayashi and Makino present the latest developments in enzymatic polymerization, while Akagi discusses the synthesis of helical polyacetylene by asymmetric polymerization in a chiral liquid crystal field. The use of living radical polymerization to develop various bioapplications, mostly by RAFT, is reviewed by Davis, Perrier, and co-workers, while Klok and co-workers discuss the synthesis of polymer brushes by living radical polymerization. Hadjichristidis and co-workers survey the living ring-opening polymerization of N-carboxyanhydrides of R-aminoacids for the synthesis of well-defined peptides, while Kricheldorf teaches us how to synthesize biodegradable and biocompatible polymers by ring-opening polymerization of various heterocyclic compounds. One of the most recent developments in polymer synthesis involves the transformation of step condensation polymerization reactions6 into chain polymerization reactions and their use in the generation of living condensation polymerization. This topic is reviewed by Yokozawa and Yokoyama. Virgil Percec was born and educated in Romania (Ph.D. 1976). He defected from his native country in 1981 and after short postdoctoral appointments at the University of Freiberg, Germany, and the University of Akron, U.S.A., he joined the Department of Macromolecular Science at Case Western Reserve University in Cleveland (1982) as an Assistant Professor. He was promoted to Associate Professor in 1984, to Professor in 1986, and to Leonard Case Jr. Chair in 1993. In 1999 he moved to the University of Pennsylvania as P. Roy Vagelos Professor of Chemistry. Percec’s research interest lies at the interface between organic, bioorganic, supramolecular, polymer chemistry, and liquid crystals, where he contributed over 620 refereed publications, 50 patents, and over 1000 endowed and invited lectures. His list of awards includes Honorary Foreign Member to the Romanian Academy (1993), Humboldt Award for Senior American Scientists (1997), NSF Research Award for Creativity in Research (1990, 1995, 2000), PTN Polymer Award from The Netherlands (2002), the ACS Award in Polymer Chemistry (2004), the Staudinger-Durrer Medal from ETH (2005), the International Award of the Society of Polymer Science from Japan (2007), and the H. F. Mark Medal from the Austrian Research Institute for Chemistry and Technology (2008). He is a Fellow of IUPAC (2001), PMSE Division of ACS (2003), AAAS (2004), and RSC (2008). He holds Doctor Honoris Causa Degrees from the Polytechnic University, Jassy, Romania, and from the University of Athens, Greece (both from 2007). He is the editor of the Journal of Polymer Science, Part A: Polymer Chemistry (since 1996) and of the book series Liquid Crystals and serves on the Editorial Boards of 20 international journals. Chem. Rev. 2009, 109, 4961–4962 4961

Self-Assembling Dendronized Dendrimers

Abstract: The amine groups from the periphery of poly(propylenimine) dendrimers [DAB-(NH2)n] (n = 4 and 8) were reacted with the carboxylic groups of five different first and second generation self-assembling dendrons. The amidation was mediated by the peptide bond forming reagent 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT)/N-methylmorpholine (NMM). All the resulting dendronized dendrimers self-assemble into helical pyramidal columns that self-organize into columnar hexagonal and columnar rectangular 2D lattices and in supramolecular spheres that self-organize into 3D Pm3n and P42/mnm tetragonal lattices. The structural and retrostructural analysis of the supramolecular dendrimers by X-ray diffraction experiments demonstrated that supramolecular dendritic spheres are assembled from various spherical fragments, including conical and half-sphere in which the DAB dendrimer is confined to their apex. Dendritic-crown is the most frequently encountered conformation of the dendronized dendrimers that is responsible for the assembly of helical pyramidal columns.

Synthesis of high glass transition temperature copolymers based on poly(vinyl chloride) via single electron transfer—Degenerative chain transfer mediated living radical polymerization (SET‐DTLRP) of vinyl chloride in water

Abstract: α,ω-di(iodo) poly(isobornyl acrylate) macroiniators (α,ω-di(iodo)PIA) with number average molecular weight from Mn,TriSEC = 11,456 to Mn,TriSEC = 94,361 were synthesized by single electron transfer-degenerative chain transfer mediated living radical polymerization (SET-DTLRP) of isobornyl acrylate (IA) initiated with iodoform (CHI3) and catalyzed by sodium dithionite (Na2S2O4) in water at 35 °C. The plots of number average molecular weight vs conversion and ln{[M]0/[M]} vs time are linear, indicating a controlled polymerization. α,ω-di(iodo) poly(isobornyl acrylate) have been used as a macroinitiator for the SET-DTLRP of vinyl chloride (VCM) leading to high Tg block copolymers PVC-b-PIA-b-PVC. The dynamic mechanical thermal analysis of the block copolymers suggests just one phase indicating that copolymer behaves as a single material. This technology provides the possibility of synthesizing materials based on PVC with higher Tg in aqueous medium. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009

Induced Helical Backbone Conformations of Self-Organizable Dendronized Polymers

Abstract: Control of function through the primary structure of a molecule presents a significant challenge with valuable rewards for nanoscience. Dendritic building blocks encoded with information that defines their three-dimensional shape (e.g., flat-tapered or conical) and how they associate with each other are referred to as self-assembling dendrons. Self-organizable dendronized polymers possess a flat-tapered or conical self-assembling dendritic side chain on each repeat unit of a linear polymer backbone. When appended to a covalent polymer, the self-assembling dendrons direct a folding process (i.e., intramolecular self-assembly). Alternatively, intermolecular self-assembly of dendrons mediated by noncovalent interactions between apex groups can generate a supramolecular polymer backbone. Self-organization, as we refer to it, is the spontaneous formation of periodic and quasiperiodic arrays from supramolecular elements. Covalent and supramolecular polymers jacketed with self-assembling dendrons self-organize. The arrays are most often comprised of cylindrical or spherical objects. The shape of the object is determined by the primary structure of the dendronized polymer: the structure of the self-assembling dendron and the length of the polymer backbone. It is therefore possible to predictably generate building blocks for single-molecule nanotechnologies or arrays of supramolecules for bottom-up self-assembly. We exploit the self-organization of polymers jacketed with self-assembling dendrons to elucidate how primary structure determines the adopted conformation and fold (i.e., secondary and tertiary structure), how the supramolecules associate (i.e., quaternary structure), and their resulting functions. A combination of experimental techniques is employed to interrogate the primary, secondary, tertiary, and quaternary structure of the self-organizable dendronized polymers. We refer to the process by which we interpolate between the various levels of structural information to rationalize function as retrostructural analysis. Retrostructural analysis validates our hypothesis that the self-assembling dendrons induce a helical backbone conformation in cylindrical self-organizable dendronized polymers. This helical conformation mediates unprecedented functions. Self-organizable dendronized polymers have emerged as powerful building blocks for nanoscience by virtue of their dimensions and ability to self-organize. Discrete cylindrical and spherical structures with well-defined dimensions can be visualized and manipulated individually. More importantly, they provide a robust framework for elucidating functions available only at the nanoscale. This Account will highlight structures and functions generated from self-organizable dendronized polymers that enable integration of the nanoworld with its macroscopic universe. Emphasis is placed on those structures and functions derived from the induced helical backbone conformation of cylindrical self-organizable dendronized polymers.

Processes for the preparation of biphenyl compounds

Abstract: The invention concerns processes for the synthesis of a compound of the formula: wherein: R 1 and R 2 are each, independently, C 1 -C 12 alkyl, CO 2 R 3 , OR 4 , R 5 (OR 6 ), or C 6 -C 18 aryl; R 3 -R 6 are each, independently, C 1 -C 12 alkyl or C 6 -C 12 aryl; and n and m are each, independently, O or an integer from 1-5; said process comprising: —contacting a compound of the formula H0-R 7 -0H with BH 3 and a compound of the formula in the presence of a nickel-containing catalyst to produce a first product, where R 7 is a C 2 -C 12 hydrocarbon group and X is a halogen, OMs or OTs; —contacting the first product in situ with a compound of the formula: in the presence of a nickel-containing catalyst to produce a compound of formula I, where Z is a halogen.

Polyvinyl chloride containing multiarmed star copolymers

Abstract: The invention concerns processes for the production of multiarmed star copolymers comprising polymerizing vinyl chloride with a multifunctional initiator in the presence of Na 2 S 2 O 4 and water. The invention also concerns polymers made from the processes and articles made from the polymers.

Two-Step, One-Pot Ni-Catalyzed Neopentylglycolborylation and Complementary Pd/Ni-Catalyzed Cross-Coupling with Aryl Halides, Mesylates, and Tosylates.

Abstract: Two-step, one-pot neopentylglycolborylation of aryl iodides and bromides catalyzed by NiCl2(dppe) and NiCl2(dppp) is reported. Electron-rich and electron-deficient aryl neopentylglycolboronates were efficiently cross-coupled with aryl iodides, bromides, chlorides, mesylates, and tosylates by exploiting complementary Pd/Ni and Ni/Ni catalysis. The borylation route was further extended to a three-step, one-pot synthesis of biaryls via in situ Ni-catalyzed borylation and Pd-mediated cross-coupling.