Showing papers on "Polymer published in 2009"
TL;DR: Fluorene-Based Copolymers ContainingPhosphorescent Complexes and Carbazole-Based Conjugated Polymers R5.1.3.
Abstract: -phenylenevinylene)s L4. Fluorene-Based Conjugated Polymers L4.1. Fluorene-Based Copolymers ContainingElectron-Rich MoietiesM4.2. Fluorene-Based Copolymers ContainingElectron-Deficient MoietiesN4.3. Fluorene-Based Copolymers ContainingPhosphorescent ComplexesQ5. Carbazole-Based Conjugated Polymers R5.1. Poly(2,7-carbazole)-Based Polymers R5.2. Indolo[3,2-
3,686 citations
TL;DR: This data indicates that self-Assembled Monolayers and Walled Carbon Nanotubes with high adhesion to Nitroxide-Mediated Polymerization have potential in the well-Defined Polymer Age.
Abstract: Keywords: Fragmentation Chain-Transfer ; Self-Assembled Monolayers ; Walled Carbon Nanotubes ; Well-Defined Polymer ; Nitroxide-Mediated Polymerization ; Block-Copolymer Brushes ; Poly(Methyl Methacrylate) Brushes ; Transfer Raft Polymerization ; Quartz-Crystal Microbalance ; Poly(Acrylic Acid) Brushes Reference EPFL-REVIEW-148464doi:10.1021/cr900045aView record in Web of Science Record created on 2010-04-23, modified on 2017-05-10
1,542 citations
TL;DR: A strategy to create photodegradable poly(ethylene glycol)–based hydrogels through rapid polymerization of cytocompatible macromers for remote manipulation of gel properties in situ is reported.
Abstract: We report a strategy to create photodegradable poly(ethylene glycol)-based hydrogels through rapid polymerization of cytocompatible macromers for remote manipulation of gel properties in situ. Postgelation control of the gel properties was demonstrated to introduce temporal changes, creation of arbitrarily shaped features, and on-demand pendant functionality release. Channels photodegraded within a hydrogel containing encapsulated cells allow cell migration. Temporal variation of the biochemical gel composition was used to influence chondrogenic differentiation of encapsulated stem cells. Photodegradable gels that allow real-time manipulation of material properties or chemistry provide dynamic environments with the scope to answer fundamental questions about material regulation of live cell function and may affect an array of applications from design of drug delivery vehicles to tissue engineering systems.
1,532 citations
TL;DR: It was found that films with finely distributed polymer/fulleride interpenetrating network exhibited improved solar cell conversion efficiency, and the results proved that polymer solar cells have a bright future.
Abstract: This paper describes synthesis and photovoltaic studies of a series of new semiconducting polymers with alternating thieno[3,4-b]thiophene and benzodithiophene units. The physical properties of these polymers were finely tuned to optimize their photovoltaic effect. The substitution of alkoxy side chains to the less electron-donating alkyl chains or introduction of electron-withdrawing fluorine into the polymer backbone reduced the HOMO energy levels of polymers. The structural modifications optimized polymers’ spectral coverage of absorption and their hole mobility, as well as miscibility with fulleride, and enhanced polymer solar cell performances. The open circuit voltage, Voc, for polymer solar cells was increased by adjusting polymer energy levels. It was found that films with finely distributed polymer/fulleride interpenetrating network exhibited improved solar cell conversion efficiency. Efficiency over 6% has been achieved in simple solar cells based on fluorinated PTB4/PC61BM films prepared from m...
1,366 citations
TL;DR: In this paper, the initiator molecules were covalently bonded to the graphene surface via a diazonium addition and the succeeding atom transfer radical polymerization linked polystyrene chains (82 wt% grafting efficiency).
Abstract: For developing high performance graphene-based nanocomposites, dispersal of graphene nanosheets in polymer hosts and precise interface control are challenging due to their strong interlayer cohesive energy and surface inertia. Here we report an efficient method to functionalize graphene nanosheets. The initiator molecules were covalently bonded to the graphene surface via a diazonium addition and the succeeding atom transfer radical polymerization linked polystyrene chains (82 wt% grafting efficiency) to the graphene nanosheets. The prominent confinement effect arising from nanosheets resulted in a 15 °C increase in the glass transition temperature of polystyrene compared to the pure polymer. The resulting polystyrene nanocomposites with 0.9 wt% graphene nanosheets revealed around 70% and 57% increases in tensile strength and Young's modulus. The protocol is believed to offer possibilities for optimizing the processing properties and interface structure of graphene-polymer nanocomposites.
1,226 citations
TL;DR: In this article, the use of pretreated natural fibers in polymer matrix-based composites has been reviewed and the effect of surface modification of natural fibers on the properties of fibers and fiber reinforced polymer composites is also discussed.
Abstract: In recent years, natural fibers reinforced composites have received much attention because of their lightweight, nonabrasive, combustible, nontoxic, low cost and biodegradable properties. Among the various natural fibers; flax, bamboo, sisal, hemp, ramie, jute, and wood fibers are of particular interest. A lot of research work has been performed all over the world on the use of natural fibers as a reinforcing material for the preparation of various types of composites. However, lack of good interfacial adhesion, low melting point, and poor resistance towards moisture make the use of natural fiber reinforced composites less attractive. Pretreatments of the natural fiber can clean the fiber surface, chemically modify the surface, stop the moisture absorption process, and increase the surface roughness. Among the various pretreatment techniques, graft copolymerization and plasma treatment are the best methods for surface modification of natural fibers. Graft copolymers of natural fibers with vinyl monomers provide better adhesion between matrix and fiber. In the present article, the use of pretreated natural fibers in polymer matrix-based composites has been reviewed. Effect of surface modification of natural fibers on the properties of fibers and fiber reinforced polymer composites has also been discussed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
1,201 citations
TL;DR: In this article, the authors present an overview of the development of proton exchange membrane fuel cells (PEMFCs), including polymer synthesis, membrane casting, physicochemical characterizations and fuel cell technologies.
1,156 citations
TL;DR: In nanopore analytics, individual molecules pass through a single nanopore giving rise to detectable temporary blockades in ionic pore current, which ranges from nucleic acids, peptides, proteins, and biomolecular complexes to organic polymers and small molecules.
Abstract: In nanopore analytics, individual molecules pass through a single nanopore giving rise to detectable temporary blockades in ionic pore current. Reflecting its simplicity, nanopore analytics has gained popularity and can be conducted with natural protein as well as man-made polymeric and inorganic pores. The spectrum of detectable analytes ranges from nucleic acids, peptides, proteins, and biomolecular complexes to organic polymers and small molecules. Apart from being an analytical tool, nanopores have developed into a general platform technology to investigate the biophysics, physicochemistry, and chemistry of individual molecules (critical review, 310 references).
1,022 citations
TL;DR: The challenging synthesis of the dendrimers attracted especially scientists with a strong organic chemistry background and led to beautifully designed macromolecules, which allowed a deeper insight into the effect of branching and functionality.
Abstract: “Life is branched” was the motto of a special issue of Macromolecular Chemistry and Physics1 on “Branched Polymers”, indicating that branching is of similar importance in the world of synthetic macromolecules as it is in nature. The significance of branched macromolecules has evolved over the last 30 years from just being considered as a side reaction in polymerization or as a precursor step in the formation of networks. Important to this change in perception of branching was the concept of “polymer architectures”, which formed on new starand graft-branched structures in the 1980s and then in the early 1990s on dendrimers and dendritic polymers. Today, clearly, controlled branching is considered to be a major aspect in the design of macromolecules and functional material. Hyperbranched (hb) polymers are a special type of dendritic polymers and have as a common feature a very high branching density with the potential of branching in each repeating unit. They are usually prepared in a one-pot synthesis, which limits the control on molar mass and branching accuracy and leads to “heterogeneous” products with a distribution in molar mass and branching. This distinguishes hyperbranched polymers from perfectly branched and monodisperse dendrimers. In the last 20 years, both classes of dendritic polymers, dendrimers as well as hb polymers, have attracted major attention because of their interesting properties resulting from the branched architecture as well as the high number of functional groups.2 The challenging synthesis of the dendrimers attracted especially scientists with a strong organic chemistry background and led to beautifully designed macromolecules, which allowed a deeper insight into the effect of branching and functionality. Dendrimers have been considered as perfect “nano-objects” where one can control perfectly size and functionality, which is of high interest in nanotechnology and biomedicine. hb polymers, however, were considered from the beginning as products suitable for larger-scale application in typical polymer fields like coatings and resins, where a perfect structure is sacrificed for an easy and affordable synthetic route. Thus, the first structures that were reported paralleled the chemistry used for linear polymers like typical polycondensation for polyester synthesis. More recently, unconventional synthetic methods have been adopted also for hb polymers and related structures. Presently, a vast variety of highly branched structures have been realized and studied regarding their properties and potential application fields. Excellent reviews appeared covering synthesis strategies, properties, and applications, like the very recent tutorial by Carlmark et al.,3 the comprehensive book on hyperbranched polymers covering extensively synthesis and application * E-mail: voit@ipfdd.de; lederer@ipfdd.de. Chem. Rev. 2009, 109, 5924–5973 5924
994 citations
TL;DR: Ionic liquids (ILs) are continuing as important media in which to effect various kinds of polymerizations, and it is particularly noteworthy that ionic polymerization are being developed in IL solvents and that atom transfer radical polymerization (ATRP) catalysts are being attached to ILs to make them more easily recoverable in living polymerizations as mentioned in this paper.
978 citations
TL;DR: A new low band gap semiconducting polymer, PTB1, was synthesized and found promising for solar energy harvesting, and an external quantum efficiency of 67% and fill-factor of 65% are achieved, both of which are among the highest values reported for a solar cell system based on a lowBand gap polymer.
Abstract: A new low band gap semiconducting polymer, PTB1, was synthesized and found promising for solar energy harvesting. Simple polymer solar cells based on PTB1 and methanofullerene [6,6]-phenyl-C71-butyric acid methyl esters (PC71BM) exhibit a solar conversion efficiency of 5.6%. An external quantum efficiency of 67% and fill-factor of 65% are achieved, both of which are among the highest values reported for a solar cell system based on a low band gap polymer.
TL;DR: This Review surveys different classes of reactive polymer precursors bearing chemoselective handles and discusses issues related to the preparation of these reactive polymers by direct polymerization of appropriately functionalized monomers as well as the post-polymerization modification of these precursor into functional polymers.
Abstract: Post-polymerization modification is based on the direct polymerization or copolymerization of monomers bearing chemoselective handles that are inert towards the polymerization conditions but can be quantitatively converted in a subsequent step into a broad range of other functional groups. The success of this method is based on the excellent conversions achievable under mild conditions, the excellent functional-group tolerance, and the orthogonality of the post-polymerization modification reactions. This Review surveys different classes of reactive polymer precursors bearing chemoselective handles and discusses issues related to the preparation of these reactive polymers by direct polymerization of appropriately functionalized monomers as well as the post-polymerization modification of these precursors into functional polymers.
TL;DR: In this paper, a review of recent developments in the synthesis of functional polymers with controlled architecture and site-specific functionality via applying controlled radical polymerization (CRP) techniques is reviewed.
TL;DR: This work suggests that the characteristics of released silver ions depend on the nature of the silver antimicrobial used and the polymer matrix, and this review focuses on the mechanisms of various silver forms as antimicrobial agents against different microorganisms and biofilms.
TL;DR: The success and degree of muco-adhesive bonding is influenced by various polymer-based properties such as the degree of cross-linking, chain length and the presence of various functional groupings as mentioned in this paper.
TL;DR: The miniemulsion process allows the formation of complex structured polymeric nanoparticles and the encapsulation of a solid or liquid, an inorganic or organic, or a hydrophobic or hydrophilic material into a polymer shell.
Abstract: The miniemulsion process allows the formation of complex structured polymeric nanoparticles and the encapsulation of a solid or liquid, an inorganic or organic, or a hydrophobic or hydrophilic material into a polymer shell. Many different materials, ranging from organic and inorganic pigments, magnetite, or other solid nanoparticles, to hydrophobic and hydrophilic liquids, such as fragrances, drugs, or photoinitators, can be encapsulated. Functionalization of the nanoparticles can also be easily obtained. Compared to polymerization processes in organic solvents, polymerization to obtain polymeric nanoparticles can be performed in environmentally friendly solvents, usually water.
TL;DR: In this paper, the authors reported the preparation of mechanically strong and ductile polyvinyl alcohol/graphene oxide composite films with a layered structure simply by vacuum filtration.
TL;DR: In this article, the vertical phase separation of spin-coated poly(3-hexylthiophene) (P3HT):fullerene derivative blends was investigated using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM).
Abstract: A method which enables the investigation of the buried interfaces without altering the properties of the polymer films is used to study vertical phase separation of spin-coated poly(3-hexylthiophene) (P3HT):fullerene derivative blends. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analysis reveals the P3HT enrichment at the free (air) surfaces and abundance of fullerene derivatives at the organic/substrate interfaces. The vertical phase separation is attributed to the surface energy difference of the components and their interactions with the substrates. This inhomogeneous distribution of the donor and acceptor components significantly affects photovoltaic device performance and makes the inverted device structure a promising choice.
TL;DR: In this article, a review of the thermal processing of starch-based polymers is presented, including both fundamental science such as microstructure, phase transition and rheology, as well as processing techniques, conditions and formulations.
TL;DR: This review discusses promising approaches to multiple controls of polymer structures, analysis systems for low-dimensional polymer assemblies and the construction of PCP-polymer nanohybrids, which are strong enticements to researchers in the areas of inorganic, materials and polymer chemistry.
Abstract: Recent developments in polymerizations within the nanochannels of porous coordination polymers (PCPs) are covered in this tutorial review. The characteristic features of PCPs are regular structures, controllable channel sizes and shapes, a designable surface functionality, and flexible frameworks, which can be utilized for precision polymer synthesis and specific polymer confinement. This review discusses promising approaches to multiple controls of polymer structures, analysis systems for low-dimensional polymer assemblies and the construction of PCP–polymer nanohybrids, which are strong enticements to researchers in the areas of inorganic, materials and polymer chemistry.
TL;DR: It is demonstrated that microwave heating in combination with the screening of comonomer reactant ratios can be used to obtain donor-acceptor copolymers with high average molecular weights and properties that make them suitable for solar cell incorporation.
Abstract: The most efficient plastic solar cells comprise a blend of conjugated polymer and a suitable electron acceptor, typically a fullerene derivative. Therefore narrow-bandgap conjugated polymers are currently sought for the fabrication of such devices. A significant challenge is being able to predict device function and performance from consideration of the molecular connectivity and dimensions of the partners within the active layer. Improved chemical syntheses are therefore required to make structurally varied polymers and enable the delineation of structure–function relationships with the aim of improving power conversion efficiencies. Here, we demonstrate that microwave heating in combination with the screening of comonomer reactant ratios can be used to obtain donor–acceptor copolymers with high average molecular weights and properties that make them suitable for solar cell incorporation. Furthermore, we highlight the importance of high molecular weight and the contribution of solubilizing side groups in determining the final device properties.
TL;DR: The biochemical and mechanical properties of fibrin have recently been exploited in numerous studies that suggest its potential for applications in medicine and bioengineering.
Abstract: Fibrin gels, prepared from fibrinogen and thrombin, the key proteins involved in blood clotting, were among the first biomaterials used to prevent bleeding and promote wound healing. The unique polymerization mechanism of fibrin, which allows control of gelation times and network architecture by variation in reaction conditions, allows formation of a wide array of soft substrates under physiological conditions. Fibrin gels have been extensively studied rheologically in part because their nonlinear elasticity, characterized by soft compliance at small strains and impressive stiffening to resist larger deformations, appears essential for their function as haemostatic plugs and as matrices for cell migration and wound healing. The filaments forming a fibrin network are among the softest in nature, allowing them to deform to large extents and stiffen but not break. The biochemical and mechanical properties of fibrin have recently been exploited in numerous studies that suggest its potential for applications in medicine and bioengineering.
TL;DR: In this article, a modified 3,4-dihydroxyphenylalanine (DOPA) and dopamine self-polymerized and adhered firm to the membrane surfaces in mild aqueous environments.
Book•
07 Jan 2009
TL;DR: In this article, the authors discuss the properties of coordination polymers in terms of magnetic properties and properties, including elasticity, leability, and magnetic properties of coordinating polymers.
Abstract: Introduction Chapter 1: Nets Chapter 2: Interpenetration Chapter 3: Malleability Chapter 4: Transition Metal Coordination Polymers Chapter 5: Lanthanoid Coordination Polymers Organometallic Networks Inorganic-Organic Hybrids Magnetic Properties of Coordination Polymers Porous Coordination Polymers Acentric and Chiral Coordination Polymers Reactive Coordination Polymers Other Properties
TL;DR: A novel triple stimuli sensitive block copolymer assembly that responds to changes in temperature, pH and redox potential is reported that provides the possibility of achieving location-specific delivery.
Abstract: Stimuli-responsive polymers are arguably the most widely considered systems for a variety of applications in biomedical arena. We report here a novel triple stimuli sensitive block copolymer assembly that responds to changes in temperature, pH and redox potential. Our block copolymer design constitutes an acid-sensitive THP-protected HEMA as the hydrophobic part and a temperature-sensitive PNIPAM as the hydrophilic part with an intervening disulfide bond. The micellar properties and the release kinetics of the encapsulated guest molecule in response to one stimulus as well as combinations of stimuli have been evaluated. Responsiveness to combination of stimuli not only allows for fine-tuning the guest molecule release kinetics, but also provides the possibility of achieving location-specific delivery.
TL;DR: In this article, the authors present a review of recent publications on the synthesis of responsive hydrogel thin films and hybrid films with entrapped nanoparticles and reagents by the chemical crosslinking of reactive polymers, layer-by-layer deposition, and block-copolymer self-assembly.
Abstract: In this brief review we address a range of interesting applications and prospects of responsive hydrogel thin films for the fabrication of “smart” responsive surfaces, membranes, sensors with various transduction mechanisms, micro/nanoactuators, and capsules. We show that hydrogel thin films compete with grafted polymers and demonstrate strong advantages for the fabrication of robust multifunctional and multiresponsive surfaces. This article reviews recent publications on the synthesis of responsive hydrogel thin films and hybrid films with entrapped nanoparticles and reagents by the chemical crosslinking of reactive polymers, layer-by-layer deposition, and block-copolymer self-assembly, as well as examining those publications to determine a range of applications.
TL;DR: A comprehensive review of the current understanding on (i) polymorphic crystallization and phase transition of biodegradable polyesters, (ii) isomorphic crystallization of poly(3-hydroxybutyrate) and (iii) poly(butylene adipate) random copolyesters, where the effects of comonomer composition and crystallization conditions are highlighted.
TL;DR: In this paper, the shape memory transition temperature of an amorphous SMP polymers is tuned by changing the crosslink density and the aliphatic epoxy chain length.
TL;DR: In this paper, the authors discuss the recent advances in using nanofibers as hosts for enzyme immobilization by two different methods, surface attachment and encapsulation, and highlight their distinct characteristics.
Abstract: Enzyme immobilization has attracted continuous attention in the fields of fine chemistry, biomedicine, and biosensor. The performance of immobilized enzyme largely depends on the structure of supports. Nanostructured supports are believed to be able to retain the catalytic activity as well as ensure the immobilization efficiency of enzyme to a high extent. Electrospinning provides a simple and versatile method to fabricate nanofibrous supports. Compared with other nanostructured supports (e.g. mesoporous silica, nanoparticles), nanofibrous supports show many advantages for their high porosity and interconnectivity. This review mainly discusses the recent advances in using nanofibers as hosts for enzyme immobilization by two different methods, surface attachment and encapsulation. Surface attachment refers to physical adsorption or covalent attachment of enzymes on pristine or modified nanofibrous supports, and encapsulation means electrospinning a mixture of enzyme and polymer. We make a detailed comparison between these two immobilization approaches and highlight their distinct characteristics. The prospective applications of enzyme immobilized electrospun nanofibers in the development of biosensors, biofuel cells and biocatalysts are also discussed.
TL;DR: A series of low-bandgap polymers based on a soluble chromophore of 3,6-dithiophen-2-yl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4dione (DPP) unit were synthesized by introducing of different electron-rich building blocks copolymerized with DPP unit as discussed by the authors.
Abstract: A series of low-bandgap polymers based on a soluble chromophore of 3,6-dithiophen-2-yl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP) unit were synthesized by introducing of different electron-rich building blocks copolymerized with DPP unit. Four new DPP-based polymers, PDPP-DTS, PDPP-F, PDPP-BDT, and PDPP-BDP, were characterized by GPC, TGA, NMR, UV−vis absorption, and electrochemical cyclic voltammetry. The results indicate that their bandgaps as well as their molecular energy levels are readily tuned by copolymerizing with different conjugated electron-donating units. In order to investigate their photovoltaic properties, polymer solar cell (PSC) devices based on PDPP-DTS, PDPP-F, PDPP-BDT, and PDPP-BDP were fabricated with a structure of ITO/PEDOT:PSS/polymers:PC70BM(1:2,w/w)/Ca/Al under the illumination of AM 1.5G, 100 mW/cm2. The power conversion efficiencies (PCE) of the four DPP-based PSC devices were measured and shown in this paper. The best performance of the PSC device was obtained by using...