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Showing papers in "Macromolecules in 2013"


Journal ArticleDOI
TL;DR: In this article, the authors focus on one particular approach to control the spatial distribution of nanoparticles (NPs) in a polymer matrix, and the properties of polymer-grafted NPs.
Abstract: A recurring challenge in the field of nanocomposites is to control the spatial distribution of nanoparticles (NPs) in a polymer matrix. This issue is of critical importance since it is now well-established that a specific NP dispersion state is necessary to optimize a desired property of polymer nanocomposites (PNCs). This Perspective focuses on one particular approach to controlling NP spatial dispersion, and hence the properties of polymer-based nanocomposites: the use of polymer-grafted NPs. Novel developments over the past decade in synthesis techniques allow us to controllably functionalize NPs with polymer chains. This has ignited considerable interest in this field, leading to significant advances in creating nanocomposites with tunable physical properties. We begin by briefly outlining the various synthetic strategies for functionalizing NPs and then discuss various methods for controllably dispersing them in a polymer matrix. The consequences of having states with controlled NP dispersion on nano...

675 citations


Journal ArticleDOI
TL;DR: In this paper, the authors provide a critical analysis of the current knowledge concerning solvent vapor annealing (SVA) of block polymer thin films and identify key challenges that will be important to overcome for future development of SVA as a practical, reliable, and universal technique for the valorization of block polymers in a wide range of technologies.
Abstract: This Perspective provides a critical analysis of the current knowledge concerning solvent vapor annealing (SVA) of block polymer thin films. Herein, we identify key challenges that will be important to overcome for future development of SVA as a practical, reliable, and universal technique for the valorization of block polymer thin films in a wide range of technologies. The Perspective includes a brief background on thin film block polymer self-assembly, a historical account of the SVA technique, an overview of the SVA fundamentals that are necessary to develop a more comprehensive picture of the overall process, and summaries of relevant and important contributions from the recent literature. We also offer our outlook on SVA and suggest important future directions.

481 citations


Journal ArticleDOI
TL;DR: In this paper, a monomer approach for renewable polymers is presented, which is based on the assumption that natural molecular biomass plays an important role in the field of polymers and can be directly used or derivatized as monomers for controlled polymerization, in a way similar to many petroleum-derived monomers.
Abstract: Natural molecular biomass plays an important role in the field of renewable polymers, as they can be directly used or derivatized as monomers for controlled polymerization, in a way similar to many petroleum-derived monomers. We deliver this perspective primarily based on a monomer approach. Biomass-derived monomers are separated into four major categories according to their natural resource origins: (1) oxygen-rich monomers including carboxylic acids (lactic acid, succinic acid, itaconic acid, and levulinic acid) and furan; (2) hydrocarbon-rich monomers including vegetable oils, fatty acids, terpenes, terpenoids and resin acids; (3) hydrocarbon monomers (bio-olefins); and (4) non-hydrocarbon monomers (carbon dioxide). A variety of emerging synthetic tools (controlled polymerization and click chemistry) are particularly summarized. An overview on future opportunities and challenges, which are critical to promote biorefinery in the production of renewable chemicals and polymers, is given.

421 citations


Journal ArticleDOI
TL;DR: In this paper, the main alternative strategies being developed with a focus on PHUs from vegetable oils and derivatives are described with the focus on biobased polyhydroxyurethanes (PHUs).
Abstract: From a green and sustainable chemistry standpoint, the current challenge in the polyurethane’s industry is to switch from petrobased polyurethanes (PUs) to biobased polyhydroxyurethanes (PHUs) This review describes the main alternative strategies being developed with a focus on PHUs from vegetable oils and derivatives The substitution of petrobased polyols by natural oil based polyols was the first route to biobased PUs to be developed The second strategy involves synthesis without the need of harmful isocyanate by the nucleophilic polyaddition of polyamines to polycyclic carbonates The technological barrier to the synthesis of biobased cyclic carbonates could be overcome by the chemical transformation of epoxidized vegetable oils or by the use of glycerine carbonate-based intermediates New families of biobased PHUs with a lower environmental footprint could be generated

299 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reported the preparation of a furan polymer, poly(2,5-furandimethylene succinate) by means of a condensation reaction between bio-based monomers.
Abstract: We report the preparation of a furan polymer, poly(2,5-furandimethylene succinate) by means of a condensation reaction between bio-based monomers. A reversible Diels–Alder reaction between furan and maleimide groups allowed the formation of network polymers cross-linked by a bismaleimide. By controlling the amount of the bismaleimide, mechanical properties were varied widely. These network polymers healed well when their broken surfaces were activated by bismaleimide solutions or solvent. The polymers also displayed excellent self-healing ability without external stimulus. This polymer class offers a wide range of possibilities to produce materials from biomass that have both practical mechanical properties and healing ability. These materials have the potential to bring great benefits to our daily lives by enhancing the safety, performance, and lifetime of products.

286 citations


Journal ArticleDOI
TL;DR: In this article, carbon-hydrogen bond activation and subsequent carbon-carbo-activation are discussed. But, the authors focus on the problem of increasing the range of properties that can be realized in π-conjugated materials.
Abstract: π-Conjugated small molecules, oligomers, and macromolecules are being used in the fabrication of a wide variety of organic electronic devices such as organic field-effect transistors (OFETs), organic photovoltaic (OPV) devices, and organic light-emitting diodes (OLEDs). Efficient syntheses involving fewer steps, fewer toxic reagents, and highly reactive compounds are needed to lower the cost of materials in a manner that is fundamentally more eco-friendly. Additionally, synthetic approaches for π-conjugated materials with more functional group tolerance are desirable to expand the range of properties that can be realized in such materials. Developing new synthetic routes to materials can both broaden the scope of science that can be explored and increase the probability that interesting materials can be developed in an economically viable manner for inclusion in consumer products. One such synthetic strategy that can impact all of these issues is carbon–hydrogen bond activation and subsequent carbon–carbo...

284 citations


Journal ArticleDOI
TL;DR: The primary role of anomalous diffusion in material self-repair for short waiting times is established, while at long waiting times the recovery of bonds across fractured interface is due to hopping diffusion of stickers between different bonded partners.
Abstract: Self-healing polymeric materials are systems that after damage can revert to their original state with full or partial recovery of mechanical strength. Using scaling theory we study a simple model of autonomic self-healing of unentangled polymer networks. In this model one of the two end monomers of each polymer chain is fixed in space mimicking dangling chains attachment to a polymer network, while the sticky monomer at the other end of each chain can form pairwise reversible bond with the sticky end of another chain. We study the reaction kinetics of reversible bonds in this simple model and analyze the different stages in the self-repair process. The formation of bridges and the recovery of the material strength across the fractured interface during the healing period occur appreciably faster after shorter waiting time, during which the fractured surfaces are kept apart. We observe the slowest formation of bridges for self-adhesion after bringing into contact two bare surfaces with equilibrium (very lo...

276 citations


Journal ArticleDOI
TL;DR: The mechanism of reversible deactivation radical polymerization (RDRP) in the presence of Cu0 has been extensively studied in the literature as mentioned in this paper, with a variety of mechanisms proposed.
Abstract: Reversible-deactivation radical polymerization (RDRP) in the presence of Cu0 is a versatile technique that can be used to create well-controlled polymers with complex architectures. Despite the facile nature of the technique, there has been a vigorous debate in the literature as to the mechanism of the reaction. One proposed mechanism, named supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP), has CuI as the major activator of alkyl halides, Cu0 acting as a supplemental activator, an inner-sphere electron transfer occurring during the activation step, and relatively slow comproportionation and disproportionation. In SARA ATRP slow activation of alkyl halides by Cu0 and comproportionation of CuII with Cu0 compensates for the small number of radicals lost to termination reactions. Alternatively, a mechanism named single electron transfer living radical polymerization (SET-LRP) assumes that the CuI species do not activate alkyl halides, but undergo instantaneous disprop...

261 citations


Journal ArticleDOI
TL;DR: The electron-donating property of the DTP unit was found to be the strongest among the most frequently used donor units such as benzodithiophene (BDT) or cyclopentadithiophen (CPDT) units in low-bandgap conjugated polymers as mentioned in this paper.
Abstract: We describe the detailed synthesis and characterization of an electron-rich building block, dithienopyran (DTP), and its application as a donor unit in low-bandgap conjugated polymers. The electron-donating property of the DTP unit was found to be the strongest among the most frequently used donor units such as benzodithiophene (BDT) or cyclopentadithiophene (CPDT) units. When the DTP unit was polymerized with the strongly electron-deficient difluorobenzothiadiazole (DFBT) unit, a regiorandom polymer (PDTP–DFBT, bandgap = 1.38 eV) was obtained. For comparison with the DTP unit, polymers containing alternating benzodithiophene (BDT) or cyclopentadithiophene (CPDT) units and the DFBT unit were synthesized (PBDT–DFBT and PCPDT–DFBT). We found that the DTP based polymer PDTP–DFBT shows significantly improved solubility and processability compared to the BDT or CPDT based polymers. Consequently, very high molecular weight and soluble PDTP–DFBT can be obtained with less bulky side chains. Interestingly, PDTP–DF...

257 citations


Journal ArticleDOI
TL;DR: P pH-dependent speciation curves were calculated using the equilibrium constants determined by potentiometric titration, providing insight into the pH dependence of histidine-metal ion coordination and guiding the design of metal coordination hydrogels.
Abstract: Transient network hydrogels cross-linked through histidine–divalent cation coordination bonds were studied by conventional rheologic methods using histidine-modified star poly(ethylene glycol) (PEG) polymers. These materials were inspired by the mussel, which is thought to use histidine–metal coordination bonds to impart self-healing properties in the mussel byssal thread. Hydrogel viscoelastic mechanical properties were studied as a function of metal, pH, concentration, and ionic strength. The equilibrium metal-binding constants were determined by dilute solution potentiometric titration of monofunctional histidine-modified methoxy-PEG and were found to be consistent with binding constants of small molecule analogues previously studied. pH-dependent speciation curves were then calculated using the equilibrium constants determined by potentiometric titration, providing insight into the pH dependence of histidine–metal ion coordination and guiding the design of metal coordination hydrogels. Gel relaxation ...

249 citations


Journal ArticleDOI
TL;DR: In this article, the synthesis, crystal structure, and physicomechanical properties of a biobased polyester prepared from 2,5-furandicarboxylic acid (FDCA) and 1,4-butanediol were described.
Abstract: This paper describes the synthesis, crystal structure, and physicomechanical properties of a biobased polyester prepared from 2,5-furandicarboxylic acid (FDCA) and 1,4-butanediol. Melt-polycondensation experiments were conducted by a two-stage polymerization using titanium tetraisopropoxide (Ti[OiPr]4) as a catalyst. Polymerization conditions (catalyst concentration, reaction time and second stage reaction temperature) were varied to optimize poly(butylene-FDCA), PBF, and molecular weight. A series of PBFs with different Mw were characterized by DSC, TGA, DMTA, X-ray diffraction and tensile testing. Influence of molecular weight and melting/crystallization enthalpy on PBF material tensile properties was explored. Cold-drawing tensile tests at room temperature for PBF with Mw 16K to 27K showed a brittle-to-ductile transition. When Mw reaches 38K, the Young modulus of PBF remains above 900 MPa, and the elongation at break increases to above 1000%. The mechanical properties, thermal properties and crystal st...

Journal ArticleDOI
TL;DR: In this paper, the authors discuss recent progress toward techniques that achieve directed self-assembly of block copolymer thin films, including substrate prepatterning, nanoimprint lithography, molecular transfer printing, solvent treatment, and zone processing approaches.
Abstract: Block copolymers have garnered significant attention in the past few decades due to their ability to self-assemble into nanoscale structures (∼10–100 nm), making them ideal for emerging nanotechnologies, such as nanolithography, nanotemplating, nanoporous membranes, and ultrahigh-density storage media. Many of these applications require thin film geometries, in which the block copolymers form well-ordered nanostructures and/or precisely controlled domain orientations. In this Perspective, we discuss recent progress toward techniques that achieve directed self-assembly of block copolymer thin films. Substrate prepatterning, nanoimprint lithography, molecular transfer printing, solvent treatment, and zone processing approaches are highlighted. Finally, we comment on recent developments in high-throughput and in situ characterization methods, and we provide future research directions for thin film nanostructure refinement.

Journal ArticleDOI
TL;DR: In this article, the authors leverage the enormous research and development efforts that have been invested in the production of high-modulus polymer fibers to advance understanding of the mechanisms for thermal transport in this class of materials.
Abstract: Polymers have many desirable properties for engineering systems–e.g., low mass density, chemical stability, and high strength-to-mass ratio–but applications of polymers in situations where heat transfer is critical are often limited by low thermal conductivity. Here, we leverage the enormous research and development efforts that have been invested in the production of high-modulus polymer fibers to advance understanding of the mechanisms for thermal transport in this class of materials. Time-domain thermoreflectance (TDTR) enables direct measurements of the axial thermal conductivity of a single polymer fiber over a wide temperature range, 80 < T < 600 K. Relaxation of thermoelastic stress in the Al film transducer has to be taken into account in the analysis of the TDTR data when the laser spot size is small because the radial modulus of the fiber is small. This stress relaxation is controlled by the velocity of the zero-order symmetric Lamb mode of a thin Al plate. We find similarly high thermal conduct...

Journal ArticleDOI
TL;DR: This Perspective describes how studies at the mat level have provided crucial knowledge about the structure and properties of electrospun nanofibers with a particular emphasis on their molecular orientation.
Abstract: Electrospinning is the most versatile and popular technique for preparing nanofibers from a very broad range of polymer systems. In spite of more than 20 years of studies, our understanding of the relationships between the microstructure and the properties of these fibers, and how they are influenced by the electrospinning conditions, remains fragmentary. This is especially true for molecular orientation—a critical parameter that is often invoked to explain the properties of fibers but that is challenging to quantify properly. Recently, the emergence of characterization techniques enabling studies at the single fiber level, including their orientation, has propelled the field in new directions and provided a wealth of new knowledge. In this Perspective, we review and discuss our current understanding of the structure and properties of electrospun nanofibers with a particular emphasis on their molecular orientation. We first describe how studies at the mat level have provided crucial knowledge about the im...

Journal ArticleDOI
TL;DR: In this paper, Lamellae-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) films, with bulk period L 0, were directed to assemble on lithographically nanopatterned surfaces.
Abstract: Lamellae-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) films, with bulk period L0, were directed to assemble on lithographically nanopatterned surfaces. The chemical pattern was comprised of “guiding” stripes of cross-linked polystyrene (X-PS) or poly(methyl methacrylate) (X-PMMA) mats, with width W, and interspatial “background” regions of a random copolymer brush of styrene and methyl methacrylate (P(S-r-MMA)). The fraction of styrene (f) in the brush was varied to control the chemistry of the background regions. The period of the pattern was Ls. After assembly, the density of the features (domains) in the block copolymer film was an integer multiple (n) of the density of features of the chemical pattern, where n = Ls/L0. The quality of the assembled PS-b-PMMA films into patterns of dense lines as a function of n, W/L0, and f was analyzed with top-down scanning electron microscopy. The most effective background chemistry for directed assembly with density multiplication corresponded to...

Journal ArticleDOI
TL;DR: Positron annihilation spectroscopy (PAS) is a novel method that provides molecular-level information about complex macromolecular structure in a manner different from, but complementary to, conventional physical and chemical methodology as mentioned in this paper.
Abstract: Positron annihilation spectroscopy (PAS) is a novel method that provides molecular-level information about complex macromolecular structure in a manner different from, but complementary to, conventional physical and chemical methodology. This paper presents a perspective of PAS in polymeric systems covering 12 aspects: historical, spacial, spherical quantum model, anisotropic structure, voids, positronium chemistry, time, positron annihilation lifetime spectroscopy and data analysis, variable monoenergetic slow positron beam techniques and depth profiling, elemental analysis, multidimensional instrumentation advances in PAS, and free volume and free-volume theories.

Journal ArticleDOI
TL;DR: In this article, the structure, morphology, and related applications of semicrystalline polymer CNT nanocomposites (PCNs) are discussed, followed by a brief discussion on transcrystallization and linear nucleation in polymers.
Abstract: Polymer nanocomposites have been an area of active research for the past 20 years. Of all potential fillers for polymer nanocomposites, carbon nanotubes (CNTs) are of particular interest due to their low mass density, high aspect ratio, and excellent mechanical, electrical, and thermal properties. In semicrystalline polymer CNT nanocomposites (PCNs), CNTs are viewed as nucleation agents that can affect polymer crystallization. However, it is challenging to quantify and compare results from different research groups, mainly due to the complexity of CNTs. Different chiralities, diameters, surface functional groups, surfactants used, and sample preparation processes can affect PCN crystallization. In this Perspective, we will focus on the structure, morphology, and related applications of semicrystalline PCNs. We will first present the introduction to semicrystalline PCNs followed by a brief discussion on transcrystallization and linear nucleation in polymers. The detailed interface structure and morphology ...

Journal ArticleDOI
TL;DR: The chain shape of polymers affects many aspects of their behavior and is governed by their intramolecular interactions as mentioned in this paper, and it is clear that a hierarchy of structural features in these polymers controls charge transport.
Abstract: The chain shape of polymers affects many aspects of their behavior and is governed by their intramolecular interactions. Delocalization of electrons along the backbone of conjugated polymers has been shown to lead to increased chain rigidity by encouraging a planar conformation. Poly(3-hexylthiophene) and other poly(3-alkylthiophenes) (P3ATs) are interesting for organic electronics applications, and it is clear that a hierarchy of structural features in these polymers controls charge transport. While other conjugated polymers are very rigid, the molecular structure of P3AT allows for two different planar conformations and a significant degree of torsion at room temperature. It is unclear, however, how their chain shape depends on variables such as side chain chemistry or regioregularity, both of which are key aspects in the molecular design of organic electronics. Small-angle neutron scattering from dilute polymer solutions indicates that the chains adopt a random coil geometry with a semiflexible backbon...

Journal ArticleDOI
TL;DR: In this article, it has been proved that surface adsorption of polymers on cellulose nanocrystal (CN) as compatibilizer, such as hydrophilic polyoxyethylene (PEO), can improve its thermal stability due to the shielding and wrapping of PEO.
Abstract: Impressive mechanical properties and reinforcing capability make cellulose nanocrystal (CN) a promising candidate as biomass nanofiller for the development of polymer-based nanocomposites. With the recent announcement of large-scale CN production, the use of industrial processing techniques for the preparation of CN-reinforced nanocomposites, such as extrusion, is highly required. However, low thermal stability of sulfuric acid-prepared CN limits the processing since most polymeric matrices are processed at temperatures close to 200 °C or above. It has been proved that surface adsorption of polymers on CN as compatibilizer, such as hydrophilic polyoxyethylene (PEO), can improve its thermal stability due to the shielding and wrapping of PEO. However, the weak combination between CN and PEO allows the free movement of surface polymer, which can induce the self-aggregation of CN and microphase separation in composites especially during melt processing. Using carboxylation–amidation reaction, short chains pol...

Journal ArticleDOI
TL;DR: In this article, a broad frequency (10−1−106 Hz) and temperature range (178−423 K) was used to probe the polymer/silica interface and two relaxation processes were identified for the composites: one corresponding to the bulklike polymer and a second one related to polymer chains close to the silica surface.
Abstract: Samples with different amounts of poly(vinyl acetate) adsorbed on silica particles were prepared in order to study their interfacial interactions and dynamics. The interface of adsorbed polymers to a substrate plays an important role in many applications such as polymer nanocomposites, thin films, and coatings. Characterization of such interfaces is thus of high importance since they were found to differ from bulk properties. Thermogravimetric analysis (TGA) is applied to analyze the amounts of polymer adsorbed on silica particles. Broadband dielectric spectroscopy (BDS) is employed in a broad frequency (10–1–106 Hz) and temperature range (178–423 K) in order to probe the polymer/silica interface. Two relaxation processes can be identified for the composites: one corresponding to the bulklike polymer and a second one related to polymer chains close to the silica surface. For the latter the dynamic glass transition is shifted to higher temperature due to reduced mobility. This effect is investigated in dep...

Journal ArticleDOI
TL;DR: In this article, a combination of transport-property measurements and structural characterization is used to demonstrate that confinement of Nafion in thin films induced thickness-dependent proton conductivity and ionic-domain structure.
Abstract: Ion-conducting polymers are important materials for a variety of electrochemical applications. Perfluorinated ionomers, such as Nafion, are the benchmark materials for proton conduction and are widely used in fuel cells and other electrochemical devices including solar-fuel generators, chlor-alkali cells, and redox flow batteries. While the behavior of Nafion in bulk membranes (10 to 100s μm thick) has been studied extensively, understanding its properties under thin-film confinement is limited. Elucidating the behavior of thin Nafion films is particularly important for the optimization of fuel-cell catalyst layers or vapor-operated solar-fuel generators, where a thin film of ionomer is responsible for the transport of ions to and from the active electrocatalytic centers. Using a combination of transport-property measurements and structural characterization, this work demonstrates that confinement of Nafion in thin films induced thickness-dependent proton conductivity and ionic-domain structure. Confining...

Journal ArticleDOI
TL;DR: In this article, molecular dynamics simulations were performed to study homogeneous nucleation of the crystal phase at about 30% supercooling from the melts of n-pentacontahectane (C150) and a linear polyethylene (C1000), both of which are long enough to exhibit the chain folding characteristic of polymer crystallization.
Abstract: Using a realistic united-atom force field, molecular dynamics simulations were performed to study homogeneous nucleation of the crystal phase at about 30% supercooling from the melts of n-pentacontahectane (C150) and a linear polyethylene (C1000), both of which are long enough to exhibit the chain folding that is characteristic of polymer crystallization. The nucleation rate was calculated and the critical nuclei were identified using a mean first-passage time analysis. The nucleation rate was found to be insensitive to the chain length in this range of molecular weight. The critical nucleus contains about 150 carbons on average and is significantly smaller than the radius of gyration of the chains, at this supercooling. A cylinder model was used to characterize the shape of the crystal nuclei and to calculate the interfacial free energies. A chain segment analysis was performed to characterize the topology of the crystal surface in terms of loops (including folds) and tails. The length distribution of lo...

Journal ArticleDOI
TL;DR: In this paper, a series of relatively straightforward calculation methods using the standard Gaussian 09 software package were evaluated on 22 different conjugated polymer model compounds at the B3lyP and CAM-B3LYP levels of theory and results compared with experiment.
Abstract: Density functional theory (DFT) calculations are useful to model orbital energies of conjugated polymers, yet discrepancy between theory and experiment exist. Here we evaluate a series of relatively straightforward calculation methods using the standard Gaussian 09 software package. Five calculations were performed on 22 different conjugated polymer model compounds at the B3LYP and CAM-B3LYP levels of theory and results compared with experiment. Chain length saturation occurs at approximately 6 and 4 repeat units for homo- and donor–acceptor type conjugated polymers, respectively. The frontier orbital energies are better approximated using B3LYP than CAM-B3LYP, and the HOMO energy can be reasonably correlated with experiment [mean signed error (MSE) = 0.22 eV]. The LUMO energies, however are poorly correlated (MSE = 0.59 eV), and we show that the molecular orbital energy of the triplet state gives a much better estimate of the experimentally determined LUMO level (MSE = −0.13 eV).

Journal ArticleDOI
TL;DR: In this paper, three microporous polyimides with uniform pore sizes were synthesized via one-pot polycondensation from tetrakis(4-aminophenyl)methane, tris-4-amphenyl)amine and 1,3,5-tris-tricornyl-benzene with pyromellitic dianhydride.
Abstract: Three microporous polyimides, MPI-1, MPI-2, and MPI-3, with uniform pores were synthesized via one-pot polycondensation from tetrakis(4-aminophenyl)methane, tris(4-aminophenyl)amine and 1,3,5-tris(4-aminophenyl)benzene with pyromellitic dianhydride, respectively. The amorphous networks exhibit excellent thermal stability, large BET surface areas up to 1454 m2 g–1, and narrow pore size distribution in the range from 5 to 6 A. Their adsorption–desorption isotherms of CO2 are reversible, and the CO2 uptakes at 273 K and 1 bar are up to 16.8 wt %. Moreover, based on the ratios of initial slopes of isotherms, the CO2/N2 and CO2/CH4 separation factors are as high as 102 and 12, respectively. The above CO2 adsorption and separation properties are attributed to the presence of abundant electron-rich heteroatoms in the polyimide networks and the unifrom ultralmicroporous structures. In addition, for MPI-1, the adsorption capacity of benzene vapor is 119.8 wt %, while the separation factors of benzene over nitrogen...

Journal ArticleDOI
TL;DR: Rose Bengal dye has been successfully integrated into the skeleton of a conjugated microporous polymer via palladium-catalyzed Sonogashira-Hagihara cross-coupling polycondensation as mentioned in this paper.
Abstract: Rose Bengal dye has been successfully integrated into the skeleton of a conjugated microporous polymer via palladium-catalyzed Sonogashira–Hagihara cross-coupling polycondensation. These polymers are stable in various solvents, including concentrated hydrochloric acid, and are thermally stable. The resulting polymers show substantial porosity and are highly active for heterogeneous photocatalytic aza-Henry reactions at room temperature for a wide range of substrates. Moreover, this noble-metal-free photocatalyst shows robust recycling capability with good retention of photoactivity over 10 cycles without significant loss of conversion (<10%). These data show that dye-functionalized conjugated microporous polymers are stable, highly active, and reusable noble-metal-free heterogeneous photo-organocatalysts.

Journal ArticleDOI
TL;DR: In this article, a simple yet novel method for fabricating tough hydrogels that are totally physically crosslinked by cooperative hydrogen bonding between a pre-existing polymer and an in situ polymerized polymer is reported.
Abstract: Novel hydrogels with excellent mechanical properties have prompted applications in biomedical and other fields. The reported tough hydrogels are usually fabricated by complicated chemical and/or physical methods. To develop more facile fabrication methods is very important for the practical applications of tough hydrogels. We report a very simple yet novel method for fabricating tough hydrogels that are totally physically cross-linked by cooperative hydrogen bonding between a pre-existing polymer and an in situ polymerized polymer. In this work, tough hydrogels are prepared by heating aqueous acrylamide (AAm) solution in the presence of poly(N-vinylpyrrolidone) (PVP) but without any chemical initiators or covalent bonding cross-linking agents. Mechanical tests of the as-prepared and swollen PVP-in situ-PAAm hydrogels show that they exhibit very high tensile strengths, high tensile extensibility, high compressive strengths, and low moduli. Comparative synthesis experiments, DSC characterization, and molecu...

Journal ArticleDOI
TL;DR: The recent discovery of a living, controlled chain-growth method for synthesizing π-conjugated polymers has ignited the field and led to the development of many new materials as discussed by the authors.
Abstract: The recent discovery of a living, controlled chain-growth method for synthesizing π-conjugated polymers has ignited the field and led to the development of many new materials. This Perspective focuses on the mechanistic underpinnings of the synthetic transformation, highlighting the controversial hypotheses and supporting data. A critical analysis of the literature revealed that the monomer scope remains largely limited to electron-rich monomers at this time. Last, a brief overview of some exciting new materials accessed via this method is provided.

Journal ArticleDOI
TL;DR: Olefin metathesis has been embraced by polymer chemists as a method for creating well-defined polymers as discussed by the authors, and it has been used extensively in the field of silicon chemistry, direct control of tacticity in precision polymers and biological applications.
Abstract: Olefin metathesis has been embraced by polymer chemists as a method for creating well-defined polymers. In particular, ADMET and ROMP have emerged as the primary modes of metathesis polymerization. ADMET reactions are now common, found in textbooks, and easy to perform if the proper techniques are chosen. Much remains to be done, however, with work now focusing on silicon chemistry, direct control of tacticity in precision polymers, biological applications, modeling crystal lattices in common polyolefins, exploring solid-state metathesis reactions, and creating water-soluble ADMET polymers.

Journal ArticleDOI
TL;DR: This article studied the viscoelastic properties of complex coacervates of poly(N,N-dimethylaminoethyl methacrylate), PDMAEMA, and poly(acrylic acid), PAA.
Abstract: Two flexible, oppositely charged polymers can form liquid-like complex coacervate phases with rich but poorly understood viscoelastic properties. They serve as an experimental model system for many biological and man-made materials made from oppositely charged macromolecules. We use rheology to systematically study the viscoelastic properties as a function of salt concentration, chain length, chain length matching, and mixing stoichiometry of model complex coacervates of poly(N,N-dimethylaminoethyl methacrylate), PDMAEMA, and poly(acrylic acid), PAA. The dynamics of making and breaking ionic bonds between the oppositely charged chains underlie all linear viscoelastic properties of the complex coacervates. We treat (clusters of) ionic bonds as sticky points and find that there is a remarkable resemblance between the relaxation spectra of these complex coacervates and the classical sticky Rouse model for single polymer systems. Salt affects all relaxation processes in the same way, giving rise to a widely a...

Journal ArticleDOI
TL;DR: In this paper, the effects of opposite counterions of different types on the friction properties of polyanionic, polycationic, and polyzwitterionic brushes were systematically investigated.
Abstract: We present a paradigm that dramatically tunes friction from superior lubrication (μ ∼ 10–3) to ultrahigh friction (μ > 1) using responsive polyelectrolyte brushes. The tunable friction is based on counterion-driven interactions in polyelectrolyte brushes that can be simply achieved by exchanging the counterions. We systematically investigated the effects of opposite counterions of different types on the friction properties of polyanionic, polycationic, and polyzwitterionic brushes. For cationic brushes with quaternary ammonium groups, the friction coefficient was progressively tuned from ∼10–3 to ∼100 according to the counterions series Cl– < ClO4– < PF6– < TFSI–. The friction of anionic brushes can be tuned by oppositely charged surfactants (tetraalkylammonium) with different length of hydrophobic tails, multivalent metal ions, and protons. The friction increase of cationic brushes is due to the dehydration and the collapse of polyelectrolyte chains induced by ion-pairing interactions. For anionic brushe...