Carbon-based Polymers Research Articles

On the “Tertiary Structure” of Poly‐Carbenes; Self‐Assembly of sp3‐Carbon‐Based Polymers into Liquid‐Crystalline Aggregates

The self-assembly of poly(ethylidene acetate) (st-PEA) into van der Waals-stabilized liquid-crystalline (LC) aggregates is reported. The LC behavior of these materials is unexpected, and unusual for flexible sp(3)-carbon backbone polymers. Although the dense packing of polar ester functionalities along the carbon backbone of st-PEA could perhaps be expected to lead directly to rigid-rod behavior, molecular modeling reveals that individual st-PEA chains are actually highly flexible and should not reveal rigid-rod induced LC behavior. Nonetheless, st-PEA clearly reveals LC behavior, both in solution and in the melt over a broad elevated temperature range. A combined set of experimental measurements, supported by MM/MD studies, suggests that the observed LC behavior is due to self-aggregation of st-PEA into higher-order aggregates. According to MM/MD modeling st-PEA single helices adopt a flexible helical structure with a preferred trans-gauche syn-syn-anti-anti orientation. Unexpectedly, similar modeling experiments suggest that three of these helices can self-assemble into triple-helical aggregates. Higher-order assemblies were not observed in the MM/MD simulations, suggesting that the triple helix is the most stable aggregate configuration. DLS data confirmed the aggregation of st-PEA into higher-order structures, and suggest the formation of rod-like particles. The dimensions derived from these light-scattering experiments correspond with st-PEA triple-helix formation. Langmuir-Blodgett surface pressure-area isotherms also point to the formation of rod-like st-PEA aggregates with similar dimensions as st-PEA triple helixes. Upon increasing the st-PEA concentration, the viscosity of the polymer solution increases strongly, and at concentrations above 20 wt % st-PEA forms an organogel. STM on this gel reveals the formation of helical aggregates on the graphite surface-solution interface with shapes and dimensions matching st-PEA triple helices, in good agreement with the structures proposed by molecular modeling. X-ray diffraction, WAXS, SAXS and solid state NMR spectroscopy studies suggest that st-PEA triple helices are also present in the solid state, up to temperatures well above the melting point of st-PEA. Formation of higher-order aggregates explains the observed LC behavior of st-PEA, emphasizing the importance of the "tertiary structure" of synthetic polymers on their material properties.

Carbon/carbon implants in the oral and maxillofacial surgery – Part 1

Over the past 20–30 years various carbon implant materials have become more interesting, because they are well accepted by the biological environment. The traditional carbon-based polymers give rise to many complications. The polymer complication may be eliminated through carbon fibres bound by pyrocarbon (carbon/carbon). Aim: The aim of this study is to present the long-term results of carbon/carbon implants. Methods: Mandibular reconstruction was performed with pure (99.99%) carbon implants in 16 patients. Predominantly tumorous cases were included (10 malignant tumors, 4 large cystic lesions and 2 augmentative processes). Results: Because the interventions had been performed 6–8 years before the last follow-up visit, the authors report long-term results. Of the 16 patients, the implants had to be removed earlier in 5 patients because of the defect that arose on the oral mucosa above the carbon plates. The most probable cause of this complication was the strain in the oral mucosa and disturbances in its blood supply (previous surgery, irradiated tissue, etc.). During the long-term follow-up, plate fracture, loosening of screws, infection or inflammation around the carbon/carbon implants were not observed. After 8 years one carbon implant was substituted with an autogenous bone. Conclusions: The clinical conclusion is that if the soft part cover is appropriate, the carbon implants are cosmetically and functionally more suitable than titanium plates. The structural and chemical investigation of the removed implant will be published in the near future. Orv. Hetil., 2012, 153, 257–262.

Controlling nanomorphology in plastic solar cells

In the global search for clean, renewable energy sources, organic photovoltaics (OPVs) have recently been given much attention. Popular modern-day organic solar cells are made from solution-processable, carbon-based polymers (e.g. the model poly(3-hexylthiophene) that are intimately blended with fullerene derivatives (e.g. [6,6]-phenyl-C71-butyric acid methyl ester) to form what is known as the dispersed bulk-heterojunction (BHJ). This BHJ architecture has produced some of the most efficient OPVs to date, with reports closing in on 10% power conversion efficiency. To push efficiencies further into double digits, many groups have identified the BHJ nanomorphology — that is, the phase separations and grain sizes within the polymer: fullerene composite — as a key aspect in need of control and improvement. As a result, many methods, including thermal annealing, slow-drying (solvent) annealing, vapor annealing, and solvent additives, have been developed and studied to promote BHJ self-organization. In this review, the authors present an overview of these methods and summarize the results they have enabled.

Structural and photophysical properties of anthracenyl and carbazolyl groups in silicone-based polymers

This paper describes a simple methodology to attach luminescent groups (anthracenyl and carbazolyl) to polysiloxanes (silicone), using hydrosilylation reactions between the Si–H groups from the silicone precursor to vinyl derivatives of the lumophores. The photophysical properties of these luminescent silicones were studied using both steady-state and dynamical photoluminescence spectroscopy. A strong correlation was obtained between the structural characteristics of the anthracenyl- and carbazolyl-based polysiloxanes, depending on the amount and the position of the Si–H bonds in the silicone precursors. For sparsely distributed Si–H groups, both the anthracenyl-labeled and carbazolyl-labeled polysiloxanes showed photophysical properties (fluorescence spectrum and fluorescence decays) similar to those of 1-alkyl anthracenyl and 1-alkyl carbazolyl derivatives, respectively. Nevertheless, for closely spaced Si–H groups, emission and decay are different. The presence of excimers was observed for anthracenyl but not for carbazolyl polysiloxanes. This latter observation is quite different from that observed for carbon-based polymers for which the carbazolyl excimer formation is a very common process probably due to the differences in the silicone structure.

Synthesis of carbon nanospheres from carbon-based network polymers

Carbon nanospheres have been successfully fabricated by simple pyrolysis of a new class of carbon-based network polymers, poly(phenylcarbyne) and poly(hydridocarbyne). The analytic results of morphology and microstructure show that the resultant nanospheres are solid graphite-like balls with the diameter from several tens to hundreds of nanometers. A mechanism based on the carbon nanoparticles self-growth process is proposed for the formation of the nanospheres.

C1 polymerisation and related C–C bond forming ‘carbeneinsertion’ reactions

In this critical review we summarise the currently available 'C1 polymerisation' techniques as valuable alternatives for 'C2 polymerisation' in the preparation of saturated main-chain carbon-based polymers. C1 polymerisation involves the growth of polymers from monomers delivering only one functionalised carbon unit (C1 monomers; typically 'carbene precursors') in each chain-growth step, which contrasts with common polymerisation of C=C bond containing substrates (C2 monomers). In the general introduction (section 1) we comment on the availability of C1 monomers and the most important differences between C1 and C2 polymerisation techniques, highlighting the opportunities provided by C1 polymerisation to prepare new polymer structures. In section 2 we describe several Lewis acid mediated C1 polymerisation reactions based on diazocompounds and sulfur ylides as C1 monomers. Some of these are 'living polymerisation' reactions which allow the synthesis of functional telechelic block-copolymers and polymethylenic homo-polymers with a wide variety of different functional end-groups at both polymer chain-ends in a controlled fashion. Miscellaneous related reactions of other C1 monomers are described in section 3. Transition metal mediated C1 polymerisation methods in section 4 allow the polymerisation of polar functionalised C1 monomers. Several homogeneous and heterogeneous catalysts are capable of producing polymers from a variety of diazo compounds, some of which even allow the formation of stereoregular polar functionalised polymers (which is a major challenge in traditional olefin polymerisation). An overview of the current state-of-the art, challenges and opportunities, as well as an overview of the available mechanistic information (sections 4 and 5) is provided. Some related C-C bond forming reactions proceeding via (migratory) carbene insertion (section 6) are also discussed (106 references).

On the Question of Ferromagnetism in Proton and He-Irradiated Carbon

Carbon-based materials are the promising candidates for future applications in novel electronics. Carbon nanotube transistors and logic gates, conducting carbon-based polymers have been already demonstrated. In addition some forms of pure carbon should reveal magnetic properties, which in principle might be use in carbon-based spintronics. There are some theoretical predictions about carbon nano-stripes, schwarzite structures, H-doped graphite, in which electron spins on π-orbitals or broken sp 3 -bonds have (in some cases) ferromagnetic alignment. The experiments seeking for ferromagnetism were performed but many of them have failed due to the presence of ferromagnetic impurities (mostly iron). Nevertheless some of the experiments demonstrated ferromagnetism in pure carbon, particularly in carbon nano-foam [1] and proton-irradiated highly oriented pyrolitic graphite (HOPG) [2]. In 2003 Esquinazi used a MeV proton beam and discovered that it trigged ferromagnetism of the HOPG sample. After irradiation the hysteresis loop was observed over the irradiated area using Magnetic Force Microscopy and SQUID measurements. Such magnetic system seems to be very interesting for both: basic science and possible application points of view. However, hardly any other experimental group has confirmed such experimental observation. This situation is embarrassing, because it is not clear if nobody tried to verify the discoveries of Esquinazi et al. or nobody has succeeded in this verification. And since the lack of the phenomenon is difficult to be publish in any paper (vide the rumor of “cold fusion” in 90-ties) there are no information about the efforts of other groups. We have tried to repeat this discovery of the gropup of Esquinazi et al. We have used He + and H + beams focused on graphite sample. The amount of charge deposited in the sample was comparable to the amount of charge used by Esquinazi. Magnetic measurements were performed in SQUID magnetometer. The magnetization of the samples before and after irradiation was compared. Unfortunately we did not observe any ferromagnetic enhancement of magnetization of our irradiated samples. Even if experiment was not the same as Esqinazi’s one, we can exclude some of the mechanisms of ferromagnetism proposed by Esquinazi.

Surface structure changes in carbon-based materials and polymers under an oxygen-plasma beam

The surface topography of samples of graphite USB-15, pyrolytic carbon PGI, pyrolitic graphite UPV-1, and polyimide PM-1E exposed to accelerated oxygen-plasma beams has been studied by scanning electron microscopy. Surface etching by fast oxygen particles results in the formation of a system of cone/column-like protrusions. As the material mass loss increases, the protrusions increase in size, and the surface topography transforms. Etching of carbon-based materials leads to enrichment of the surface layer with carbon, which is most pronounced in the boron-doped graphite.

Dynamic Bone Quality-A Non-Invasive Measure of Bone's Biomechanical Property

Carbon-based electroactive polymers (EAPs) are core materials for actuator applications. Introducing conductive fillers into EAPs is considered an effective method to improve the actuating performance, due to the enhanced dielectric properties achieved. This work describes the elaboration and characterization of polyurethane (PU)/oxygen-functionalized graphene (OFG) composite films. Results revealed that for the nanocomposites, a large increase in dielectric constant was obtained without a great mechanical reinforcement, whereas there was no improvement in electromechanical performance as compared to pure polyurethane. The possible reasons for these discordant results were thus investigated with the help of multiscale studies. The importance of measuring the dielectric and mechanical properties under the same conditions as those used to drive actuators could be pointed out. Using high electric field values led to a better prediction of the electromechanical coefficient M31 for pure PU at low frequency, but did not completely explain the decreasing M31 found for the composites. The discrepancy could be due to the moderate adhesion between the polymer and the graphene nanoplatelets, but also to the competition between the increased dielectric constant and the decreased electric field seen by the polymer, induced by MWS interfacial polarization.

Carbon-Encapsulated Magnetic Nanoparticles Based on Fe, Mn, and Cr for Spintronics Applications

Carbon-based nanostructured materials are the promising candidates for future applications in novel electronics. Unique flexibility in sp-hybridization of carbon valences orbitals results in different stable carbon allotropic forms, affinity for bonding with other atoms and gives nearly ten million different chemical compounds, with the potential use in miniaturized electronics. Carbon nanotube transistors and logic gates, conducting carbonbased polymers have been already demonstrated. Graphite is one of the candidates for future electronics – single layers of graphite (so called graphene) forms two dimensional materials and show many interesting physical properties in the presence of magnetic field like half integer quantum Hall effect, electron– hole degeneracy and vanishing carrier mass near the point of charge neutrality. Intercalation of graphite with various elements yields charge-transfer compounds which may be consider as an analog of semiconductor doping. In this communication we propose to integrate ferromagnetic nano-materials with several graphene layers in so-called carbon-encapsulated magnetic nanoparticles (CEMNPs). Such hybrid structures posses interesting chemical and physical properties. The carbon shell protects the encapsulated crystallites from the oxidation and further agglomeration. On the other hand magnetic field from the core nanomagnet should influence on graphite band electrons. Morphology of nanosized Mn, Fe and Cr-based CEMNPs was studied by transmission electron microscopy. Magnetic properties of encapsulated Mn, Fe and Cr (and their carbides) were studied by means of SQUID magnetometry. The nanometer-sized particles showed superparamagnetic behavior at high temperatures, similar for Mn, Fe and Cr, while at low temperatures different behavior was observed, depending on composition of magnetic cores. For Fe-based CEMNPs Mossbauer spectroscopy was used to investigate chemical composition. Clear evidence of the presence of α-Fe and metastable γ-Fe phase was found.

Modification of surface properties of carbon-based and polymeric materials through fluorination routes: From fundamental research to industrial applications

The outstanding characteristics of fluorine gas, e.g., extreme reactivity and oxidizing power, and the utmost electronegativity of F − ion, lead to very strong bonds between fluorine and most of the other elements of the periodical table. Treatments involving F 2, fluorinated gases and rf plasma-enhanced fluorination (PEF) constitute exceptional tools for modifying the surface properties of materials. Many advantages of these techniques can be indeed outlined, when compared to more conventional methods: low-temperature reactions (even at room temperature), chemical modifications limited to surface only without changing the bulk properties, possible non-equilibrium reactions. Depending on the type of starting materials and employed techniques, the improved properties may concern wettability, adhesion, chemical stability, barrier properties, biocompatibility, grafting, mechanical behavior. Several examples of surface fluorination will be given on various types of carbon-based materials, elastomers and polymers.

Transition metal ions: weak links for strong polymers.

Extending macromolecular chemistry beyond carbon-based polymers offers fascinating perspectives and an enormous potential to improve the capacity of macromolecular materials with new dynamic properties.

The Trinity of Life: The Genome, the Proteome, and the Mineral Chemical Elements

In this article the major changes in evolution from the simplest prokaryote cells to man and his industrial activity are described as a progressive change in the organization of chemistry in spatial compartments. The changes reflect the changing availability of chemical elements, produced first through the unavoidable production of oxygen by organisms and most recently through man's exploitation of the environment. We assume that initially Earth had a reducing environment from which it was necessary for organisms to obtain 20 chemical elements in simple cells.Particularly important was the need to make carbon-based polymers from CO2, CO, H2O, and nitrogen, using energy from the sun. These polymers had to be, and have to be to this day, made in a central reducing compartment, the cytoplasm, and the release of oxygen, O2, was therefore unavoidable. The oxygen then converted the reduced forms of elements of the primitive environment into more oxidized states. The process was slow as oxygen tension rose to it...

Diamond and diamond-like carbon from a preceramic polymer.

The synthesis of poly(hydridocarbyne), one of a class of carbon-based random network polymers and a structural isomer of polyacetlyene, is reported. The network backbone of this polymer is primarily composed of tetrahedrally hybridized carbon atoms, each bearing one hydride substituent and linked via three carbon-carbon single bonds into a three-dimensional random network of fused rings. This atomic-level carbon network backbone confers unusual properties on the polymer, including facile thermal decomposition to form diamond or diamond-like carbon high-quality films at atmospheric pressure, by direct deposition or by chemical vapor deposition (CVD), without the use of hydrogen or any other reagent.

Electron correlation effects in electron-hole recombination in organic light-emitting diodes

We develop a general theory of electron-hole recombination in organic light-emitting diodes that leads to formation of emissive singlet excitons and nonemissive triplet excitons. We briefly review other existing theories and show how our approach is substantively different from these theories. Using an exact time-dependent approach to the interchain/intermolecular charge transfer within a long--range interacting model we find that (i) the relative yield of the singlet exciton in polymers is considerably larger than the 25% predicted from statistical considerations, (ii) the singlet exciton yield increases with chain length in oligomers, and (iii) in small molecules containing nitrogen heteroatoms, the relative yield of the singlet exciton is considerably smaller and may be even close to 25%. The above results are independent of whether or not the bond-charge repulsion, ${X}_{\ensuremath{\perp}},$ is included in the interchain part of the Hamiltonian for the two-chain system. The larger (smaller) yield of the singlet (triplet) exciton in carbon-based long-chain polymers is a consequence of both its ionic (covalent) nature and smaller (larger) binding energy. In nitrogen containing monomers, wave functions are closer to the noninteracting limit, and this decreases (increases) the relative yield of the singlet (triplet) exciton. Our results are in qualitative agreement with electroluminescence experiments involving both molecular and polymeric light emitters. The time-dependent approach developed here for describing intermolecular charge-transfer processes is completely general and may be applied to many other such processes.

Photoprobe Study of Siloxane Polymers. 3. Local Free Volume of Polymethylsilsesquioxane Probed by Photoisomerization of Azobenzene

We have investigated the local free volume and its thermal fluctuation in an amorphous polymethylsilsesquioxane (PMSQ) consisting only of T3 (CH3SiO3/2) and T2 (CH3Si(OH)O2/2) units using photoisomerization of azobenzene molecularly dispersed in the PMSQ films as a photoprobe over a wide temperature range (4−300 K). Photoisomerization profiles are discussed on the basis of three parameters, i.e., first-order plots, final cis fractions, and three-component analysis, for uncured and silanol-condensation-cured PMSQ's. The final cis fraction in the uncured PMSQ decreases markedly below 250 K, which has never been observed in linear polysiloxanes, MQ resins, or carbon-based polymers. The effect of low-molecular-weight components in the PMSQ was evaluated using fractionated PMSQ's by molecular weight. The effect of hydrogen bonding by a silanol group was also studied by temperature dependence of infrared spectra. These results suggest that the low-molecular-weight components with silanol groups fill local vacan...

Starch: as simple as A, B, C?

Most of the starch utilized world-wide comes from a relatively small number of crops, the most important Starch is the main carbohydrate reserve in plants and being maize, potato, wheat, and tapioca with smaller an important part of our nutrition. Increasingly, it is amounts from rice, sorghum, sweet potato, arrowroot, being seen by industry as a useful raw material to sago, and mung beans. In general, starches from tapioca include in foodstuffs and with which to produce other and sorghum are used only for food, whereas those from carbon-based polymers. Our understanding of starch maize, potato and wheat are used for food and other, biosynthesis and chemistry has advanced rapidly over non-food, purposes. Within Europe, the main sources of the last few years, but our knowledge of how this starch are maize, wheat and potato, although in Sweden translates into structure and thence into physico- and Finland small quantities of oats and barley are used chemical properties and function is still lacking. Here, for non-food purposes (Batchelor et al., 1996). we have reviewed this information with an emphasis Starch forms the main source of energy in the human on genetics and physical properties, especially using diet and comprises on average about 30% of the UK diet data from the model crop, pea (Pisum sativum L.). by weight, mainly in the form of bread and pasta products produced from milled wheat seeds. In general, native

Bandgap Oscillation in Polyphenanthrenes

The electronic structures of carbon-based ladder polymers and polynuclear aromatic hydrocarbons (PAHs) with acene- and phenanthrene-edge structures are studied with an approximate molecular-orbital method. The difference between polyacene and polyphenanthrene can be derived from detailed orbital interaction analyses of anthracene and phenanthrene. The fragment molecular-orbital (FMO) method successfully characterizes the distinct electronic structures of the two small PAHs with different types of edges. We shed light on the electronic structures of ladder polymers with the phenanthrene-edge structure, PPh(n), in which n is the number of cis-polyene chains included. With an increase in width of the ladder polymers, the bandgap of PPh(n) approaches zero with a behavior that has a periodicity of 3. The PPh(n) series are classified into three subgroups: small-gap (metallic) PPh(3m + 1), large-gap PPh(3m + 2), and medium-gap PPh(3m), where m = 0, 1, 2, .... The oscillating behavior in the bandgap of the three...

Synthesis and characterization of polycarbynes, a new class of carbon-based network polymers

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis and characterization of polycarbynes, a new class of carbon-based network polymersGlenn T. Visscher and Patricia A. BianconiCite this: J. Am. Chem. Soc. 1994, 116, 5, 1805–1811Publication Date (Print):March 1, 1994Publication History Published online1 May 2002Published inissue 1 March 1994https://doi.org/10.1021/ja00084a023RIGHTS & PERMISSIONSArticle Views312Altmetric-Citations34LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1016 KB) Get e-Alerts Get e-Alerts

Poly(phenylcarbyne): A Polymer Precursor to Diamond-Like Carbon

The synthesis of poly(phenylcarbyne), one of a class of carbon-based random network polymers, is reported. The network backbone of this polymer is composed of tetrahedrally hybridized carbon atoms, each bearing one phenyl substituent and linking, by means of three carbon-carbon single bonds, into a three-dimensional random network of fused rings. This atomic-level carbon network backbone confers unusual properties on the polymer, including facile thermal decomposition, which yields diamond or diamond-like carbon phases at atmospheric pressure.