Bis-ortho-diynylarene Research Articles

High carbon yielding and melt processable bis-ortho-diynylarene (BODA)-derived resins for rapid processing of dense carbon/carbon composites

Bis-ortho-diynylarene (BODA)-derived resins undergo thermal, radical-mediated Bergman cyclization to predominately naphthalene diradicals which propagate in a stepwise fashion to highly branched processable intermediates that are amenable to current composite fabrication techniques prior to network cure and subsequent carbonization. Post-carbonization analysis reveals significantly higher density and consolidation in the BODA-derived carbon/carbon (C/C) over existing phenolic-based C/Cs without the need for arduous, multiple infusion and carbonization steps. The modular BODA approach combines and controls: (1) variable melt processability dictated by terminal or spacer group substitution, (2) mild cure kinetics via a non-autocatalytic reaction, (3) high carbon yield (>80%) to provide relatively dense (∼1.55 g/cm3) C/C substrates after a single carbonization at 1000 °C, and (4) remarkable efficiencies that allow fast carbonization ramp rates (10 °C/min) while maintaining high density. Isothermal DSC kinetics, monomer melt stability in air, order/disorder characterization by Raman and WAXS, resin processing under selected air environments, and fractured cross-section analyses of C/C composites by SEM is discussed.

Bis-ortho-diynylarene polymerization as a route to solid and hollow carbon fibers

The preparation, fabrication, and carbonization of bis-ortho-diynylarene (BODA)-derived polymers are described. BODA monomers undergo thermal step-growth polymerization to reactive and processable branched polyarylene intermediates. Well-defined intermediates with controlled conversion, molecular weight and viscosity, along with solution or melt processing allow for control in ultimate carbon structure. Fabrication followed by thermal cure and carbonization results in solid or hollow carbon fiber prototypes with interesting thermal and electrical properties. The BODA polymerization and fiber formation were investigated by differential scanning calorimetry, and gel permeation chromatography. The thermal behavior and stability of fibers was measured by thermogravimetric analysis. The surface crystallinity of fibers was studied by Raman spectroscopy. The conductivity of fibers was measured by a multimeter. The surface morphology and dimensions of the fibers were examined by scanning electron microscopy.

Carbonization and thermal expansion of glassy carbon derived from bis- ortho-diynylarenes

Bis- ortho-diynylarene (BODA) monomers form rigid polynaphthalene networks via thermal Bergman cyclizations at 300–400 °C. Upon further heating to 1000 °C, glassy carbon with high yield (>80%) is formed from the polynaphthalene precursor. Dilatometry was used to determine the linear coefficient of thermal expansion (CTE) of various BODA-derived glassy carbon. The measured CTE was similar to other glassy carbon-based systems ranging from 3.20 to 6.92 × 10 −6 °C −1 over 20–1000 °C. An increase in short-range order was apparent when polynaphthalene networks were carbonized to 1500 °C; the CTE observed for such thermal cycling was 2.85–2.93 × 10 −6 °C −1 over 20–1000 °C. Using dilatometry also provided insight on the carbonization mechanism to provide optimization of glassy carbon yields during thermal cycling.

Synthesis and polymerization of a new nitrogen-containing bis-ortho-diynylarene monomer

This study focuses on the preparation, characterization, and optical properties of new bis(3,4-diphenylethynylphenyl)phenylamine. This is the first nitrogen-containing bis-ortho-diynylarene (BODA) monomer having a nitrogen atom as the spacer group. BODA monomers are usually prepared from common bisphenols, thereby providing great synthetic versatility and the opportunity to develop a wide array of novel polyarylene thermosets by varying the aromatic spacer group. The new bis(3,4-bisphenylethynylphenyl)phenylamine was synthesized in five steps. This compound emits an intense blue color (λ = 438 nm) upon irradiation by UV light and may be suitable for use as an emitting layer in electroluminescent devices. Bis-(3,4-bisphenylethynylphenyl)phenylamine and its polymer have photoluminescence quantum yields 34 and 38%, respectively, and long excited-state lifetimes of 3.2 and 3.6 ns, respectively. The structure of the monomer and its polymer were characterized using spectroscopic techniques including Ultraviolet–visible Spectrophotometer, Photoluminescence Spectrophotometer, Fourier Transform infrared spectroscopy, and Gel Permeation Chromatography. The polymerizations were studied by Differential Scanning Calorimeter. The amount of weight loss and the thermostability of the nitrogen-containing polymer were determined from thermogravimetric analysis. The electrical conductivity of neat HCl-doped BODA-derived polymer film was measured according to the standard four-point probe technique. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6988–6996, 2006

Two concomitant polymorphs of 3,3′,4,4′-tetrakis(phenylethynyl)-1,1′-[2,2,2,-trifluoro- 1-(trifluromethyl)ethanediyl]bisbenzene

A representative compound of bis-ortho-diynyl arene (BODA), with a general formula [(m,p)R2–Ph]2 –X, where R: –C≡C–Ph and X: >C(CF3)2 has been structurally characterized. The compound is being investigated as a monomer for high-performance polyarylene networks and glassy carbon precursors. The bis(trifluoromethyl) derivative crystallizes in two concomitant polymorphic forms. The two polymorphs form a monotropic system with melting points of 436 and 463 K. The metastable form yields monoclinic crystals (P21/n, Z=4). a=12.677(3) A, b=11.677(2) A, c=24.026(5) A, β=93.79(3)°. The thermodynamically stable form is monoclinic as well (P21/c, Z=8), a=10.7983(6) A, b=30.628(2) A, c=21.648(1) A, β=94.737(1)° with small voids indicating less efficient packing. The two polymorphs contain different conformers of the rotationally flexible molecule.

In situ EPR spectroscopy of aromatic diyne cyclopolymerization.

Electron paramagnetic resonance (EPR) spectroscopy was successfully used for the first time to follow the Bergman cyclization of bis-ortho-diynyl arene (BODA) compounds. Five BODA monomers with different spacer (X) and terminal groups (R) were compared. In situ polymerization via EPR spectroscopy yielded first-order rate expressions. Monomers with spacer -O- or -C(CF(3))(2) and terminal group R = Ph exhibited similar kinetic behavior upon thermal polymerization, whereas monomers with pyridine and thiophene terminal groups gave significantly higher rates of polymerization over phenyl-terminated derivatives. A model compound, 1,2-bis(phenylethynyl)benzene, was used to probe the polymerization mechanism, and radical intermediates were found to be stable indefinitely at room temperature.

Novel Network Polymer for Templated Carbon Photonic Crystal Structures

Inverse opaline photonic crystal structures are created from carbon precursor polymer networks derived from the thermal Bergman cyclopolymerization of bis-ortho-diynyl arene (BODA) monomers. A new hydroxy-functional BODA monomer was prepared that exhibited excellent compatibility with silica opal templates. Monomer melt infiltration of the template, in situ thermal polymerization, and pyrolysis, followed by removal of the silica with HF affords a carbon inverse opal structure that conserves the original dimensions of the template. The photonic crystal was characterized by the reflectance spectra, and the refractive index of the carbon was estimated. The functionality of the carbon opal as a sensor element was demonstrated with water/acetonitrile mixtures and reveals a bandstop shift of 13 nm over a refractive index change of 0.011.

Synthesis and thermal cyclopolymerization of heterocycle containing bis- ortho-diynyl arenes

A new class of heteroatom terminated bis- ortho-diynyl arene (BODA) compounds have been synthesized via efficient in situ palladium catalyzed cross coupling between tetra alkynyl silanes and aryl bromides and iodides. BODA monomers undergo Bergman-type cyclization upon heating, and afford processable intermediates and ultimately network polymers. The new heterocycle terminated oligomers are compared to phenyl terminated derivatives and exhibit bathochromic shifts (25 nm) in their emission spectra.

Substituent effects on Bergman cyclopolymerization kinetics of bis- ortho-diynylarene (BODA) monomers by dynamic scanning calorimetry

Bis- ortho-diynylarene (BODA) monomers polymerize thermally via the Bergman cyclization and diradical intermediates. The structure reactivity relationships of eight BODA monomers and their kinetics were studied by differential scanning calorimetry (DSC). The spacer (X=C(CF 3) 2, C(CH 3) 2, O, a bond) groups and alkyne terminal (R=Ph, Si(CH 3) 3,  iso-propanol, pyridine, thiophene) groups were varied and the effect on polymerization rate was determined. Among the phenyl-terminated monomers, only the isopropylidene spacer group imparts a significant increase on the cure onset temperature and the activation energy. However, the terminal (R) groups play a significant role in polymerization rate of BODA monomers.

Bergman cyclopolymerization kinetics of bis-ortho-diynylarenes to polynaphthalene networks. A comparison of calorimetric methods

Bis-ortho-diynylarene (BODA) monomers undergo radical mediated Bergman-type cycloaddition polymerization to yield polynaphthalene networks. This report describes the use of conventional and modulated temperature differential scanning calorimetry to compute the cure kinetic parameters of BODA monomers with different spacer groups. Three different kinetic methods employed here utilize non-isothermal dynamic thermal profiles to estimate activation energies (Ea=28.7–33.5kcal/mol [120–140kJ/mol]) and the first order rate constants (k∼10−5s−1 at 210°C) of polymerization. The results obtained from these methods show surprisingly good mutual agreement and also reveal that varying the spacer group has marginal effect on the cure kinetics. It has also been shown that the reaction kinetic information obtained from the dynamic methods must be corrected, when applied under isothermal conditions, to account for sample vitrification. The correction factor has been estimated using modulated temperature differential scanning calorimetry which is capable of monitoring the sample heat capacity in real time.