Divergent synthesis of novel unsymmetrical dendrons containing photosensitizing units

The synthesis, characterization and singlet oxygen quantum yield of novel unsymmetrical dendrons containing photosensitizing units at their periphery is reported. Boc-protected 2,2′-(ethylenedioxy)-bis-ethylamine reacted with methyl acrylate and ethylene diamine to give half-dendrimers 4 and 5 with 2 and 4 end groups, respectively. Amine-tethered porphyrins and compounds 4 and 5 were efficiently coupled in DMF at 100 °C to give the functionalized dendrons. UV-visible and fluorescence emission spectra showed that the photophysical properties of the porphyrins were retained in the dendrimers.     

Coumarin-cored carbazole dendrimers as solution-processed non-doped green emitters for electroluminescent devices

A series of green-emitting thiophenyl coumarin-cored carbazole dendrimers containing carbazole dendrons up to the third generation as substituent were synthesized and characterization. Their optical, thermal, electrochemical, and electroluminescent properties as non-doped solution-processed light-emitters for OLEDs were investigated. By incorporating carbazole dendrons in the molecule, we are able to reduce the crystallization and retain the high emissive ability of a planar thiophenyl coumarin fluorescent core in the solid state as well as improve the thermal stability of the material. These dendrimers showed a bright-green fluorescence and can form morphologically stable amorphous thin films with glass-transition temperatures as high as 285 °C. Simple structured solution-processed OLEDs using these materials as hole-transporting non-doped emitters and BCP as a buffer layer emit a stable green electroluminescence (λ_EL=502–526 nm) with high luminance efficiencies (up to 7.92 cd/A at 7.39 mA/cm²) and high green color purity (CIE=0.26, 0.62, which are close to the pure green color).     

Controlled thermal decomposition of NaSi to derive silicon clathrate compounds

Formation conditions of two types of sodium containing silicon clathrate compounds were determined by the controlled thermal decomposition of sodium monosilicide NaSi under vacuum. The decomposition began at 360 °C. Much higher decomposition temperatures and the presence of sodium metal vapor were favorable for the formation of type I clathrate compound Na₈Si₄₆. Type II clathrate compound Na_xSi₁₃₆ was obtained as a single phase at a decomposition temperature <440 °C under the condition without sodium metal vapor. The type I clathrate compound was decomposed to crystalline Si above 520 °C. The type II clathrate compound was thermally more stable, and retained at least up to 550 °C in vacuum.     

Thermal Stability of Periodic Mesoporous SiCO Glasses

Periodic Mesoporous Organosilicas (PMOs) with 2D-hexagonal and cubic Pm3n structures have been prepared from bis(trialkoxysilyl)ethane and cetyltrimethylammonium chloride. The two samples have been pyrolyzed under argon up to 1000 °C. Study by X-ray diffraction (synchrotron radiation) allows the thermal stability of both structures to be followed as a function of the pyrolysis temperature. While the 2D-hexagonal structure collapses after pyrolysis at 800 °C, the cubic Pm3n structure is retained up to 1000 °C. Further characterizations were performed by ²⁹Si MAS-NMR, N₂ adsorption-desorption experiments and elemental analysis. At 1000 °C, the first sample can be described as a mixture of silica and a free C phase, while the cubic one is a true SiCO glass with mixed SiC_xO_{4 – x} units (x = 0,1,2) and a very large surface area of 730 m²/g.     

Thermal degradation of aliphatic hyperbranched polyesters and their derivatives

In this study results of thermal degradation of aliphatic hyperbranched polyesters, AHBP, and their derivatives, determined by non-isothermal thermogravimetric analysis in inert atmosphere (N₂) are presented. The thermal stability of linear polyester PHPA (polyhydroxypivalic acid), additionally synthesized from hydroxypivalic acid, was also studied. AHBP samples, from second to tenth pseudo-generation, were synthesized starting from 2,2-bis(hydroxymethyl)propionic acid and di-trimethylolpropane. Modification of some selected AHBP samples was accomplished with the propionyl and benzoyl chloride, as well as with stearic acid. Thermal degradation of AHBP samples starts in the region between 250 °C and 275 °C and it ends around 430 °C. The thermal stability of AHBP samples increases with the number of end groups in the macromolecule, as well as with the modification of end groups with stearic acid and propionyl chloride. An AHBP sample of the fourth pseudo-generation, where all -OH end groups are modified with benzoyl chloride, shows lower thermal stability than the corresponding unmodified sample. The thermal stability of the linear polyester PHPA is lower than the thermal stability of the AHBP samples of the similar molar mass. The activation energies of thermal degradation for all synthesized AHBP samples were also calculated.     

Interaction of water-soluble polypyridylphenylene dendrimers with a polymethacrylate anion

Cationic water-soluble dendrimers have been prepared by the alkylation of pyridyl groups in polypyridylphenylene dendrimers of the first four generations, and their interaction with a polymethacrylate anion has been studied. The stability of polyelectrolyte complexes in aqueoussaline solutions has been studied by fluorimetric titration with the use of the pyrenyl-tagged polyanion, and it has been shown that the stability of these complexes significantly increases with the dendrimer generation number and the content of hydrophobic phenylene groups. Based on sedimentation analysis and turbidimetric titration, it is inferred that a significant part of charged groups of dendrimers are inaccessible to interaction with the polyanion and that water-soluble nonstoichiometric polyelectrolyte complexes develop in mixtures of higher generation dendrimers. Modeling results of this study may be useful for designing efficient cationic dendrimer carriers of genetic material and hydrophobic physiologically active compounds.     

Thermal Stability of Bis-Piperidine Benzoylacetonates of Some Transition Metals

Bis-piperidine complexes of benzoylacetonates of Mn(II), Co(II), Cd(II) and Ni(II) were prepared. Thermogravimetric analysis (TG) demonstrated that Mn(II) bis-piperidine benzoylacetonate was stable up to 90°C, while Co(II) bis-piperidine benzoylacetonate was stable up to 100°C, whereas Cd(II) bis-piperidine benzoylacetonate was stable up to only 50°C. Its first decomposition step was completed at 110°C. Ni(II) bis-piperidine benzoylacetonate found to be stable up to 110°C. The stabilities of the complexes of these metals therefore follow the sequence Cd²⁺<Mn²⁺<Co²⁺<Ni²⁺. The complex of Cd(II) was the least stable of all the compounds studied.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermal stability of silver sulfathiazole-epoxy resin network

The aim of this study is to evaluate the thermal stability and thermal degradation behavior of an epoxy network based on bisphenol A modified with silver sulfathiazole and crosslinked with ethylenediamine. The sample was studied by thermogravimetric analysis coupled with differential scanning calorimetry over a range of temperature between 30 and 600 °C in N₂ atmosphere and using heating rates of 5, 10, 15 and 20 °C min⁻¹. The kinetic parameters of thermal degradation process were calculated. Fourier transforms infrared spectroscopy and mass spectroscopy coupled to thermogravimetry was used to identify the volatile products resulting from the degradation of the network. The study showed that the sample is stable up to temperatures exceeding 290 °C. The major degradation volatile products identified were: ammonia, water, carbon dioxide and compounds with aromatic structure such as bisphenol A and its degradation products.     

Synthesis and thermal behavior of Janus dendrimers,part 2

The thermal properties of twelve Janus-type dendrimers up to the second generation were evaluated by termogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Compounds consist of the dendritic bisMPA based polyester moieties, and either 3,4-bis-dodecyloxybenzoic acid, 3,5-bis-dodecyloxybenzoic acid or 3,4,5-tris-dodecyloxybenzoic acid moieties, attached to opposite sides of the pentaerythritol core. The thermal stability of the compounds was evaluated by TGA, displaying onset decomposition temperatures (T_d) at around 250 °C. DSC measurements upon heating and cooling confirmed that OH terminated Janus dendrimers featuring large polarity difference in opposite sides display liquid crystalline phases with exception of 3,5-type G1 dendrimer; while acetonide terminated dendrimers displayed merely melting transitions. Dendrimers having terminal alkyl chains at positions 3,4 or 3,4,5 in aromatic moieties exhibited enantiotropic mesophases. However, the thermal behavior of the dendrimers with 3,5-substitution pattern was different: the 3,5-type G1 dendrimer exhibit a lack of mesomorphic transition, and in the case of the 3,5-type G2 dendrimer, the mesophase was absent in the first heating scan but was observed during the subsequent cooling and heating scans at the rate of 10 °C/min.     

Metal (Fe, Co, Ni) Nanoparticles in Silica Gels: Preparation and Magnetic Properties

Metal containing silica gels with a Me/Si molar ratio between 0.01 and 0.2 are submitted to thermal treatment under hydrogen within the temperature range 600 to 1000°C. The changes occurring during these treatments are followed by X-ray diffraction, transmission electron microscopy, Mössbauer spectrometry and static magnetization measurements.During these treatments, nickel is nearly totally reduced to metal particles, the mean size of which increases from 3 to 10 nm with increasing temperature, but does not vary appreciably with nickel content. These particles exhibit a classical superparamagnetic behavior and are stable towards reoxidation when reexposed to air at room temperature.Iron and cobalt behave in a notably different manner. First, in both cases, silicates may be formed during the thermal treatment and consequently the reduction to the metallic state is not complete unless it occurs at high temperature (1000°C and above). Secondly, the particles formed are much less stable toward reoxidation, especially in the case of iron. Accordingly, the evolution of the magnetic behavior is much more complex than in the case of nickel.     

Synthesis and properties of hole-transporting indolo[3,2-b]carbazole-based hydrazones with reactive functional groups

The synthesis of indolo[3,2-b]carbazole-based mono- and dihydrazones with reactive vinylbenzyl or vinyloxyethyl functional groups at the nitrogen atom of hydrazine moiety is reported. The thermal, optical, photophysical, electrochemical and photoelectrical properties of the synthesized compounds are described. They exhibit moderate thermal stability with 5% weight loss temperatures ranging from 273 to 343 °C. Self-polymerization of the monomers with vinylbenzyl functional groups starts at around 180 °C. The values of ionization potentials of the compounds measured by cyclic voltammetry are in the range of 4.94–5.00 eV and those estimated by electron photoemission in air range from 4.99 to 5.21 eV. Electron affinities range from −2.28 to −2.23 eV. The molecular structure of these hydrazones allows stable amorphous films to be prepared and the hole drift mobilities of the films exceed 10⁻³ cm²/V s at high electric fields.     

Thermal stabilities and flame retardancies of nitrogen-phosphorus flame retardants based on bisphosphoramidates

Various nitrogen-phosphorus (P-N) compounds based on phosphoramidate were synthesized as model compounds to investigate the relationships among the chemical structure of linker connecting diphenylphoryl groups between the phosphoramidates, the N content, thermal stability, and flame-retarding ability. The flame-retarding efficiencies were evaluated by the limiting oxygen index (LOI) and UL-94 vertical test methods. It was found that bisphosphoramidates are more thermally stable and produce more charred residues when compared to the corresponding bisphosphate compounds. Aromatic phosphoramidates show fairly good flame retardancy for PC and UL-94 V-0 ratings are achieved with addition of as small amount as 3-5 wt%. However, no rating is found for ABS at 30 wt% loading of bisphosphoramidate FRs which leave the remarkably high residues at 600 °C. The thermogravimetric analysis (TGA) results indicate that these compounds work in condensed phase rather than in gas phase. The effect of chemical structure of linker on the flame retardancy is also discussed.     

Meltable phenylethynyl-capped oligoimide resins derived from 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene and 3,4′-oxydianiline

A series of meltable oligoimide resins with controlled molecular weights by reactive phenylethynyl endcapping groups have been prepared by the thermal polycondensation of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) with the aromatic diamine mixtures consisting of different mole ratios of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (1,4,4-6FAPB) and 3,4′-oxydianiline (3,4′-ODA) in the presence of 4-phenylethynylphthalic anhydride (PEPA) as molecular weight-controlling and reactive endcapping reagent. Experimental results indicated that the molecular weight-controlled oligoimide resins were mixtures containing a series of biphenylethynyl-endcapped oligoimides with different chemical structures and different molecular weights. The typical oligoimide resins could be melted at temperatures of 300 °C to yield stable molten fluid with melt viscosity of 13.4 Pa s, which was suitable for melt processing. The molten oligoimide resins could be further polymer chain extended and crosslinked by thermal curing of the reactive phenylethynyl groups to give strong and tough thermosetted polyimides. Thus, the oligoimide resin with calculated molecular weight of 2500 exhibited not only good meltability with low melt viscosity, but also high melt stability and fluidability at temperatures of <300 °C. After thermal curing, the obtained thermosetted polyimide showed high glass transition temperature (>316 °C, DMA), excellent thermal stability with initial thermal decomposition temperature of 588 °C and good mechanical properties with flexural strength of 159.1 MPa, flexural moduli of 3.3 GPa, tensile strength of 94.7 MPa and elongation at breakage of 9.0%.     

The effect of thermal treatment on the properties of some natural phosphates

The properties of Tunisian phosphorite and Kola-apatite were studied after thermal treatment up to 1000°C. It was established that they preserved their reactivity unchanged during acidic treatment to give phosphoric acid and phosphoric fertilizers under the investigated experimental conditions.

---

Zusammenfassung Thermische Eigenschaften von tunesischem Phosphorit und Kola-Apatit wurden nach Erhitzen bis 1000°C untersucht. Es wurde festgestellt, daß ihre Reaktivität durch eine Säurebehandlung zu Phosphorsäure und Phosphordüngemitteln unter den untersuchten experimentellen Bedingungen nicht verändert wird.

     

A novel type of Si-containing poly(urethane-imide)s: synthesis, characterization and electrical properties

A novel type of a Si-containing poly(urethane-imide) (PUI) was prepared by two different methods. In the first method, Si-containing polyurethane (PU) prepolymer having isocyanate end groups was prepared by the reaction of diphenylsilanediol (DSiD) and toluene diisocyanate (TDI). Subsequently the PU prepolymer was reacted with pyromellitic dianhydride (PMDA) or benzophenonetetracarboxylic dianhydride (BTDA) in N-methyl pyrolidone (NMP) to form Si-containing modified polyimide directly. In the second method, PU prepolymer was reacted with diaminodiphenylether (DDE) or diaminodiphenylsulfone (DDS) in order to prepare an amine telechelic PU prepolymer. Finally, the PU prepolymer having diamine end groups was reacted with PMDA or BTDA to form a Si-containing modified polyimide. Cast films prepared by second method were thermally treated at 160 °C to give a series of clear, transparent PUI films. Thermogravimetric analysis indicated that the thermal degradation of PUI starts at 265 °C which is higher than degradation temperature of conventional PU, confirming that the introduction of imide groups improved the thermal stability of PU.To characterize the modified polyimides and their films, TGA, FTIR, SEM and inherent viscosity analyses were carried out. The dielectrical properties were investigated by the frequency-capacitance method. Dielectric constant, dielectric breakdown strength, moisture uptake and solubility properties of the films were also investigated.     

Enhancing the thermal stability of poly(methyl methacrylate) by removing the chains with weak links in a continuous polymerization

A novel method is proposed to produce PMMA with excellent thermal stability by a continuous process composed of polymerization and devolatilization steps. It is based on the fact that free radical polymerized PMMA is a mixture of polymer chains with different structure, a small fraction of which, containing head-to-head linkages or unsaturated ends, is less thermally stable and the major portion without those defect structures which is much more stable. Our idea is selectively remove the unstable chains from this mixture by pre-decomposing them at suitable temperatures in a continuous process, leaving the stable portion as the final PMMA product. The results showed that during the continuous process, the chains with head-to-head linkages were eliminated by conducting the polymerization at 155 °C, and then the chains with unsaturated ends were removed by devolatilization at 300 °C. The final PMMA was thermally stable up to 313 °C.     

Synthesis, characterization, and thermal properties of new silarylene-siloxane-acetylene polymers

New silarylene-siloxane-acetylene polymers have been synthesized by coupling reactions employing 1,3-bis(p-ethynylphenyl)-1,1,3,3-tetraphenyldisiloxane (3) as the key monomer. Their thermal properties have been evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). All of the new polymers showed good thermal stability, with their temperatures at 5% weight loss (T_d5) being higher than 540 °C under nitrogen and higher than 460 °C in air. Their char yields at 1000 °C under N₂ were above 80%. Broad exothermic peaks, attributable to reaction of the acetylenic units, were observed by DSC analysis in the temperature range 270-450 °C.     

Structural manipulation of pyrochlores: Thermal evolution of metastable Gd2(Ti1−yZry)2O7 powders prepared by mechanical milling

The structural and microstructural characteristics of metastable Gd₂(Ti_1−yZr_y)₂O₇ powders prepared by mechanical milling have been studied by a combination of XRD and Raman spectroscopy. Irrespective of their Zr content, as-prepared powder phases present an anion-deficient fluorite-type of structure as opposed to the pyrochlore equilibrium configuration obtained for the same solid solution by other synthetic routes. These fluorites are stable versus thermal activation, at least up to temperatures of 800 °C. For the Ti-rich compositions, thermal treatments at higher temperatures facilitate the rearrangement of the cation and anion substructures and the relaxation of mechanochemically induced defects whereas for compositions with high Zr content, the fluorite crystal structure is retained even at temperatures as high as 1200 °C. Interestingly enough, transient pyrochlores showing a very unusual cation distribution were observed during the thermally induced defect-recovery process.     

Organotin stability during storage of marine waters and sediments

Summary The stability of organotin compounds in water and sediment samples during storage and pre-treatment is of paramount importance. This study presents experiments with butyltin compounds showing that the storage of filtered natural seawater in the dark at pH 2 in pyrex glass bottles is suitable to preserve the stability of tributyltin (TBT) over 4 months both at 20–25°C and 4°C. The other butyltin compounds (mono- and dibutyltin) are stable at 4°C but display some losses at 25°C. A poor recovery of butyltins in turbid water hampered the assessment of the stability on a quantitative basis: however, it could be demonstrated on a qualitative basis that the butyltin stability is uneasily achieved in water samples with high suspended matter. Finally, wet storage and freezing are found to be suitable to preserve the tributyltin stability in sediments, as well as ovendrying (at 50°C), freeze-drying and air-drying. Mono- and dibutyltin are generally subject to changes during the storage of sediments using the different methods.     

P and H NMR studies of the transesterification polymerization of polyphosphonate oligomers

Polymeric phosphonate esters are an interesting class of organophosphorus polymers because both the polymer backbone and phosphorus substituents can be modified. These polymers have been prepared by ring-opening polymerizations of cyclic phosphites, stoichiometric polycondensations of dimethyl phosphonate with diols in conjunction with diazomethane treatment and by transesterification of polyphosphonate oligomers. Our initial attempts to prepare high molecular weight polymeric phosphonate esters by the transesterification methods were unsuccessful. Results indicate that the reactions of dimethyl phosphonate with diols to form polyphosphonate oligomers with only methyl phosphonate end groups are plagued by a serious side reaction that forms phosphonic acid end groups. These end groups do not participate in the transesterification reaction and limit the molecular weights of the polymers that can be obtained. The phosphonic acid end groups can be converted into reactive methyl phosphonate end groups by treatment with diazomethane, however diazomethane is explosive and the polymerization is slow. An alternative route for the production of high molecular weight polymers is the transesterification of the 1,12-bis(methyl phosphonato)dodecane, formed by the reaction of excess dimethyl phosphonate and 1,12-dodecanediol, with a Na₂CO₃ promoter. This allows polymers with molecular weights of up to 4.5×10⁴ to be prepared, and no phosphonic acid end groups are observed in these polymers. Thermal analyses of the poly(1,12-dodecamethylene phosphonate) have shown that this polymer has reasonable thermal stability (onset of thermal decomposition at 273 °C). This polymer also undergoes a cold crystallization process at 15 °C similar to that which has been observed in some polyesters, polyamides and elastomers.