Synthesis and thermal stability of hydrotalcites based upon gallium

Hydrotalcites based upon gallium as a replacement for aluminium in hydrotalcite over a Mg/Al ratio of 2:1 to 4:1 were synthesised. The d(003) spacing varied from 7.83 Å for the 2:1 hydrotalcite to 8.15 Å for the 3:1 gallium containing hydrotalcite. A comparison is made with the Mg/Al hydrotalcite in which the d(003) spacing for the Mg/Al hydrotalcite varied from 7.62 Å for the 2:1 Mg hydrotalcite to 7.98 Å for the 4:1 hydrotalcite. The thermal stability of the gallium containing hydrotalcite was determined using thermogravimetric analysis. Four mass loss steps at 77, 263–280, 485 and 828 °C with mass losses of 10.23, 21.55, 5.20 and 7.58% are attributed to dehydration, dehydroxylation and decarbonation. The thermal stability of the gallium containing hydrotalcite is slightly less than the aluminium hydrotalcite.     

Synthesis and thermal stability of a novel phosphorus-nitrogen containing intumescent flame retardant

A novel phosphorus-nitrogen containing intumescent flame retardant （P-N IFR） was prepared via the reaction of dichlor-opentate with N-methylaniline. The structure of the product was confirmed by ^1H NMR, ^31p NMR, MS and IR. TGA analysis showed it has effective thermal stability.     

含季戊四醇磷酸酯阻燃剂的合成与表征

采用1-氧代-4-羟甲基-2,6,7-三氧杂-1-磷杂双环[2.2.2]辛烷(PEPA)、三氯氧磷、双酚A和双酚S为反应物,合成了两个新型添加型阻燃剂:双酚A双[二(1-氧代-1-磷杂-2,6,7-三氧杂双环辛烷-4-亚甲基)]磷酸酯(BAPP)和双酚S双[二(1-氧代-1-磷杂-2,6,7-三氧杂双环辛烷-4-亚甲基)]磷酸酯(BSPP),通过元素分析、FT-IR和1H NMR等表征了标题化合物的结构,结果表明,所合成的标题化合物的结构与预期一致。热失重分析结果证明,BAPP和BSPP质量损失5%(wt)时的温度分别为343.6℃和352.3℃,600℃残余量分别达46.6%和55.5%,具有较高的热稳定性和结炭性能。阻燃性能实验证明,E-51环氧树脂中分别添加质量分数为18.2%(wt)的BAPP和BSPP时,极限氧指数分别为32.2%和31.8%,均能达到UL 94 V-0级。     

Synthesis and thermal stability of xylene-formaldehyde resins

o-,p- andm-xylene have been condensed with formaldehyde using paratoluene sulphonic acid as a catalyst and acetic acid/acetic anhydride as a solvent. The xylene-formaldehyde resins thus obtained have been characterised by IR and NMR spectra. The average molecular weight of the resin samples was determined by vapour pressure osmometry. Kinetic parameters were determined by differential thermal analysis, thermogravimetry and differential scanning calorimetry.     

Synthesis and thermal stability of ZnO nanowires

ZnO nanowires (NWs) were synthesized on Au-coated Si (100) substrates by vapor transport method. The effect of high temperature annealing on the structural and chemical composition as well as thermal stability was studied. The as-prepared ZnO NWs was nearly stoichiometric and identified as hexagonal ZnO phase. After annealing at 1,473 K, the atomic ratio of O/Zn, the intensity of the diffraction peaks, and the diameter of nanowires were increased. The ZnO NWs were fragmented into nanocrystals and the fragments coalesced with each other after annealing at 1,673 K. The thermal stability of ZnO NWs was studied by thermo-gravimetric (TG) analysis. A sharp increase in the TG curves was observed and can be attributed to the oxidation of some possibly presented Zn atoms. The activation energy of oxidation of Zn interstitial atoms was found to be 484.81 kJ mol^?1. A mass gain peak was observed after annealing at 1,473 K, but it was completely eliminated after annealing at 1,673 K.     

Synthesis and thermal stability of benzoxazine nitroxides

A new class of stable nitroxides (aminoxyls) having a 1,4-benzoxazine structure were synthesized and the corresponding thermal stability tested. All derivatives were stable in the entire range of temperatures employed, except those having a benzyl or a tert-butyl group at the β-position with respect to the aminoxyl function, which underwent radical fragmentation. Such a behavior allowed a kinetic study, carried out by means of EPR spectroscopy, to determine the corresponding rate constants and activation parameters (E(a)). Appropriate DFT calculations were performed for all nitroxides including also the thermally stable ones, in order to study the geometries of the fragmentation transition States as well as to compute the corresponding bond dissociation enthalpies (BDH), useful for further modeling purposes. The data obtained were interpreted on the basis of the relative stability of the leaving radical, according to the corresponding E(a) and BDH, whereas in the case of tert-butyl derivatives steric hindrance should play a determinant role, as evidenced by a comparison of the geometric, kinetic, and thermodynamic parameters upon the whole series.     

Synthesis and nonlinear optical properties of polyacetylenes containing oxadiazole and thiophene pendant groups with high thermal stability

A series of random copolymers poly(3‐ethynylthiophene)‐copoly(2‐(4‐decyloxyphenyl)‐5‐(4‐ethynylphenyl)‐1,3,4‐oxadiazole) with different oxadiazole content ( P2 – P4 ) and homopolymer poly(3‐ethynylthiophene) ( P1 ) as well as poly(2‐(4‐decyloxyphenyl)‐5‐(4‐ethynylphenyl)‐1,3,4‐oxadiazole) ( P5 ) were prepared. The copolymers ( P2 – P4 ) are completely soluble in common organic solvents. The structures and properties of all polymers were characterized and evaluated by FTIR, ¹H NMR, ¹³C NMR, TGA, UV, PL, GPC, and nonlinear optical (NLO) analyses. The incorporation of diaryl‐oxadiazole into polyacetylene‐containing thiophene significantly endows copolymers with higher thermal stability, which may origin from the synergetic effect of the “jacket effect” of diaryl‐oxadiazole units and the effect of retarding or eliminating a few 6π‐electrocycliaztion proceeds of oxadiazole‐containing polyacetylene due to the hindrance of thiophene units. When the copolymer ( P3 ) posses more regular alternating thiophene pendants and oxadiazole pendants arrangement along the polymer backbone, it shows good thermal stability (T_d up to 388 °C) and larger third‐order nonlinear optical susceptibility (χ(3) up to 11.0 × 10^?11 esu). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis and reactivity studies of a manganese 'microperoxidase' containing b-type heme

Mn(III)protoporphyrin IX-6(7)-gly-gly-his methyl ester (MnGGH) has been prepared by condensation of glycyl-glycyl-L-histidine methyl ester with the propionic side chains of Mn(III)protoporphyrin IX. It was characterised by mass spectrometry and UV/VIS spectroscopy. Stopped-flow spectrophotometry was used to study the reaction of the Mn 'microperoxidase' with hydrogen peroxide. The formation of active intermediates analogous to previously described metal-hydroperoxo (compound 0) and metal-oxo (compound I) intermediates of the 'natural' Fe(III) microperoxidase-8 and Mn(III) microperoxidase-8 was observed. The rate of formation of the MnGGH-based compound I analogue was found to increase dramatically with increasing pH. A steady-state kinetic analysis of the catalytic peroxidase activity of MnGGH towards K4[Fe(CN)6], L-tyrosine methyl ester, o-dianisidine, o-methoxyphenol and ascorbic acid showed that the peroxidase reaction proceeds via the formation of a microperoxidase-substrate complex followed by electron transfer from the substrate to the metal. The reactivity of MnGGH depends on the size and hydrophobicity of the substrate, and these properties appear to influence the rate of the electron transfer, which is the rate-limiting step for the whole process. MnGGH showed higher reactivity towards reducing substrates than its Fe(iii) analogue.     

Synthesis and characterization of novel vinyl copolymers containing N-vinylphthalimide: Comonomers reactivity ratios and thermal stability

N-Vinylphthalimide (NVPh) was copolymerized with p-methylstyrene (PMS), p-methoxystyrene (PMOS) and p-chlorostyrene (PClS) at 60 °C, with 2,2′-azo-bis-isobutyronitrile as an initiator. Copolymer composition was determined by elemental analysis in case of the N-vinylphthalimide and p-methylstyrene comonomer pair, whereas proton nuclear magnetic resonance was used for the analysis of the two other copolymers.The reactivity ratios for each comonomer pair were estimated by the classical Fineman-Ross and Kelen-Tüdõs linear techniques. These data showed that N-vinylphthalimide was less reactive in all the cases and that the comonomer distribution, that was basically random in the poly(N-vinylphthalimide-co-p-methylstyrene) and poly(N-vinylphthalimide-co-p-chlorostyrene) copolymers, was rather alternate in the third poly(N-vinylphthalimide-co-p-methoxystyrene) copolymer. The difference observed in the reactivity ratios was discussed in reference to the structure of the comonomer units and the parent radicals. The thermal properties of the copolymers and model homopolymers were investigated by differential scanning calorimetry and thermogravimetric analysis.     

Synthesis and thermal studies of heterocyclic siloxanes containing boron

Eight- and six-membered cycloborasiloxanes containing two and one boron atoms respectively are strained ring compounds which undergo ring opening polymerization and ring–ring transformation reactions on thermolysis. Prolonged heating at 200°C results in volatilization of the cyclic boroxine (PhBO)₃, whereas rapid heating of either compound to 1500°C in an inert atmosphere does not result in loss of boron, but affords instead an amorphous residue containing silicon carbide, boron oxide and carbon. Upon further pyrolysis at 1700°C the final product consists of microcrystalline silicon carbide in which are embedded large crystals of boron carbide.     

含双螺环三聚磷腈单元的苯并噁嗪树脂的结构和热稳定性

以双螺环取代三聚磷腈基双苯甲酰氯和4-氨基(N-苯基)苯并噁嗪单体为原料合成了一种含双螺环取代三聚磷腈结构单元的苯并噁嗪树脂单体(HCP-5);采用傅立叶变换红外光谱仪(FT-IR)和核磁共振谱仪(1 H NMR,13 C NMR,31P NMR)表征了苯并噁嗪树脂单体的结构,基于FT-IR和示差扫描量热法研究了其固化行为,并利用热重分析和示差热重分析研究了HCP-5树脂单体、均聚物及其与双酚A型苯并噁嗪树脂(Bz)共聚物的热稳定性.结果表明,HCP-5均聚物具有很好的热稳定性和成炭性,其在317℃下的热失重为5%,在800℃下的残炭率为50%,可用于普通苯并噁嗪树脂改性.此外,HCP-5/Bz(1∶1;质量分数)共聚物在332℃下的热失重为5%,在800℃下的残炭率为48%.     

Effects of the nanofiller size and aspect ratio on the thermal and rheological behavior of PEG nanocomposites containing boehmites or hydrotalcites

Journal of Thermal Analysis and Calorimetry - In this work, polyethylene glycol nanocomposites containing different nanofillers (namely hydrotalcites or boehmites, at 5 mass% loading) were...     

Synthesis and thermal stability of secondary sugar allyltin derivatives

Reaction of sugar allylic mesylates with tri-n-butyltin cuprate affords the primary and secondary allyltin derivatives: Sug-CHCH-CH₂SnBu₃ and Sug-CH(SnBu₃)-CHCH₂ with the latter predominating. The S_N2′ addition led almost exclusively to one isomer with the S configuration at the newly created stereogenic center. Only traces of the opposite R isomer were formed. Both stereoisomers of secondary allyltins decompose at high temperature (140°C) with elimination of the tin moiety and opening of the sugar ring. The main S isomer gives the dienoaldehyde CH₂CH-CHCH-[(CHOR)₃]-CHO with the cis geometry across the internal double bond. The minor R isomer provides the trans dienoaldehyde under the same conditions. These results strongly suggest the concerted (E2) mechanism of thermal decomposition of secondary sugar allyltin derivatives.     

Synthesis and thermal characterization of phosphorus containing siliconized epoxy resins

Siliconized epoxy matrix resin was developed by reacting diglycidyl ethers of bisphenol A (DGEBA) type epoxy resin with hydroxyl terminated polydimethylsiloxane (silicone) modifier, using γ-aminopropyltriethoxysilane crosslinker and dibutyltindilaurate catalyst. The siliconized epoxy resin was cured with 4, 4-diaminodiphenylmethane (DDM), 1,6-hexanediamine (HDA), and bis (4-aminophenyl) phenylphosphate (BAPP). The BAPP cured epoxy and siliconized epoxy resins exhibit better flame-retardant behaviour than DDM and HDA cured resins. The thermal stability and flame-retardant property of the cured epoxy resins were studied by thermal gravimetric analysis (TGA) and limiting oxygen index (LOI). The glass transition temperatures (T_g) were measured by differential scanning calorimetry (DSC) and the surface morphology was studied by scanning electron microscopy (SEM). The heat deflection temperature (HDT) and moisture absorption studies were carried out as per standard testing procedure. The thermal stability and flame-retardant properties of the cured epoxy resins were improved by the incorporation of both silicone and phosphorus moieties. The synergistic effect of silicone and phosphorus enhanced the limiting oxygen index values, which was observed for siliconized epoxy resins cured with phosphorus containing diamine compound.     

Synthesis and thermal polymerization of perylene bisimide containing benzocyclobutene groups

Fourfold benzocyclobutene-functionalized perylene bisimide（PBI 4） has been synthesized and its structure was characterized by FTIR,MS and NMR.PBI 4 can react either with itself,or the appropriate dienophiles to form the corresponding products under appropriate temperature.The polymer film obtained from the reaction of PBI 4 with methyl vinyl silicone rubber possessed excellent film forming properties including flatness.The optical properties of PBI 4 and polymer film obtained from the reaction of PBI 4 and methyl vinyl silicone rubber have been determined by UV/vis and fluorescence spectroscopy.     

Synthesis and thermal properties of diurethanes containing various mesogenic units

Abstract

Five homologous series of diurethanes containing mesogenic moieties were synthesized by addition reactions of ω-alkenols to aromatic diisocyanates. The thermal behaviour of the compounds was studied by differential scanning calorimetry and on the hot stage of a polarizing microscope. Thermotropic liquid crystal behaviour was found for the diurethanes having a central core of more than two aromatic rings. Smectic C mesophases were observed for the derivatives of 4,4″-p-terphenylene and nematic mesophases for the diurethanes containing a di(4-phenylene)terephthalate unit. The compounds of both series possess high transition temperatures and narrow mesomorphic ranges.     

Synthesis and thermal stability of silicon-containing esters of phosphorus acids

A number of trialkylsilylmethyl diphenyl phosphates MeRR′SiCH₂OP(O)(OPh)₂ (1a-e: R=Et (a), Pr (b), CF₃CH₂CH₂ (c, e), Me₃SiCH₂ (d); R′=Me (a-d), Et (e)) were synthesized and their thermal rearrangement, of the 1,2-shift type, was studied. The rearrangement consists of the migration of an alkyl group from Si atom to the methylene carbon atom and gives the corresponding silyl esters. The rate of the rearrangement was found to increase in the order1d<1b<1a<1 (R=R′=Me)<1c corresponding to the enhancement of the total inductive effect (−I) of the substituents at the Si atom. The relative migration ability of the substituents at the Si atom, determined by GC/MS analysis of the disiloxane fraction resulting from hydrolysis of pyrolyzed phosphates1a-e, increases in the order R=Pr<Et<CF₃CH₂CH₂<Me≪Me₃SiCH₂, which differs substantially from the order in which the rate of the rearrangement of phosphates1a-d changes. The electronegativity of the migrating group affects noticeably the relative ability to migrate. For Part 4, see Ref. 1. Deceased. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 1767–1772, September, 1998.     

Synthesis of nanocrystalline zinc manganese oxide by thermal decomposition of new dinuclear manganese(III) precursors

Nanocrystalline manganese-doped zinc oxide was synthesized by thermal decomposition of a zinc oxide sol with two new dinuclear manganese(III) complexes as precursor. Thermal analysis results indicated that the decomposition of manganese precursors occurred at 269 and 314 °C. X-ray structural analysis shows the presence of dimanganese core in the complexes and the binding of the ligands to the manganese(III) is through N₂O₂. The manganese-doped zinc oxide composite was characterized by means of X-ray diffraction, scanning electron microscopy, and UV–Vis spectroscopy. Structural properties of the composites elucidated that the manganese ions have substituted the zinc ions without changing the wurtzite structure of zinc oxide.