Dication ethers. 7. Dication ether salts from cyclic bisureas

The bicyclic bisureas 2 react with triflic anhydride to give the dication ether salts 4 . Further transformation of the remaining carbonyl groups of 4 into bis-carbenium ether linkages was not possible. The monocyclic bisurea 8 yields the dicationic heterocycle 9 in an intramolecular fashion. The structure of 9 , which is the first dication ether salt with an endocyclic ether linkage, was established by independent synthesis from 10 as well as by its hydrolysis to give the hemi-protonated bisurea 11 .     

Spatial structure of bicyclic bisureas

The method of molecular mechanics has been used to examine the spatial structure of bicyclooctane, bicyclononane, bicyclodecane, purone, and spiran bicyclic bisureas (BBU). Bicyclononanediones have been shown to exist in a planar form with planar urea groups, whereas spiro[5,5]undecanedione exists in the chair-chair form. On introducing N-alkyl groups, steric hindrance in bicyclooctane and bicyclononane BBU is eliminated by reorientation of the urea fragment NCN, and in bicyclodecane BBU, by reorientation of the CNCNC fragment.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9,. pp. 2024–2027, September, 1989.     

Microwave-assisted selective and efficient synthesis of 1,3,5-triazinyl mono and bisureas

An efficient and sustainable microwave-assisted approach for the one-step preparation of a wide range of 1,3,5-triazinyl mono- and bisureas has been developed, combining solvent-free conditions and microwave irradiation. In these conditions the very unreactive amino groups of 1,3,5-triazine-2,4-diamines successfully react with phenylisocyanate to yield selectively mono and bisureas.     

The effect of different impact modifiers in halogen-free flame retarded polycarbonate blends - II. Fire behaviour

In this second of a series of two papers, the fire behaviour of halogen-free flame retarded polycarbonate (PC) blends with different impact modifiers was studied. The impact modifiers were acrylonitrile-butadiene-styrene (ABS), a poly(n-butyl acrylate) rubber (PBA) with a poly(methyl methacrylate) (PMMA) shell and two silicone-acrylate rubbers consisting of PBA with different amounts of polydimethylsiloxane (PDMS) and different shell materials (PMMA and styrene-acrylonitrile, SAN). The flame retardant was bisphenol A bis(diphenyl phosphate) (BDP). Flammability was determined by LOI and UL 94. The burning behaviour under forced flaming conditions was studied by cone calorimeter under different external irradiations and by pyrolysis combustion flow calorimeter measurements. The exchange of ABS with the pure acrylate rubber worsened flammability, while similar results were obtained in cone calorimeter measurements. The exchange of ABS with the silicone-acrylate rubbers is promising, particularly with higher amounts of PDMS. In flammability tests strongly enhanced LOI values were obtained and therefore silicone-acrylate rubbers look like promising alternatives for ABS.     

Synthesis of epoxide hydrolase sEH inhibitors and study of its inhibitory properties

Russian Chemical Bulletin - Adamantyl-containing 1,3-disubstituted ureas, bisureas, and biscarbamates containing different spacers between the ureylene or the carbamate groups and the adamantyl...     

Synthesis And Biological Activities of 4-Neoalkyl-2,6,7-Trioxa-1-PhosphabicycIo[2.2.2] Octanes

4-Alkyl derivatives of 2,6,7-trioxa-1-phosphabicyclo[2.2.2] octanes are extensively used for spectroscopic studies and are candidates for use as flame retardants, vinyl resin stabilizers and antioxidants^[1-4]. Bicyclic phosphates are antagonist of GABA receptor, further research show that these compounds act on the chloride ion channel connecting with GABA receptor. So bicyclic phosphate can act as drugs to probe the Cl^- channel. Our preliminary pharmacological results indicate that these bicyclic phosphorus compounds should be handled with great care because of their high toxicity to mammals. Some derivatives of bicyclic phosphates have been prepared in our laboratory.     

The effect of different impact modifiers in halogen-free flame retarded polycarbonate blends - I. Pyrolysis

In this first of two papers, the thermal decomposition of bisphenol A bis(diphenyl phosphate)-flame retarded polycarbonate (PC) blends with different impact modifiers was studied. The impact modifiers were an acrylonitrile-butadiene-styrene (ABS), a poly(n-butyl acrylate) (PBA) rubber with a poly(methyl methacrylate) (PMMA) shell and two silicone-acrylate rubbers consisting of PBA with different amounts of polydimethylsiloxane (PDMS) and different shells (PMMA and styrene-acrylonitrile, SAN). The focus of this work was to study the impact of the acrylate and silicon-acrylate rubbers with respect to pyrolysis and flame retardancy in comparison to common ABS. Thermogravimetry (TG) was performed to investigate the pyrolysis behaviour and reaction kinetics. TG in combination with FTIR identified the pyrolysis gases. Solid residues were investigated by FTIR-ATR. PC/ABS shows two-step decomposition, with PC decomposing independently from ABS at higher temperatures. Pure acrylate rubber destabilises PC due to interactions between the rubber and PC, which leads to earlier decomposition of PC. Using silicone-acrylate rubbers led to similar results as PC/ABS with respect to pyrolysis, reaction kinetics and analysis of the solid residue; hence the exchange of ABS for the silicone-acrylate rubbers is possible.     

Effect of a novel phosphorous-nitrogen containing intumescent flame retardant on the fire retardancy and the thermal behaviour of poly(butylene terephthalate)

A novel phosphorus-nitrogen containing intumescent flame retardant (P-N IFR) was prepared via the reaction of a caged bicyclic phosphorus (PEPA) compound and 4,4′-diamino diphenyl methane (DDM) in two steps. The product was added to poly(butylene terephthalate) (PBT) to obtain halogen-free flame retarded polyester. UL-94 test, thermogravimetry and in situ infrared spectroscopy were used to characterize the flammability, thermal degradation properties and the char-forming process. It was shown that the phosphorus-nitrogen containing compound could improve both the flame retardancy and thermal stability more effectively than other P-N flame retardants. Furthermore, it was a good char-forming agent incorporated with the co-addition of polyurethane (PU) when the combustion occurred. The formation of P-N structure was incorporated in the char layer.     

The influence of flame retardants on the properties of sealing ethylene-propylene-diene monomer rubber

This paper presents the results of investigating the structure, the combustibility, and the basic physical and mechanical properties of sealing ethylene-propylene-diene monomer rubber specimens filled with flame retardants such as aluminum and magnesium hydroxides of different dispersity. It is shown that an increase in the flame-retardant particle size causes a change in the structure and the properties of the rubbers and increases their combustibility.     

Effect of the content of ethyl cellulose-rubber blend on physicochemical properties of adhesive compositions

Results of comprehensive systematic physicochemical studies of the blends of ethyl cellulose and butadiene-acrylonitrile rubbers are reported. It is shown that the addition of butadiene-acrylonitrile rubbers to ethyl cellulose results in the formation of ethyl cellulose-butadiene-acrylonitrile rubber thermoelastoplastic complexes due to the elastification of the thermoplastic polymorphous structure of ethyl cellulose with enhanced impact strength and heat resistance.     

A chemical modification approach for improving the oil resistance of ethylene-propylene copolymers

The need for a low-cost and weather, high-temperature and oil-resistant rubber is well-established in the market place. Such products have the potential to replace high cost rubbers and/or oil-resistant rubbers that lack weather and high-temperature resistance. The present study aims at increasing the polarity of EP(D)M rubber by chemical modification and cross-linking of EPM copolymer grafted with maleic anhydride (EPM-g-MA). First, it is shown that the oil resistance of rubbers can be predicted using calculated solubility parameters. Next, a variety of modified EPMs has been designed, directed at a high polarity in combination with a relatively low glass transition temperature, and have subsequently been prepared to validate the concepts experimentally. The various modification approaches resulted in (significantly) improved oil resistance and are in fair agreement with the calculated oil swell data. It is concluded that new rubber materials based on EPM-g-MA can be developed, that may replace existing oil-resistant elastomers.     

Diene Rubber Modification Using Thiol-Type Derivatives

Thiol-containing antioxidants such as 4-(mercaptoacetamido)-diphenylamine (MADA) undergo ready addition of-SH groups to the double bonds in diene rubbers in the presence of initiators. The reaction is a radical chain process leading to rubbers with improved thermooxidative resistance. The modification reaction has been carried out on high cis-polyisoprene and polybutadiene, and conditions under which the physicochemical properties (e.g., inherent viscosity, gel content, and microstructure) are less affected have been found. An oxygen absorption test and DSC were used as rapid methods for evaluation of thermooxidative stability of modified rubbers. The superiority of rubbers with MADA chemically attached (ranging from 1 to 4 phr) was shown by a circulating air oven test and by an extraction process which simulates the aggressive environments experienced by many rubbers under practical conditions. The results obtained show that a small degree of modification (1 phr MADA) is large enough to provide good thermooxidative stability without alteration of the molecular characteristics of the parent rubbers. At higher degrees, cistrans isomerization can occur.     

Synthesis and Structure of A Novel Caged Bicyclic Phosphate Flame Retardant

IntroductionThe ecological safety of polymer flame retardant has become a major subject in the modern polymer industry, and there is an international demand for the control of polymer flammability without the use of halogenated additives. Consequently, current research is mainly focused on looking for environmental friendly additives in the form of organophosphorus compounds, which are being thought as the alternatives of the halogen containing flame retardants1. Among the organophosphorus fla…     

Cross-linking of titanosiloxane oligomers and properties of materials with vulcanized titanosiloxane coatings

The structuring of the liquid titansiloxan oligomer at higher temperatures is studied. The properties of cover materials were investigated. It is shown that the materials have a high fire resistance and physical and mechanical properties compared to materials with vulcanized cover on the base of liquid siloxane rubbers.     

Unraveling chemical structure of laminar premixed tetralin flames at low pressure with photoionization mass spectrometry and kinetic modeling

This work reports an investigation on laminar premixed flames of tetralin at 30 Torr and equivalence ratios of 0.7 and 1.7. Measurements of the chemical structure including identification and mole fraction measurements of free radicals, isomers, and polycyclic aromatic hydrocarbons (PAHs) were performed using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV‐PIMS). A kinetic model with 296 species and 1 577 reactions was developed and validated against the flame chemical structure data measured in this work. Modeling analysis reveals the key reaction pathways in tetralin decomposition and PAHs formation. The H‐atom abstraction reactions by H, O, and OH are found to control the consumption of tetralin in the lean flame, while those by H play the dominant role in the rich flame. Indene and naphthalene have very high concentration levels in the rich tetralin flame due to the existence of direct formation pathways from the decomposition of tetralin. The two bicyclic PAHs and their radicals play significant roles in the PAHs growth process of tetralin combustion, which results in the high sooting tendency of tetralin compared to those of alkylbenzenes with smaller or same carbon atom numbers.     

Synthesis, application and flame retardancy mechanism of a novel flame retardant containing silicon and caged bicyclic phosphate for polyamide 6

A novel flame retardant containing silicon and caged bicyclic phosphate groups, tri(2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-1-oxo-4-hydroxymethyl) phenylsilane (TPPSi) was successfully synthesized. The chemical structure of TPPSi was characterized by FTIR, ¹H NMR and ³¹P NMR. The application of TPPSi (25 wt%) as a flame retardant in polyamide 6 (PA6) not only gains satisfied flame retardancy and smoke suppression, but also retains the high toughness and inherent appearance of pure PA6. The influence of TPPSi on the decomposition pathway of PA6 was discussed based on TG-FTIR and FTIR analysis. The interaction between TPPSi and PA6 at high temperature alters the decomposition pathway of PA6 resulting in the formation of the residue containing phosphorus and silicon. The heat and smoke release behaviors at different external heat fluxes were measured by cone calorimeter, and the fire residue was analyzed by SEM-EDX. The condensed phase action resulting from the barrier effect of residue is proposed to be the major flame retardancy mechanism of TPPSi in PA6, with the fuel reduction action as the minor.     

Synthesis of a Modifier for Rubbers with Silica-filler by Reaction of <Emphasis Type="Italic">N-tert</Emphasis>-Butyl-2-benzothiazolylsulfenamide with Trimethylolpropane Triglycidyl Ether and Characterization of the Reaction Product

Reaction of N-tert-butyl-2-benzothiazolylsulfenamide with trimethylolpropane triglycidyl ether was performed, and the product was characterized and studied as an additive to rubber. Interaction of this additive with rubber was studied by the method of equilibrium swelling. The additive was found to increase the amount of cross-links in the polymer matrix and to improve the process characteristics of rubber stocks with silica, decreasing their viscosity and vulcanization time and enhancing the resistance to scorching. The use of this additive allows preparation of vulcanized rubbers with higher modulus, compared to the rubbers modified with the product of the reaction of methacrylic acid with trimethylolpropane triglycidyl ether.     

7,7′‐Diamino‐2,2′‐diindolylmethane: A Building Block for Highly Efficient and Selective Anion Receptors—Studies in Solution and in the Solid State

The easy‐to‐make 7,7′‐diamino‐2,2′‐diindolylmethane was used as a building block for the construction of anion receptors operating by hydrogen bonds. Its various bisamide and bisurea derivatives were designed and synthesised as acyclic as well as macrocyclic molecules, then their structural and anion binding properties were studied in solution and in the solid state. The bisamide receptors demonstrate high affinity towards oxoanions in highly polar and partially aqueous solutions (DMSO with up to 25 % H₂O) with significant selectivity for dihydrogen phosphate. Remarkably, the bisurea‐based molecules are able to bind anionic guests even in pure methanol and show selectivity toward tetrahedral oxoanions, that is, hydrogen sulphate and dihydrogen phosphate. X‐ray analysis revealed that both classes of molecules adopt a similar conformation in the solid state: a bent sheet shape with a binding pocket equipped with hydrogen‐bond donors (four for the amides and six for the bisureas), whose orientation is particularly tailored for oxoanions. The results of ROESY NMR experiments are in agreement with the findings for the solid state and confirmed that both bisamides and bisureas can easily adapt the conformation with convergent hydrogen‐bond donors, which is highly suitable for anion binding.     

Synthesis and application of amino resinous intumescent flame retardants

A kind of amino resinous intumescent flame retardants (IFR) was firstly synthesized, and the structure of the main composition was determined to be a caged bicyclic macromolecule containing phosphorus. The 30% weight of IFR was added into the flexible polyurethane foam (FPUF) to get retardant FPUF which has 26.5% of the limiting oxygen index. The date of CONE show that the heat release, smoke and gas of the flame retardant FPUF are much decreased and the activation energy decreases by 54 kJ·mol⁻¹. It shows that the IFR can catalyze decomposition and carbonization of FPUF. __________ Translated from Transactions of Beijing Institute of Technology, 2008, 28(5) (in Chinese)     

Reactivities of silane coupling agents in the silica/rubber composites: Theoretical insights into the relationships between energy barriers and electronic characteristics

Si69 and Si75, typical commodities of silane coupling agents, are often employed in tire recipes to work as the bridges connecting silica and polymers, with which rolling resistance and wet traction are enhanced without loss in abrasion resistance. In this article, the reactivities of Si69 and Si75 with silica and various rubbers were theoretically investigated by using density functional theory (DFT). When the agents were coupled with silica, not only the acid+water condition but also the pure acid condition was confirmed to readily trigger the condensation reactions. The corresponding Gibbs free energy barriers were related to the charge distributions of reaction regions. As the agents suffered from the homolysis of central S S bonds, the generated single-S-tailer radicals (R S·) showed significantly higher reactivities of both the radical addition and the α-H transfer reactions with rubbers, due to the stronger radical philicities of the terminal sulfur radicals with larger condensed local softnesses [s⁰(S)]. When the agents underwent the heterolysis of central S S bonds, the terminal sulfur anions with smaller s⁻(S) indices, however, facilitated the nucleophilic addition reactions with rubbers. Several derivative indices based on the condensed local softnesses were also proposed here to shed light on the reactivities from the viewpoint of the relationship between energy barriers and electronic characteristics. The above findings pave the way for the design of new kinds of silane coupling agents using computer-aided techniques, and meanwhile, provide references for the practical application of Si69 and Si75 to the silica/rubbers systems.