Epoxides In Presence Research Articles

Polyurethane dispersion/carboxylated nitrile butadiene rubber blends produced by a greener dual crosslinking approach

A latex blend comprising polyurethane dispersion (PUD) and carboxylated nitrile butadiene rubber (XNBR) in an 80:20 ratio was prepared in the presence of epoxide and organo-modified siloxane crosslinkers. The aim of the study was to enhance the tensile, thermal, and chemical properties of the PUD/XNBR latex blend without the incorporation of sulphur and accelerator. Studies revealed that the combined action of epoxide and organo-modified siloxane crosslinker demonstrated adequate intermolecular hydrogen bonding, thereby resulting in superior tensile strength. Differential scanning calorimetry (DSC) analysis showed alterations in chain orientation and melting enthalpy due to the introduction of two crosslinkers that impart ordered hydrogen bonding to a certain degree. The compactness of the structure of the cure molecule may be closely related to the heating enthalpy, as in the following sequence, PUD80/XNBR20/E1 will have a loosely packed structure, followed by PUD80/XNBR20/E0.5S0.5 and PUD80/XNBR20/S1. Chemical swelling studies revealed the impact of crosslinker combinations on hydrogen bonding (both ordered and disordered), affirming the consequential enhancement in chemical resistance. This study confirms that the attained intermolecular hydrogen bonding results in desirable mechanical and chemical resistance performance, making the latex blend suitable for glove applications.

Ultrafast Epoxy‐Anhydride Photopolyaddition Reaction

AbstractThe conventional epoxy/anhydride reaction is quite slow (more than one hour to reach full conversion at room temperature (RT)) and usually requires thermal treatment at rather high temperature. Ideally, the reaction should be triggered by light for on demand systems i.e. very fast polymerizations (in few seconds) can be carried out in mild conditions (at RT with low energy consumption using cheap and safe light emitting diode (LED) light). In this work, a new approach is proposed with an ultrafast epoxy/anhydride photopolyaddition reaction that can be triggered by near‐UV/visible light. Therefore, a photoinitiating system is developed to cure epoxides in presence of anhydrides as hardeners without any external heat and in a short time scale i.e. few seconds upon light vs. hours at RT without light. Excellent polymerization performances can be observed upon LED@405nm irradiation with full epoxy function conversion. The polymerization kinetics are followed both by real‐time FTIR and real‐time photorheology experiments. As example of the high performance of this new photoactivated epoxy/anhydride process, the curing of epoxy/glass fibre composites is presented. Remarkably, an excellent depth of cure can be obtained in only 20 seconds of irradiation with a LED@405 nm.

Sequence Selective Polymerization Catalysis: A New Route to ABA Block Copoly(ester-b-carbonate-b-ester)

The preparation of ABA type block copoly(ester-b-carbonate-b-ester) from a mixture of e-caprolactone, cyclohexene oxide, and carbon dioxide monomers and using a single catalyst is presented. By using a dinuclear zinc catalyst, both the ring-opening polymerization of e-caprolactone and the ring-opening copolymerization of cyclohexene oxide and carbon dioxide are achieved. The catalyst shows high selectivity, activity, and control in the ring-opening copolymerization, yielding poly(cyclohexene carbonate) polyols, i.e., α,ω-dihydroxyl end-capped polycarbonates. It also functions efficiently under immortal conditions, and in particular, the addition of various equivalents of water enables the selective preparation of polyols and control over the polymers’ molecular weights and dispersities. The catalyst is also active for the ring-opening polymerization of e-caprolactone but only in the presence of epoxide, generating α,ω-dihydroxyl-terminated polycaprolactones. It is also possible to combine the two polymeri...

Cationic copolymerization behavior of epoxide and 3-isochromanone

Cationic copolymerization of n-butyl glycidyl ether (BGE) and 3-isochromanone (ICM) was investigated using trifluoromethanesulfonic acid (TfOH) as an initiator at 100 °C. In the copolymerization, the reactive site of ICM with the propagating cation was completely different from that in its homopolymerization: in the former, the propagating cation reacted with the carbonyl oxygen of ICM, while in the latter, the propagating cation reacted with the aromatic ring of ICM. In spite of the potential of ICM to undergo the homopolymerization, in the present copolymerization, ICM was consumed smoothly only in the presence of epoxide. As a result, the copolymerization proceeded in a statistic manner to afford the corresponding copolymer bearing ICM-derived ester linkages distributed in the main chain. Cationic copolymerization of bisphenol A-diglycidyl ether and ICM was also performed to synthesize the corresponding networked polymer. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4213–4220

Accelerating effects of N‐aryl‐N′,N′‐dialkyl ureas on epoxy‐dicyandiamide curing system

AbstractThis report focuses on epoxy‐dicyandiamide (DICY) curing system accelerated by N‐aryl‐N′,N′‐dialkyl urea, aiming at clarifying the accelerating mechanism and the relationship between accelerating effect and molecular structure of the accelerators. Nine N‐aryl‐N′,N′‐dialkyl ureas were synthesized and investigated with measurements of differential scanning calorimetry, thermo gravimetric/differential thermal analysis and NMR spectroscopy. The results revealed that the ureas released the corresponding secondary amines by the thermal dissociation in the presence of epoxide, which led to the formation of tertiary amines that catalyze the addition reaction of DICY to epoxide. Moreover, a tendency that the ureas able to release more compact amines exhibited higher acceleration effects was discovered. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Molybdenum Peroxo Nanohybrid Compounds in Different Structures and Catalytic Properties

The new nanohybrid of molybdenum peroxo compounds based on pyridine dicarboxylate ligands were synthesized by employing one-pot procedure in aqueous media and characterized by infrared (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermal analysis (TGA/DTA). The prepared compounds were used as catalysts for the epoxidation of cyclohexene and cyclooctene in a mild condition. Results showed that these molybdenum peroxo compounds have significant potentials as oxidants in oxygen atom transfer reactions. These reagents oxidized olefins to epoxides in presence of hydrogen peroxide with high conversions and selectivity. Comparison of the relative reactivity of those compounds shows that the electronic nature of ligands influences the rate and activity of oxygen transfer reaction. It is also found that the addition of organic ligands not only prevented the formation of diols in epoxidation of alkenes, but also increased the reaction rate.

Neurofurans, Novel Indices of Oxidant Stress Derived from Docosahexaenoic Acid

Isoeicosanoids are free radical-catalyzed isomers of the enzymatic products of arachidonic acid. They are formed in situ in cell membranes, are cleaved, circulate, and are excreted in urine. Isomers of prostaglandin F(2alpha), the F(2)-isoprostanes, have emerged as sensitive indices of lipid peroxidation in vivo. Analogous compounds formed from docosahexaenoic acid (DHA) are termed neuroprostanes and are more abundant than isoprostanes (iPs) in brain. Isofurans are another class of isoeicosanoids characterized by a substituted tetrahydrofuran ring. They are preferentially formed, relative to iPs, under conditions of elevated oxygen tension. Here, we report the discovery of neurofurans (nFs), the analogous family of compounds formed from DHA. Formation of nFs is characterized by mass spectrometry and confirmed by oxidation of DHA in vitro and following CCl(4) administration in liver in vivo. It is demonstrated that the levels of nFs are elevated in the brain cortex of a mouse model of Alzheimer disease and are depressed in mouse brain cortex by deletion of p47(phox), an essential component of the phagocyte NADPH oxidase. Measurement of the nFs may ultimately prove useful in diagnosis, timing, and selection of dose in the treatment and chemoprevention of neurodegenerative disease.

Synthesis, characterization of a new bicobalt complex [Co 2L 2(C 2H 5OH) 2Cl 2] and application in cyclic carbonate synthesis

A novel bicobalt complex [Co 2L 2(C 2H 5OH) 2Cl 2] supported by 2-hydroxyisophthalaldehyde oxime was synthesized. This complex is an efficient catalyst for the coupling reaction of carbon dioxide and epoxides in presence of phenyltrimethylammonium tribromide (PTAT).

Isolation and structure determination of triterpenes from Iris tectorum

Four iridal-type triterpenoids, two of which were new compounds, have been isolated from rhizomes of Iris tectorum Maxim. Their structures were determined by 1D and 2D NMR spectroscopy and ESI-MS spectrometry. The compounds were identified as the iritectols A and B, and the known iridobelamal A and isoiridogermanal. The presence of epoxide and tetrahydrofuran functions are not common in previously isolated iridal-type triterpenoids.

Carbohydrate-Modified Fused Pyranosylidene Complexes via Radical Addition of Epoxides to Unsaturated Metal Carbenes

Alkenyl and alkynyl carbene complexes of chromium and tungsten undergo a diastereoselective cyclization upon reaction with epoxides in presence of [Cp 2TiCl] 2. trans-Fused tetrahydropyranosylidene complexes are obtained from the radical addition of cyclohexene oxide to monosaccharide-derived vinylcarbene tungsten complexes. The benzyl-protected 1,2-anhydro-α- d-glucopyranose adds to styryl and alkynyl carbene complexes to give bicyclic trans-fused tetrahydro- and dihydropyranosylidene complexes as well as the acyclic addition products.

Cyclization of Sclareol Epoxides Catalyzed by Boron Trifluoride in Methanol

Methoxylated cyclic ether derivatives are synthesized in one step directly from sclareol epoxides in presence of catalytic amount of boron trifluoride in methanol.

Random copolymerization of ε‐caprolactone and trimethylene carbonate with rare earth catalysts

Random copolymerization of trimethylene carbonate (TMC) with ϵ-caprolactone (CL) catalyzed by rare earth chloride-epoxide or rare earth isopropoxide has been investigated for the first time. It was found that in the presence of epoxide, rare earth chlorides have high activities for the copolymerization, giving high-molecular-weight random copolymer P(CL-co-TMC) with a narrow molecular weight distribution. Light rare earth chloride-propylene oxide systems are more effective for the copolymerization than heavy rare earth chloride-propylene oxide systems. For the rare earth chloride-epoxide catalyst system, epoxide is the requisite component, and its amount affects the catalytic activity; while rare earth isopropoxide can catalyze the copolymerization alone. The preparative conditions of the copolymer with NdCl3-5PO system were studied. The reactivity ratios of CL and TMC copolymerization with NdCl3-5PO determined by Fineman-Ross method are 1.60 for rTMC and 0.72 for rCL, respectively. The copolymers were characterized by 1H- and 13C-NMR, GPC, and DSC. The mechanism study shows that the rare earth alkoxide is the active species that initiates the ring opening copolymerization of CL and TMC with acyl-oxygen bond cleavages of the monomers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2131–2139, 1997

Random copolymerization of ?-caprolactone and trimethylene carbonate with rare earth catalysts

Random copolymerization of trimethylene carbonate (TMC) with ϵ-caprolactone (CL) catalyzed by rare earth chloride-epoxide or rare earth isopropoxide has been investigated for the first time. It was found that in the presence of epoxide, rare earth chlorides have high activities for the copolymerization, giving high-molecular-weight random copolymer P(CL-co-TMC) with a narrow molecular weight distribution. Light rare earth chloride-propylene oxide systems are more effective for the copolymerization than heavy rare earth chloride-propylene oxide systems. For the rare earth chloride-epoxide catalyst system, epoxide is the requisite component, and its amount affects the catalytic activity; while rare earth isopropoxide can catalyze the copolymerization alone. The preparative conditions of the copolymer with NdCl3-5PO system were studied. The reactivity ratios of CL and TMC copolymerization with NdCl3-5PO determined by Fineman-Ross method are 1.60 for rTMC and 0.72 for rCL, respectively. The copolymers were characterized by 1H- and 13C-NMR, GPC, and DSC. The mechanism study shows that the rare earth alkoxide is the active species that initiates the ring opening copolymerization of CL and TMC with acyl-oxygen bond cleavages of the monomers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2131–2139, 1997

Characteristics and Mechanism of ε-Caprolactone Polymerization with Rare Earth Halide Systems

Ring-opening polymerization of e-caprolactone catalyzed by rare earth halides and rare earth halide−epoxide has been carried out for the first time. It was found that rare earth halides have low activities for the polymerization of e-caprolactone, but in the presence of epoxide, rare earth halides are highly active for the bulk and solution polymerization of e-caprolactone, with high molecular weight poly(e-caprolactone) (PCL) formed. With the NdCl3−20PO system, PCL with a molecular weight of 22.4 × 104 can be easily obtained at 30 °C, and the molecular weight of PCL can be increased to 42 × 104 at 60 °C with a catalyst efficiency of 100 × 104 g of PCL/mol of NdCl3. The catalytic activities of the rare earth halides are affected by the kind of rare earth element, halogen, epoxide, amount of added epoxide, catalyst concentration, and polymerization temperature. It has been found that rare earth halides react with epoxide and produce halogen rare earth alkoxides: (X3-xLn{[OCH(R)CH2]yX}x, X = Cl, Br, I). A ...

Catalyzed reactions of epoxide groups on the solid polymer phase

The catalytic reaction of epoxide bonded on a grafted isotactic polypropylene powder with acids and amines in the presence of organic liquids is studied. The speciality of this reaction is that relatively high catalyst concentrations are used, due to the presence of epoxide in the heterogeneous phase. Rate constants of bonding of model compounds, and also compounds with special effect by means of epoxide groups are quoted.

Reactions of alkene epoxides with methyl isothiocyanate

1. In conjunction with triethylamine or pyridine alkene epoxides serve as catalysts for the trimerization of methyl isothiocyanate. 2. Methyl isothiocyanate trimer readily reacts with alkene epoxides in presence of TEAB with formation of the previously undescribed spiro compounds (I), (IV), (V), and (VI). When heated, the latter break down into alkene episulfides and trimethyldithio-s-triazine-2,4,6(1H,3H,5H)-trione. 3. The further heating of trimethyldithio-s-triazine-2,4,6(1H,3H,5H)-trione with ethylene oxide in presence of TEAB leads, via the formation of intermediately isolated spiro compounds, to trimethyl-s-triazine-2,4,6(1H,3H,5H)-trione. In this way all the sulfur atoms of trimethyl-s-triazine-2,4,6(1H,3H,5H)-trithione are replaced by oxygen atoms.