Showing papers on "Vinyl acetate published in 2005"

Highly active, regioselective, and enantioselective hydroformylation with Rh catalysts ligated by Bis-3,4-diazaphospholanes.

Abstract: Azines made by the reaction of hydrazine with ortho-formylbenzoic acid react with 1,2-diphosphinobenzene and either succinyl chloride or phthaloyl chloride in ca. 30% yield to give rac-bis-3,4-diazaphospholanes bearing benzoic acid groups in the 2 and 5 positions. Condensation of the benzoic acid functionalities with enantiomerically pure amines affords diastereomeric benzoamides which can be separated by flash chromatography. Application of the resolved bis-3,4-diazaphosholanes to Rh-catalyzed enantioselective hydroformylation of styrene, allyl cyanide, and vinyl acetate under mild pressures (20−500 psig of CO/H2) and temperatures (40−120 °C) reveals high activities and selectivities for all three substrates. At 60 °C and 500 psig syn gas, the best ligand provides outstanding regio- and enantioselectivities (styrene, 89% ee, b:l = 30:1; allyl cyanide, 87% ee, b:l = 4.8:1; vinyl acetate, 95% ee, b:l = 40:1) while achieving turnover frequencies of ca. 3000 h-1.

Poly(vinyl ester) star polymers via xanthate-mediated living radical polymerization: From poly(vinyl alcohol) to glycopolymer stars

Abstract: Poly(vinyl ester) stars have been synthesized via different macromolecular design via interchange of xanthate (MADIX)/reversible addition−fragmentation chain transfer (RAFT) polymerization methodologies. Two approaches were investigated. The first method involved attaching the xanthate functionality to the core via a nonfragmenting covalent bond (Z-group approach). The second approach involved attaching the xanthate functionality to the core via a fragmenting covalent bond (R-group approach). The R-group approach yielded well-defined poly(vinyl acetate), poly(vinyl pivalate), and poly(vinyl neodecanoate) stars with narrow polydispersities (PDI ≤ 1.4). In contrast, the molecular weight distributions of poly(vinyl acetate) stars prepared using the Z-approach tended to broaden at moderate to high conversions. We attribute this broadening to steric congestion around the xanthate functionality, restricting the access of monomer to the CS bonds. The R-group approach was also found to be superior for preparing p...

Reactions of vinyl acetate and vinyl trifluoroacetate with cationic diimine Pd(II) and Ni(II) alkyl complexes: identification of problems connected with copolymerizations of these monomers with ethylene.

Abstract: Vinyl acetate (VA) and vinyl trifluoroacetate (VAf) react with [(N∧N)Pd(Me)(L)][X] (M = Pd, Ni, (N∧N) = N,N‘-1,2-acenaphthylenediylidene bis(2,6-dimethyl aniline), Arf = 3,5-trifluoromethyl phenyl, L = ArfCN, Et2O; X = B(Arf)4-, SbF6-) to form π-adducts 3 and 5 at −40 °C. Binding affinities relative to ethylene have been determined. Migratory insertion occurs in a 2,1 fashion (ΔG⧧ = 19.4 kcal/mol, 0 °C for VA, and 17.4 kcal/mol, −40 °C for VAf) to yield five-membered chelate complexes [(N∧N)Pd(κ2-CH(Et)(OC(O)CH3))]+, 4, and [(N∧N)Pd(κ2-CH(Et)(OC(O)CF3))]+, 6. When VA is added to [(N∧N)Ni(CH3)]+, an equilibrium mixture of an η2 olefin complex, 8c, and a κ-oxygen complex, 8o, results. Insertion occurs from the η2 olefin complex, 8c (ΔG⧧ = 15.5 kcal/mol, −51 °C), in both a 2,1 and a 1,2 fashion to generate a mixture of five- and six-membered chelates, 92,1 and 91,2. VAf inserts into the Ni−CH3 bond (−80 °C) to form a five-membered chelate with no detectable intermediate. Thermolysis of the Pd chelates result...

Interaction of paraffin wax gels with ethylene/vinyl acetate-co-polymers

Abstract: The commercial grades of ethylene/vinyl acetate (EVA) co-polymers have found application as “pour point” depressants in refined fuels. This study focuses on their behavior as additives to crude oils, where the intent is to reduce the yield stress of the gels that can form when the oil exits the reservoir. The model crude oils consisted of 4 wt % wax in decane. At EVA dosage levels of ∼200 ppm, the reduction in yield stress is 3 orders of magnitude for the C36 wax, whereas the reduction is 1 order of magnitude for C32 and only 3-fold for the C28 wax. This decrease in efficiency with decreasing wax carbon number indicates that the EVA materials would not provide an adequate reduction in yield stress to ensure against gelation in pipeline transport. Neutron scattering studies, as a function of temperature, of the self-assembly of the EVA co-polymers show dramatically different aggregated structures in decane. The EVA with the lowest ethylene content shows scattering that increases with a power-law exponent o...

Synthesis of End-Functional Poly(vinyl acetate) by Cobalt-Mediated Radical Polymerization

Abstract: Poly(vinyl acetate) (PVAc) chains prepared by cobalt-mediated radical polymerization in the presence of cobalt(II) acetylacetonate (Co(acac)2) were quenched by radical scavengers, such as thiol compounds and nitroxides, to displace the covalently bonded Co(acac)2 moiety and to end-cap them with a reactive group. The cobalt complex was completely removed by filtration, as confirmed by the induction coupled plasma (ICP) analysis of the polymer before and after treatment. Growing poly(vinyl acetate) chains can be end-functionalized either by addition of an appropriately functionalized nonpolymerizable olefin or by displacement of the Co(acac)2 moiety by a functionalized nitroxide. This strategy allows PVAc to be synthesized with a predictable molecular weight, a reasonably low polydispersity (Mw/Mn ∼ 1.1−1.3), and a functional ω end group, e.g., hydroxyl and epoxy.

Micro-humidity sensors based on a processable polyaniline blend

Abstract: Polyaniline was blended with either polyvinyl alcohol or a butyl acrylate/vinyl acetate copolymer and used as a sensing medium in the construction of a resistance-based humidity sensor. The design utilised 125 μm polyester-insulated platinum wire as conducting electrodes that were dip-coated in conducting polymer. The sensors had an overall final thickness of less than 150 μm and showed high sensitivity, low resistance, and good reversibility without hysteresis. Some drift in the response was attributed to slow oxidation of the polyaniline that could be reduced by the application of appropriate barrier coatings.

Synthesis of Poly(vinyl acetate) and Poly(vinyl alcohol) Containing Block Copolymers by Combination of Cobalt-Mediated Radical Polymerization and ATRP

Abstract: Poly(vinyl acetate) (PVAc) chains of a low polydispersity (Mw/Mn ∼ 1.1−1.2) have been prepared by cobalt-mediated radical polymerization of vinyl acetate (VAc). They have been end-capped by an activated bromide by addition of an α-bromoester or an α-bromoketone containing nitroxide and converted into effective macroinitiators for the atom transfer radical polymerization of styrene (Sty), ethyl acrylate, and methyl methacrylate. Because each block is formed by a controlled process, well-defined PVAc containing diblock copolymers are easily prepared. The PVAc-b-PS copolymers synthesized from α-bromoketone end-capped PVAc can be converted into well-defined poly(vinyl alcohol)-b-polystyrene amphiphiles by methanolysis of the poly(vinyl acetate) block. Self-association of an amphiphilic poly(vinyl alcohol)(3500)-b-polystyrene(16 600) in a (4/1) water/tetrahydrofuran mixture results in the formation of vesicles as observed by transmission electron microscopy.

Xanthate-Mediated Living Radical Polymerization of Vinyl Acetate in Miniemulsion

Abstract: The MADIX/RAFT mechanism, employing a xanthate as the reversible chain-transfer agent, has been shown to facilitate the living radical polymerization of vinyl acetate in miniemulsion Methyl (ethoxycarbonothioyl)sulfanyl acetate (MESA) successfully mediated the polymerization which was initiated with either of the water-soluble initiators 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride (VA-060) or 2,2'-azobis[2(2-dimidazolin-2-yl)propane] dihydrochloride (VA-044) The polymerizations exhibit living characteristics, demonstrated by the evolution of molecular weight distributions The formulation of the miniemulsion produced stable latexes with no coagulum

Effect of ligand and n-butyl acrylate on cobalt-mediated radical polymerization of vinyl acetate

Abstract: The electron-withdrawing effect of the ligand in the cobalt complex was studied in cobalt-mediated radical polymerization of vinyl acetate (VOAc) initiated by 2,2‘-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70). The polymerization of VOAc with V-70 and a series of bis(acetylacetonate)cobalt derivatives, Co(R1COCHCOR2)2 (R1 = R2 = CH3 (1), R1 = CF3, R2 = CH3 (2), R1 = R2 = CF3 (3)), was conducted under the same conditions. Complexes 1 and 2 successfully mediated the radical polymerization of VOAc, resulting in poly(VOAc) with predetermined Mn and low polydispersity. In contrast, complex 3 did not control the radical polymerization of VOAc, resulting in poly(VOAc) with higher molecular weight and higher polydispersity. While complex 1 was not able to control the radical polymerization of n-butyl acrylate (nBA), the copolymerization of nBA with various amounts of VOAc (9%, 23%, and 50%) in the presence of V-70 and 1 showed that Mn and Mw/Mn of copolymers decreased with increasing VOAc ratio. This indicat...

Oxygenated Hydrocarbon Ionic Surfactants Exhibit CO2 Solubility

Abstract: Several oxygenated hydrocarbons, including acetylated sugars, poly(propylene glycol), and oligo(vinyl acetate), have been used to generate CO2-soluble ionic surfactants. Surfactants with vinyl acetate tails yielded the most promising results, exhibiting levels of CO2 solubility comparable to those associated with fluorinated ionic surfactants. For example, a sodium sulfate with single, oligomeric vinyl acetate (VAc) tails consisting of 10 VAc repeat units was 7 wt % soluble in CO2 at 25 °C and 48 MPa. Upon introduction of water to these systems, only surfactants with the oligomeric vinyl acetate tails exhibited spectroscopic evidence of a polar environment that was capable of solubilizing the methyl orange into the CO2-rich phase. For example, a single-phase solution of CO2, 0.15 wt % sodium bis(vinyl acetate)8 sulfosuccinate, and water, at water loading (W) values ranging from 10 to 40 at 25 °C and 34.5 MPa, exhibited a methyl orange peak at 423 nm. This result indicated that the core of a reverse micell...

Influence of M w of LDPE and vinyl acetate content of EVA on the rheology of polymer modified asphalt

Abstract: Asphalt binder was modi- fied by low-density polyethylene (LDPE) and ethyl vinyl acetate (EVA) polymers to investigate the structure-property relationships of polymer-modified asphalt (PMA). The PMA was prepared in a high- shear blender at 160 � C. The opti- mum blending time (OBT) for each polymer was determined following a separate investigation. OBT was influenced by Mw, MWD, and polymer structure. The influence of Mw of LDPE and vinyl acetate (VA) content of EVA on PMAs was studied by rheological tools. Poly- mer modification improved the rhe- ological properties of base asphalt. EVA-PMAs were found to be less temperature sensitive than LDPE- modified asphalts. LDPE modifica- tion increased flow activation energy (Ea) but EVA modification de- creased Ea. Both VA content and Mw of LDPE have influenced the storage stability of PMAs. The low- temperature properties of PMAs and short ageing tests were not influ- enced by polymer type. On the other hand, the high-temperature proper- ties of PMAs were strongly influ- enced by Mw of LDPE and VA content of EVA. Overall, EVA with low VA content showed the best temperature resistance to high- temperature deformations, the highest upper service temperature as well as the best storage stability.

Poly(vinyl acetate) and Poly(vinyl propionate) Star Polymers via Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization

Abstract: Poly(vinyl acetate) and poly(vinyl propionate) star polymers with four arms were produced via reversible addition fragmentation chain transfer (RAFT) polymerization, employing a tetra-functional xanthate as the RAFT agent, in which the stabilizing groups are linked to the core. These novel star-like RAFT agents induced living/controlled behavior in both the vinyl acetate polymerization at 60 °C and in the vinyl propionate polymerization at 90 °C, respectively, leading to star polymers with minimum polydispersities of 1.2 and maximum apparent number average molecular weights of about 50,000 g·mol-1. The microstructure of the star polymers was confirmed by electrospray ionization mass spectrometry.

Effect of impurities in cumyl dithiobenzoate on RAFT-mediated polymerizations

Abstract: The effect of the purity of cumyl dithiobenzoate (CDB) on the rate of polymerization was determined. It was shown that possible byproducts from the synthesis of xanthate reversible addition-fragmentation chain transfer (RAFT) polymerization agents produced an inhibition period in the polymerization of vinyl acetate. The results show that the impurities in cumyl dithiobenzoate act to inhibit or retard the polymerization of 2-hydroxyethyl methacrylate (HEMA), styrene, and MA. The addition of the starting agent DTBA also acts to inhibit the polymerization.

Electrical conductivity and electromagnetic interference shielding effectiveness of polyaniline–ethylene vinyl acetate composites

Abstract: Electrical conductivity and electromagnetic interference (EMI) shielding effectiveness at microwave (200–2000 MHz) and X-band (8–12 GHz) frequency range of polyaniline (PAni) composites were studied. It has been observed that EMI shielding of conductive polyaniline (PAni)–ethylene vinyl acetate composites increases with the increase in the loading levels of the conductive polymer doped with dodecylbenzene sulfonic acid. The result indicates that the composites having higher PAni loading (>23%) can be used for EMI shielding materials and those with lower PAni loading can be used for the dissipation of electrostatic charge. Copyright © 2004 Society of Chemical Industry

Influence of vinyl acetate-versatic vinylester copolymer on the microstructural characteristics of cement pastes

Abstract: To understand the principles of polymer modification and its interference in the formation of some phases of Portland cement composites, several techniques are adopted such as Fourier Transform Infrared Spectroscopy and Thermogravimetric Analysis. In this study, these techniques were adopted to verify the influence of VA/VeoVA copolymer in seven pastes of high-early-strength portland cement twenty-eight days old, being four pastes with different polymer content and the same water/cement ratio, and the other three with extra water content increased by polymer content. In addition, scanning electronic microscopy was employed to verify the formation of copolymer film. The results showed possible interaction between acetate anion from the partial hydrolysis of copolymer and Ca++ ion from C2S and C3S hydration. Moreover, the magnitude of the decrease of portlandite formation is directly affected by water/cement ratio. By SEM analyses, the formation of two matrices, being one organic and the other inorganic, was also observed.

Synthesis and Characterization of Starch-Poly(vinyl Acetate) Graft Copolymers and their Saponified Form

Abstract: A redox initiation system based on potassium persulfate/acetone sodium bisulphite (KPS/ASBS) was developed to initiate the graft copolymerization of vinyl acetate (VAc) monomer onto corn starch in aqueous solution. The grafting reaction was studied with respect to grafting yield (GY), grafting efficiency (GE) and total conversion (TC) and results obtained were compared with those a well-established redox initiation system namely potassium persulfate/sodium bisulphite (KPS/SBS). The effect of reaction variables such as redox initiator concentration, liquor ratio, reaction time and temperature as well as VAc concentration were investigated. The GY, GE and TC increased significantly with increase of the redox initiation concentration up to 8/16 mmol/l irrespective of the initiation system used. Moreover, optimal grafting was obtained at 60 ○C for KPS/ASBS redox system and 70 ○C for KPS/SBS redox system. Saponification of poly (vinyl acetate)-starch graft copolymers were effected using NaOH in three different bath media (n-hexane, acetone or methanol) to convert starch-g-poly(vinyl acetate) to starch-g-poly(vinyl alcohol). Higher extent of solubility in hot water of the saponified form was achieved by using a bath containing n-hexane/sodium hydroxide; however, increasing the graft yield higher than 26.3% decreases the solubility. The structures and thermal stability of starch, grafted starch copolymer and saponified grafted starch copolymer were characterized by infrared spectroscopy and thermogravimetric analysis. Moreover, the rheological behavior as well as sizing performance of the saponified grafted starch copolymers were evaluated and compared with the native starch and commercial polyvinyl alcohol.

Elucidation of the Reaction Mechanism for the Palladium‐Catalyzed Synthesis of Vinyl Acetate

Abstract: The first, suggested by Samanos et al. , involves the coupling of ethylene directly with chemisorbed acetate. The resulting acetoxyethyl–palladium intermediate then undergoes b-hydride elimination to form vinyl acetate. Alternatively, ethylene could first dehydrogenate to form a vinyl–palladium intermediate, which then couples with an acetate species adsorbed on the surface to form the VAM directly. This latter mechanism was proposed by Moiseev et al. 4] as well as by Nakamura and Yasui. We have recently shown that ethylene in the gas phase reacts with a model-catalyst surface of h-acetate moieties adsorbed on a Pd(111) surface precovered with a (252) oxygen overlayer to form the VAM, thus implying that the acetate species is the precursor to formation of the VAM. The structures of the adsorbed h-acetate and ethylene species were determined separately on a Pd(111) surface by using low-energy electron diffraction (LEED) and reflectionabsorption IR spectroscopy (RAIRS), which showed that both species adsorb on the bridge site. Herein, we discuss the investigation into the nature of the reaction pathway by using isotopically labeled reactants, which allowed the mechanism for the formation of the VAM to be unequivocally identified. The RAIRS experiments were performed in an ultrahigh vacuum apparatus; the experimental procedure has been described in detail elsewhere. Kinetic measurements were typically carried out by the collection of spectra over 100 scans, which is a relatively short procedure that took 25 seconds because of the large intensity of the asymmetric vibrational mode of the acetate moiety (O-C-O) at 1414 cm . Some experiments were carried out with a larger number of scans to yield spectra with better signal-tonoise ratios and, therefore, allow additional surface species to be identified. A flux of ethylene impinged onto the sample from a collimated dosing source to obtain an enhanced flux at the Pd(111) single-crystal surface while the background pressure was minimized. C2H4 (Matheson, Research Grade), acetic acid (Aldrich, 99.99 + %), C2D4 (CIL, 98% D), CD2CH2 (CDN, 99% D), CHDCHD (CDN, cis/ trans mixture, 99% D), and O2 (CIL, 95% O2) were transferred into glass bottles, which were attached to the gas-handling line for introduction into the vacuum chamber. It has been shown previously that acetate species adsorbed on a Pd(111)–O(252) surface undergoes reaction with ethylene in the gas phase to yield the VAM. The experimental titration curves obtained with acetate species can be explained by using a procedure described previously, in which it was assumed that adsorbed ethylene underwent reaction with the acetate species and that ethylene adsorption was blocked by the acetate species. Acetate species adsorbed on clean Pd(111) surfaces (namely, in the absence of the (252) oxygen overlayer) are also removed by reaction with ethylene and also can be analyzed by using the same procedure used to reproduce the kinetic data for the oxygen-covered Pd(111) surface; furthermore, these acetate species yield similar rate constants to those found for reactions on the oxygen-covered surface, and therefore the presence of coadsorbed oxygen does not substantially affect the reaction kinetics. A series of IR spectra for the reaction of the acetate species on a clean Pd(111) surface was collected just after the acetate moieties had been completely removed using C2H4, C2H4 (on an O-covered surface), and C2D4 (Figure 1). The spectrum of CO on the Pd(111) surface is shown for comparison (Figure 1a). The CO exposure was selected to

Co-production of vinyl acetate and ethyl acetate

Abstract: A method of co-producing vinyl acetate and ethyl acetate includes: (a) reacting ethylene, acetic acid and oxygen to form vinyl acetate and at least a minor amount of ethyl acetate; (b) providing a crude product stream containing the vinyl acetate and ethyl acetate of step (a) and acetic acid to a distillation tower; (c) separating the crude product stream into: (i) a vinyl acetate product stream enriched in vinyl acetate with respect to the crude product stream; (ii) an acid recycle stream enriched in acetic acid with respect to the crude product stream; (iii) a mixed sidestream containing vinyl acetate and ethyl acetate, the mixed sidestream being enriched in ethyl acetate with respect to the vinyl acetate product stream; and (d) hydrogenating vinyl acetate in the mixed sidestream to provide an ethyl acetate product stream.

Computer-Aided Design of a Destabilized RAFT Adduct Radical: Toward Improved RAFT Agents for Styrene-block-Vinyl Acetate Copolymers

Abstract: High-level ab initio molecular orbital calculations indicate that a fluorine Z substituent significantly destabilizes the RAFT adduct radical, R'SO•(Z)SR, relative to known Z substituents. This destabilization of the RAFT adduct radical lowers the fragmentation enthalpy relative to normal dithioesters, but without stabilizing the C=S bond of the product RAFT agent, as in xanthate- or dithiocarbamate-mediated polymerization. On the basis of these calculations, it is predicted that, provided appropriate R groups are chosen, RAFT agents containing fluorine Z substituents (i.e., S=C(F)SR, fluorodithioformates, or "F-RAFT" agents) should provide a basis for improved control of monomers with reactive propagating radicals (such as vinyl acetate) and should have the advantage that their C=S bonds remain reactive enough for control of monomers with more stable propagating radicals (such as styrene) and hence the production of styrene-vinyl acetate copolymers.

Morphological influence on mechanical characterization of ethylene-vinyl acetate copolymer–clay nanocomposites

Abstract: Ethylene-vinyl acetate copolymer (EVA)/montmorillonite (MMT) clay nanocomposites with varying degree of intercalation and exfoliation have been prepared using direct melt blending techniques with various degrees of polarity (9, 18, and 28 wt% vinyl acetate [VA]) and two different types of clay modification. Morphological characterization using wide-angle X-ray scattering (WAXS) and transmission electron microscopy (TEM) have indicated/confirmed the presence of intercalation and/or a combination of intercalation and exfoliation existing in the nanocomposites. The effects of these (simple intercalation or mixed intercalation/exfoliation) states and the effect of changing matrix polarity (by changing VA wt% content) on the nanocomposite mechanical behavior were studied. There is sufficient evidence from the mechanical studies that 1) the presence of nanoclay can simultaneously improve modulus and strength of the nanocomposites, and 2) the mechanical properties are a combined function of the clay concentration and the nanocomposite morphology (due to the VA wt% and presence of clay). It is shown here that interrelation between the VA wt% content and the clay exfoliation affects the mechanical properties in a way that has a positive and increasing slope with increasing loading of clay. It is shown that a clear understanding of the nanocomposite mechanical properties can be obtained from its morphological analysis.