Vinyl acetal dimerization

NR, styrene-butadiene mbber (SBR), polybutadiene rubber, nitrile mbber, acrylic copolymer, ethylene-vinyl acetate (EVA) copolymer, and A-B-A type block copolymer with conjugated dienes have been used to prepare pressure-sensitive adhesives by EB radiation [116-126]. It is not necessary to heat up the sample to join the elastomeric joints. This has only been possible due to cross-linking procedure by EB irradiation [127]. Polyfunctional acrylates, tackifier resin, and other additives have also been used to improve adhesive properties. Sasaki et al. [128] have studied the EB radiation-curable pressure-sensitive adhesives from dimer acid-based polyester urethane diacrylate with various methacrylate monomers. Acrylamide has been polymerized in the intercalation space of montmorillonite using an EB. The polymerization condition has been studied using a statistical method. The product shows a good water adsorption and retention capacity [129]. 

Another example of type iii-a is the trifluoromethylation of double bonds by electrolysis of trifluoroacetic acid in the presence of olefins. Methyl vinyl ketone, vinyl acetate, diethyl fumarate, diethyl maleate, Ai-ethylmaleimide, and 2,5-dihydrothiophene-l,1-dioxide were examined as olefins. The products were bis-trifluoromethylated additive dimers (66) (type iii-a) and monomers (67) (type... 

DKR of secondary alcohol is achieved by coupling enzyme-catalyzed resolution with metal-catalyzed racemization. For efficient DKR, these catalyhc reactions must be compatible with each other. In the case of DKR of secondary alcohol with the lipase-ruthenium combinahon, the use of a proper acyl donor (required for enzymatic reaction) is parhcularly crucial because metal catalyst can react with the acyl donor or its deacylated form. Popular vinyl acetate is incompatible with all the ruthenium complexes, while isopropenyl acetate can be used with most monomeric ruthenium complexes. p-Chlorophenyl acetate (PCPA) is the best acyl donor for use with dimeric ruthenium complex 1. On the other hand, reaction temperature is another crucial factor. Many enzymes lose their activities at elevated temperatures. Thus, the racemizahon catalyst should show good catalytic efficiency at room temperature to be combined with these enzymes. One representative example is subtilisin. This enzyme rapidly loses catalytic activities at elevated temperatures and gradually even at ambient temperature. It therefore is compatible with the racemization catalysts 6-9, showing good activities at ambient temperature. In case the racemization catalyst requires an elevated temperature, CALB is the best counterpart. 

Butacite - [KETENES, KETENE DIMERS AND RELATED SUBSTANCES] (Vol 14) - [VINYLPOLYMERS - VINYL ACETAL POLYMERS] (Vol 24)... 

To get an idea about the relative volatilities of components we proceed with a simple flash of the outlet reactor mixture at 33 °C and 9 bar. The selection of the thermodynamic method is important since the mixture contains both supercritical and condensable components, some highly polar. From the gas-separation viewpoint an equation of state with capabilities for polar species should be the first choice, as SR-Polar in Aspen Plus [16]. From the liquid-separation viewpoint liquid-activity models are recommended, such as Wilson, NRTL or Uniquac, with the Hayden O Connell option for handling the vapor-phase dimerization of the acetic acid [3]. Note that SR-Polar makes use of interaction parameters for C2H4, C2H6 and C02, but neglects the others, while the liquid-activity models account only for the interactions among vinyl acetate, acetic acid and water. To overcome this problem a mixed manner is selected, in which the condensable components are treated by a liquid-activity model and the gaseous species by the Henry law. 

The formation of vinyl acetate from ethylene was first reported by Moiseev et al. (31), The compound was obtained by reaction of ethylene with PdCl2 in an acetic acid solution containing sodium acetate. Whether in this medium vinyl acetate formation occurs via the monomeric [PdCla C2H4] TT-complex, postulated as intermediate in the Wacker acetaldehyde process, or via the dimer (C2H4 PdCl2)2, previously described by... 

Anderson (2) and Kharasch (22, 23), was not established. [The complexes described by Anderson and Kharasch are believed today to be dimers of [PdCb C2H4] (7, 25, 28)]. Moiseev et al. left both possibilities open. Stern and Spector (37) favored the dimeric intermediate. They obtained vinyl acetate in 22 mole % yield, by reaction of ethylene with PdCl2 in isooctane containing acetic acid and NaoHP04. 

C-H bond fission and the production of ethynyl radicals. Butadiyne and vinyl acetate are formed when the T -shaped ethyne dimer is irradiated at 193 nm in argon or xenon. The dynamics of the photodissociation of propyne and allene have been studied. The H2 elimination from propyne is a minor route for propyne dissociation and the major path identified in this study is loss of the alkyne hydrogen. A study of the photodissociation dynamics of allene and propyne has been reported and this work has demonstrated that allene gives rise to a propargyl radical while propyne yields the propynyl radical. Other research has examined the photodissociation of propyne and allene by irradiation at 193 nm. ... 

Coextrusion of L-lactide (a cyclic dimer lactone of lactic acid) with hydroxy-terminated poly(caprolactone) in the presence of stannous octoate gave a block copolymer.74 Block copolymers can also be used as compatibilizers for the homopolymers, in addition to having interesting properties in their own right.75 Copolymers of ethylene and vinyl acetate can be treated with methanol and a little sodium methoxide to remove some of the acetate groups from the copolymer.76 The by-product methyl acetate comes out the vent of the extruder. n-Butyl alcohol can be used in the same way.77 The product copolymer is useful as a gas barrier coating on films for packaging food. 

By-products formed during their preparation (e.g., ethylbenzene and divin-ylbenzenes in styrene acetaldehyde in vinyl acetate) added stabilizers (inhibitors) autoxidation and decomposition products of the monomers (e.g., peroxides in dienes, benzaldehyde in styrene, hydrogen cyanide in acrylonitrile) impurities that derive from the method of storage of the monomer (e.g., traces of metal or alkali from the vessels, tap grease etc.) dimers, trimers, and polymers that are generally soluble in the monomer, but sometimes precipitate, for example, polyac-rylOTiitrile from acrylonitrile. Likewise, in polycondensation reactions it is important to remove reactive impurities because they can cause considerable interference during the polyreaction. 

A two-step gear pump (Fig. 15) was used to introduce the gas into the hot-melt adhesive. Foamability was later found to vary with the polymers used. Polyethylene is excellent for foaming. Polypropylene, polyester, and 12-polyamide (Nylon 12) are also very good. Styrene-butadiene and ethylene-vinyl acetate are good and dimer acid polyamide is fair. ... 

The coordination complex chemistry in zeolites provides a very useful conceptual bridge to coordination-chemistry controlled catalysis in the liquid phase. This is discussed in this chapter for the oxidation of ethylene to produce vinyl acetate from acetic acid and ethylene. The catalytic system appears to consist of dimeric or trimeric Pd complexes. The elementary reaction steps can take place in the direct contact with the metal centers, the so-called inner-sphere mechanism. The reaction can also proceed through an outer-sphere mechanism in which proton transfer between reactants and acetate plays an essential role. 

Kinetic studies of the Pd -catalysed exchange of VP (vinyl propionate) with acetic acid solvent to give vinyl acetate in the presence of sodium acetate are complicated by equilibria between three Pd species (Scheme 15). The dimer is significantly more... 

The RCMs and the LLE for the ternary systems using vinyl acetate or ethyl acetate as entrainer are shown in Figures 13.28 and 13.29, respectively. The NRTL parameters used in the simulation are given in Table 13.5. The Hayden-O Connell second virial coefficient model with association parameters is used to account for the dimerization of acetic acid in... 

In a similar analysis of the temperature dependence of viscosity for a series of polystyrenes of sharp molecular weight distribution and a wide range of molecular weights, Pierson and Kovacs obtained fo/B from equation 34 for each sample and found it to be a linear function of 1 /M in accordance with equation 67. This plot is also included in Fig. 11-13. The constant A was about 54 g/mole at 0°C. Comparison of these constants with the molecular weight of a dimer (172 for poly(vinyl acetate), 208 for polystyrene) indicates that the additional free volume associated with a pair of molecular ends is about 30% of the total volume associated with two monomer units. 

Analogous results were obtained with vinyl acetate/acrylonitrile and with ethyl vinyl ether/acrylonitrile, however with these systems, the relative yields of dimeric products were much higher (20 - 30%). 

In the vinyl acetate/acrylonitrile system, we have also examined the effect of added Lewis acids as these are known to enhance alternation in alternating copolymerisation. In the presence of zinc chloride, no dimeric products were observed. Nor were the normal addition products 11 and 12 observed. The major products fornied were 5 (55%), 13 (20%) and 14 (25%). Similar results were obtained with ferric chloride. Thus with 4% FeCla, the ratio of 5 13 14 was 84 10 6 with 60% FeCls, the ratio changed to 25 3 72 respectively. Apparently Lewis acids catalyse the p-fragmentation of rerr-butoxyl radicals (or of di-ferr-butyl peroxalate) and/or slow the rate of addition of the (electrophilic) ferr-butoxyl radicals to both vinyl acetate and acrylonitrile. The product 14 is thought to arise via hydrogen-abstraction from vinyl... 

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