Vinyl acetate equilibrium concentration

If two different polymers can be dissolved successfully in a common solvent, a molecular intermixing of the dissolved macromolecules should occur due to the fast establishment of the thermodynamic equilibrium. The difficulty with this procedure is due to the fact that very many polymers become incompatible above a certain concentration when their solutions in a common solvent are combined. This means that the originally homogeneous solutions of polymers A and B separate into two phases when being combined, whereby each of the phases contain different quantitative proportions A B [e.g., polystyrene and poly(vinyl acetate) in toluene]. But even when two polymers have been dissolved sue-... 

Fig. 19 n-< A > isotherms for 72 mol % PVP/PVAc mixed monolayers on water at 25 °C by stepwise addition and compression. Surface pressure 77 for 72 mol % polyfvinyl palmitate)/poly(vinyl acetate) binary mixture as a function of area per monomer. The surface concentration was controlled as noted in the plot. For the stepwise-addition technique, lens formation was observed in the region where the two techniques differ for 77 lOmNm-1. For the plot, the mixture required stabilization times considerably longer than the 1-2 hours allowed between points to form equilibrium films. < A > = average area per monomer... 

For a reversible reaction an increase in the acyl donor concentration results in higher product yields. In this case the chemical equilibrium is shifted towards synthesis. On the other hand, high concentrations of substrates may cause inhibition and the reaction is slowed down. For (R)-l-phenylethyl acetate formation the effect of the substrate vinyl acetate/l-phenylethanol molar ratio on the final conversion was studied. The results are presented on Figure 8.3. A higher yield of the enantiopure compound was achieved when raising the acyl donor molar concentration with respect to the alcohol concentration. A conversion of 49.9% was obtained at an acyl donor/alcohol molar ratio of 9/1. After 5 h of reaction at tested conditions a complete conversion of (R)-l-phenylethanol into the enantiopure (R)-l-phenylethyl acetate was attained. The enantiomeric excess for reactants (eeR) was 99.9%. 

The variable that has the most significant impact on the economics of an extractive distillation is the solvent-to-feed (S/F) ratio. For closeboiling or pinched nonazeotropic mixtures, no minimum-solvent flow rate is required to effect the separation, as the separation is always theoretically possible (if not economical) in the absence of the solvent. However, the extent of enhancement of the relative volatility is largely determined by the solvent concentration and hence the S/F ratio. The relative volatility tends to increase as the S/F ratio increases. Thus, a given separation can be accomplished in fewer equilibrium stages. As an illustration, the total number of theoretical stages required as a function of S/F ratio is plotted in Fig. 13-75a for the separation of the nonazeotropic mixture of vinyl acetate and ethyl acetate using phenol as the solvent. 

At high [Pd(II)] concentrations, the kinetics are similar to those for hydration of vinyl acetate in wet acetic acid. At low [Pd(II)] and [LiCl] concentrations, the rate is essentially independent of Pd(II). One possibility is that trace amounts of water are being formed by the following equilibrium which may be catalyzed by metal salts in the system ... 

The equilibrium concentrations [M] of the monomer at the poly-merization equilibrium fluctuate widely according to the constitution. At 25°C, it is found, for example, in bulk polymerization that [M] is 10" mol/dm for vinyl acetate, 10 mol/dm for styrene, 10" mol/dm for methyl methacrylate, and 2.8 mol/dm for a-methyl styrene. Since the equilibrium concentrations are related to the free energy of polymerization, and this depends on the enthalpy and entropy of polymerization, then it is necessary to determine the influence of the constitution on HZp and S p. 

Catalysed Diels-Alder reactions continue to provide interesting results. The reactions of methylcyclopentadiene (which has an equilibrium concentration consisting of 45 %, 54%, and 1 % of the 1-, 2-, and 5-methyl isomers respectively) with vinyl acetate (uncatalysed) and with a a-chloroacrylonitrile (cupric fluoroborate catalysed) have been examined. Conversion of the initial adducts so obtained to the corresponding methylnorborn-5-en-2-ones (211)—(214) revealed a remarkable difference in regio-selectivity in the initial [4 + 2] reactions the uncatalysed (catalysed) reaction product percentages being 13.5 (57), 16(9), 38 (32), and 32.5 (2) respectively. The usual ortho/para orientation is increased by the catalysis, (211) -t- (213) accounting for 89% rather than 57.5 % of the reaction mixture, and the much lower proportion of (213) -t- (214) in the catalysed process (34 % vs. 70.5 %) indicates much less isomerization of 1-methyl-... 

Equations (11) and (12) show that devolatilization is strongly affected by the thermodynamic equilibria of the VOCs between different phases. High values of the polymer partides/aqueous-phase partition coefficient imply that the concentration in the aqueous phase will be low and hence it will be difficult to remove the VOC from the particles. Similarly, a low value of the Henry s law constant means that the concentration of VOCs in the gas phase is low and hence, devolatilization will be difficult. Figure 18.7 shows the kinetics of devolatilization of vinyl acetate, acetaldehyde, and n-butanol in a VAc/BA/AA latex, and that of BA in a BA/S/AA latex by stripping in laboratory-scale equipment, under equilibrium conditions. It can be seen that the devolatilization of BA was slow due to the high affinity (high feS,) of BA to the polymer particles. The removal of n-butanol was also very slow because of its high solubility in the aqueous phase and low vapor pressure (a low value of the Henry s law constant). 

The DSC traces in the center of Fig. 4.33 show the behavior of three copolymers of ethylene and vinyl acetate. Not only does the melting temperature drop sharply with increasing vinyl acetate concentration, the size of the melting peak decreases more than expected from the comonomer content, so that one expects to reach a completely amorphous copolymer at a concentration of about 10 mol-%. Clearly such decrease in crystallinity cannot be an equilibrium effect. Also, the decrease in melting temperature has been shown in many copolymers to be more than expected by equilibrium thermodynamics (see also Sect. 4.6.3 and Ref. 65). 

Difltiision of emcamide in linear low density polyethylene, LLDPE, also shows that the diflftision coefficient of erueamide increases with temperature. The diffixsion coefficient was found to increase with temperature for erueamide in polypropylene and ethylene-propylene copolymer. Thickness of a film in which diffusion process occurs was found to be an important variable in terms of time required to attain equilibrium concentration throughout the film. This can be illustrated by the data in Figure 7.3, which show that concentration of amide on the surface of vinyl acetate copolymer grows until it reaches a certain equilibrium determined by polymer, additive, its concentration, and temperature. " Amide diffusion rate was also foimd to inerease with an increase in its concentration in bulk. ... 

Fig. 6. Log-log representation of the shear modulus as a functkin of the equilibrium volume hraction of polymer for PVAC gels swollen in toluene. The dotted line describe the dependence of the osmotic pressure on concentration for semi-dilute solutions of linear poly(vinyl acetate) in toluene, calculated from an experimental fit. From Zrinyi et al.. M, ti are expressed in N m , c in g cm . From Vink ...

Additions of acetals and orthoesters to enol ethers probably represent the most intensively studied class of Lewis acid promoted reactions in the chemistry of aliphatic compounds. Since usually catalytic amounts of BFg OEta have been employed, concentration control (rule A) should predominate. Unlike the solvolyses of alkyl halides, the acid catalyzed hydrolyses of acetals and orthoesters do not follow a rate equilibrium relationship so that the corresponding hydrolysis rates cannot be used for the analysis of electrophilic addition reactions. We have, therefore, carried out competition experiments to determine relative reactivities of acetals and orthoesters towards methyl vinyl ether in presence of catalytic amounts of BF3 0Et2 (Figure 11). As the reactivity order towards other ir nucleophiles can be expected to be similar, the krei values of Figure 11 can be used to rationalize or predict the results of acetal and orthoester additions 1 1 Adducts can only be generated selectively if the k ei values of the designed products are smaller than the k Qi values of the reactants. 

The second method involves end-quenching of living polymers with appropriate nucleophiles. Although this approach appears to be more attractive than the first one, in situ end funaionali-zation of the living ends is limited to nucleophiles that do not react with the Lewis add coinitiator. Because the ionization equilibrium is shifted to the covalent spedes, the concentration of the ionic active species is very low. Quantitative functionalization can only be accomplished when ionization takes place continuously in the presence of nudeophile. Quenching the vinyl ether polymerization with the malonate anion,certain silyl enol ethers " and silyl ketene acetals have been successfully used to synthesize end-functionalized poly(vinyl ethers). Alkyl amines, " ring-substituted anilines, " " alcohols, " and water " have also been used to quench the vinyl... 

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