Dispersion PVAC

Besides organocobalt complexes, organostibine has also been found to be able to mediate controlled/ diving polymerization of many vinyl monomers. " For example, Yamago et al reported that at 60 °C the polymerization of VAc mediated by a-dimethylstibanyl ester reached 92% conversion in 5 h and produced narrowly dispersed PVAc (PDl = 1.26), but no detailed reaction kinetics was provided in their study.Kamigaito et al. very recently found that a manganese carbonyl complex [Mn2(CO)io] coupled with an alkyl iodide ( -I)... 

Mowicoll Poly(vinyl acetate) dispersions, PVAc Hoechst Celanese Corp. 

DIsodium nonoxynoMO sulibsuccinate dispersant, PVAC emulsion polymerization... 

Transparent, homogeneous hybrids using a 50 50 PVAc-to-TEOS mixture and an acid-catalyzed reaction have been produced and characterized by dsc and dms (46). Dsc indicated only a slight increase in the T of the hybrid with incorporation of sihca. Dynamic mechanical tan 8 responses indicate a strong interaction between the organic and inorganic phases and, hence, weU-dispersed phases that lead to high modulus mbbery plateaus. 

Suspension Polymerization. At very low levels of stabilizer, eg, 0.1 wt %, the polymer does not form a creamy dispersion that stays indefinitely suspended in the aqueous phase but forms small beads that setde and may be easily separated by filtration (qv) (69). This suspension or pearl polymerization process has been used to prepare polymers for adhesive and coating appHcations and for conversion to poly(vinyl alcohol). Products in bead form are available from several commercial suppHers of PVAc resins. Suspension polymerizations are carried out with monomer-soluble initiators predominantly, with low levels of stabilizers. Suspension copolymerization processes for the production of vinyl acetate—ethylene bead products have been described and the properties of the copolymers determined (70). Continuous tubular polymerization of vinyl acetate in suspension (71,72) yields stable dispersions of beads with narrow particle size distributions at high yields. 

Fillers (calcium carbonate, calcium sulfate, aluminum oxide, bentonites, wood flour) increase the solid content of the dispersion. They are added up to 50%, based on PVAc. The purpose of the addition is the reduction of the penetration depth, provision of thixotropic behavior of the adhesive, gap filling properties and the reduction of the costs. Disadvantage can be the increase of the white point and a possible higher tool wear. 

Other components in PVAc-formulations are defoamers, stabilizers, filler dispersants, preservatives, thickeners (hydroxyethylcellulose, carboxymethylcellu-lose), polyvinyl alcohols, starch, wetting agents, tackifiers, solvents (alcoholes, ketone, esters), flame retardants and others. 

One can read letters through the porous PVA-PVAc film in benzene, but one cannot do so in cyclohexane nor in the case of the blank. This is supported by the fact that the refractive indices of benzene are close to that of PVA, but the refractive index of cyclohexane is far from that of PVA. When the porous film was dipped in a mixed solvent of benzene and cyclohexane (8.0 2.0 in weight), it became semi-transparent. To make this point clearer, the refractive index and the dispersive power of polymers and organic solvents were measured. The results are shown in Table 3, which shows that the refractive index of PVA is near that of benzene and that the dispersion power of aliphatic compounds is lower than that of aromatic compounds. 

For example, the parameters g = 0.77, h = 0.94, p = 1.4, and C = 0.158 measured for a polymer sample and compared with the plots in Figures 7.11 through 7.13 were most consistent with athree-arm star monodisperse polymer a poly disperse three-arm star would have g= 1.12,/ = 1.05,p= 1.6, and C close to 0.2. °° The second example was poly(vinyl acetate) (PVAc) prepared by emulsion polymerization. Since no data for linear equivalent were available, g and h were not calculated. At lower conversion/MW p= 1.84 was found, only slightly higher than the theoretically expected p = 1.73 for a randomly branched architecture, p slightly decreased with increasing M, indicating... 

The determination of adsorption isotherms at liquid-solid interfaces involves a mass balance on the amount of polymer added to the dispersion, which requires the separation of the liquid phase from the particle phase. Centrifugation is often used for this separation, under the assumption that the adsorption-desorption equilibrium does not change during this process. Serum replacement (6) allows the separation of the liquid phase without assumptions as to the configuration of the adsorbed polymer molecules. This method has been used to determine the adsorption isotherms of anionic and nonionic emulsifiers on various types of latex particles (7,8). This paper describes the adsorption of fully and partially hydrolyzed PVA on different-size PS latex particles. PS latex was chosen over polyvinyl acetate (PVAc) latex because of its well-characterized surface PVAc latexes will be studied later. 

PVAc, PVA and PVB are used in a vast number of different applications [19]. The most common use of PVAc-based dispersions and dispersible polymer powders is in the construction and adhesives industry. The polymeric binders are used as... 

The chromatograms of the several injected PVAc samples were corrected for axial dispersion (8-11) and number and weight average diameters were estimated. The resulting distributions and diameter averages showed that the latex samples from the batch runs were "almost monodispersed (8). This was further supported by the fact that estimated average diameters were very close to the "peak" average diameters (Table III). 

We have studied the dispersibility of several pure PVAc-styrene graft copolymers with one PS branch in various selective solvents mainly at room temperature5. The experiment was done with two kinds of dried samples one was recovered from a tetrahydrofuran solution by pouring it into water and the other from a benzene solution which was poured into n-hexane. Let us refer to the former sample as A and the latter sample as B. Due to the difference in solubility of each polymer sequence in those solvents, sample A is supposed to have approximately such a microstructure that PVAc chains are extended and PS chains collapsed, while sample B has the inverse structure. A similar tendency was also pointed out by Merrett12. The results are summarized in Table 2. 

Table 2. Dispersibility of PVAc-styrene graft copolymers in various solvents from dried samples at room temperature graft copolymer/solvent = 1/100 (w/v)...

Polyvinylacetate (PVAc) has not been used in the pharmaceutical held until recently. During the polymerization, especially at high conversion, free radicals are transferred to dead polymers, resulting in the formation of branched polymers. These branched polymers are susceptible to deterioration. Because the PVAc latex particles are produced by an emulsion polymerization technique, this provides a good process for the water-based dispersion in him coatings. The main purpose of this polymer is the him coating of sustained release dosage forms. The polymer is used as a precursor in the production of polyvinylalcohol (PVA), which cannot be prepared directly by polymerization due to the unstable, isomeric monomer of acetaldehyde. 

PVAc-dispersion with plasticizer, adhesive for laminating textile/textile and textile/paper, filling agent for textile finishing. 

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