Polyvinyl acetate, 413 Table

Exercise 29-17 Polyvinyl alcohol prepared by hydrolysis of polyethenyl ethanoate (polyvinyl acetate Table 29-1) does not react with measurable amounts of periodic acid or lead tetraethanoate (Sections 16-9A and 20-4A). However, periodic acid or lead tetraethanoate treatment of the polymer does decrease the number-average molecular weight, for a typical sample from 25,000 to 5000. Explain what these results mean in terms of the polymerstructures and the mechanism of the polymerization. 

Polyvinylacetate aq emulsion for use as a binder in non-metallic cartridge cases is covered by US Mil Spec, Polyvinyl Acetate Aqueous Emulsion (PAAE) (For use in Ammunition) , MIL-P-50855(MU) (31 March 1971). The requirements and criteria are in Table 1... 

In order to estimate the branching factor e for polyvinyl acetate we have analyzed the SEC data obtained on sample PVAc-E4 using the MWBD method with various e values. This sample was synthesized under kinetically controlled conditions (isothermal, T = 60°C, [AIBN] = 10"5 g-mole/1, conversion level of 48.5 percent). The SEC measurements were made at 25°C in tetrahydro-furan. The Mark-Houwink coefficients used for linear polyvinyl acetate are those suggested by Graessley (21), namely K = 5.1 x 10"5 dl/gm and a = 0.791. The whole polymer M, Mj, and B j values obtained are listed in Table II. 

TABLE 15.1. Osmotic Pressure Data for Polyvinyl Acetate in Methyl Ethyl Ketone at 10°C... 

Table 15.1 contains osmotic pressure data calculated from the work of Browning and Ferry [3] for solutions of polyvinyl acetate in methyl ethyl ketone at 10°C. Plot H/vv against w, fit the data to a quadratic polynomial, and calculate the number-average molar mass from the intercept with the n/w axis. 

Another attractive quality of the PVA is its outstanding chemical stability. Peter and Stefan ( ) investigated the chemical stability of PVA vis a vis a series of solvents and reagents and some of their results are summarized in Table I. This table presents a comparison between the chemical resistances of PVA, polyvinyl butyral(PVB), polyvinyl acetate(PVAc), and cellulose acetate(CA). It is evident from this table that the PVA is considerably more stable than the rest of the tested materials. 

Polyvinyl Acetate. Two polyvinyl acetate samples (PVAc 1 and PVAc 3) also were analyzed. Both samples have been shown to be branched by Hamlelec (50) by a SEC/LALLS study. Table 8 shows the results obtained from SEC/Vlscometry along with some of the available data. It is seen that the intrinsic viscosity values for... 

TABLE 8. SEC/VISCOMETRy RESULTS OF TWO POLYVINYL ACETATE SAMPLES... 

Fig. 5.18. Reduced compliance vs cM /qMc for solutions and undiluted sample of linear, narrow distribution polymers. The lines for polyethylene and (polydimethyl siloxane) are based on G (w) data as reported by Mills (204). Points are selected values for polyvinyl acetate solutions, O (176) and 9 (195), and undiluted 1,4 polybutadiene, (202) and - (203) The values of Mc were taken from Table 5.2...

The following Table 2.4 lists the components of the basic formulation that were successful in dissolving polyvinyl acetate and polybutyral in ethanol with an adjusted viscosity for proper application to tissue. 

In a microorganism prone environment, it is preferable to protect a dressing with a preservative such as chlorhexidine to prevent the contamination of the dressing. It is necessary to consider the solubility of an agent in the liquid phase of the dressing during the selection of an antimicrobial agent. The formulated polyvinyl acetate and polybutyral materials were dissolved in ethanol that is also a solvent for chlorhexidine diacetate. The information (Block, 2001) in Table 2.12 provides solubilities of chlorhexidine compounds in different solvents. 

Emulsion Polymerization A typical recipe is give in Table I. Emulsion polymerization was carried out at 60°C under a nitrogen atmosphere using a batch process. Theoretical solids content in all the formulations was 25%, and generally the conversions were better than 98%. A polyvinyl acetate homopolymer and two poly (vinyl acetate-butyl acrylate) copolymers having VA/BA composition of 85/15 and 70/30 were prepared according to the above procedure. 

Fig. 2. Re-establishment of Hammett correlation for halogen-substituted phenols in the reaction with polyvinyl acetate radical. The straight line represents the Hammett equation found for 26 compounds (No. 12 in Table 3). Key o non-halogen substituted phenols including 2,6-dimethylphenols, excluding 2,6-t-Bu2-4-substituted-phenols halogen-substituted phenols.

TABLE 3-3. Typical Polymer Parameters of Cellulose and Hydroxyethyl Cellulose Compared with Polyvinyl Acetate"... 

Casein adhesives experienced similar problems. Once the industry recognized that they were not waterproof, as was originally believed, they were rapidly replaced by resorcinols in most structural, cold-set applications where pressure was easily applied. Crosslinking polyvinyl acetates became preferable in some nonstructural, cold-set applications. Cheaper PF resins took over those exterior applications that allowed the use of heat and pressure. UF resins took over many interior applications on the basis of superior costs and mold resistance. Although the basic raw material cost is not a complete picture of the costs of its adhesive derivatives, it is a fairly good index. Table III shows how casein and blood compare with their competition at the present time. Although the exact prices of these materials fluctuate considerably, the approximate order of their costs has not changed much in the last 15 years. The materials are listed in order of cost. 

Table II Pharmacopeial specifications for polyvinyl acetate phthalate. ...

Solubility soluble in ethanol and methanol sparingly soluble in acetone and propan-2-ol practically insoluble in chloroform, dichloromethane, and water. In buffer solutions, polyvinyl acetate phthalate (200mg/L) is insoluble below pH 5 and becomes soluble at pH values above 5. Polyvinyl acetate pththalate shows a sharp solubility response with pH this occurs at pH 4.5-5.0, which is lower than for most other polymers used for enteric coatings. Solubility is also influenced by ionic strength. See Table III. 

Evaluation of quantum yield of acetic acid formation at light intensity (L=254 nm) 1=1 TO quant/cm sec gives the value =().()2 close to the value of quantum yield of ester groups destruction (=0,015), measured in similar conditions [162]. Close value of quantum yield of acetic acid formation 0=0,01 has been obtained in the case of polyvinyl acetate photolysis at lower intensity - I=5,7T0 " quant/cm sec [163]. Data on effect of temperature on the rate of acetic formation are given in Table 1. Activation energy of the reaction of acetic acid formation at CA irradiation, calculated according to these results, is E,=9,66 kJ/mole, which is characteristic for photoprocesses. 

It may be seen from Table IV that values of a found for solutions of polyvinyl acetate in toluene are systematically higher than for those for corresponding solutions of polymethyl methacrylate. This confirms the known fact that the polyvinyl chain has a greater mobility than the polymethacrylate chain. 

Typical physical properties of a polyvinyl acetate copolymer emulsion suitable for use with cement are given in Table 3. 

Fio. 1. Variation of the kinetic isotope effect with substituents of phenol in hydrogen atom abstraction by polyvinyl acetate radicals. The straight line representsequation (26). Key Nos. 26-30 in Table 2. o Nos. 31 and 32 in Table 2. A No. 33 in Table 2. 

Useful polyvinyl acetate dispersions are milk-white, high-solids dispersions of vinyl acetate homopolymer in water. Such dispersions have excellent mechanical and chemical stability. Typical properties of a preferred polyvinyl acetate dispersion are given in the following table. Commercially available dispersions with similar characteristics are Monsanto s S-55L, Borden s Polyco 11755, Air Products Vynac XX-210, and Seydel Wooley s Seycorez C-79. 

Compressive Strength and Core Hardness Versus Elapsed Time on Storage at 73°F + 2°F and 50% Relative Humidity of Portage 515 Sand Cores made with 5% Sodium Silicate -1.94% Silica sol - 2% Polyvinyl Acetate Aqueous Dispersion -2% Pitch Uncoated and Coated with Various Core Washes (Grades of Binder Components in Table 15.1)... 

This is an example of the use of an amorphous silica-sodium silicate composition of Si02/Na20 ratio 5 1 as a binder for foundry sand cores, a polyvinyl acetate aqueous dispersion as a co-binder and additive for durability, and pitch as an aid to improve shake-out and casting surface finish (see Table 64.4). 

Experimental plan. Table 1 presents the experimental plan of this study. High-strength concrete with 25% W/B and incorporating 20% fly ash (FA) and 10% silica fume (SF) was fabricated. A number of trial mixes were performed to secure 700 mm slump flow and 3. 0% air content. For the polymer resin, ethylene vinyl acetate copolymer (EVA-P) and polyvinyl acetate copolymer (PVA-P) powders and PVA (PVA-F) and polypropylene (PP-F) fibers were applied. The dosages ranged from 0.1% to 0.5% for powder-type resins and from 0.05% to 0.15% for fiber-type polymers. 

Solvent transfer constants of various solvents for vinyl acetate are shown in Table 4.5 [16]. Polyvinyl acetate, as the raw material of polyvinyl alcohol for fiber, is produced by solution polymerization of vinyl acetate. In most cases, methanol is employed as the solvent. Solvent transfer constant, Cs, is one of the most important features for the selection of the solvent (see below in Section 4.2.2.5). 

There are four kinds of polymerization processes bulk, solution, emulsion, and suspension polymerization. As Table 4.7 shows [24], the heat of polymerization of vinyl acetate is high compared to other monomers hence, the control of temperature is difficult in bulk polymerization. In the case of emulsion and suspension polymerization, it is somewhat troublesome to separate dispersed polyvinyl acetate particles from the aqueous medium, and it is necessary to remove the emulsifier and stabilizer completely because these substances induce problems in the process of fiber-making. 

The stereospecificity of PVA derived from various vinyl polymers, where the above-mentioned two NMR spectroscopies are utilized, are listed in Table 4.8. Polyvinyl alcohol derived from polyvinyl acetate is almost atactic and independent of polymerization temperature. Polyvinyl alcohol derived from poly-i-butylvinylether, polybenzylvinylether, and poly-vinyltrimethylsilylether are isotactic-rich, while those derived from polyvinyl formate, polyvinyl trifluoroacetate, polyvinyl pivalate, and polyvinyltrimethylsilylether (polymerized in a polar solvent) are syndiotaetie-rich. 

Typical examples of the mixed emulsion-spinning of polyvinyl chloride, polyethylene, poly-vinylidene chloride, and polyvinyl acetate, and some properties of the mixed fibers are shown in Table 4.26. The measurement of the fiber properties is carried out after hot-drawing in dry air at 180°C, heat treatment for 100 sec at 250°C, and acetalization for 40 min at 70°C without tension. The draw ratios shown in the table are the highest possible ratios under the given experimental conditions. In most cases, there is a maximum possible draw ratio at a certain mixing ratio. However, only the results of experiments at mixing ratios of 1 3 and 1 1 are shown in the table. 

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