Polyvinyl alcohol hydrolysis

A polyvinyl alcohol is obtained by suspension polymerization of vinyl acetate and the cross-linking agent, triallyl isocyanurate, with a triazine ring followed by alkali hydrolysis. The polyvinyl alcohol gel is used as packing for gel-... 

Colloids of a-FejOj are made by hydrolysis of FeClj and subsequent dialysis of the sol. Polyvinyl alcohol is often used as a stabilizing agent. The band gap in Fe203 is 2.2 eV. In some of the studies on colloidal Fc203 free radicals were generated by ionizing radiation and electron transfer reactions with the colloidal particles investigated. Buxton et al. observed a cathodic dissolution of a-FCjOj in acidic... 

Polyvinyl alcohol(PVA) was obtained from the Kurarey Co.,Ltd. Japan the molecular weight and the degree of hydrolysis were determined by the supplier as 88,000 and 80 %, respectively. The molecular weight and the molecular weight distribution data of the polymer samples are shown in Table 1. 

Polyvinyl alcohol (PVA) produced by the hydrolysis of PVAc has the following repeating unit ... 

Hydrolysis of Polyvinyl Acetals Derived from Polyvinyl Alcohols... 

Noma, Oya and Nakamura [33] examined the reaction of nitrating polyvinyl alcohol and concluded that neither nitration with a mixture of nitric and sulphuric acid, nor nitration with nitric and acetic acid can bring about the esterification of all the hydroxyl group. This is probably due to simultaneous hydrolysis. They recommend nitrating either with a composition of nitric add and acetic anhydride or a solution of nitric acid in carbon tetrachloride, where by a higher nitrated product, softening at a temperature of 40-50°C, is obtained. 

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. 

Chemical modification of polymers continues to be an active field of research [1-5]. It is a common means of changing and optimising the physical, mechanical and technological properties of polymers [5-7]. It is also a unique route to produce polymers with unusual chemical structure and composition that are otherwise inaccessible or very difficult to prepare by conventional polymerisation methods. For example, hydrogenated nitrile rubber (HNBR) which has a structure which resembles that of the copolymer ethylene and acrylonitrile, is very difficult to prepare by conventional copolymerisation of the monomers. Polyvinyl alcohol can only be prepared by hydrolysis of polyvinyl acetate. Most of the rubbers or rubbery materials have unsaturation in their main chain and/or in their pendent groups. So these materials are very susceptible towards chemical reactions compared to their saturated counterparts. 

The polyvinyl alcohol is soluble in hot water, and the solution is wet-spun into a coagulating bath consisting of a concentrated solution of sodium sulfate. The fibers are heat-treated to provide temporary stability so that they may be converted to the formal derivative by treatment with an aqueous solution of formaldehyde and sulfuric acid. This final product resists hydrolysis up to the boiling point of water. It seems reasonable to assume that it contains hemiacetal groups and some unreacted hydroxyls on the polymer chain as... 

Electrophoresis protein separation membranes have been prepared by step-growth condensation of water-soluble polyvinyl alcohol with selected water-soluble difunctional crosslinking agents. These membranes have broad pore size ranges, restricted pore size distribution, greater resistance to hydrolysis in an alkaline medium, and improved gel clarity when higher amounts of crosslinkers are used. 

However, in a recent publication, Shirinyan, Mnatsalianov, et al. (20) find that differences between the rates of vinyl acetate emulsion polymerisation observed with samples of similar polyvinyl alcohols manufactured by the same process In three different factories could be attributed to a condensation product of acetaldehyde derived from hydrolysis of residual vinyl acetate this gave rise to a conjugated ketone type ultra-violet spectrum and could be extracted from the polyvinyl alcohol under suitable conditions. This could be the uncontrolled factor which appears to have confounded nmuiy of the experiments reported here. Even more recently the same laboratory ( ) has reported that there Is an optimum sequence length of hydroxyl groups in the polyvinyl cdcohol-acetate block copolymer for polymerisation rate and dispersion stability. 

The effects of commercial grades of polyvinyl alcohol obtained from several manufacturers on the rate of polymerisation of vinyl acetate aqueous solutions and emulsions initiated by potassium persulphate at 60°C have been investigated. Increasing concentrations of polyvinyl alcohol in the same range tend to reduce the rate of polymerisation of the solutions but Increase the rate of polymerisation of emulsions. Considerable differences were noted between the effects of nominally simileir grades from different sources. Attempts to correlate the effect on the rate of polymerisation of vinyl acetate solutions with the acetyl content and molecular weight of the polyvinyl alcohol appear to have been confounded by an uncontrolled variable. A subsequent publication from the U.S.S.R. indicates that this may be the concentration of a by-product formed during the hydrolysis of the polyvinyl acetate. Other factors which may account for the effects are also discussed. 

Polyvinyl alcohol (PVA) is a water-soluble polymer with a glass transition temperature, T, of 80 °C. Although its name implies a homopolymer stmcture, the structure of commercial PVA is a copolymer of vinyl alcohol and vinyl acetate as seen in Fig. 4.2. PVA is made by the incomplete hydrolysis of polyvinyl acetate... 

Polyvinyl alcohol (PVA) Synthetic, hydrolysis product of polyvinylacetate CH OH Substituted polyethylene chain... 

Polyvinyl alcohol is produced through the hydrolysis of polyvinyl acetate. The repeating unit of vinyl alcohol is not used as the starting material because it cannot be obtained in the quantities and purity required for polymerization purposes. The hydrolysis proceeds rapidly in methanol, ethanol, or a mixture of alcohol and methyl acetate, using alkalis or mineral acids as catalysts. 

Polyvinyl alcohol is another widely used material, often as a surface coating because of its high biocompatibility (Fig. ID). Usually, it can be obtained by the hydrolysis of polyvinyl acetate, with varying amounts... 

Polyvinyl alcohol is manufactured indirectly by the hydrolysis of poly (vinyl... 

Waste Disposal. All processes must include some form of washing step to remove impurities from the bottles. If the adhesive, poly(vinylacetate), PVA, is to be separated through dissolution or hydrolysis to poly(vinyl alcohol), the waste stream will contain PVA and/or dissolved polyvinyl alcohol in addition to the other contaminants which must be removed. Paper fibers are another major source of impurities. For a lOMM Ib/yr plant about 75,(XX) Ib/yr PVA will be removed via the effluent. Environmental regulations probably require that this problem be addressed, especially since polyvinyl alcohol is an excellent foaming agent. 

Polyvinyl alcohol (PVA) is the hydrolysis product of polyvinyl acetate. Depending on the hydrolysis conditions, there are fully hydrolysed PVA and partially hydrolysed PVA, as shown in Fig. 5.4a and b, respectively. 

Polyvinyl alcohols (PVAl) are manufactured by saponification of vinyl acetate polymers (PVAc). Properties of PVC using PVAl as a protective colloid are influenced by the solution viscosity of the PVAl, i.e. the degree of polymerization of the PVAc and the degree of saponification. Polyvinyl alcohols of 75-90% hydrolysis are primary suspension agents for S-PVC, whereas polyvinyl alcohols of 25-40% hydrolysis are secondary suspension agents, which control the agglomeration of the primary particles. Partially hydrolyzed PVAc can be block or random polymers. 

Pd on polyvinyl alcohol, 244 Hydrogenolysis, 187, 241 Hydrolysis, acetal, 108 amide, 212... 

Dry, unplasticized polyvinyl alcohol powders are white to Cream colored, soften at about 200 with decompn. Com. mercial polyvinyl alcohols have different concents of residual acetyl groups and therefore different viscosity characteristics. The first code number following the trads name indicates the degree of hydrolysis, while the second set of num. bers indicates the approx viscosity in centipoises (4% aq sola at 207- Polyvinyl alcohols are essentially sol in hot and cold water, but those coded 20-105 require alcohol-water mix. tures. Aq solns are colloidal and compatible with lower alcohols. Pure aq solns are neutral or faintly acid and subject to mold growth. Insol in petroleum solvents. 

For example, name such as polyvinyl alcohol refers to a hypothetical source, since this polymer is obtained by hydrolysis of polyvinylacetate. In spite of deficiencies, the source-based nomenclature is still entrenched in the literature. It is also the basis for naming and classifying copolymers (see Table 1.6). 

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