Partially hydrolyzed PVA

In addition to polymer standards, a number of broad distribution, water-soluble polymers can be characterized on TSK-PW columns using universal calibration. These include both fully and partially hydrolyzed PVA, PAAM, PEE, and dextran. PVA, the world s largest-volume, synthetic, water-soluble polymer, was first successfully separated on TSK-PW columns by Hashimota et al. (10). In the 1980s, the use of low-angle, laser light-scattering detection... 

FIGURE 20.6 DRI chromatograms of partially hydrolyzed PVA (low molecular weight type) using TSK-PW columns. 

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. 

These results confirm the existence of weak or labile floes at partial PVA coverage, particularly with the high-molecular-weight fully-hydrolyzed Vinol 325 and Vinol 350. In contrast, the partially-hydrolyzed Vinol 523, which is comparable in molecular weight to the Vinol 325, gave an adsorption isotherm with little scatter, indicating the absence of flocculation. Partially hydrolyzed PVA shows specific interactions with polystyrene surfaces (mentioned below), and the absence of flocculation in this case is consistent with the theory proposed by Clark and Lai (14) for bridging flocculation. 

Prolonged heating of the PVA solution has negligible effect on its properties. However, the addition of strong acid or base to solutions of partially hydrolyzed PVA can increase the degree of hydrolysis. 

PVA is further modified to obtain polyvinylacetatephthalate (PVAcP), which is used in enteric coatings. PVAcP is prepared from the reaction of partially hydrolyzed polyvinyl alcohol, sodium acetate and phthalic anhydride. It consists of 55 to 62% of phthalyl groups. The PVA used is a low molecular weight grade with 87 to 89 mole% hydrolyzed. Since only vinyl alcohol portions of the partially hydrolyzed PVA are phthalated, the acetyl content remains constant before and after the reaction. 

Figure 8.4 PANI colloids obtained by enzymatic polymerization of aniline in presence of different steric stabilizers, (a) Partially hydrolyzed PVA, (b) fully hydrolyzed PVA, (c) PNIPAM, and...

Among these surfactants, partially hydrolyzed PVA is mostly used, because it gives the smallest microspheres. 

The progress of hydration is also characterized by a shift of the S-0 asymmetric stretching vibration (v3) to higher wave numbers (929 to 974 cm ), due to the reaction of the Si04 units during C-S-H formation. The bands, associated with the polymer itself, can be detected only for PVA unmodified, recorded at -1740 cm which arises due to the carbonyl bond (C=0) of the acetate group found in partially hydrolyzed PVA polymer. 

Aqueous SEC/LALLS circumvents the problems of SEC calibration for PVA because it measures absolute molecular weight on-line. SEC/LALLS was successfully used to measure the absolute molecular weight of fully and partially hydrolyzed PVA over a wide range of molecular weights by this author (25,26). This was the first reported use of aqueous SEC/LALLS for absolute molecular... 

The Mark-Houwink constants for partially hydrolyzed PVA in HjO/CHjCN (80 20) are similar to those for fully hydrolyzed PVA in 0.10 M NaNOj (Table... 

Concentration (DRI), FALLS, and viscometry chromatograms for a high-molecular-weight, partially hydrolyzed PVA. 

In general, the characterization of partially hydrolyzed PVA needs further investigation to understand better the impact of hydrophobic interactions. The use of other organic, mobile-phase modifiers, such as V-methylpyrrolidone or dimethyl sulfoxide, is a possible approach. 

Table 6 Comparison of Molecular Weights for Partially Hydrolyzed PVA PVA type...

Characterization of partially hydrolyzed PVA by viscometry is complicated by secondary, hydrophobic interaction effects. These effects can be minimized using a suitable aqueous mobile phase with an organic modifier such as acetonitrile. 

Partially hydrolyzed PVA is typically used in food industry. PVA is an odorless and tasteless, translucent, white or cream-colored granular powder. It is used as a moisture barrier film for food supplement tablets and for foods that contain inclusions or dry food with inclusions that need to be protected from moisture uptake. PVA is not known to occur as a natural product because it forms from hydrolysis. It is soluble in water and slightly soluble in ethanol, but it is insoluble in other organic solvents. A 5% solution of PVA typically exhibits a pH in the range of 5.0-6.5. PVA has a melting point of 180-190°C. It has a molecular weight of between 26,300 and 30,000 and a degree of hydrolysis of 86.5-89%. 

Efforts were also centered on the search for a practical solvent system that will exhibit an LCST with poly(methyl methacrylate) PMMA and poly(vinyl acetate) PVA. Results are recently being presented in the hterature (Caneba et al., 2009). For the PVA/solvent system, no LCST data were reported in the hterature, except for a citation on LCST behavior for partially hydrolyzed PVA in water. Cloudpoint experiments on PVA with mixtures of alcohol (ethanol, isopropanol, -butanol, t-butanol) and water resulted in LCST behavior below 97°C. 

The hydroxyl groups in PVA contribute to strong hydrogen bonding both intra- and intermolecularly, which reduces solubility in water. The presence of residual acetate groups in partially hydrolyzed PVA weakens these hydrogen bonds and allows solubility at lower temperatures. 

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