Water-reducible polymers properties

Water-Reducible Polymers. Water-reducible polymers have been developed in recent years in an effort to overcome the deficiencies of aqueous emulsions and to make the handling properties of water-based systems more like those of traditional solvent systems. In principle, any solution acrylic polymer can be rendered water reducible by polymerizing the monomers in a water-miscible organic solvent and by Increasing the acrylic or methacrylic acid content so that the addition of water and some solubilizing amine will maintain the polymer in solution. 

The major limitation of this approach to a low-emission coating is the fact that in order to meet Rule 66 requirements the polymer solids must be high and, as a consequence, the molecular weight must be kept low. As a result, water-reducible polymers are restricted to thermosetting vehicles if adequate performance properties are to be maintained. In applications where thermosetting vehicles are required, this is no particular disadvantage since carboxyl and hydroxyl functionality is already present in the backbone to render the polymer water soluble. 

The original Polacolot negative had water-coated intedayers of gelatin (60). The SX-70 and Polacolot 2 negatives use as intedayers a combination of a polymeric latex with a water-soluble polymer. A key development was the constmction of lattices that function as temporary batnets, reducing interimage problems. The water-soluble polymer functions as a permeator, so that the harder properties ate tunable (61). 

Weathering. This generally occurs as a result of the combined effect of water absorption and exposure to ultra-violet radiation (u-v). Absorption of water can have a plasticizing action on plastics which increases flexibility but ultimately (on elimination of the water) results in embrittlement, while u-v causes breakdown of the bonds in the polymer chain. The result is general deterioration of physical properties. A loss of colour or clarity (or both) may also occur. Absorption of water reduces dimensional stability of moulded articles. Most thermoplastics, in particular cellulose derivatives, are affected, and also polyethylene, PVC, and nylons. 

Both nonionic and anionic surfactants have been evaluated in this application (488,489) including internal olefin sulfonates (487, 490), linear alkylxylene sulfonates (490), petroleum sulfonates (491), alcohol ethoxysulfates (487,489,492). Ethoxylated alcohols have been added to some anionic surfactant formulations to improve interfacial properties (486). The use of water thickening polymers, either xanthan or polyacrylamide to reduce injected fluid mobility mobility has been proposed for both alkaline flooding (493) and surfactant enhanced alkaline flooding (492). Crosslinked polymers have been used to increase volumetric sweep efficiency of surfactant - polymer - alkaline agent formulations (493). 

Surface-bound, neutral, hydrophilic polymers such as polyethers and polysaccharides dramatically reduce protein adsorption [26-28], The passivity of these surfaces has been attributed to steric repulsion, bound water, high polymer mobility, and excluded volume effects, all of which render adsorption unfavorable. Consequently, these polymer modified surfaces have proven useful as biomaterials. Specific applications include artificial implants, intraocular and contact lenses, and catheters. Additionally, the inherent nondenaturing properties of these compounds has led to their use as effective tethers for affinity ligands, surface-bound biochemical assays, and biosensors. 

Solubilizable Dispersions (19). The chemistry of solubilizable acrylic dispersions is a hybrid of emulsion and water-reducible technology. These polymers are synthesized by emulsion techniques but contain acidic or basic functionality that renders them water soluble upon neutralization with an appropriate titrant. For example, if the solubilizing functionality is acidic, the polymer will behave like an emulsion below a certain critical pH range, like a highly swollen emulsion within the critical pH range, and like a true water-soluble polymer at sufficiently high pH values. Such polymers offer a favorable balance of properties for many coating applications. 

Analogously to water, alcohols (used in the form of polyols) also cause a chain-transfer reaction during the cationic polymerization of epoxides. Polyols (polyvalent alcohols with an average molecular weight from several hundred to several thousand grams/mole) are often utihzed in technical formulations. These serve to reduce the network density of the polymerized epoxide and therefore make the material less brittle. At the same time the reactivity also is influenced and the susceptibiHty of the polymerization rate and polymer properties to the influence of air humidity is reduced. This is important, as the influence of air humidity is difficult to reproduce in technical appHcations. 

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