MODIFICATION WITH WATER-SOLUBLE POLYMERS

In the modification with water-soluble polymers such as cellulose derivatives and polyvinyl alcohol, small amounts of the polymers are added as powders or aqueous solutions to cement mortar and concrete during mixing. Such a modification mainly improves their workability because of the surface activity of the water-soluble polymers, and prevents the dryout phenomena (explained in Ch. 4, Sec. 3.1, Water Retention). The prevention of the dry-out is interpreted in terms of an increase in the viscosity of the water phase in the modified cement mortar and concrete and a sealing effect due to the formation of very thin and water-impervious film in them. In general, the water-soluble polymers hardly contribute to an improvement in the strength of the modified systems. 

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The concept of hydrophobe modification of water-soluble polymers may have arisen from the hydrophobic half-esters of maleic anhydride-methyl vinyl ether copolymers, which were commercially available products in the 1960s (i). Replacement of the methyl vinyl ether with styrene produced more stable copolymers in general (2), but hydrophobes attached through the ester... 

The modification of water soluble polymers for tailored solution behavior has been of interest to many research groups seeking different end uses. Enhanced oil recovery, fracturing fluids, flocculation, associative thickeners, personal care products and many other applications exist for polymers of unique solution behavior. Although the ultimate applications may differ, a common goal of researchers in the water soluble polymer field is a solution viscosity enhanced through polymer-polymer intermolecular associations, often with the stipulation that associations must remain intact in the presence of mono- and divalent salts. To this end our research group has extensively studied the properties of several classes of water soluble polymers. While the majority of our studies have involved ampholytic systems ampholytic ionomers [1], polyampholytes [2,3], polysulfobetaines [4,5] and liquid crystalline ionomers [6], we recently have been... 

Chain-Growth Associative Thickeners. Preparation of hydrophobically modified, water-soluble polymer in aqueous media by a chain-growth mechanism presents a unique challenge in that the hydrophobically modified monomers are surface active and form micelles (50). Although the initiation and propagation occurs primarily in the aqueous phase, when the propagating radical enters the micelle the hydrophobically modified monomers then polymerize in blocks. In addition, the hydrophobically modified monomer possesses a different reactivity ratio (42) than the unmodified monomer, and the composition of the polymer chain therefore varies considerably with conversion (57). The most extensively studied monomer of this class has been acrylamide, but there have been others such as the modification of PVAlc. Pyridine (58) was one of the first chain-growth polymers to be hydrophobically modified. This modification is a post-polymerization alkylation reaction and produces a random distribution of hydrophobic units. 

Fullerenes and their water soluble derivatives are of great deal interest for scientific research due to their biological activity [1]. Therefor, the problems of modification and functionalization of nanomaterials to obtain their water soluble derivatives are very challenging task. In present work we have investigated low-temperature y -induced copolymerization of vinyl monomers such as acrylamide and acrylic acid with fullerene C6o to obtain their water soluble polymers containing fullerene. 

Modification of cement mortar and concrete by small amounts of water-soluble polymers such as cellulose derivatives and polyvinyl alcohol is used popularly for improving workability. In this case, the water-soluble polymers are mixed with the mortar and concrete as powders or aqueous solutions, and act as plasticizers because of their surface activity. 

It is well known that it is difficult to achieve miscibility of two polymers. However, it is often possible to obtain apparently stable solutions in which two polymers are dissolved without phase separation. Examples of water-soluble polymers that were mixed with PVA and spun by wetspinning are polyacrylic acid, sodium carboxymethyl cellulose, various proteins, and polyvinyl aminoacetals. The most common objective of mixed-spinning was the modification of dyeing properties, but this method is also applied to modify many other properties of PVA fiber. 

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