Polyacids

These acids have a very moderate action on aluminium. 

In solutions containing 5% (pH 1.7), 30% (pH 1.0), and 50% (pH 0.6) tartric or citric acid, the decrease of thickness is less than 10 pm per year at room temperature. 

The dissolution rate increases with temperature. At 50 °C, the thickness decreases at a rate of 0.1 mm per year. 

A great deal of equipment in aluminium is used for the production, storage and transportation of these acids. Aluminium modifies neither the aspect nor the taste of these acids or solutions thereof. 

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Biodegradation results from the pH drop such a detergent polymer experiences as it leaves the alkaline laundry environment (pH ca 10) and enters the sewage or ground water environment (pH close to neutral) the polymer (now a polyacid rather than a salt) is unstable and hydrolyzes to monomer which rapidly biodegrades. The chemistry has been reported ia many patents (186) and several pubHcations (187,188). 

According to this mechanism, the reaction rate is proportional to the concentration of hydronium ion and is independent of the associated anion, ie, rate = / [CH3Hg][H3 0 ]. However, the acid anion may play a marked role in hydration rate, eg, phosphomolybdate and phosphotungstate anions exhibit hydration rates two or three times that of sulfate or phosphate (78). Association of the polyacid anion with the propyl carbonium ion is suggested. Protonation of propylene occurs more readily than that of ethylene as a result of the formation of a more stable secondary carbonium ion. Thus higher conversions are achieved in propylene hydration. 

Poly(methyl vinyl ether) [34465-52-6] because of its water solubility, continues to generate commercial interest. It is soluble in all proportions and exhibits a well-defined cloud point of 33°C. Like other polybases, ie, polymers capable of accepting acidic protons, such as poly(ethylene oxide) and poly(vinyl pyrroHdone), each monomer unit can accept a proton in the presence of large anions, such as anionic surfactants, Hl, or polyacids, to form a wide variety of complexes. 

Oxygen has also been shown to insert into butadiene over a VPO catalyst, producing furan [110-00-9] (94). Under electrochemical conditions butadiene and oxygen react at 100°C and 0.3 amps and 0.43 volts producing tetrahydrofuran [109-99-9]. The selectivity to THF was 90% at 18% conversion (95). THF can also be made via direct catalytic oxidation of butadiene with oxygen. Active catalysts are based on Pd in conjunction with polyacids (96), Se, Te, and Sb compounds in the presence of CU2CI2, LiCl2 (97), or Bi—Mo (98). 

Polycarboxylate Cements. Polycarboxylate cements (30,31) are made by mixing a 2inc oxide-based powder and an aqueous solution of poly(acryHc acid) [9003-01 ] or similar polyacid (see Acrylic acid). The biological effects of these cements on soft and minerali2ed tissues are mild (32). 

When freshly mixed, the carboxyHc acid groups convert to carboxjiates, which seems to signify chemical adhesion mainly via the calcium of the hydroxyapatite phase of tooth stmcture (32,34—39). The adhesion to dentin is reduced because there is less mineral available in this substrate, but bonding can be enhanced by the use of minerali2ing solutions (35—38). Polycarboxylate cement also adheres to stainless steel and clean alloys based on multivalent metals, but not to dental porcelain, resin-based materials, or gold alloys (28,40). It has been shown that basic calcium phosphate powders, eg, tetracalcium phosphate [1306-01-0], Ca4(P0 20, can be substituted for 2inc oxide to form strong, hydrolytically stable cements from aqueous solution of polyacids (41,42). 

The powder contains 2inc oxide and magnesium oxide (36), and the Hquid contains an aqueous solution of an acryHc polycarboxyHc acid. Water settable cements have been formulated by inclusion of the soHd polyacid in the powdered base component. The set cement mainly consists of partially reacted and unreacted 2inc oxides in an amorphous polycarboxylate matrix (27,28). 

H-Bonding, Strongly Associative (HBSA) Water Primary amides Secondary amides Polyacids Dicarboy lic acids Monohydro) acids Polyj)henols Oximes Hydroj laniines Amino alcohols Polyols... 

This potential reflects itself in the titration curves of weak polyacids such as poly(acrylic acid) and poly(methacrylic acid) [32]. Apparent dissociation constants of such polyacids change with the dissociation degree of the polyacid because the work to remove a proton from the acid site into the bulk water phase depends on the surface potential of the polyelectrolyte. 

Orthophosphoric acid containing three acid OH groups in the molecule offers many opportunities for the realization of surface-active molecular structures. But phosphoric acid also possesses the ability to form polyacids in an widespread manner. Pyrophophoric acid and triphosphoric acid are substances that have been known for a long time. This presents further possibilities for interesting synthesis. 

The dispersing ability of surfactants is important in many applications. The possibility of varying the HLB of phosphorus-containing surfactants in a broad range and their ability to form polyacid anions lead to a great interest in phosphorus-containing surfactants as dispersants. 

Extensive data are given in the Uterature for the potentiometric titration of polymer acids which may be used to study the behaviour of polyelectrolyte systems under different conditions. For poly(a-D) galacturonic acid there are few data of this kind, especially in connection with the occurrence of a conformational transition induced by pH variations, or with the effect brought about by the addition or the exchange of counterions. Since for a polyacid not exhibiting a conformational transition in the course of titration, pK K denoting the apparent dissociation constant) increases monotonously with degree... 

The purpose of this study is to consider in more detail the influence of the size and nature of the counterion on the degree and extent of dissociation of poly(a-D)galacturonic acid already discussed in a previous paper [2], particularly to check the effect of screening the charges on the polyacid in the presence of different counterions. 

Commercially available poly(a-D)galacturonic acid PGA) was purchased from Fluka Chemie. To obtain an aqueous solution of the polyacid, insoluble PGA was converted to its soluble sodium salt and then percolated through a cation-exchange resin in the H-form [3]. 

Flood, H., Forland, T. Roald, B. (1947). The acidic and basic properties of oxides. III. Relative acid-base strengths of some polyacids. Acta Chemica Scandinavica, 1, 790-8. 

Hodd, K. A. Reader, A. L. (1976). The formation and hydrolytic stability of metal ion-polyacid gels. British Polymer Journal, 8, 131-9. 

Large bound monovalent cations, e.g. tetrabutylammonium ions, are too large to penetrate any of the hydration regions. However, the smaller lithium, sodium and potassium ions are able to penetrate the outermost hydration region of the neutralized polyacid and this is accompanied by volume increases (Figure 4.9). These cations are probably not site-bound but are mobile in the outer cylindrical region of hydration (Figure 4.10). 

Conformation depends on the degree of ionization and concentration of the polyion, the type and concentration of the counterion and the interaction between counterion and polyion. Extension is favoured by low concentrations of counterion and polyion. Conformational change is also affected by the extent of the charge on the polyion. As the charge on a polyion increases, the chain uncoils and expands under the influence of repulsive forces. Thus, the neutralization of a polyacid is accompanied by... 

Ionization of the carboxyl groups is accompanied by binding of the cations. But if counterions are site-bound the charge on the carboxyl groups is neutralized and chain contraction results. A special case is that of the polyacid which adopts a contracted form because the close association of hydrogen ions with carboxyl groups results in a neutral chain. 

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