Poly alkenoic acid s

The polyelectrolyte cements are modern materials that have adhesive properties and are formed by the cement-forming reaction between a poly(alkenoic acid), typically poly(acrylic acid), PAA, in concentrated aqueous solution, and a cation-releasing base. The base may be a metal oxide, in particular zinc oxide, a silicate mineral or an aluminosilicate glass. The presence of a polyacid in these cements gives them the valuable property of adhesion. The structures of some poly(alkenoic acid)s are shown in Figure 5.1. 

Figure 5.1 The structure of poly(alkenoic acid)s containing acrylic, itaconic, maleic and 3-butene 1,2,3-tricarboxylic acid units.

Poly(alkenoic acid)s may be prepared as follows. 200 cm of a solution containing between 0-5 and 2-5 g of ammonium persulphate contained in a flask is heated to a controlled temperature, lying between 80 and 95 °C, while purging with nitrogen to displace dissolved oxygen. Two solutions. Solution (/) and Solution (II) are added, in the ratio 3-4 10, to the flask charge, with continuous stirring, over a period of two hours. These solutions are ... 

The poly(alkenoic acid)s used in glass polyalkenoate cement are generally similar to those used in zinc polycarboxylate cements. They are homopolymers of acrylic acid and its copolymers with itaconic add, maleic add and other monomers e.g. 3-butene 1,2,3-tricarboxylic add. They have already been described in Section 5.3. The poly(acrylic add) is not always contained in the liquid. Sometimes the dry add is blended with glass powder and the cement is activated by mixing with water or an aqueous solution of tartaric add (McLean, Wilson Prosser, 1984 Prosser et al., 1984). 

Ellis, J., Jackson, A. M., Scott, R. P. Wilson, A. D. (1990). Adhesion of carboxylate cements to hydroxyapatite. III. Adsorption of poly(alkenoic acid)s. Biomaterials, 11, 379-84. 

The glasses are similar to those used in glass-ionomer cements but their reactivity towards acids has to be less, as orthophosphoric add is a stronger acid than the poly(alkenoic acid)s. The consequence is that the Al/Si ratio, which determines reactivity, is lower than in the glass-ionomer cement glasses. 

Polymeric aliphatic carboxylates, the poly(alkenoic add)s, were very much more strongly adsorbed than the difunctional carboxylates (Ellis et al., 1990). Results showed that adsorption depended on the conformation of the polyanion. When extended, as in dilute solutions, a polyanion is adsorbed onto a relatively large number of sites and further adsorption is hindered. Thus, increases in acidity (and concentration) were found to result in greater adsorption because the polyanion adopted a more compact... 

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