Abstract
To study the binding of free calcium ions in aqueous solutions using poly (acrylic acid) with various molecular weights, potentiometric titration of their polyelectrolytes was carried out, and a calcium ion electrode was used to measure the free calcium ion in the solution. The precipitation reaction occurred, when the concentration of the polyelectrolytes had a mean molecular weight of about 100×104 was 4×10-3N and the concentration of calciam ion ([Ca]) in the solution was 8mM and when that of the polyelectrolyte had a mean molecular weight of about 35×104 was 8×10-3 and[Ca]was 16mM. Their precipitates contained the unreacted carboxyl groups with calcium. On the other hand, the binding molar ratio between the carboxyl group and calcium ion was about 2:1 for the polyelectrolytes(35×104 molecular weight, 4×10-3), and about 3:1 for the concentration of 8×10-3N.The reaction of the poly(acrylic acid)s with calcium ions was affected by the molecular weight and concentration of the polyelectrolytes.The tensile bond strength of the polycarboxylate cements using poly (acrylic acid) with various mean molecular weights to stainless steel became maximum at a mean molecular weight of about 15×104. The reduction in the strength of cements using a higher mean molecular weight polyelectrolyte may be due to the existence of unreacted carboxyl group in the cements.
