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Polyphosphate Chain Stability in Magnesia-Polyphosphate Cements

Polyphosphates of the general formula Na n H 2 P n O 3n+1 ·H 2 O, n = 6, 15, 70, where n is the average degree of polymerization, have been synthesized and characterized by 31 P NMR and HPLC. Aqueous solutions of these polyphosphates react at room temperature with magnesia to form cement pastes that harden to amorphous materials. The compressive strengths and porosities obtained are similar to those of MgO-(NH 4 )H 2 P 3 O 10 -H 2 O cements. Although polyphosphate chain length does not have a significant effect on the strength of the cement, 31 P MAS-NMR spectroscopy showed that the degree of polyphosphate chain degradation decreases as the average degree of polymerization, n, increases.