Bonding of alkaline and alkaline earth cations in Na‐Ca‐Sr polyphosphate glasses

Abstract Dissolution of phosphates bioglasses, for bone regeneration or controlled ion release, is a key property to be tuned by adequate selection of chemical species. Mixed Na‐Sr and Na‐Ca polyphosphate glasses exhibit definite bonding preferences of the stronger cations to O from chain‐end phosphates (Q ¹ ) instead of random bonding to the network (Q ¹ and Q ² ). This behavior is important for the control of dissolution, as hydration starts from the reaction of H with O in Q ¹ . To analyze this bonding preference in glasses with two alkaline earths competing for O, mixed Na‐Ca‐Sr polyphosphates (0.57‐ x ) Na ₂ O· x /2 SrO· x /2 CaO·0.43 P ₂ O ₅ (0 ≤ x ≤ 0.30 molar fraction) were considered. ³¹ P nuclear magnetic resonance was used to analyze the short‐range environments of Q ⁿ groups, detecting preferential bonding of Ca and Sr to Q ¹ . To probe variations in the medium‐range organization of the network induced by Ca or Sr, glasses with compositions (0.57‐ x ) Na ₂ O· x MO·0.43 P ₂ O ₅ (M = Ca,Sr; 0 ≤ x ≤0.30 molar fraction), were analyzed using ³¹ P‐double‐quantum techniques. An increase in mutual Q ² self‐connectivity relative to the base Na‐polyphosphate network was detected as Ca or Sr were added, indicating conversion of linear phosphate chains into rings.