Preparation and structure of organic-inorganic hybrid low-melting phosphite glasses from phosphonic acid H 3 PO 3
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An organic–inorganic, hybrid, low-melting glass free of pollution elements such as Pb and F was prepared through nonaqueous acid–base reactions of Si–Cl + P–OH → Si–O–P + HCl↑ and Sn–Cl + P–OH → Sn–O–P + HCl↑ using phosphonic acid (H3PO3), dimethyldichlorosilane (Me2SiCl2), and tin(II)chloride (SnCl2) as starting materials. Transparent, colorless, and homogeneous phosphite glass was successfully obtained. The formation of P–O–Si linkage and the disappearance of P–OH were confirmed by 31P nuclear magnetic resonance spectra. With increasing Si content, the glass-transition temperature decreased, reflecting the decrease of the average linkage number per one cation.
I. INTRODUCTION
Recently, organic–inorganic hybrid low-melting glasses in the ternary system of SnO–Me2SiO–P2O5 have been successfully prepared through a nonaqueous acid–base reaction Si–Cl + P–OH → Si–O–P + HCl↑.1–3 Detailed structure of the glasses was examined by several methods such as differential scanning calorimetry (DSC), infrared (IR) spectroscopy, 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and ab initio molecular orbital (MO) calculations. Organic–inorganic hybrid low-melting glasses in the quaternary system of Me3SiO0.5–Me2SiO–SnO–P2O5 have also been prepared by nonaqueous acid–base reaction.4 The obtained hybrid glasses exhibited lower glass-transition temperature (Tg) changing from 25 to −50 °C with increasing –OSiMe3. Thus, termination of the oxide framework by the organic functional group (–OSiMe3) decreased the network dimension, lowering the glass-transition temperature. In our previous paper,4 we mainly dealt with the design of the structure of hybrid low-melting glasses. When the hybrid precursors were prepared, the produced molecules were not only one kind. For example, when the starting composition of the precursor was Me3SiCl:H3PO4 ⳱ 1:1, 29.8 mol% H3PO4 remained unreacted whereas three type of molecules [O⳱P(OSiMe3)(OH)2:46.3 mol%, O⳱P(OSiMe3)2(OH):20.6 mol%, and O⳱P(OSiMe3)3: 3.3 mol%] were simultaneously produced. To design the exact glass structure, O⳱P(OSiMe3)(OH)2 should be the unique product.
a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 5, May 2003
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To avoid the above-mentioned problem, we chose phosphonic acid H3PO3 in place of phosphoric acid H3PO4. The phosphorus atom in H3PO3 is not pentavalent as in H3PO4, but trivalent. H3PO3 has two P–OH bonds, one P⳱O double bond, and one P–H nonbridging bond [Fig. 1(a)]. If H3PO3 is used as one of the starting materials for preparing glass, P–H non-bridging bond plays the same structural part as P–O–SiMe3 linkage [Fig. 1(b)]. Due to the P–H non-bridging bond, it seems easier to design the glass structure with H3PO3. For this report, organic–inorganic hybrid low-melting glasses were prepared from H 3 PO 3 . The obtained samples were characterized by DSC, IR, and NMR spectroscopies. The correlation between the Tg and the stru
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