Structural Analysis of a Melaminium Polyphosphate from X-ray Powder Diffraction and Solid-State NMR Data

Abstract

The crystal structure of the environmentally friendly flame retardant melaminium polyphosphate (MPoly) (2,4,6-triamino-1,3,5-triazinium‚PO 3 ) n was determined by a direct-space global optimization technique from X-ray powder diffraction data. Solid-state NMR was used to corroborate the proposed hydrogen-bonding model and to determine the average degree of polymerization (n > 100). An analysis of the crystal structure of MPoly reveals aspects of molecular geometry and packing that are characteristic for melamine-containing compounds and polyphosphate salts. A comparison of MPoly with the crystal structures of its precursors melaminium orthophosphate (MP) and melaminium dihydrogenpyrophosphate (MPy) provides insight in the mechanism of the endothermic dehydration processes that takes place in the reaction path MP f MPy f MPoly. Solid-state NMR characterization of various samples of the same batch showed inhomogeneities in the MPoly composition. Various quantities of orthophosphates were found, which cannot be assigned to be MP.

Structure of Tetrakis(melaminium) Bis(dihydrogenphosphate) Monohydrogenphosphate Trihydrate from X-ray Powder Diffraction and Solid-State NMR Spectroscopy

“…However, the melaminelayer packing and the packing of the phosphate moieties relative to the melamine layers differ considerably from the types of melamine-phosphate packing found before. [2][3][4][5] With Organa two types of models were found. In the first type ( Figure 2, type I) the phosphate layers were positioned at the b-axis coordinates y ∼ 0.0 and y ∼0.5, while the centers of the melamine layers were at y ∼ 0.25 and y ∼ 0.75.…”

“…4 One-and two-dimensional high-resolution solid-state 1 H NMR was used at high external magnetic field in combination with fast magic-angle-spinning of the sample to gain detailed information about the proton positions, proximities, and the hydrogen bonding network in MP. 5 In addition, we determined the geometry of the NH and NH 2 groups in MP by 15 N-1 H heteronuclear recoupling experiments and could show that these geometries can only be convincingly obtained by solid-state NMR.…”

Environmentally friendly flame retardants. A detailed solid-state NMR study of melamine orthophosphate

“…36 Jahromi et al performed simple onedimensional 13 C and 31 P spectroscopy on MP, MPy, MPoly and mixtures of MPoly with polyamides 37 Our recent studies of the structure of MPy and MPoly included high-resolution 1 H spectroscopy, 31 P spectroscopy and 31 P-1 H HETCOR spectroscopy. 13,14 In view of possible mechanistic studies of the process underlying the flame-retardant capabilities of melamine phosphates, an in-depth characterization of the base material is essential. In this contribution, we apply a host of solidstate NMR techniques to gain detailed information about the proton positions, proximities and the hydrogen-bonding network in MP.…”

Delamination of sodium montmorillonite in PA6 in the presence of melamine polyphosphate

“…Exfoliation of the clay is usually obtained in extrusion process when PA6 is mixed with organically modified clay. There is a small peak at 2θ = 8.3° which originates from the crystal structure of MPP . In the presented research, the exfoliation of the clay was obtained for virgin, hydrophilic sodium MMT.…”

“…There is a small peak at 2θ = 8.3°which originates from the crystal structure of MPP. [23] In the presented research, the exfoliation of the clay was obtained for virgin, hydrophilic sodium MMT. This effect was obtained as a result of addition of a second filler to the extrusion process.…”