Organically Modified Aluminophosphates:  Transformation of Boehmite into Nanoparticles and Fibers Containing Aluminodiethylphosphate Tectons

Abstract

The reaction of boehmite with diethyl phosphoric acid generated in situ in a boiling water solution of triethyl phosphate has been studied in detail. Two kinds of solid products have been isolated and characterized by elemental and XPS analysis, in addition to XRD, TGA, FT-IR, SEM, and MAS NMR techniques. One of them precipitates from the reaction mixture in the form of fibers containing needlelike hexagonal crystals with the unit-cell parameters a = 21.105(4) Å and c = 9.112(2) Å ( V = 3515(1) Å 3 ). The crystalline structure comprises hexagonally packed catena Al[OP(O)(OC 2 H 5 ) 2 ] 3 chains. The other ones form a colloidal dispersion of spherical nanoparticles that consist of a boehmite core covered by aluminodiethylphosphate chains. The NMR studies of the reaction mixture indicate that water soluble aluminophosphate species are also formed in the systems studied. These species are suggested to act as nutrients for the growth of aluminophosphate structures. Colloidal particles and fibers have been included into the polyurethane matrix by in situ polyaddition. The SEM images of the composites surface cross-section shows that spherical nanoparticles are homogeneously distributed in the polymers, whereas fibers tend to agglomerate. Some mechanical reinforcement of the surface of polyurethanes has been accomplished as indicated by the abrasive wear test and AFM images.