Looking for new hybrid polymer fillers: Synthesis of nanosized alfa-type Zr(IV) organophosphonates through an unconventional topotactic anion exchange reaction

Gels of alfa-type zirconium(IV) phosphate alkylphosphonates, ZP(C n)x, were prepared by reacting, at room temperature, propanol intercalated nanosized alfa-zirconium phosphate (?-ZrP) with propanol solutions of alkylphosphonic acids (H2Cn, n = number of carbon atoms in the alkyl chain = 4, 5, 6), with (H2C n/Zr) molar ratios in the range 0.4-4.0. 31P MAS NMR showed the presence of resonances due to the phosphate and phosphonate groups bonded to the Zr atoms mainly by three oxygen atoms, as in the ?-type layer. The composition of the ZP(Cn)x materials, obtained by thermogravimetric analysis, ranges from x ? 0.2 to x ? 1.1. On the basis of the NMR data and of the analysis of the X-ray patterns of gels and powders, it is inferred that the ZP(Cn)x compounds have an ?-type layered structure and that the reaction between alfa-ZrP and H2Cn is a topotactic anion exchange process. The evolution of the X-ray patterns during propanol deintercalation is consistent with a random distribution of the alkylphosphonate groups on the ?-type layers which gives rise to porous pathways in the interlayer region. To test the possibility of using ZP(Cn)x as mechanical reinforcement of a polymer matrix, a starch membrane filled with 5 wt % ZP(C6) 0.54 was prepared and characterized by stress-strain mechanical tests. Besides an excellent flexibility, this membrane exhibited a proportional increase of the Young's modulus by 230% in comparison with neat starch.