Synthesis and molecular structure of [Ti4(OPri)8(µ,η2-OCH2CHCHCH2O)2(µ3,η2-OCH2CHCHCH2O)2]. Application to the elaboration of low density, microcellular, doped organic materials

Abstract

The reaction between Ti(OPrⁱ)₄ and cis-but-2-ene-1,4-diol [HOCH₂CHCHCH₂OH] in 1∶1 stoichiometry at room temperature gave [Ti₄(OPrⁱ)₈(µ,η²-OCH₂CHCHCH₂O)₂(µ₃,η²-OCH₂CHCHCH₂O)₂] 1 which was characterized by single crystal X-ray diffraction. Its molecular structure consists of an open-shell tetranuclear polyhedron with terminal isopropoxide ligands while the unsaturated diolates act as bridging-chelating ligands assembling five- and six-coordinated metals. The Ti–O bond lengths are in the range 1.77(1)–2.12(1) Å with Ti–OPrⁱ<Ti–η²-OC₆H₄O<Ti–µ-OC₆H₄O. Compound 1 was used for doping polystyrene foams elaborated by a emulsion/polymerization (w/o) process with traces of titania. Microcellular polystyrene foams with a low density (0.048–0.055 g cm^–3) doped with titania (0.72–1.5 Ti wt%) have been obtained. The influence of a number of parameters such as the nature of the radical initiator, of the precursor, of an electrolyte and of the amount of surfactant, on the properties of the foams has been evaluated. The influence of various polymerizable ligands, but-2-ene-1,4-diolate, 2-(methacryloyloxy)ethyl acetoacetate and 3-allyloxy-1,2-propanediolate, has been investigated. The results indicate the first of these to give the best results. The precursors were characterized by FTIR, ¹H NMR, elemental analysis and the foams by IR, elemental analysis, SEM/EDX and compressibility measurements.