Synthesis And Characterization Of Functionalized Polyhedral Oligomeric Silsesquioxanes (POSS) And The Properties Of Their Epoxy Composites

In this thesis, the incompletely closed heptameric siloxane ((C5H9)7Si7O12(OH)3) was synthesized by the controlled hydrolysis of cyclopentyltrichlorosilane (C5H9SiCl3). The condensation of heptameric siloxane and phenyltrichlorosilane (C6H5SiCl3) produced the closed 1-phenyl-3,5,7,9,11,13,15-heptacyclopentylpentacycol-[9.5.1.13.9.15,15.17.13]octasiloxane (POSS 1), which was functionalized with a nitryl to form POSS 2 (1-(2(4)-nitrylphenyl)-3,5,7,9,11,13,15-heptacyclopentylpentacycol-[9.5.1.13.9.15,15.17.13]octasiloxane). And POSS 2 was reduced to POSS 3 (1-(2(4)-aminophenyl)-3,5,7,9,11,13,15-heptacyclopentylpentacycol-[9.5.1.13.9.15,15.17.13]octasiloxane) which was a POSS-amine. The structure of the three novel POSSs were characterized by FTIR,1HNMR,13CNMR,29SiNMR. The crystal structure of the three novel POSS were determined by Wide-Angle X-ray Diffraction (WAXD). And their diffraction lines were indexed by Ito method and trial method, respectively. The indexing results showed that all the crystal belong to the rhombohedral system with simple lattice. All the cell parameters of the three POSSs were listed as below: POSS 1: a=16.9422 ?, c=17.7804 ?, V=4419.9 ?3; POSS 2, a=16.9449 ?, c=17.7059 ?, V=4402.80 ?3; POSS 3, a=16.9498 ?, c=17.7907 ?, V=4426.44?3. The structure of every POSS is equivalent to a hexagonal unit cell with parameters of POSS 1, a=11.4370 ?, α=95.58°, V=1473.27 ?3; POSS 2, a=11.4255?, α=95.72°, V=1467.57?3; POSS 3, a=11.4429?, α=95.57°, V=1475.48?3.A series of diglycidyl ether of bis phenol A epoxy (DGEBPA) blends with nonfuncitonalized-POSS, POSS 1, were prepared by solution casting and then curing, while the composites of epoxy/functionalized-POSS, POSS 3, 4 (1-(3'-aminopropyl)-3,5,7,9,11,13,15-heptacyclohexylpentacycol-[9.5.1.13.9.15,15.17.13]octasiloxane) were prepared by solution grafting and then curing. The miscibility of POSS and epoxy was determined by WAXD. The functionalized POSS, POSS 3 and POSS 4, incorporated into the epoxy network are well dispersed in the composite, probably on the molecular scale, even at high POSS content (15 phr), while the nonfunctionalized POSS, POSS 1, was dispersed as crystallite. The thermal properties of the blends and composites were studied by DSC. The FTIR spectra were used to investigate the structure-property relationship of these blends and composites, and the Tg enhancement mechanism is discussed in detail. The bending storage modulus, E', and bending tanδ were investigated by DMTA. The bending storage modulus, E' of epoxy/POSS 3 and epoxy/POSS 4 at T < Tg decline as the content of POSS increasing and are all less than the neat epoxy. At T > Tg, the bending storage modulus, E', are much higher than the neat epoxy and the more the POSS content, the higher the E'. The tanδpeak intensity of the three epoxy/POSS decline as the content of POSS in the system increasing. But the width of the tanδpeak are all the same.