[Li‐Si‐O]‐MFI: A New Microporous Lithosilicate with the MFI Topology.

Abstract

Structure Structure D 2000 [Li-Si-O]-MFI: A New Microporous Lithosilicate with the MFI Topology. -The lithosilicate of title is prepared hydrothermally from LiOH, Si(O-Me) 4 , and Pr 4 NOH (autoclave, 175°C, 7 d).[Li-Si-O]-MFI crystallizes in the orthorhombic space group P212121 and is a framework zeolite related to ZSM-5 with a Li/Si ratio of 4:92. Single-crystal synchrotron X-ray diffraction data, 29 Si NMR, and IR spectroscopy indicate that Li is randomly distributed over the framework sites. In addition, Li occupies ordered positions on extraframework sites that are occluded in voids outlined by the double five-or six-membered rings. The strong interaction between the extraframework Li cations and the negatively charged framework may be responsible for the distortion of the lattice from Pnma, the usual symmetry associated with as-synthesized members of the MFI-family, to its subgroup symmetry P2 1 2 1 2 1 . -(PARK, S.-H.; LIU, H.; KLEINSORGE, M.; GREY, C. P.; TOBY, B. H.; PARISE*, J. B.; Chem. Mater. 16 (2004) 13, 2605-2614; Dep. Geosci., State Univ. N. Y., Stony Brook, NY 11794, USA; Eng.) -Schramke 35-010

Hyperbranched Polysiloxanes Based on Polyhedral Oligomeric Silsesquioxane Cages with Ultra-High Molecular Weight and Structural Tuneability

“…The structural feature of crystal 1 sheds light into the structure of polymer 1 . As shown in Figure 2 , the cyclopentasiloxane rings on the side of POSS cage in crystal 1 are all significantly distorted to one direction presumably due to the crowded surface of the POSS cage, and therefore the cyclopentasiloxane ring in crystal 1 should be more constrained than regular ones [ 40 , 41 , 42 , 43 ]. In other words, there will be lesser chance for the polymer to close up and stop growing due to the crowded space, and this facilitates the formation of high MW polymers.…”