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Issue 43, 2009
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Understanding the physico-chemical properties of polyhedral oligomeric silsesquioxanes: a variable temperature multidisciplinary study

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Abstract

This work is focused on a multidisciplinary study of a completely condensed octaisobutyl-silsesquioxane (IBUPOSS) as a model of the alkyl POSS family. IBUPOSS is characterized by the presence of eight isobutyl groups bonded to the corners of the siliceous framework. Differential scanning calorimetric measurements and an innovative simultaneous in situ Raman/XRPD experiment suggested that IBUPOSS undergoes a solid phase transition around 330 K, and indicated that this transition is related to a change in the conformational freedom of the isobutyl chains. The X-ray powder diffraction (XRPD) pattern of the high temperature phase was indexed in the high symmetry [R[3 with combining macron]m] space group. The Raman data indicated a larger mobility of the aliphatic side chains at high temperature, thus inducing a disorder in the IBUPOSS moiety. Multidimensional heteronuclear solid-state NMR experiments were employed to probe the structural and motional features of the observed phase transition. The various conformations can be accounted for by a pseudo-D3h symmetry able to obey to the [R[3 with combining macron]m] space group. Simulations on molecular mechanics and dynamics, together with quantum-chemical calculations, confirmed this hypothesis and gave some hints on the conformational mobility and the energetic features of IBUPOSS, a base material with relevant applications in catalysis and polymer science.

Graphical abstract: Understanding the physico-chemical properties of polyhedral oligomeric silsesquioxanes: a variable temperature multidisciplinary study

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Supplementary files

Article information


Submitted
06 Jul 2009
Accepted
25 Aug 2009
First published
16 Sep 2009

Phys. Chem. Chem. Phys., 2009,11, 10087-10094
Article type
Paper

Understanding the physico-chemical properties of polyhedral oligomeric silsesquioxanes: a variable temperature multidisciplinary study

G. Croce, F. Carniato, M. Milanesio, E. Boccaleri, G. Paul, W. van Beek and L. Marchese, Phys. Chem. Chem. Phys., 2009, 11, 10087
DOI: 10.1039/B913246E

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