Understanding the physico-chemical properties of polyhedral oligomeric silsesquioxanes: a variable temperature multidisciplinary study
Understanding the physico-chemical properties of polyhedral oligomeric silsesquioxanes: a variable temperature multidisciplinary study
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DOI：
10.1039/b913246e
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发表时间：
2009-01-01
影响因子：
3.3
通讯作者：
Marchese, Leonardo
中科院分区：
文献类型：
--
作者：
Croce, Gianluca;Carniato, Fabio;Marchese, Leonardo
这项工作的重点是一个完全缩合的八异丁基倍半硅氧烷（IBUPOSS）作为烷基POSS家族的模型的多学科研究。IBUPOSS的特征在于存在键合到硅质骨架的角上的八个异丁基。差示扫描量热法测量和创新的同时在原位拉曼/XRPD实验表明，IBUPOSS经历了固相转变约330 K，并表示，这种转变是有关的异丁基链的构象自由的变化。高温相的X射线粉末衍射（XRPD）图谱在高对称性[R（3）over barm]空间群中进行了索引。的拉曼数据表明在高温下的脂肪族侧链的更大的流动性，从而诱导在IBUPOSS部分的无序。多维异相固体核磁共振实验被用来探测所观察到的相变的结构和运动特征。各种构象可以由伪D-3 h对称性来解释，该对称性能够服从[R（3）over barm]空间群。分子力学和动力学的模拟，连同量子化学计算，证实了这一假设，并给出了一些提示的构象流动性和能量的特点IBUPOSS，一个基础材料与相关的应用在催化和聚合物科学。
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) over barm] 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-D-3h symmetry able to obey to the [R (3) over barm] 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.