Atomistic packing model and free volume distribution of a polymer with intrinsic microporosity (PIM-1)
Atomistic packing model and free volume distribution of a polymer with intrinsic microporosity (PIM-1)
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DOI：
10.1016/j.memsci.2008.02.038
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发表时间：
2008-06-20
影响因子：
9.5
通讯作者：
Hofmann, Dieter
中科院分区：
文献类型：
--
作者：
Heuchel, Matthias;Fritsch, Detlev;Hofmann, Dieter
PIM-1是一种新型聚合物，属于“本征微孔聚合物”（PIM），本文建立了PIM-1的原子堆积模型。PIM-1的分子结构包含刚性梯形聚合物结构内的扭曲位点（螺环中心）。氮吸附实验表明，在玻璃态下捕获大量互连自由体积的聚合物在许多方面表现得像微孔材料。通过基于力场的分子力学和分子动力学方法获得的模型允许预测小气体的渗透性质，在77 K下的N（2）-吸附等温线的计算，和自由体积分布的测定。采用Gusev-Suter过渡态理论（TST）计算了He、H（2）、Ar、O（2）、N（2）、CH（4）和N2的气体溶解度和扩散系数。结果表明，该吸附等温线与实验数据（因子1-4）吻合较好，表明该吸附等温线具有微孔材料的典型吸附特性。得到的微孔体积与相应的实验值吻合良好。从模型中得到的自由体积元素的尺寸分布函数在5-15埃的孔隙宽度范围内与从实验吸附数据得到的结果吻合得很好，并与Horvath-Kawazoe方法分析。在骨干二面角分布揭示了一定的，意想不到的灵活性之间的螺旋中心，作为连接链接的平面段。(C)2008 Elsevier B. V.保留所有权利。
Atomistic packing models have been built for PIM-1, a polymer belonging to a recently developed new type of "polymers of intrinsic microporosity" (PIMs). The molecular structure of PIM-1 contains sites of contortion (spiro-centres) within a rigid ladder polymer structure. Nitrogen sorption experiments have shown that the polymer, which traps in the glassy state a large amount of interconnected free volume, behaves in many respects like a microporous material. The models obtained by force field-based molecular mechanics and molecular dynamic methods allow a prediction of permeation properties of small gasses, the calculation of N(2)-sorption isotherms at 77 K, and a determination of free volume distributions. The Gusev-Suter transition state theory (TST) was used to calculate gas solubility and diffusion coefficients for He, H(2), Ar, O(2), N(2), CH(4), and Xe. Good agreement with experimental data (factors 1-4) was found. The calculated nitrogen adsorption isotherm at 77 K shows properties typical for sorption on microporous materials. The obtained microporous volume is in good agreement with the respective experimental value. The size distribution function of free volume elements derived from the models agrees well in its range of pore width of 5-15 angstrom with results obtained from experimental sorption data and analyzed with the Horvath-Kawazoe method. Dihedral angle distributions in the backbone reveal a certain, unexpected flexibility of plane segments between the spiro-centres which act as connecting links. (C) 2008 Elsevier B.V. All rights reserved.