Molecular simulation on structure-property relationship of polyimides with methylene spacing groups in biphenyl side chain
Molecular simulation on structure-property relationship of polyimides with methylene spacing groups in biphenyl side chain
复制标题
联苯侧链亚甲基间隔基团聚酰亚胺构效关系的分子模拟
DOI：
10.1016/j.commatsci.2006.10.019
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发表时间：
2007-06-01
影响因子：
3.3
通讯作者：
Gu, Yi
中科院分区：
文献类型：
--
作者：
Pan, Rui;Liu, Xikui;Gu, Yi
在我们的早期研究中，通过对联苯侧链上具有不同亚甲基间隔基团但具有相同主链的三种合成聚酰亚胺（PP0DA-PI、PP2DA-PI和PP6DA-PI）的实验表明，联苯侧链上具有六个亚甲基间隔基团的PP6DA-PI比不具有亚甲基间隔基团的PP0DA-PI和联苯侧链上具有两个亚甲基间隔基团的PP2DA-PI具有更低的特性粘度、密度和玻璃化转变温度，但保持了联苯侧链上具有两个亚甲基间隔基团的PP2DA-PI的特性粘度、密度和玻璃化转变温度。机械性能与 PP0DA-PI 和 PP2DA-PI 相当。本文的目的是解释亚甲基间隔基团的添加导致聚酰亚胺性能的多样性；采用分子力学和分子动力学技术生成合理的分子模型，建立聚酰亚胺的结构-性能关系。获得了许多有趣的结果，如下所示。链构象建模表明，PP0DA-PI中的联苯侧基几乎垂直于主链，而PP6DA-PI中的联苯侧基几乎平行于主链，这表明PP6DA-PI表现出强烈的链内相互作用，导致主链和侧链之间的原位增强相互作用，通过联苯侧链中两个苯基的电荷密度、偶极矩和力电流特性验证。 PP6DA-PI中的这种增强，原有的模量得到了一定程度的提高。同时，虽然由于二胺单体的N原子上的电荷密度较高，PP6DA的反应性更强，但侧链的本体结构阻碍了单体的聚合过程，导致PP6DA-PAA的特性粘度较低。由于该系统中侧链弯曲，PP6DA-PI 的密度不会随着链长的增加而过度降低。此外，利用构象网格扫描，势能等值线图表明，联苯侧链中亚甲基间隔基团的添加降低了主链同步旋转键的能垒，从而降低了PP6DA-PI的玻璃化转变温度。 (C) 2006 Elsevier B.V. 保留所有权利。
In our early research, the experiment of three synthesized polyimides (PP0DA-PI, PP2DA-PI and PP6DA-PI) with different methylene spacing groups in biphenyl side chain but with the same backbone reveals that the PP6DA-PI with six methylene flexible spacing groups in biphenyl side chain has lower intrinsic viscosity, density and glass transition temperature than those of the PP0DA-PI without methylene spacing group and PP2DA-PI with two methylene spacing groups in biphenyl side chains but keeps the mechanical property to that of the PP0DA-PI and PP2DA-PI. The aim of this paper is to explain the addition of the methylene spacing groups leading to the diversity of polyimide's properties; molecular mechanics and molecular dynamics techniques were adapted to generate reasonable molecular models to establish the structure-property relationship of polyimide. Lots of interesting results have been obtained as follows. The modeling of chain conformation shows that the biphenyl side groups in PP0DA-PI are almost vertical to the backbone, whereas the biphenyl side groups in PP6DA-PI are almost parallel to the backbone indicating that PP6DA-PI exhibits a strong intra-chain interaction leading to in situ reinforcement interaction between the main chain and the side chain validated by the charge density, dipole moment and force current property of the two phenyls in biphenyl side chains. For this reinforcement in PP6DA-PI, the original modulus has been enhanced to some extent. Meanwhile, though the PP6DA would be more reactive due to higher charge density on N atom of the diamine monomer, the bulk structure of the side chain hindering the polymerization approach of the monomers leads to lower intrinsic viscosity of PP6DA-PAA. The density of PP6DA-PI does not decrease excessively with respect to the increase in chain length because of the bended side chain in this system. Furthermore, using conformational grid scan, potential energy contour map illuminates that the addition of the methylene spacing group in biphenyl side chain decreases the energy barrier in synchronous rotational bonds of the backbone resulting in lower glass transition temperature of PP6DA-PI. (C) 2006 Elsevier B.V. All rights reserved.