Modifying the Structure and Dynamics of Ionomers through Counterion Sterics
Modifying the Structure and Dynamics of Ionomers through Counterion Sterics
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DOI：
10.1021/acs.macromol.9b02116
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发表时间：
2020-03-10
期刊：
影响因子：
5.5
通讯作者：
Coughlin, E. Bryan
中科院分区：
文献类型：
--
作者：
Enokida, Joshua S.;Hu, Weiguo;Coughlin, E. Bryan
采用一系列对称的四烷基铵抗衡离子，以钠（Na）为对照，研究了抗衡离子对低玻璃化转变温度、无定形聚（异戊二烯-苯乙烯磺酸盐）共聚物的结构和动力学的影响.通过用改进的硬球模型拟合共聚物的X射线散射曲线，实现了对聚集体结构的详细分析。增加从Na到TEA的反立体导致聚集体的轻微变化，其中一些离子基团存在于异戊二烯基质中。对于更受阻的TPA和TBA抗衡离子，发生了相当大的破坏的结构。使用固态NMR，动态力学分析，和流变学，共聚物的动力学上的反立体的效果进行了测定。的T-1 p，松弛的共聚物揭示了刚性异戊二烯馏分，与离子簇，和一个移动的异戊二烯基体馏分。具有较大抗衡离子的共聚物表现出在高频率下的动态模量的增加和在低频率下的动态模量的减少，除了具有更快的分子动力学。这两个观察结果归因于异戊二烯基质中离子基团的掺入增加和偶极-偶极相互作用的筛选。
The role of counterion sterics on the structure and dynamics of a low glass transition temperature, amorphous poly(isoprene-ran-styrenesulfonate) copolymer was investigated using a series of symmetric, tetraalkylammonium counterions with methyl (TMA), ethyl (TEA), propyl (TPA), and butyl (TBA) pendent groups, in addition to a sodium (Na) control. A detailed analysis of the aggregate structure was achieved by fitting the copolymers' X-ray scattering profiles with a modified hard sphere model. Increasing the counterion sterics from Na to TEA resulted in slight changes to the aggregates with some ionic groups present in the isoprene matrix. For the more hindered TPA and TBA counterions, considerable disruption of the structure occurred. Using solid-state NMR, dynamic mechanical analysis, and rheology, the effect of the counterion sterics on the copolymer's dynamics was determined. The T-1p, relaxation of the copolymers revealed a rigid isoprene fraction, associated with the ion clusters, and a mobile isoprene matrix fraction. Copolymers with larger counterions exhibited an increase in the dynamic moduli at high frequency and a decrease in the dynamic moduli at lower frequencies in addition to possessing faster molecular dynamics. These two observations are attributed to an increased incorporation of ionic groups into the isoprene matrix and screening of the dipole-dipole interactions.