Department of Chemistry, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
J Chem Phys. 2013 May 21;138(19):194907. doi: 10.1063/1.4804654.
Polymer backbone dynamics of single ion conducting poly(ethylene oxide) (PEO)-based ionomer samples with low glass transition temperatures (T(g)) have been investigated using solid-state nuclear magnetic resonance. Experiments detecting (13)C with (1)H decoupling under magic angle spinning (MAS) conditions identified the different components of the polymer backbone (PEO spacer and isophthalate groups) and their relative mobilities for a suite of lithium- and sodium-containing ionomer samples with varying cation contents. Variable temperature (203-373 K) (1)H-(13)C cross-polarization MAS (CP-MAS) experiments also provided qualitative assessment of the differences in the motions of the polymer backbone components as a function of cation content and identity. Each of the main backbone components exhibit distinct motions, following the trends expected for motional characteristics based on earlier Quasi Elastic Neutron Scattering and (1)H spin-lattice relaxation rate measurements. Previous (1)H and (7)Li spin-lattice relaxation measurements focused on both the polymer backbone and cation motion on the nanosecond timescale. The studies presented here assess the slower timescale motion of the polymer backbone allowing for a more comprehensive understanding of the polymer dynamics. The temperature dependences of (13)C linewidths were used to both qualitatively and quantitatively examine the effects of cation content and identity on PEO spacer mobility. Variable contact time (1)H-(13)C CP-MAS experiments were used to further assess the motions of the polymer backbone on the microsecond timescale. The motion of the PEO spacer, reported via the rate of magnetization transfer from (1)H to (13)C nuclei, becomes similar for T≳1.1 T(g) in all ionic samples, indicating that at similar elevated reduced temperatures the motions of the polymer backbones on the microsecond timescale become insensitive to ion interactions. These results present an improved picture, beyond those of previous findings, for the dependence of backbone dynamics on cation density (and here, cation identity as well) in these amorphous PEO-based ionomer systems.
使用固态核磁共振研究了具有低玻璃化转变温度 (T(g)) 的聚（氧化乙烯）（PEO）基离聚物样品中单个离子的聚合物主链动力学。在魔角旋转 (MAS) 条件下检测 (1)H 去耦的 (13)C 的实验确定了聚合物主链的不同组成部分（PEO 间隔基和间苯二甲酸酯基团）及其相对迁移率，这些实验是针对一系列具有不同阳离子含量的含锂和含钠离聚物样品进行的。变温（203-373 K）（1）H-(13)C 交叉极化 MAS（CP-MAS）实验也定性评估了聚合物主链组成部分的运动随阳离子含量和种类的变化差异。每个主要的主链组成部分都表现出不同的运动，这与基于早期准弹性中子散射和（1）H 自旋晶格弛豫率测量的运动特性趋势一致。之前的（1）H 和（7）Li 自旋晶格弛豫测量主要集中在聚合物主链和纳米秒时间尺度上的阳离子运动上。本文介绍的研究评估了聚合物主链较慢的时间尺度运动，从而可以更全面地了解聚合物动力学。（13)C 线宽的温度依赖性用于定性和定量研究阳离子含量和种类对 PEO 间隔基迁移率的影响。使用可变接触时间（1）H-(13)C CP-MAS 实验进一步评估了微秒时间尺度上聚合物主链的运动。通过从（1）H 到（13)C 核的磁化转移速率来报告 PEO 间隔基的运动，在所有离子样品中，当 T≳1.1 T(g) 时，其运动变得相似，这表明在相似的升高的约化温度下，微秒时间尺度上聚合物主链的运动对离子相互作用不敏感。这些结果提供了一个比以前的发现更完善的图像，说明了在这些无定形 PEO 基离聚物系统中，聚合物动力学对阳离子密度（这里还有阳离子种类）的依赖性。
