Solid-State NMR Analysis of Chain Packing and Dynamics in Polycarbonates

旋转回声双共振（REDOR）固态核磁共振将用于确定聚碳酸酯中典型的链的局部填充，目前用于工程应用。十种聚碳酸酯在不同位置的2H， 13C和19F标签。REDOR将用于测量这些标记聚碳酸酯的各种均匀共混物中的特定异核距离。这些REDOR实验将允许一个聚碳酸酯的环和侧链相对于它的环、异丙烯和相邻的碳酸盐进行定位。初步的REDOR实验证实了该方法在聚碳酸酯链式填料中确定局部顺序的可行性。仅中心带交换检测（CODEX）将用于表征在机械重要的1-100 Hz频率范围内300 K下由REDOR检测的相同聚碳酸酯的运动分子细节。在标准CODEX实验中，自旋相干性是由转子同步脉冲作用于13C化学位移张量产生的。如果相干性是由作用于异核偶极张量的脉冲产生的，那么REDOR和CODEX实验的结果是直接相关的。知识价值。旋转回声双共振（REDOR）精确测量了魔角自旋条件下偶极耦合自旋对之间的异核距离。如果用不同的稳定同位素（例如2H和13C）标记两种可混溶聚合物，则13C{2H} REDOR可用于确定链间距离和取向，从而确定局部链的排列。混合是用高浓度的观察核和低浓度的脱相核来完成的，这样REDOR结果就可以用成对耦合的简单求和来解释。距离的分布是必需的，但不是特定的包装模型。在同一实验中，使用REDOR和CODEX相结合的方法确定聚碳酸酯玻璃中机械上重要的缓慢运动属于特定类型的包装安排。这种新方法将是实现将玻璃聚合物的分子性质与其宏观行为联系起来的长期目标的重要一步。更广泛的影响。一些材料实验室正在研究含有偶氮苯侧链的高tg非晶聚酯用于（可擦除的）全息光学数据存储。当被线偏振光照射时，这些聚酯具有二向色性（各向异性吸收）和双折射性（各向异性折射）。侧链排序的容易性和双轴双折射的观察表明，在主链排列中，预先的局部排序是重要的。聚碳酸酯是数据存储薄膜的良好候选材料。它们具有机械韧性，高Tg，可以与光敏侧链合成，并且在主链填充中显示局部有序。REDOR和食品法典对其包装和动态特性的描述应有助于开发新的数据存储材料。聚合物和材料科学是很好的话题，可以用来向社会宣传现代技术。聚合物是直观的，不需要必要的背景来理解结构生物学，例如。PI是圣路易斯K-8科学教师正规教育培训计划的积极参与者，并计划在未来四年继续这一努力。他将质谱和核磁共振的基本思想应用于熟悉的物体，比如塑料（尤其是耐冲击的聚碳酸酯！）材料科学对本科生和研究生也很有吸引力。PI将包括本科生在提出的聚合物工作，并将培训研究生和博士后学生使用聚碳酸酯核磁共振问题，提供仪器，理论和现代固态核磁共振实际应用经验的丰富组合。

Rotational-echo double resonance (REDOR) solid-state NMR will be used to determine the local packing of chains in polycarbonates typical of those currently used in engineering applications. Ten polycarbonates are on hand with differently positioned 2H, 13C, and 19F labels. REDOR will be used to measure specific heteronuclear distances in a variety of homogeneous blends of these labeled polycarbonates. These REDOR experiments will allow the rings and sidechains of one polycarbonate to be located relative to the rings, isopropylidenes, and carbonates of its neighbors. Preliminary REDOR experiments have confirmed the feasibility of this approach for the determination of local order in polycarbonate chain packing.Centerband-only detection of exchange (CODEX) will be used to characterize the molecular details of motion in the mechanically important 1-100 Hz frequency regime at 300 K for the same polycarbonates examined by REDOR. In the standard CODEX experiment, spin coherence is created by rotor-synchronized pulses acting on a 13C chemical shift tensor. If the coherence is instead created by pulses acting on a heteronuclear dipolar tensor, then the results of REDOR and CODEX experiments are directly correlated. Intellectual Merit. Rotational-echo double resonance (REDOR) measures accurately heteronuclear distances between dipolar-coupled spin pairs under magic-angle spinning conditions. If two miscible polymers are specifically labeled with different stable isotopes (2H and 13C, for example), then 13C{2H} REDOR can be used to determine interchain distances and orientation, which define local chain packing. The blending is done with the observed nucleus at high concentration and the dephasing nucleus at low concentration so that the REDOR results are interpreted in terms of simple sums of pair-wise couplings. Distributions of distances are required but not specific packing models. The mechanically important slow motions in a polycarbonate glass are identified as belonging to a specific type of packing arrangement using a combination of REDOR and CODEX in the same experiment. This new approach will be an important step in reaching the long-term goal of connecting the molecular properties of glassy polymers with their macroscopic behavior.Broader Impact. High-Tg amorphous polyesters containing azobenzene sidechains are being examined in several materials laboratories for use in (eraseable) holographic optical data storage. These polyesters have dichroic (anisotropic absorption) and birefringent (anisotropic refraction) properties when illuminated by linearly polarized light. The ease of ordering of sidechains and the observation of biaxial birefringence suggest that prior local order in mainchain packing is important. Polycarbonates are good candidates for data-storage thin films. They are mechanically tough, have high Tg's, can be synthesized with photosensitive sidechains, and show local order in mainchain packing. The characterization of their packing and dynamics by REDOR and CODEX should help in the development of new data-storage materials.Polymers and materials science are good topics to use in reaching out to inform the community about modern technology. Polymers are intuitive and do not require the background necessary to understand structural biology, for example. The PI is an active participant in a formal education training program for St. Louis K-8 science teachers and plans to continue this effort for the next four years. He applies the basic ideas of mass spectrometry and nuclear magnetic resonance to familiar objects like plastics (especially impact-resistant polycarbonates!). Materials science is also attractive to undergraduates and graduates. The PI will include undergraduates in the proposed polymer work, and will train both graduate students and postdoctoral students using polycarbonate-NMR problems to provide a rich mix of instrumentation, theory, and experience in practical applications of modern solid-state NMR.