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

聚碳酸酯链堆积和动力学的固态核磁共振分析

• 批准号: 0451685
• 负责人: Jacob Schaefer
• 金额: $ 42万
• 依托单位: Washington University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-03-15 至 2009-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0451685&HistoricalAwards=false
• 关键词: Solid; State; NMR; Analysis; Chain

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.

旋转回波双共振(REDOR)固态核磁共振将被用来确定聚碳酸酯中链的局部堆积，这是目前工程应用中的典型应用。手头有十种聚碳酸酯，标签位置不同，有2H、13C和19F。REDOR将被用来测量这些标记聚碳酸酯的各种均匀混合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其邻近的环、异丙基和碳酸盐进行定位。初步的REDOR实验已经证实了这种方法用于确定聚碳酸酯链式堆积的局部有序性的可行性。对于REDOR所检测的相同聚碳酸酯，将使用仅中心带交换检测(CODEX)来表征在300K下具有机械重要性的1-100赫兹频率范围内的分子运动细节。在标准的CODEX实验中，自旋相干性是由作用于13C化学位移张量的转子同步脉冲产生的。如果相干性是由作用在异核偶极张量上的脉冲产生的，那么REDOR实验和CODEX实验的结果是直接相关的。智力上的功绩。旋转回波双共振(REDOR)在魔角旋转条件下精确测量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(如2H和13C)专门标记两种可混溶聚合物，那么13C{2H}REDOR可以用来确定链间距离和取向，这定义了局部链堆积。混合是在高浓度下观察到的核和在低浓度下退相的核进行的，因此用简单的成对耦合之和来解释Redor的结果。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，将聚碳酸酯玻璃中机械上重要的慢动作识别为属于特定类型的包装布置。这一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。含有偶氮苯侧链的高Tg无定形聚酯正在几个材料实验室进行测试，用于(可擦除)全息光学数据存储。这些聚酯在线偏振光照射下具有二向色性(各向异性吸收)和双折射(各向异性折射)特性。侧链的易序性和双轴双折射的观察表明，主链填料中的优先局部有序是重要的。聚碳酸酯是很好的数据存储薄膜候选材料。它们具有机械韧性，具有较高的玻璃化转变温度，可以与光敏侧链合成，并在主链堆积中表现出局部有序。REDOR和CODEX对它们的包装和动力学的表征应该有助于开发新的数据存储材料。聚合物和材料科学是向社区宣传现代技术的好话题。例如，聚合物是直观的，不需要了解结构生物学所必需的背景知识。该协会是圣路易斯K-8科学教师正式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。他将质谱学和核磁共振的基本思想应用到塑料(尤其是抗冲击聚碳酸酯)等熟悉的物体上。材料科学对本科生和毕业生也很有吸引力。PI将包括建议的聚合物工作的本科生，并将培训研究生和博士后使用聚碳酸酯-核磁共振问题，以提供丰富的仪器，理论和现代固态核磁共振的实际应用经验的组合。