Intermolecular magnetic dipole-dipole-interaction in 1H NMR of polymer melts and intermolecular dynamic correlations in polymer chains

聚合物熔体 1H NMR 中的分子间磁偶极-偶极相互作用以及聚合物链中的分子间动态相关性

• 批准号: 238391017
• 负责人: Professor Dr. Siegfried Stapf
• 金额: --
• 依托单位: Russian Foundation for Basic Research
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2018-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/238391017?language=en
• 关键词: Intermolecular; magnetic; dipole; interaction; 1H

The dynamics of polymers in the melt has been explained for several decades by two complementary models, the Rouse ansatz and the reptation model. They describe the interactions in the limiting cases of short and long chains, respectively, where the transition occurs at the onset of entanglements. The mean squared displacement (MSD) of individual segments is frequently employed as a suitable parameter for these dynamics, with the segments themselves being assumed as abstract units – internal rotations and vibrations occur on much shorter timescales and are not covered by the mentioned models.The MSD is directly accessible by, for instance, NMR field gradient methods or neutron scattering, and the theoretical predictions, i.e. the characteristic time dependences, were confirmed repeatedly, so that Rouse and reptation models are considered as satisfactory descriptions. In addition, indirect methods exist which determine related quantities, first and foremost one needs to mention NMR relaxation which has successfully been employed in polymer melt studies for about 30 years. Only during recent years methods have been developed that are able to separate between intra- and intermolecular dipolar interactions of the chain molecules by making use of isotopic dilution in deuterated polymers. While this approach initially served only the purpose to isolate the MSD from relaxation data, it does contain valuable information about long-range dynamic correlations in the melt which is insufficiently described by the classical models. In the context of these studies, systematic deviations from the predictions of the reptation model have been found, first in NMR relaxometry, later also by alternative methods, in particular by analysis of echo decay functions within the first period of this research project. Specifically, we have found, for three chemically different polymers of high molecular weight, a contribution of the intermolecular interaction that is clearly at variance with reptation theory and suggests the validity of isotropic dynamic models rather than reptation which assumes the existence of a – on a certain timescale – rigid tube. In the planned continuation of this project, we would like to cover a broad range of combinations of molecular weights and temperatures as well as boundary conditions (confinement) for poly (ethylene oxide) as a suitable model polymer; with this approach we want to verify our earlier findings and deepen our understanding of polymer dynamics. To this end, we also employ deuteron and possibly carbon relaxation studies. The project will be accompanied by Prof. Nail Fatkullin who will further refine the theoretical description – for instance by specifically computing the dynamics of chain ends, or by addressing the temporal evolution during encoding periods of NMR experiments – and who will support the choice of optimized experimental parameters for allowing discrimination between concurring model approaches.

几十年来，熔体中聚合物的动力学一直由两个互补的模型来解释，即Rouse模型和爬行模型。他们分别描述了短链和长链极限情况下的相互作用，其中转变发生在纠缠开始时。单个段的均方位移（MSD）经常被用作这些动力学的合适参数，其中段本身被假定为抽象单元-内部旋转和振动发生在短得多的时间尺度上，并且不被所提到的模型所覆盖。MSD可以通过例如NMR场梯度方法或中子散射直接获得，并且理论预测，即特征时间依赖性，反复确认，因此Rouse和爬行模型被认为是令人满意的描述。此外，存在确定相关量的间接方法，首先需要提及已成功用于聚合物熔体研究约30年的NMR弛豫。仅在最近几年中，已经开发出能够通过利用氘代聚合物中的同位素稀释来分离链分子的分子内和分子间偶极相互作用的方法。虽然这种方法最初只服务的目的是从弛豫数据隔离的MSD，它确实包含有价值的信息，在熔体中的远程动态相关性是不够的经典模型描述。在这些研究的背景下，已经发现了爬行模型的预测的系统偏差，首先是在NMR弛豫测量中，后来也通过替代方法，特别是通过本研究项目的第一阶段内的回波衰减函数的分析。具体而言，我们已经发现，对于三种化学性质不同的高分子量聚合物，分子间相互作用的贡献，这显然是在与爬行理论的差异，并建议各向同性的动态模型，而不是爬行假设存在的一个-在一定的时间尺度-刚性管的有效性。在这个项目的计划延续中，我们希望涵盖广泛的分子量和温度的组合以及聚（环氧乙烷）作为合适的模型聚合物的边界条件（限制）;通过这种方法，我们希望验证我们早期的发现并加深我们对聚合物动力学的理解。为此，我们也采用氘和可能的碳弛豫研究。该项目将由Nail Fatkullin教授陪同，他将进一步完善理论描述-例如通过专门计算链端的动力学，或通过解决NMR实验编码期间的时间演变-并将支持优化实验参数的选择，以便区分并发模型方法。