Polyolefin Miscibility: New Insights from an Experimental Molecular Perspective

聚烯烃是一类经济上和技术上都很重要的材料。作为所有聚合物的一个子集，茂金属聚合物是众所周知的，但茂金属聚合催化的持续改进已经证明，通过共聚、共混和复合可以增强其物理性能。因此，聚烯烃及其混合物的应用范围广泛，从低成本的一次性食品包装到航空航天结构设计的多组分复合材料。在所有情况下，涉及的不仅仅是纯聚合物，这是大多数，共混或复合材料的形态和局部结构决定了材料的最终物理和性能特性。令人惊讶的是，聚烯烃共混物的第一原理混合规则并不为人所知，因为这些化学上简单的聚合物违反了溶解性和溶解度的惯例。知识价值。在分子或链水平上明显缺乏实验数据表明，块状聚烯烃混合物中的链结构/混相关系远未实现。固体核磁共振实验的微观到介观（即埃到几十纳米）长度尺度可以以非侵入性的方式解决这一缺陷。通过获取链特定数据（动力学和距离）来解决长期存在的关于链填充和链结构相对重要性的问题，可以检查每个在确定熵和焓对整体相行为的贡献方面的作用。更广泛的影响。围绕聚烯烃相行为的基本科学问题，特别是熔体或固体状态下的非晶态聚烯烃，影响深远，因为这些非极性、非晶体聚合物的混合物构成了大分子热力学的一个极限类别。因此，聚烯烃及其共混物是聚合物科学中一些长期问题实验研究的理想体系。例如，块状聚烯烃是浓缩体系，具有许多自由度。考虑到聚烯烃可能的不同链结构，分子内部和分子之间的不同自由度（合理引入动态异质性波动）是否可以确定并与相行为/相转变相关？非晶大分子相变的长度尺度和时间尺度，如液晶中的相变，已经在构型熵论证的背景下进行了描述。我们能否使用散装聚烯烃及其共混物，在局部链水平（1-10纳米）上提供非侵入性实验来证实这一观点？如果非相互作用分子中的玻璃形成是由构型熵损失驱动的，那么分子水平（小于聚合物的旋转半径）实验能否检测和定义局部Tg ？这些数据可以用来帮助扩大当前聚合物相行为的热力学模型的范围，以包括构型熵的贡献吗？通过这个项目，PI一直并将继续积极参与各级教育。该项目通过NCSU化学系的公共宣传主任的努力，在小学、初中和高中的场所展示了物理科学和聚合物科学的多个演示。此外，该项目的多学科方面（光谱学、高分子化学、高分子物理、材料科学）继续吸引着该系优秀的本科生和研究生。

Polyolefins comprise an economically and technologically important class of materials.As a subset of all polymers, they are in general well-known, but continuing improvements inmetallocene polymerization catalysis have demonstrated that enhanced physical properties areaccessible through copolymerization, blending, and composites. Consequently, polyolefins andtheir blends span the gamut of possible applications, ranging from low-cost disposable foodpackaging to multicomponent composites for aerospace structural design. In all cases involving more than just a pure polymer, which is the majority, the morphology and local structure of the blend or composite determines the final physical and performance properties of the material.Surprisingly, first-principle mixing rules for polyolefin blends are not known, as thesechemically simple polymers defy like dissolves like solubility conventions. Intellectual Merit. A conspicuous lack of experimental data at the molecular or chain levelsuggests that chain-structure/miscibility relationships in bulk polyolefin mixtures are far frombeing realized. The microscopic to mesoscopic (i.e. angstroms to tens of nanometers) lengthscales accessible by solids NMR experiments can address this deficiency in a non-invasivemanner. Through acquisition of the chain-specific data (dynamics and distance) needed toresolve long-standing questions about the relative importance of chain packing and chainarchitecture, the role of each in determining entropic versus enthalpic contributions to the overallphase behavior may be examined. Broader Impact. The fundamental scientific questions surrounding polyolefin phase behavior,particularly for amorphous polyolefins in the melt or solid states, are far reaching in thatmixtures of these nonpolar, noncrystalline polymers constitute a limiting class ofmacromolecular thermodynamics. As such, polyolefins and their blends are ideal systems for theexperimental study of some long-standing questions in polymer science. For example, bulkamorphous polyolefins are concentrated systems, with many degrees of freedom. Given thevarying chain architectures possible with polyolefins, can distinct degrees of freedom within andbetween molecules (rational introduction of dynamic heterogeneity fluctuations) be identifiedand related to phase behavior/phase transitions? The length-scale and time-scale of phasetransitions in amorphous macromolecules, like those in liquid crystals, have been described inthe context of configurational entropy arguments. Can we, using bulk polyolefins and theirblends, provide non-invasive experimental confirmation of this view at the local chain level (1-10 nm)? If glass formation in non-interacting molecules is driven by loss of configurationalentropy, can molecular level (less than the polymer radius of gyration) experiments detect anddefine local Tg's? Can this data be used to help broaden the scope of current thermodynamicmodels of polymer phase behavior to include configurational entropy contributions? The PI has been, and will continue to be, an active participant at all levels of educationthrough this project. The PI, whose efforts are leveraged through the public outreach director inthe NCSU chemistry department, has presented multiple demonstrations in physical science, andpolymer science, at elementary, middle, and high school venues. Moreover, themultidisciplinary aspect of this project (spectroscopy, polymer chemistry, polymer physics,materials science) continues to attract top undergraduate and graduate students in the department.