GOALI: Microscopic Basis of Polymer-Supercritical Fluid Phase Behavior: Polymer-Solvent Interactions and Chain Stiffness

摘要CTS-9729720 McHugh，M./约翰霍普金斯大学 这是一个工业界和约翰霍普金斯大学之间的GOALI合作项目。本文提出的研究的长期目标是开发新一代基于超临界流体（SCF）的聚合物加工技术。 然而，SCF溶剂-聚合物溶液行为的严格模型，无论是在宏观和微观水平上，仍处于发展的初期阶段。 因此，特别难以设计可靠有效的化学工艺，利用SCF溶剂的独特特性和能力。 因此，当前的研究目标是解决SCF-聚合物溶液的物理和化学问题。 除了高压相行为测量，各种散射技术将被用来研究SCF聚合物溶液在升高的压力和温度。对于每个聚合物-SCF对，将在宽范围的P-T空间上测量浊点曲线，以调节相对于熵对混合吉布斯自由能的贡献的能量相互作用。 SCF-聚合物相互作用相对于SCF-SCF和聚合物链段-链段相互作用的平衡的粗粒度指示可以从P-T空间中的浊点曲线的特征的检查中收集。 光散射技术，然后将被用来探测聚合物的尺寸和在单相区域的相互作用。 静态光散射将用于确定聚合物的回转半径和第二渗透可变系数。测得的第二渗透维里系数定义了溶液中聚合物的等效硬球半径。 动态光散射将用于测量聚合物流体力学半径。 硬球和流体动力学半径的比较产生洞察的相互作用，发生在亚大分子长度尺度的解决方案。 小角中子散射将用于确定聚合物的持久性和轮廓长度在超临界流体溶剂环境。 持久性长度值对于确定聚合物构象熵对相行为和聚合物链段-溶剂相互作用的影响特别有用。 这种超分子到大分子长度尺度的方法将使我们能够更详细地了解支配所观察到的溶液行为的分子热力学原理。 相行为和散射的研究将集中在几个不同的分子简单的SCF溶剂和两个不同类别的均聚物：非极性聚（烯烃）和极性聚合物。 聚合物将在主链结构上变化，以揭示聚合物结晶度、链支化、极性和氢键对单相区域中的相行为和链尺寸的影响。 我们还将研究链的“刚性”的影响，通过关注具有相似的分子间势能函数，但不同的统计段长度的聚合物，如聚（丙烯酸酯）和聚（甲基丙烯酸酯）。 选择聚合物-超临界流体溶剂系统以隔离特定现象，并且因此允许系统地探索支配聚合物在超临界流体溶剂中的溶解度和行为的因素。

ABSTRACT CTS-9729720 McHugh, M./Johns Hopkins U. This is a GOALI Collaboration project between industry and Johns Hopkins. The long-term objective of the research proposed here is to develop a new generation of supercritical fluid (SCF)-based technologies for polymer processing. However, rigorous models for SCF solvent-polymer solution behavior, both at the macroscopic and the microscopic levels, are still in the nascent stages of development. It is, therefore, exceptionally difficult to design reliably efficiently chemical processes that utilize the unique characteristics and capabilities of SCF solvents. Hence, the immediate research objective is to address the physics and chemistry of SCF-polymer solutions. In addition to high-pressure phase behavior measurements, a variety of scattering techniques will be utilized to investigate SCF-polymer solutions at elevated pressures and temperatures.. For each polymer-SCF pair, the cloud-point curve will be measured over a broad range of P-T space to modulate energetic interactions relative to entropic contributions to the Gibbs free energy of mixing. A coarse-grain indication of the balance of SCF-polymer interactions relative to SCF-SCF and polymer segment-segment interactions can be gleaned from an examination of the characteristics of the cloud-point curve in P-T space. Light scattering techniques will then be used to probe polymer dimensions and interactions in the single-phase region. Static light scattering will be used to determine polymer radii of gyration and second osmotic varial coefficients. The measured second osmotic virial coefficient defines an equivalent hard sphere radius for the polymers in solution. Dynamic light scattering will be used to measure the polymer hydrodynamics radius. A comparison of the hard sphere and hydrodynamic radii yields insight into the interactions that occur in the solution at submacromolecular length scales. Small angle neutron scattering will be used to determine the polymer persistence and contour lengths in an SCF solvent environment. Perrsistence length values are particularly useful for determining the influence of polymer conformational entropy on phase behavior and polymer segment-solvent interactions. This supremolecular to macromolecular length scale approach will enable us to develop a more detailed understanding of the molecular thermodynamic principles that govern the observed solution behavior. The phase behavior and scattering studies will focus on several different molecularly simple SCF solvents and two different classes of homopolymers: nonpolar poly(olefins) and polar polymers. The polymers will vary in backbone architecture to reveal the influence of polymer crystallinity, chain branching, polarity, and hydrogen bonding on the phase behavior and the chain dimensions in the single-phase region. We will also investigate the impact of chain "stiffiness" by focusing on polymers that have similar intermolecular potential functions, but different statistical segment lengths, such as poly(acrylates) and poly(methacrylates). The polymer-SCF solvent systems are chosen to isolate particular phenomena and, thus, allow a systematic exploration of the factors that govern polymer solubility and behavior in SCF solvents.