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

摘要CTS-9729720麦克休博士/约翰霍普金斯大学这是工业界和约翰霍普金斯大学之间的一个目标合作项目。该研究的长期目标是开发基于超临界流体(SCF)的新一代聚合物加工技术。然而，SCF溶剂-聚合物溶液行为的严格模型，无论是在宏观层面还是微观层面，都仍处于发展的初级阶段。因此，利用超临界流体溶剂的独特特性和能力设计可靠、高效的化学工艺是格外困难的。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。除了高压相态测量外，还将利用各种散射技术来研究压力和温度升高时的超临界流体聚合物溶液。对于每个聚合物-超临界流体对，浊点曲线将在很大的P-T空间范围内测量，以调制相对于混合吉布斯自由能的熵贡献的能量相互作用。通过对P-T空间浊点曲线特征的考察，可以获得SCF-聚合物相互作用相对于SCF-SCF以及聚合物链段-链段相互作用平衡的粗粒度指示。然后将使用光散射技术来探测单相区中的聚合物尺寸和相互作用。静态光散射将被用来确定聚合物的回转半径和第二渗透变系数。测得的第二渗透维里系数定义了聚合物在溶液中的等效硬球半径。采用动态光散射法测量聚合物的流体力学半径。通过比较硬球半径和流体动力学半径，可以深入了解亚大分子长度尺度下溶液中发生的相互作用。小角中子散射将被用来确定聚合物在超临界流体溶剂环境中的持久性和等高线长度。持久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理解支配所观察到的溶液行为的分子热力学原理。相行为和散射研究将集中在几种不同的分子简单的超临界流体溶剂和两种不同类型的均聚物：非极性聚烯烃和极性聚合物。聚合物的主链结构会有所不同，以揭示聚合物结晶度、链支化、极性和氢键对单相区相行为和链尺寸的影响。我们还将通过关注具有相似分子间势函数但统计链段长度不同的聚合物，如聚丙烯酸酯和聚甲基丙烯酸酯，来研究链“刚性”的影响。选择聚合物-SCF溶剂系统来隔离特定的现象，从而允许系统地探索控制聚合物在SCF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.