Molecular Symmetry and Polymer-Polymer Thermodynamics

对大块聚合物体系（包括聚合物-聚合物混合物和嵌段共聚物）相行为的理论描述通常假设组分之间的分子对称。最近对模型线性聚烯烃均聚物和嵌段共聚物的实验表明，这些材料的相行为和表面偏析倾向与构象对称参数的差异有关。对称参数表征聚合物（或块）在构象和体积上填充空间的方式的差异。在存在对称破缺面或微域界面时，参数的差异将分别为优先润湿或特定界面曲率提供熵驱动力。这些效应将通过制备定义良好的聚烯烃并使用各种方法研究它们的体相行为和表面性质来进行实验检验。通过阴离子合成的不饱和烃聚合物催化加氢制备聚烯烃模型样品。体相行为将通过动态力学光谱和小角中子散射（SANS）测量来建立，目的是建立对称参数与在有序-无序转变附近发现的各种有序相之间的关系。表面研究将集中在两类材料：线性和星形均聚物混合物和星形嵌段共聚物。中子和x射线反射以及SIMS实验将用于确定对称参数的变化如何影响表面偏析。该研究项目的总体目标是通过利用构象和结构对称来开发操纵聚合物-聚合物热力学的方法，以指导先进聚合物基材料的合理设计。

Bates Theoretical descriptions of the phase behavior of bulk polymer systems, including polymer-polymer mixtures and block copolymers, have generally assumed molecular symmetry between components. Recent experiments with model linear polyolefin homopolymers and block copolymers have demonstrated that the phase behavior, and surface segregation tendencies, of these materials can be correlated with differences in the conformational symmetry parameter. The symmetry parameter characterizes differences in the manner in which polymers (or blocks) fill space conformationally versus volumetrically. In the presence of a symmetry breaking surface, or at a microdomain interface, differences in the parameter will provide an entropic driving force for preferential wetting, or a specific interfacial curvature, respectively. These effects will be examined experimentally by preparing well-defined polyolefins and studying their bulk phase behavior and surface properties using a variety of methods. Model polyolefin specimens will be produced through the catalytic hydrogenation of anionically synthesized unsaturated hydrocarbon polymers. Bulk phase behavior will be established using dynamic mechanical spectroscopy and small-angle neutron scattering (SANS) measurements, with the objective of establishing relationships between the symmetry parameters and the various ordered phases found near the order- disorder transition. Surface studies will focus on two classes of materials: linear and star homopolymer mixtures and starblock copolymers. Neutron and X-ray reflections, and SIMS experiments will be used to determine how variations in the symmetry parameters influence surface segregation. %%% The overall goal of this research project is to develop methods for manipulating polymer-polymer thermodynamics by exploiting conformational and architectural symmetry, in order to guide the rational design of advanced polymer-based materials.