Structuring Polymer Crystals through Macromolecular Architecture

聚合物的结晶对它们的性质有着深远的影响，并支撑着它们的许多应用。即使是简单的均聚物在结晶时也表现出层次结构，不同的性质主要由不同的结构特征控制，例如熔点取决于晶体厚度，刚度取决于晶体的连续性和取向。通常，只能对这些关键的结构特征进行粗控制。我们的研究目标是合成能够自发自组装的聚合物，通过合成改变大分子结构，使其介观结构（厚度和取向）可以精确定向，并在大范围内调谐。为此，我们将利用活开环复分解聚合（ROMP）所提供的结构控制。我们寻求的不是将晶体限制在离散的微域内（球体或圆柱体），而是建立微域支架，通过结晶或通过熔体中的块间排斥形成，这使得晶体可以像传统的均聚物结晶一样长得更远，但对最终结构的控制要大得多。活ROMP提供了两种全烃、高结晶块（氢化聚降冰片烯，hPN和线性聚乙烯，LPE），它们与一系列其他高分子量的非结晶饱和烃块熔融混溶。此外，通过Promerus电子材料公司的合作者提供的烷基降冰片烯（aN）和四环十二烯（TD）库，可以在玻璃化转变温度的200℃范围内调节非晶块的物理性质。我们建议探索的一些结构和我们预期的不寻常的特征是：hPN-hPaN-hPN三嵌段共聚物，它应该表现出通过hPN和hPaN嵌段长度可调节的平衡晶体厚度，以及可以与当前的全无定形嵌段共聚物相媲美或超过的热塑性弹性体行为；玻璃晶hPTD-hPN和hPTD-LPE双块，其中我们将阐明决定晶体厚度和熔点的特征；结晶型hPN-LPE双块，我们试图在中尺度上证明晶体多态性；以及ABC三嵌段共聚物，其中单个嵌段可以是橡胶状、玻璃状或高度结晶，作为产生具有不对称表面的晶体和控制相对于微畴界面的晶体取向的手段。拟议的工作将在奖励期间为2至3名研究生和3至6名本科生提供综合研究和教育经验，特别是包括代表性不足的群体的成员。学生将在内部和外部展示他们的工作，而研究生将同时担任研究人员，学生和导师的角色，从而确保研究和教育之间的整合。PI和学生们将在自由科学中心（新泽西州泽西城）通过开发和展示展示聚合物材料不同寻常和有用特性的演示，通过科学宣传吸引公众。PI和学生们还将支持默瑟县3-8年级的基于工具包的科学教育，并根据县和州的教育目标，寻求引入围绕有机和聚合物材料的工具包。

Crystallization of polymers has a profound impact on their properties, and underpins many of their applications. Even simple homopolymers show a hierarchical structure when they crystallize, with different properties principally controlled by different structural features, e.g., melting point dependent on crystal thickness, stiffness dependent on crystal continuity and orientation. Ordinarily, only coarse control can be exerted over these key structural features. Our research aim is to synthesize polymers which will spontaneously self-assemble to give crystals whose mesoscopic structure (thickness and orientation) can be precisely directed, and tuned over broad ranges by altering the macromolecular architecture through synthesis. To this end, we will avail ourselves of the architectural control afforded by living ring-opening metathesis polymerization (ROMP). We seek not to confine crystals within discrete microdomains (spheres or cylinders), but rather to establish microdomain scaffolds, formed either by crystallization or through interblock repulsion in the melt, which permit the crystals to grow for extended distances as in conventional homopolymer crystallization, but with considerably greater control over the final structure. Living ROMP provided access to two allhydrocarbon, highly-crystalline blocks (hydrogenated polynorbornene, hPN, and linear polyethylene, LPE) which are melt-miscible with a range of other noncrystallizable saturated hydrocarbon blocks at high molecular weights. Moreover, the physical properties of the amorphous block can be tuned over a wide range a 200oC range in glass transition temperature, for example via a library of alkylnorbornenes (aN) and tetracyclododecenes (TD) provided by collaborators at Promerus Electronic Materials. Some of the architectures which we propose to explore, and the unusual features which we anticipate, are: hPN-hPaN-hPN triblock copolymers, which should show equilibrium crystal thicknesses tunable through the hPN and hPaN block lengths, as well as thermoplastic elastomer behavior which could rival or surpass that of current all-amorphous block copolymers; glassy-crystalline hPTD-hPN and hPTD-LPE diblocks, where we will elucidate the features which dictate the crystal thickness and melting point; crystallinecrystalline hPN-LPE diblocks, where we seek to demonstrate crystal polymorphism at the mesoscale; and ABC triblock copolymers, where the individual blocks may be rubbery, glassy, or highly crystalline, as a means to generate crystallites with asymmetric surfaces and to control the orientation of the crystallites relative to the microdomain interfaces.The proposed work will provide an integrated research and educational experience for two to three graduate students and three to six undergraduates over the period of the award, especially including members of underrepresented groups. Students will present their work both internally and externally, while graduate students will have concurrent roles as researchers, students, and mentors, thus ensuring integration between research and education. The PI and students will engage the general public through science outreach at the Liberty Science Center (Jersey City, NJ), by developing and presenting demonstrations illustrating the unusual and useful properties of polymeric materials. The PI and students will also support of kit-based science education for Grades 3-8 in Mercer County, and seek to introduce a kit revolving around organic and polymeric materials, following county and state educational objectives.