Driving Structure Formation in Block Copolymers by Crystallization

聚合物的结晶对其性能有着深远的影响，并支撑着其许多应用。 相比之下，嵌段共聚物中的自组装通常由嵌段之间的排斥驱动。 我们建议将这两种自组装基序联合收割机组合成聚合物，其设计为在结晶时自发地且可再现地形成复杂结构。 一个主要的焦点将是三组分嵌段共聚物，形成单相（无序）熔体，但其中一个嵌段的结晶触发其他两个嵌段之间的微相分离。 在一个领域中，将通过活性开环复分解聚合（ROMP）来合成具有以下结构的明确定义的五嵌段和三嵌段星星聚合物：（结晶-玻璃态-橡胶态）n以形成单相熔体。 端嵌段的结晶诱导从混合物中分离所附的玻璃态嵌段，从而产生具有复合玻璃态/橡胶态硬域的热塑性弹性体。 其次，这一概念将扩展到更一般的ABC三嵌段，其中橡胶态B和C嵌段之间的分离是由A嵌段从单相熔体中结晶驱动的。 这些聚合物将通过阴离子聚合或通过ROMP至阴离子聚合转化来合成; B和C嵌段将各自为无规共聚物，其中Flory相互作用参数λ可以通过调节组成来连续调节，从而允许独立于λ N调节嵌段长度（N）。 最后，我们将研究新的烯烃二嵌段共聚物生产的烯烃直接聚合。 虽然这些聚合物在熔体中形成的相分离结构持续到固态，但它们对在其中形成的晶体的取向几乎没有限制。 这项工作将结合联合收割机合成与详细的结构表征，无论是通过电子显微镜，特别是通过内部和同步加速器为基础的小角度和广角X射线散射，并与机械性能测量，以阐明结构性能的关系。 非技术摘要：拟议的工作旨在定义？设计规则？对于特定类别的材料：半结晶嵌段共聚物，其性质涵盖从橡胶到塑料的范围。 拟议的工作将开发可以像塑料一样容易加工（和再加工或回收）的材料，但它可以像橡胶一样伸展，也可以抵抗溶剂（如汽油或机油）的溶解。 关键是了解这些材料的内部结构与其性能之间的关系，以便合理设计材料，使其具有所需的性能（如弹性或耐溶剂性），并根据需要快速开发。 拟议的工作将提供一个综合的研究和教育经验，为两到三个研究生，三到六个本科生，特别是包括代表性不足的群体的成员，这些学生？通过与陶氏化学和普罗默鲁斯电子材料公司的工业合作者的互动，将丰富经验。 PI和学生将通过科学外展活动吸引公众？在普林斯顿大学校园，在附近的学校，并在自由科学中心（泽西城，新泽西州）。 一个具体目标是促进中学生，包括特伦顿公立学校系统的中学生对科学和技术的兴趣和欣赏。

TECHNICAL SUMMARY: Crystallization of polymers has a profound impact on their properties, and underpins many of their applications. By contrast, self-assembly in block copolymers is typically driven by repulsion between the blocks. We propose to combine these two self-assembling motifs into polymers designed to spontaneously and reproducibly form complex structures upon crystallization. A principal focus will be on three-component block copolymers which form single-phase (disordered) melts, but where crystallization of one block triggers microphase separation between the other two blocks. In one area, well-defined pentablock and triblock star polymers having the architecture: (crystalline-glassy-rubbery)n will be synthesized by living ring-opening metathesis polymerization (ROMP) to form a single-phase melt. Crystallization of the endblocks induces a separation of the attached glassy blocks from the mixture, yielding thermoplastic elastomers with composite glassy/rubbery hard domains. Second, this concept will be extended to a more general class of ABC triblocks, where separation between the rubbery B and C blocks is driven by crystallization of the A block from a single-phase melt. These polymers will be synthesized by anionic polymerization, or by a ROMP-to-anionic polymerization transformation; the B and C blocks will each be random copolymers, where the Flory interaction parameter ÷ can be continuously tuned by adjusting the composition, allowing block length (N) to be adjusted independent of ÷N. Finally, we will investigate new olefin diblock copolymers produced by direct polymerization of the olefins. Though the phase-separated structures formed by these polymers in the melt persist into the solid state, they exert surprisingly little restriction on the orientation of the crystals which form within them. The work will combine synthesis with detailed structural characterization, both by electron microscopy and especially by in-house and synchrotron-based small- and wide-angle x-ray scattering, and with mechanical property measurements to elucidate the structure-property relationships. NON-TECHNICAL SUMMARY: The proposed work aims to define the ?design rules? for a particular class of materials: semicrystalline block copolymers, whose properties span the range from rubbers to plastics. The proposed work will develop materials which can be easily processed (and reprocessed or recycled) like a plastic, but which can stretch like a rubber and also resist dissolving in solvents (like gasoline or motor oil). The key is understanding the relationships between the internal structures of these materials and their properties, so that materials can be rationally designed to have the desired properties (such as elasticity or solvent resistance), and can be developed quickly as needs arise. The proposed work will provide an integrated research and educational experience for two to three graduate students, and three to six undergraduates, especially including members of underrepresented groups, and these students? experience will be enriched by interactions with industrial collaborators at Dow Chemical and Promerus Electronic Materials. The PI and students will engage the general public through science outreach?on the Princeton University campus, at nearby schools, and at the Liberty Science Center (Jersey City, NJ). A specific aim is to promote interest in, and appreciation for, science and technology among middle school students, including those in the Trenton public school system.