CAREER: Dynamic Polymer Materials with Advanced Polymer Architecture and Carbon Nanotube Reinforcements

第一部分： 非技术总结本项目旨在通过明智地选择分子结构和纳米级增强来开发具有增强的机械性能和导电性的聚合物材料。引入“动态债券”（即，可以在不同基团之间交换的化学键）进入聚合物材料中，可以导致自修复性能和在材料受到外部损坏的情况下增强的稳定性。然而，当施加外力时，这也可能导致形状的永久变化，这可能限制应用中的实用性。该提案中开发的聚合物将在同一材料中加入不同类型的动态键，以实现自修复特性与长期稳定性的结合。有必要了解潜在的聚合物结构如何影响动态交联聚合物的性能。底层聚合物的结构将为此目的进行调整，并且通过引入碳纳米管来实现额外的增强，这将改善机械性能和导电性。 这项研究预计将生产出具有更长寿命和可再加工性的材料，因为动态粘合具有愈合性能。这将使下一代聚合物材料具有延长的使用寿命，降低更换成本，改善机械性能，提高导电性。在这项研究中开发的材料合成策略可以转化为增材制造，从而实现一系列具有复杂结构的定制材料。该项目还将包括外展活动，将动态交联聚合物放在K-12学生手中，并为K-12教师开展继续教育活动。该项目还将开发教育工具，促进批判性思维和课堂参与，以培训下一代科学家，并推动他们在科学领域从事富有成效的职业。此外，该项目将吸引不同背景的学生参与研究生和本科生的研究，以促进传统上代表性不足的人群参与STEM领域。 技术总结 本研究将开发包含双动态交联的定义明确的聚合物，其中在一种聚合物材料中使用快速交换的非共价连接体和在外部刺激下交换的动态共价连接体。这将产生结合动态粘合所赋予的韧性、延展性、可再加工性和自愈合特性的联合收割机材料，同时保持传统热固性材料的机械稳定性和抗蠕变性。该研究将通过将双重动态交联与可控结构的聚合物和将碳纳米管增强物结合到基体的新策略相结合来产生新材料。 通过控制链长、交联剂沿着链的位置和交联剂的密度来合成聚合物。Diels-Alder化学将用于动态键合碳纳米管增强材料。先进的结构，如互穿网络和嵌段聚合物将被引入，以提高机械性能。每种材料的性能将通过大量的机械和电气测试进行评估，并导致宏观性能与基础聚合物结构的相关性。本研究的具体目标是：1.通过精确控制链长和交联剂沿聚合物主链的沿着位置，创建双动态单和互穿网络。2.利用碳纳米管与基体之间的动态键来增强双重动态交联聚合物.精确控制聚合物的微观结构，制备互穿网络和单网络碳纳米管复合材料.阐明聚合物结构和微观结构与材料的机械和电气性能之间的结构-性能相关性。教育活动集中在三个关键领域：1）与中学教师和学生的外联; 2）开发新的学科; 3）增加STEM的多样性。第一个领域将包括对K-12学生的非共价和动态共价交联剂聚合物材料的推广，以及教师的继续教育活动。第二个领域将侧重于工具，让学生反思自己的学习，并发展实验和课堂活动之间的联系。第三个领域将增加传统上代表性不足的群体的学生参与STEM学习和研究。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARYThis project aims to develop polymeric materials with enhanced mechanical properties and electrical conductivity through judicious choice of molecular structure and nanoscale reinforcement. Introducing "dynamic bonds" (i.e., chemical bonds that can be exchanged between different groups) into a polymeric material can lead to self-healing properties and enhanced stability in case of external damage to the material. However, this can also lead to permanent changes in shape when external forces are applied, which could limit utility in applications. The polymers developed in this proposal will incorporate different types of dynamic bonds into the same material to enable the combination of self-healable properties with long-term stability. There is a need to understand how the underlying polymer structure impacts the properties of dynamically cross-linked polymers. The structure of the underlying polymer will be tuned for this purpose and additional reinforcement will be enabled by incorporation of carbon nanotubes, which will improve mechanical properties and electrical conductivity. This research is anticipated to produce materials with enhanced lifetime and reprocessability due to the healing properties enabled by dynamic bonding. This will enable the next generation of polymeric materials to have extended useful lifetime, with reduced replacement costs, improved performance against mechanical challenges, and enhanced conductivity. The material synthesis strategies developed in this research could be translated to additive manufacturing enabling a range of tailor-made materials with complex structures. This project will also include outreach activities that place dynamically cross-linked polymers in the hands of K-12 students and develop continuing education activities for K-12 teachers. This project will also develop educational tools to promote critical thinking and involvement in classrooms to train the next generation of scientists and propel them to productive careers in science. Further, this project will engage students of diverse backgrounds in graduate and undergraduate research, to foster participation in STEM fields from populations that are traditionally underrepresented.PART 2: TECHNICAL SUMMARY This research will develop well-defined polymers containing dual-dynamic crosslinking, where both a non-covalent linker that exchanges rapidly and a dynamic covalent linker that exchanges under external stimulus are used in one polymer material. This will create materials that combine the toughness, malleability, reprocessability and self-healing character imparted by dynamic bonding while retaining mechanical stability and resistance to creep of traditional thermosets. The research will lead to new materials by combining dual dynamic crosslinking with polymers of controlled structure and new strategies for bonding carbon nanotube reinforcements to the matrix. Polymers will be synthesized with control over chain-length, placement of crosslinkers along the chain, and density of crosslinkers. Diels-Alder chemistry will be used to dynamically bond the carbon nanotube reinforcements. Advanced structures such as interpenetrating networks and segmented polymers will be introduced to improve mechanical properties. Performance of each material will be evaluated through a number of mechanical and electrical tests, and lead to correlation of macroscopic properties with the underlying polymer structure. Specific objectives of this research are:1. Create dual dynamic single and interpenetrating networks with precise control over chain length and crosslinker placement along the polymer backbone.2. Reinforce dual dynamically crosslinked polymers using dynamic bonds between carbon nanotubes and the matrix.3. Make interpenetrating network and single network carbon nanotube composite materials with precise control over polymer microstructure.4. Elucidate structure-property correlations between the polymer architecture and microstructure and the mechanical and electrical properties of the materials.Educational activities focus on three key areas: 1) Outreach to secondary school teachers and students; 2) Development of new pedagogies; 3) Increasing diversity in STEM. The first area will include outreach to K-12 students on polymeric materials with non-covalent and dynamic covalent crosslinkers, as well as continuing education activities for teachers. The second area will focus on tools to engage students to reflect on their own learning, and develop connections between experiments and classroom activities. The third area will increase involvement of students from traditionally underrepresented groups in STEM studies and research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.