Photoinitiated Reactions in Covalent Adaptable Networks

主要研究者：Bowman，Christopher Institution：科罗拉多大学提案编号：1264298标题：共价自适应网络中的光引发反应交联聚合物网络，也通常称为热固性材料，代表了最普遍的聚合物系统之一，被用于复合材料，生物医学设备，牙科材料，涂料，粘合剂，光学元件和光刻。虽然这些共价交联的结构赋予了许多非常理想的特征，特别是在力学方面，但它们在很大程度上将聚合物体系的后续形状和性能限制在聚合结束时实现的那些。在这里，PI计划使用一种独特的热固性系统，该系统将必要的共价交联结构与内部官能团相结合，这些官能团在暴露于光时发生加成-断裂反应，使网络重新排列。这种以受控方式断裂和改革键的反应能力使这些材料能够表现出许多在其它热固性材料中不常见的独特性能，例如应力松弛、降低的聚合诱导应力、以几何图形方式限定形状和形貌的能力，作为多级形状记忆聚合物（SMP）并具有局部减轻应力的能力，作为防止灾难性材料失效的手段。最终，在施加必要的刺激后，这些材料“适应”或响应于它们的条件，并且被称为共价可适应网络（CAN）。PI计划利用光作为该反应过程的最有效和最有能力的触发器之一，因为光可以实现对促进网络性质和行为变化的反应的4D（时间加3D空间）控制。这项工作是为了推进CAN的开发，因为可以通过光诱导自由基的产生来控制。总体目标是创造新的、功能性的CAN基材料，其更容易形成，能够实现完全和可重复的适应，并有助于实现新的特性，包括形成任意的形貌和折射率特征、光热SMP和应力触发的网络松弛。该研究计划分为四个主要科学方向：（i）开发新的单体、聚合物，并基于系统的分子结构变化理解CAN中的结构-性质关系，（ii）在能够对形貌、形状和折射率进行4D光刻控制的反应中实施那些CAN，（iii）开发组合的自适应/非自适应网络以实现多级SMP行为，和（四）在施加应力时分裂成自由基的机械化学物质的用途，以“聪明”的方式。每个科学方向都与不同的本科生和研究生群体的教育和培训相结合。该项目的获得将有助于理解聚合物网络动力学，并有助于开发比传统热固性材料具有显著优势的材料。通过曝光，通过促进光热SMP，以及通过开发热固性聚合物可以延长使用寿命的技术，可以实现材料形状和性能的巨大变化，从而实现潜在的突破。例如，简单地通过改变灰度级以光刻方式形成多高度特征（没有溶剂并且不接触曝光区域）的能力代表了破坏性抗蚀剂技术，其中在机械变形期间的单次曝光将用于仅通过改变每个位置处的强度来创建复杂的高度阵列。类似地，形成具有自主缓解应力能力的智能热固性材料可以显著提高这些材料的使用寿命，特别是在复合材料中以及与其他方法一起使用时，以可愈合的网络。成功完成这项工作应该具有重要的智力价值，通过理解与键断裂和重组相关的反应动力学如何决定网络结构，在增强CAN和其它热固性材料中的形成-结构-性质关系方面，以及在创造新的单体和材料类别方面，所述单体和材料类别将热固性材料的益处与利用光触发所需性质和形状变化的能力结合联合收割机。这种方法将同时具有与启动新的博士学位课程和培训不同人员在化学反应和聚合物网络的独特组合相关的更广泛的影响，同时还使时空控制的关键缺失元素在这种新的，强大的材料的范例。这些新的控制和更简单的实施反应和材料的实施将有利于一系列聚合物应用，包括SMP，粘合剂，光刻胶，光学元件，复合材料，涂层和生物医学材料。

PI: Bowman, Christopher Institution: University of ColoradoProposal Number: 1264298Title:Photoinitiated Reactions in Covalent Adaptable NetworksCrosslinked polymer networks, also often referred to as thermosets, represent one of the most ubiquitous polymer systems, being used in composites, biomedical devices, dental materials, coatings, adhesives, optical components, and photolithography. While these covalently crosslinked structures impart a number of highly desirable features, particularly with respect to the mechanics, they largely limit the subsequent shape and performance of the polymer system to those that are achieved at the end of the polymerization. Here, the PI plans to work with a distinct class of thermosetting systems that combine the necessary covalently crosslinked structure with internal functional groups that undergo addition-fragmentation reactions upon exposure to light that enable the network to rearrange. This reactive ability to break and reform bonds in a controlled manner enables these materials to demonstrate a number of unique properties not commonly found in other thermosets, such as stress relaxation, reduced polymerization induced stress, the ability to photolithographically define shape and topography, to act as multistage shape memory polymers (SMPs) and to have the ability to alleviate stress locally as a means for preventing catastrophic material failure. Ultimately, upon application of the necessary stimulus, these materials "adapt" or respond to their conditions and have been referred to as Covalent Adaptable Networks (CANs). The PI plans to utilize light as one of the most potent and capable triggers for this reactive process as light enables 4D (temporal plus 3D spatial) control of the reactions that facilitate the network property and behavioral changes.This work is to advance the development of CANs, as controllable by photoinduced radical generation. The overall objective is to create novel, functional CAN-based materials that are more readily formed, enable complete and repeatable adaptation, and facilitate the achievement of new properties including the formation of arbitrary topographical and refractive index features, photothermal SMPs, and stress-triggered network relaxation. The research program is divided into four principal scientific directions: (i) development of new monomers, polymers and understanding of structure-property relationships in CANs based on systematic molecular structural variations, (ii) the implementation of those CANs in reactions that enable 4D lithographic control of topography, shape and refractive index, (iii) the development of combined adaptable/non-adaptable networks to achieve multistage SMP behavior, and (iv) use of mechanochemical species that cleave into radicals upon application of stress to induce stress relaxation and prevent catastrophic material failure in a "smart" manner. Each scientific direction is coupled to education and training of a diverse group of undergraduate and graduate students. Attainment will facilitate understanding of polymer network dynamics as well as development of materials that have significant advantages over conventional thermosets.Potential breakthroughs will be achieved by enabling dramatic changes in material shape and properties by exposure to light, by facilitating photothermal SMPs and by developing techniques through which thermosetting polymers could have extended service lifetimes. For example, the ability to form multiheight features photolithographically (without solvents and without contact to the exposed area) simply by changing the grayscale level represents a disruptive resist technology where a single exposure during a mechanical deformation will be used to create a complex array of heights just by changing the intensity at each location. Similarly, forming smart thermosetting materials that have the capacity to autonomously alleviate stress could lead to significantly enhanced service lifetimes of these materials, particularly in composite materials and when used with other approaches to healable networks.Successful completion of this work should have significant intellectual merit through understanding of how reaction dynamics associated with bond breakage and reformation dictate the network structure, in enhancing formation-structure-property relationships in CANs and other thermosets, and in the creation of new monomers and classes of materials that combine the benefits of thermosets with the ability to trigger desired property and shape changes with light. This approach will simultaneously have significant broader impacts associated with the launching of a new PhD degree program and the training of diverse personnel in a unique combination of chemical reactions and polymer networks while also enabling a critical missing element of spatiotemporal control in this new, powerful material's paradigm. Implementation of these newly controlled and more simply implemented reactions and materials will benefit an array of polymer applications including SMPs, adhesives, photolithographic resists, optical elements, composites, coatings, and biomedical materials.