Photoinitiated Reactions in Covalent Adaptable Networks

PI：Bowman，Christopher Institution：美国科罗拉多大学提案编号：1264298题目：在共价自适应网络中的光引发反应交联聚合物网络，通常也称为热固性聚合物网络，代表着最普遍的聚合物体系之一，被用于复合材料、生物医疗设备、牙科材料、涂层、粘合剂、光学元件和光刻。虽然这些共价交联结构提供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限制了聚合物体系随后的形状和性能，仅限于聚合结束时获得的形状和性能。在这里，PI计划与一类不同的热固性系统合作，这些热固性系统将必要的共价交联结构与内部官能团结合在一起，这些官能团在光照下经历加成-碎裂反应，使网络能够重新排列。这种以受控方式断裂和改造键的反应能力使这些材料表现出许多其他热固性材料所不具备的独特性能，例如应力松弛、降低聚合诱导应力、能够通过光刻定义形状和形貌、充当多阶段形状记忆聚合物(SMPS)以及能够局部缓解应力以防止灾难性的材料失效。最终，在施加必要的刺激后，这些材料“适应”或对其条件作出反应，并被称为共价适应网络(CAN)。PI计划利用光作为这一反应过程最有效和最有能力的触发器之一，因为光能够对促进网络性质和行为变化的反应进行4D(时间和3D空间)控制。这项工作是为了促进通过光诱导自由基产生来控制的罐头的发展。总体目标是创造新的、更容易形成的基于CaN的功能材料，使其能够完全和可重复地适应，并促进实现新的性能，包括形成任意的地形和折射率特征、光热SMP和应力触发的网络弛豫。研究计划分为四个主要的科学方向：(I)基于系统的分子结构变化开发新的单体、聚合物和了解罐头中的结构-性能关系；(Ii)将这些罐头应用于反应中，使其能够对地形、形状和折射率进行4D光刻控制；(Iii)开发组合的适应性/非适应性网络，以实现多级SMP行为；以及(Iv)使用在施加应力时裂解成自由基的机械力化学物种，以“智能”的方式诱导应力松弛和防止灾难性的材料失效。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。这将有助于理解聚合物网络动力学，以及开发出比传统热固性材料具有显著优势的材料。潜在的突破将通过光照使材料形状和性能发生巨大变化，通过促进光热开关和通过开发热固性聚合物可以延长使用寿命的技术来实现。例如，仅通过更改灰度级别即可通过光刻(不含溶剂且不接触曝光区域)形成多高度特征的能力代表了一种颠覆性抗蚀剂技术，其中在机械变形期间的单次曝光将被用于仅通过改变每个位置的强度来创建复杂的高度阵列。同样，形成能够自主缓解应力的智能热固性材料可以显著延长这些材料的使用寿命，特别是在复合材料中，当与其他方法一起使用时，可以治愈网络。成功完成这项工作应该具有显著的智力优势，因为它理解了与键断裂和重整相关的反应动力学如何决定网络结构，在增强罐头和其他热固性材料中的形成-结构-性质关系，以及在创造新的单体和材料类别方面，这些单体和材料类别结合了热固性材料的优点与触发所需性质和用光改变形状的能力。这一方法将同时产生重大的更广泛的影响，与启动新的博士学位计划和培训不同的人员在化学反应和聚合物网络的独特组合，同时也允许在这种新的，强大的材料范式的时空控制的关键缺失的元素。这些新控制和更简单实现的反应和材料的实现将使一系列聚合物应用受益，包括SMPS、粘合剂、光刻抗蚀剂、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.