Photoinitiated Reactions in Covalent Adaptable Networks

PI: Bowman， Christopher机构：科罗拉多大学提案号：1264298标题：共价适应性网络中的光引发反应交联聚合物网络，也通常被称为热固性聚合物，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，光学元件和光平版印刷。虽然这些共价交联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限制了聚合物体系的后续形状和性能，只能达到聚合结束时达到的水平。在这里，PI计划使用一种独特的热固性系统，将必要的共价交联结构与内部官能团结合起来，这些官能团在暴露于光线下发生附加-破碎反应，从而使网络重新排列。这种以可控方式破坏和重组键的反应能力使这些材料展示了许多在其他热固性材料中不常见的独特性能，例如应力松弛，减少聚合引起的应力，光刻定义形状和地形的能力，作为多阶段形状记忆聚合物（SMPs），并具有局部缓解应力的能力，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”或对它们的条件作出反应，并被称为共价适应网络（can）。PI计划利用光作为该反应过程中最有效和最有能力的触发器之一，因为光可以实现4D（时间加3D空间）控制反应，从而促进网络属性和行为变化。本工作旨在促进光诱导自由基生成可控的can的发展。总体目标是创造更容易形成的新型功能性can材料，实现完整和可重复的适应，并促进新特性的实现，包括任意地形和折射率特征的形成，光热smp和应力触发网络松弛。研究计划分为四个主要的科学方向：(i)基于系统分子结构变化开发新的单体、聚合物和理解can的结构-性质关系，（ii）在反应中实现这些can，从而实现对地形、形状和折射率的4D光版控制，（iii）开发组合自适应/非自适应网络，以实现多阶段SMP行为。（iv）使用机械化学物质，在施加应力时分裂成自由基，以“智能”的方式诱导应力松弛，防止灾难性的材料失效。每个科学方向都与不同群体的本科生和研究生的教育和培训相结合。这将有助于理解聚合物网络动力学，以及开发比传统热固性材料有显著优势的材料。潜在的突破将通过暴露在光线下使材料形状和性能发生巨大变化，通过促进光热smp以及通过开发热固性聚合物延长使用寿命的技术来实现。例如，仅通过改变灰度级别就可以在光刻上形成多高度特征（不使用溶剂，也不与曝光区域接触），这代表了一种破坏性抗蚀技术，其中在机械变形期间的单次曝光将用于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可治愈网络方法一起使用时。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，增强can和其他热固性材料的形成-结构-性能关系，以及创造新的单体和材料类别，将热固性材料的优点与触发所需性能和形状随光变化的能力结合起来，这项工作的成功完成应该具有重大的智力价值。这种方法将同时对新的博士学位课程的启动和对化学反应和聚合物网络独特组合的不同人员的培训产生重大的更广泛的影响，同时也使这种新型强大材料范式中时空控制的关键缺失元素成为可能。这些新控制的、更简单的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.