Combining Reversible and Permanent Crosslinks in Thermosets for High Technology Applications

技术概述：由热可逆交联组成的聚合物网络在可修补、可回收和智能材料中很受欢迎。这些材料具有响应光照射或温度变化等刺激的能力，从而改变材料性能，影响从超材料和生物材料到微器件、增材制造和光刻等领域。在这里，一类热可逆的聚合物网络将基于Diels-Alder网络开发；然而，通过将这些网络与另外两种巯基-乙烯基点击反应中的一种结合使用，将探索出一种具有基础和实用优势的新型材料。对热可逆网络的理解将转化为几种方法，以实现这些聚合物作为智能、自修复材料的潜力。特别是，控制消除均匀部分交联的热可逆性（即通过Michael加成反应）或可逆交联的时空控制应该创造新的材料，方法和理解，使聚合物网络和后续设备的复杂制造和物理化学图案在3D中。具体来说，(i)将创造出结合热可逆性网络和传统不可逆性网络的新型聚合物材料，包括以时空可控的方式消除热可逆性的能力；（ii）网络结构将系统地变化，可逆键结构与流变学、力学和愈合行为之间的关系将被评估。（iii）将开发用于3D设备增材制造方法的直接写入和逐层方法，以及（iv）将创建具有与玻璃化转变和交联可逆性相关的两种不同热转变的双级形状记忆聚合物。非技术总结：热固性塑料材料作为一个价值数十亿美元的产业，在高科技应用中无处不在，从牙科材料到增材制造，从光伏涂料到先进光学材料等等。这些聚合物是高功能的特种材料，其性能在很大程度上取决于底层的分子结构，传统上由不可逆的分子键组成。虽然这种结构产生了这些材料的许多期望属性，但同样的结构限制了它们的行为，并阻止它们自我修复、可回收或能够改变它们的永久形状。在这里，通过开发这些材料的特殊分子方法，使结构在适当的时间和条件下可逆，将形成热固性聚合物，将传统热固性材料的最佳特征与智能、反应性材料的最佳特征结合起来。这种方法将用于开发改进的材料和方法，用于通过增材制造制造复杂的3D部件，新型光学应用，以及用作可改造，可回收和可治疗的热固性聚合物。除了技术进步之外，这种方法同时对聚合物化学、材料科学和光学跨学科组合的未来劳动力培训具有重要的更广泛的影响。参与该项目的研究生和本科生还将参与科罗拉多大学新材料科学与工程博士学位的启动，这将为材料科学和工程人才培养高素质的研究人员。

TECHNICAL SUMMARY:Polymer networks composed of thermally reversible crosslinks have become popular in mendable, recyclable, and smart materials. These materials have the ability to respond to stimuli such as light exposure or temperature change with a change in material properties, impacting fields from metamaterials and biomaterials to microdevices, additive manufacturing and photolithography. Here, a class of thermoreversible polymer networks will be developed based on Diels-Alder networks; however, by using those networks in combination with one of two other thiol-vinyl click reactions, a new class of materials offering fundamental and practical advantages will be explored. Understanding of thermoreversible networks will be translated into several approaches for achieving the potential of these polymers to be used as smart, self-healing materials. In particular, controlled elimination of thermoreversiblity (i.e., through a Michael addition reaction) either of a uniform fraction of the crosslinks or with spatiotemporal control of the reversible crosslinks should create novel materials, approaches and understanding that enables the complex fabrication and physicochemical patterning of polymer networks and subsequent devices in 3D. Specifically, (i) new polymeric materials will be created that combine thermoreversible networks with conventional irreversible networks, including the ability to eliminate the thermoreversibility in a spatiotemporally controlled manner, (ii) the network structure will be systematically varied and the relationship between reversible bond structures and rheological, mechanical, and healing behavior will be assessed, (iii) direct-write and layer-by-layer approaches for additive manufacturing approaches to 3D devices will be developed, and (iv) dual-stage shape-memory polymers will be created with two distinct thermal transitions associated with the glass transition and the crosslink reversibility.NON-TECHNICAL SUMMARY:Thermosetting plastic materials, as a multibillion dollar industry, are ubiquitous in high technology applications that range broadly from dental materials to additive manufacturing to photovoltaic coatings to advanced optical materials and many others. These polymers are highly functional, specialty materials whose performance is largely dependent on the underlying molecular structure, which is comprised traditionally of irreversible molecular bonds. While this structure gives rise to many of the desired attributes of these materials, that same structure limits their behavior and prevents them from being self-healing, recyclable, or able to change their permanent shapes. Here, through the development of special molecular approaches to these materials that renders the structure reversible at appropriate times and conditions, thermosetting polymers will be formed that combine the optimal features of traditional thermosets with those of smart, responsive materials. This approach will be used to develop improved materials and approaches for use in the fabrication of complex 3D parts by additive manufacturing, novel optical applications, and use as reformable, recyclable, and healable thermosetting polymers. Beyond the technological advances, this approach simultaneously has significant broader impacts associated with the training of a future workforce in an interdisciplinary combination of polymer chemistry, materials science, and optics. The graduate and undergraduate students involved in this project will also participate in the launching of a new Materials Science and Engineering PhD degree at the University of Colorado that will lead to the training of highly qualified researchers for the materials science and engineering workforce.