Tailored Chain Sequences of Pendant Functional Groups and Resulting Phase Behavior of Gel-State Functionalized Blocky Copolymers

嵌段共聚物是一类独特的长链分子（聚合物），由两个不同的链（嵌段）在其一端连接在一起组成。如果这些块体具有明显不同的化学性质，那么它们可能能够自我组装成有序的物理结构，从而赋予与单个块体的性质非常不同，而且往往更好的材料性质。不幸的是，与合成一种典型的单块共聚物相比，嵌段共聚物的化学合成通常要复杂得多，能源密集型和昂贵得多。虽然聚合物化学家在开发合成嵌段共聚物的新方法方面取得了显著进展，但商业上的成功仍然有限，而且往往只应用于高成本领域，如先进的医疗设备或半导体制造。在这个项目中，将采用一种新的物理方法，通过选择性地修改商业聚合物链上的特定单元序列，以一种直接的、经济上有吸引力的方式创建块状共聚物。这里的突破性方法涉及在凝胶状态下进行化学反应，从而使链的特定部分基本上不受修饰化学反应的影响。这项研究将为加速定制嵌段共聚物组件的创建提供重大进展，并增强对下一代膜技术的基本见解。鉴于我们社会面临的巨大挑战，该项目将提供成本效益高、易于获得的替代材料，以满足水净化膜、用于清洁能源转换的燃料电池膜以及用于医疗和保健行业的环保材料的关键需求。该项目的跨学科研究活动，从纯化学到材料结构和性质，将为渴望在科学和技术先进的社会中为我国的领导地位做出贡献的学生和研究人员提供大量的教育机会。本项目将重点研究一种新的方法，即在凝胶状态的半结晶均聚物上使用直接的聚合后化学反应来制造块状共聚物。由于反应只发生在半晶网络中可接近的非晶链段上，这种新的物理过程产生了非随机的、块状的功能结合，是合成嵌段共聚物的复杂聚合机制的一种简单替代方法。基于最近的发现，半结晶聚合物，如间异规聚苯乙烯和聚醚醚酮，可以在非均相凝胶状态下溴化，作为一种简单的方法来创建具有定制序列分布的块状共聚物，该项目旨在利用溴化芳香族模板的丰富替代化学物质来创造各种各样的新型嵌段共聚物，作为系统地操纵相行为的手段，从而形成具有定制性能的有序形态。除了取代化学外，半结晶凝胶的形态参数将通过控制温度、浓度和溶剂来改变，从而精确地影响功能化和非功能化链段的序列。该项目面临的重大挑战是：我们现在能否通过调整这些新型凝胶态功能化嵌段共聚物体系的化学成分，来指导有序相分离结构域的形成，就像在传统嵌段共聚物中观察到的那样？块状共聚物的膜将在结构上为能量转换和水净化应用量身定制。本项目研究活动的跨学科性质，从纯化学到材料结构和性质，将有助于培养多样化的研究人员群体，包括代表性不足的群体。教育外展活动将通过关注旨在确保建立一个更健康、更节能的全球社会的前沿研究，吸引所有年龄段的公民参与。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识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 SUMMARYBlock copolymers are a unique class of long chain molecules (polymers) that are made up of two different chains (blocks) attached together at one of their ends. If the blocks possess distinctly different chemical properties, then they may be capable of self-assembling into well-ordered physical structures that impart material properties that are very different, and often better, than the properties of the individual blocks alone. Unfortunately, the chemical synthesis of block copolymers is generally much more complicated, energy intensive, and expensive compared to that employed in synthesizing a typical commodity polymer of just one block. While polymer chemists have made remarkable progress in developing new ways to synthesize block copolymers, commercial success has been limited and often relegated to applications in high-cost fields such as advanced medical devices or semiconductor manufacture. In this project, a new physical approach will be used to create blocky copolymers in a straightforward, economically-attractive fashion by selectively modifying specific sequences of units along the chains of commercially available polymers. The breakthrough approach here involves performing chemistry in the gel state, whereby specific portions of the chains are essentially hidden from the modifying chemistry. This research will provide significant advancements in accelerating the creation of tailored block copolymer assemblies and enhance fundamental insight toward next-generation membrane technologies. With respect to the grand challenges facing our society, this project will provide cost-effective, readily available alternative materials needed to meet critical demands for water purification membranes, fuel cell membranes for clean energy conversion, and environmentally-friendly materials for the medical and healthcare industries. The interdisciplinary nature of research activities in this project, ranging from pure chemistry to materials structure and properties, will provide a plethora of educational opportunities to a diverse community of students and researchers eager to contribute to our nation's leadership in a scientifically and technologically advanced society.PART 2: TECHNICAL SUMMARYThis project will focus on a new way to create blocky copolymers using straightforward, post polymerization chemistries on semi-crystalline homopolymers in the gel state. With reactions upon only the accessible amorphous chain segments within the semi-crystalline network, this new physical process yields a non-random, blocky incorporation of functionality, and is a simple alternative to the complex polymerization mechanisms that are conventionally employed in the synthesis of block copolymers. Building upon recent discoveries that semi-crystalline polymers, such as syndiotactic polystyrene and poly(ether ether ketone), can be brominated in the heterogeneous gel-state as a simple way to create blocky copolymers with tailored sequence distributions, this project aims to engage a wealth of substitution chemistries available with brominated aromatic templates to create a wide variety of new blocky copolymers as a means to systematically manipulate phase behavior and thus the formation of ordered morphologies with tailored properties. In addition to the substitution chemistries, the morphological parameters of the semi-crystalline gel will be altered by controlled temperature, concentration, and solvent to precisely affect the sequences of functionalized and non-functionalized chain segments. The grand challenge to be addressed in this project will be: Can we now direct the formation of ordered phase-separated domains, similar to that observed with conventional block copolymers, by tailoring the chemical composition of these new, gel-state functionalized, blocky copolymer systems? Membranes of the blocky copolymers will be architecturally tailored for energy conversion and water purification applications. The interdisciplinary nature of research activities in this project, ranging from pure chemistry to materials structure and properties, will help to educate a diverse community of researchers, including underrepresented groups. Educational outreach activities will engage citizens of all ages through the focus on cutting-edge research aimed at ensuring a healthier, more energy-efficient global society.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.