Effect of Chain-ends on the Mixed Polymer Brush Morphology

聚合物刷是一种长而细的分子，用化学方法固定在表面上，形成一层致密的薄涂层，改变表面特性。虽然表面的化学锚定为涂层提供了所需的机械强度，但聚合物的化学和结构使其能够与环境沟通。因此，这些涂层在解决材料科学和人类健康问题方面具有广泛的相关性。当固定在电子活性表面上时，它们可以作为快速检测生物流体中生物标志物的传感器，指导再生医学的细胞生长，抵抗表面上微生物的沉积，控制电池中的电荷流动，控制相关界面的摩擦。等。该研究项目将开发新的合成方法，使这些聚合物刷具有良好的结构和化学性质。所开发的方法产量高，简单，可在广泛的表面上重现，因此可以被涂料行业采用。该计划将开发表征方法，以帮助在分子水平上理解所得结构。该研究项目将通过REU项目与研究生导师合作，激励和参与聚合物科学和工程研究的本科生。教育模块也将通过威斯康星大学麦迪逊分校的化学教育研究所进行传播，这是一个致力于通过外展和教育研究进行STEM教育的国家中心。本研究项目将开发一种高度通用的方法，在基材上使用可交联的共聚物涂层生长混合a /B聚合物刷，该共聚物涂层含有可聚合的引发剂（聚合物）作为共聚单体。混合A/B聚合物刷由化学上不同的A链和B链随机接枝到表面。它们的密度、高度和组成随溶剂环境的变化而变化。这些聚合物刷具有高链接枝密度、A和B接枝点分布均匀、分子量可控、组成可控等特点。理论预测，与嵌段共聚物相比，混合刷的相分离临界点降低，并形成纳米级形态。然而，实验研究未能证实这些预测。理论与实验的差距主要在于：a)缺乏可控制接枝比、可预测链长、高接枝密度混合刷均匀生长的实验方法；b)缺乏理论和实验中对链端基的考虑；c)缺乏研究形貌的表征方法。在这个项目中，目标是了解链端密度、大小、分布和类型对A/B混合刷形态的作用。这在很大程度上是一个实验和理论上尚未探索的领域。本研究的关键方面将是制定附加选择链端基团的合成策略，通过x射线光电子能谱和共振软x射线散射（RSoXS）的组合来量化功能化程度和链端分布，以及通过散射和先进显微镜技术的结合来研究链端功能化对侧相偏析的影响。通过这些实验获得的形态学见解将有助于对聚合物刷的更广泛的理解和应用。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智力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 SUMMARYPolymer brushes are long stringy molecules that are chemically anchored to a surface to form a dense, thin coating that alters the surface properties. While the chemical anchoring to the surface provides the required mechanical strength to the coating, the chemistry and structure of the polymer enables communication with the environment. Hence, these coatings have broad relevance in solving problems in materials science and in human health. They can act as sensors for rapid detection of biomarkers in biofluids when anchored to electronically active surfaces, direct cell growth for regenerative medicine, resist deposition of micro-organisms on surfaces, control flow of charge in batteries, control friction at relevant interfaces., etc. This research program will develop new synthetic methodologies to make these polymer brushes with well defined structure and chemistry. The methodology developed is high yielding, simple and reproducible on a wide range of surfaces, hence can be adapted by the coating industry. This program will develop characterization methods to aid in the molecular level understanding of the resulting structure. The research program will serve to inspire and involve undergraduate students in polymer science and engineering research, by working with graduate student mentors, through the REU program. Educational modules will also be developed for dissemination through UW-Madison’s institute for Chemical Education, a national center dedicated to STEM education through outreach and education research. PART 2: TECHNICAL SUMMARYThe research program will develop a highly versatile approach to grow mixed A/B polymer brushes from a substrate using a cross-linkable copolymer coating, which contains a polymerizable initiator (inimer) as a comonomer. Mixed A/B polymer brushes consist of chemically distinct A and B chains, randomly grafted to the surface. They show changing density, height and composition profile as a function of solvent environment. These polymer brushes will have high chain grafting density, uniform distribution of A and B graft points, controlled molecular weights, and excellent control over composition. Theory predicts the lowering of critical point for phase separation in mixed brushes compared to block copolymers, and the formation of nanoscale morphology. However, experimental studies have fallen short of validating these predictions. The gap between theory and experiments is attributable to lack of: a) experimental methods for uniform growth of high grafting density mixed brushes with controllable grafting ratios, and predictable chain lengths, (b) accounting for chain end-groups in theory and experiments, and (c) characterization methods to study the morphology. In this project the goal is to understand the role of chain-end density, size, distribution, and type on the A/B mixed brush morphology. This is a largely experimentally and theoretically unexplored area in polymer brushes. Key aspects of this research will be to develop synthetic strategies to append select chain end groups, quantification of the extent of functionalization and chain-end distribution by a combination of X-ray photoelectron spectroscopy and Resonant Soft X-ray scattering (RSoXS), and studying the effect of chain-end functionalization on lateral phase segregation by a combination of scattering and advanced microscopy techniques. The morphological insight developed through these experiments will contribute towards the broader understanding and application of polymer brushes..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.