Tailoring Assemblies of Surface-Anchored Polymers by "Grafting from" Free Radical Polymerization

技术摘要：本项目的主要目标是获得表面引发的自由基聚合的详细了解，以及其扩展到受控的自由基聚合，并将这些知识应用于制备具有定制和空间调制的聚合物接枝物分布的基底。 本工作主要有四个目标：首先，自由基聚合将被用来建立引发剂密度，聚合物接枝密度，分子量和多分散指数之间的关系。 将制造在聚合物接枝密度和分子量方面具有独立变化的正交梯度的基底，其包含从基底结合的引发剂生长的聚合物。 活化与非活化引发剂位点的量以及聚合物接枝密度和接枝物的分子量将通过表面敏感分析技术进行定量。 其次，偶氮基引发体系将被用来监测通过反向原子转移自由基聚合生长的聚合物刷的特性。 虽然这种转变已被大量研究，它从来没有被执行？嫁接的聚合。 通过在不同温度和过渡金属盐浓度下使用聚合物接枝密度/分子量正交梯度，将加速多分散指数和聚合动力学的预期差异。 第三，将利用UV活化偶氮引发剂的能力来形成与基底结合的微米级大分子梯度。 通过利用微流控反应器，将通过沿微流控通道沿着局部混合两种单体流并通过使用穿过光掩模的UV照射来实现微尺度聚合物图案化。 第四，作为种子项目，将利用微波诱导的自由基聚合来提供局部基底加热，以便通过同时冷却单体溶液和通过微波局部加热基底来使增长动力学与引发步骤解耦，这迄今为止是不可能的。表面引发剂密度和接枝聚合物密度之间的关系以前从未以系统的方式研究过，当考虑聚合物刷应用的广度和深度时，这是至关重要的。 虽然先进材料具有很高的价值，但经济限制了它们的使用，将它们严格限制在绝对必要的领域。 为此，从成本和性能的角度来看，制造可以施加到各种表面的薄的化学和结构定制的涂层是有利的。 通过这样做，人们可以实现对原始基底及其周围环境之间的界面的完全控制，只需几纳米的工程涂层材料。 这些聚合物结构的应用范围从制备化学和结构定制的膜防止船舶污染到控制体内生物材料界面，以及无数其他技术应用，包括（但不限于）润滑、抗絮凝、颗粒组装、蛋白质吸附、细胞信号传导和纳米级分子运动。 我们的推广和教育工作补充了科学方面的工作，包括：i）培训研究生，ii）在弗吉尼亚州阿拉拉特的一所小学开展外联活动，iii）通过北卡罗来纳州立大学的凯南研究员和科学之家项目，吸引当地K-12教师和学生参加我们的跨学科研究工作，以及iv）在NC州立大学为本科生和研究生组织国家和国际科学会议。

TECHNICAL SUMMARY:The principal goal of this project is to gain a detailed understanding of surface-initiated free radical polymerization, as well as its extension to controlled radical polymerization, and apply this knowledge towards preparing substrates with tailored and spatially-modulated distributions of polymeric grafts. There are four main objectives of this work:First, free radical polymerization will be used to establish the relationship between the initiator density, polymer grafting density, molecular weight, and polydispersity index. Substrates with independently varied orthogonal gradients in polymer grafting density and molecular weight will be fabricated comprising polymers grown from substrate-bound initiators. The amount of activated vs. non-activated initiator sites and polymer grafting density and molecular weight of the grafts will be quantified by means of surface-sensitive analytical techniques. Second, azo-based initiator system will be employed to monitor the characteristics of polymer brushes grown via reverse atom transfer radical polymerization. While this transformation has been studied in bulk, it has never been performed in ?grafting from? polymerizations. Expected differences in polydispersity index and polymerization kinetics will be expedited through use of polymer grafting density/molecular weight orthogonal gradients at varying temperatures and transition metal salt concentrations. Third, the ability to UV-activate the azo-initiators will be exploited to form substrate-bound micrometer-sized macromolecular gradients. By utilizing microfluidic reactors microscale polymer patterning will be accomplished by locally intermixing two monomer streams along the microfluidic channel and by employing UV irradiation through photomasks. Fourth, as a seed project, microwave-induced free radical polymerization will be utilized to provide local substrate heating in order to de-couple the kinetics of propagation from the initiation step, which heretofore has not been possible, by concurrently cooling the monomer solution and heating the substrate locally by microwave.NON-TECHNICAL SUMMARY:The relationship between surface initiator density and grafted polymer density, which has never been investigated in a systematic way before, is of critical importance when considering the breadth and depth of applications of polymer brushes. While advanced materials have high value, economics limit their use, strictly confining them to those areas where they are absolutely necessary. To this end it is advantageous, from both cost and performance standpoint, to fabricate thin chemically and structurally tailored coatings that can be applied to various surfaces. By doing so, one can attain full control over the interface between the original substrate and its surroundings with just a few nm of engineered coating material. Applications of these polymeric structures range from preparing chemically and structurally tailored films preventing fouling of ships to controlling biomaterial interfaces in vivo, as well as countless other technological applications, including (but not limited to), lubrication, anti-flocculation, particle assembly, protein adsorption, cell signaling, and nanoscale molecular motion. Our outreach and education efforts, which complement the scientific aspect of the work, include: i) training graduate students, ii) outreach activities in an elementary school in Ararat, VA, and iii) attracting local K-12 teachers and students to take part in our interdisciplinary research endeavors through the Kenan Fellows and the Science House programs at NC State University, and iv) organizing national and international scientific meetings for undergraduate and graduate students at NC State University.