Controlled Radical Polymerization for Novel Soft Materials

该研究计划的广泛目标是合成、表征和加工新型嵌段、随机和梯度共聚物，用于为有机光伏/发光二极管(OPV/OLED)材料量身定做的刺激响应聚合物。我们应用了最先进的受控自由基聚合(CRP)技术，以获得对此类应用至关重要的必要微观结构。CRP接近真正的“活性”聚合方法中发现的微结构控制，而不需要后者所需的详尽的纯化、官能团保护和无空气条件。此外，CRP可以连接不同的嵌段和/或单体，否则无法通过离子聚合实现，并提供了在分散的水介质中进行可控聚合的可能性。这种多功能性允许前所未有的无数种可能的组合来实现所需的纳米结构材料。特别是，我们使用了一种名为氮氧化物介导的聚合反应(NMP)的CRP技术，与其他CRP方法相比具有一些有利的特点。例如，它不需要金属催化剂或硫基链转移剂，这些催化剂或硫基链转移剂可能会作为杂质存在，可能会影响刺激响应性生物医学材料和有机电子材料的性能。 NMP的一个传统缺点是它对苯乙烯单体聚合的限制-这在很大程度上通过使用第二代烷氧胺引发剂(如BlocBuilder)而得到解除，这种引发剂能够实现丙烯酸酯的均聚合，并通过使用少量的共聚单体(通常是~5-10摩尔%的苯乙烯)聚合富甲基丙烯酸酯的组成。我们已经研究了添加了官能团的控制共单体，例如咔唑-功能控制共单体(例如。VBK)在刺激响应型聚甲基丙烯酸酯中赋予电子给体/荧光性质。我们用核磁共振和电子自旋共振来鉴定物种和了解自由基共聚合动力学。值得注意的是，我们发现自由基竞聚率是决定用BlocBuilder引发剂维持受控甲基丙烯酸酯聚合所需的共聚单体数量的关键。将我们的应用范围扩展到OPV/OLED，我们已经开始研究控制共聚单体中的电子受体基团，如恶二唑。我们最近发现，即使均聚反应受到控制，并不是所有的苯乙烯类共单体都能有效地作为甲基丙烯酸酯的控制器。因此，短期目标是通过伪Hammett参数分析来确定共单体给体/受体官能团对富含甲基丙烯酸酯的NMP的影响，这将使如何将这种官能团结合到所需的聚甲基丙烯酸酯中。 追求电子给体/受体侧链聚合物的长期目标是利用它们更容易加工的优势，并将它们自组装成有序的结构域，而这些结构域不一定存在于与OPV/OLED相关的典型的刚性、片状主链聚合物中。我们的初步研究将考察可以作为水性胶乳的给体-受体嵌段共聚物的组合，然后选择性地去除聚甲基丙烯酸酯的结构域(例如。通过光刻)。此外，已应用于其他嵌段共聚体系的结构域放大和外延生长将被尝试，因为很少有研究涉及侧链供体/受体共聚物的直接自组装，尽管有报道称形态对器件性能起着关键作用。该项目通过NMP专注于刺激响应性和OPV/OLED材料，是一个独特的利基市场，将为HQP(2名博士)提供可移植到加拿大经济许多关键部门的合成和加工技能。

The research program's broad objective is to synthesize, characterize and process novel block, random and gradient copolymers for tailored stimuli-responsive polymers to organic photovoltaic/light emitting diode (OPV/OLED) materials. We have applied state-of-the-art controlled radical polymerization (CRP) techniques to achieve the requisite microstructure vital for such applications. CRP approaches the control of microstructure found in truly "living" polymerization methods without the exhaustive purification, functional group protection and air-free conditions required of the latter. Further, CRP can link different blocks and/or monomers which otherwise could not achieved by ionic polymerization and offers the possibility of controlled polymerization in dispersed aqueous media. This versatility allows an unprecedented myriad of possible combinations to achieve desired nano-structured materials. In particular, we use a CRP technique termed nitroxide mediated polymerization (NMP), which has some favourable characteristics compared to other CRP methods. For example, it does not require metallic-containing catalysts or sulfur-based chain transfer agents that may remain as impurities which may affect the performance of stimuli-responsive biomedical materials and organic electronic materials. A traditional drawback to NMP was its restriction to the polymerization of styrenic monomers – this has been largely lifted by the use of second-generation alkoxyamine initiators such as BlocBuilder, which has enabled the homopolymerization of acrylates and the polymerization of methacrylate-rich compositions by using a small amount of co-monomer (typically styrenic ~ 5-10 mol%). We have examined controlling co-monomers that have added functionality such as the carbazole-functional controlling co-monomer (eg. VBK) to impart electron-donating/fluorescent properties in stimuli-responsive poly(methacrylates). We applied NMR and ESR to identify species and understand radical copolymerization kinetics. Notably, we found radical reactivity ratios were pivotal in determining how little co-monomer was necessary to maintain a controlled methacrylate polymerization with BlocBuilder initiators. Extending our scope to OPV/OLED applications, we have begun examining electron-acceptor groups in the controlling co-monomer, such as oxadiazoles. We have recently found that not all styrenic co-monomers are effective as controllers for methacrylates, even if the homopolymerizations were controlled. A short-term objective is thus to determine the effect of co-monomer donor/acceptor functionality on methacrylate-rich NMP via a pseudo-Hammett parameter analysis, which will enable how to incorporate such functionality into the desired poly(methacrylate). The longer-term goal for pursuing the electron-donor/acceptor side chain polymers is to take advantage of their easier processability and to self-assemble them into well-ordered domains not necessarily found in the typically stiff, lamellar main-chain polymers associated with OPV/OLEDs. Our initial studies will examine the combination of donor-acceptor block copolymers that could be applied as a water-borne latex, followed by selective removal of the poly(methacrylate) domain (eg. via photolithography). Further, domain amplification and epitaxial growth that has been applied in other block copolymer systems will be attempted as few studies have addressed directed self-assembly of side-chain donor/acceptor copolymers, despite reports of the critical role of morphology on device performance. The program focus on stimuli-responsive and OPV/OLED materials via NMP is a unique niche and will provide HQP (2 PhDs) with synthetic and processing skills that are portable to many vital sectors of the Canadian economy.