Photoinduced Initiation of Olefin Polymerizations

在化学系大分子、超分子和纳米化学项目的支持下，Brian K. Long和他在田纳西大学诺克斯维尔分校的团队正在开发一种称为光引发烯烃聚合的新聚合方法的机械见解和理解。 烯烃是由碳和氢组成的小有机分子，其中每个碳通过常规化学键与另一个碳键合，另一个独特的键称为π键。 当这个π键断裂时，就会产生一个反应性分子，可以加成到另一个烯烃上。 这个过程可以重复多次，从而形成长链大分子，通常称为聚合物或塑料。 塑料在许多方面使我们的社会受益。 事实上，在过去的70年里，塑料帮助航空技术向前迈出了巨大的步伐，包括卫星、航天飞机、飞机和导弹的进步。 此外，建筑、电子、包装和运输行业都从塑料的使用中受益匪浅。 在这项研究中，烯烃聚合将引发光，与酸和金属物种的组合。 在这些聚合中使用光是有利的，因为它以非侵入性的方式引起化学键的断裂并且是环境友好的。 将进行复杂的研究，以便从机理上理解如何使用这三种组分的组合来控制烯烃的聚合。 这些调查预计将提供深入了解如何生产塑料与控制长度的聚合物链和架构。 如果成功，所获得的基础知识将使许多先进应用所需的化学物质成为可能，例如烯烃基3D打印聚合物。 研究跨越多个学科，包括聚合物化学，聚合物科学，有机金属化学和工程。因此，它将为有关学生提供一个跨领域的教育机会。 研究团队还将努力通过田纳西-诺克斯维尔大学SMaRT实习计划以及阿巴拉契亚学生促进研究与教育一体化（ASPIRE）计划从代表性不足的群体中招募本科生。 本研究将着重于利用光生酸剂活化均相茂金属和后茂金属催化剂用于乙烯、丙烯和高级α-烯烃的可控聚合。 为了实现这一重要目标，第一个目标将集中在详细的机制和动力学研究的二烷基取代的锆和铪前催化剂的光诱导活化。 所设计的策略将通过用光酸产生剂（PAG）代替常用的布朗斯台德酸活化剂来阻断预催化剂活化途径。 该PAG/预催化剂混合物在没有光的情况下将是休眠的，但是在照射时将产生烯烃的配位-插入聚合所需的开放配位位点。 第二个目标将应用产生的知识和原理，以控制聚烯烃的立构规整度和分子量分布。 最后，在最后一个目标中，将开发烯烃聚合的非均相光诱导引发，重点关注使用乙烯或丙烯的气态进料在表面上控制聚烯烃膜的形成。 如果成功，与这项研究相关的基础研究将扩大基于光的3D打印聚合物类型的库，包括聚烯烃。 该奖项反映了NSF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。

With the support of the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, Brian K. Long and his team at the University of Tennessee-Knoxville are developing mechanistic insight and understanding of a new polymerization methodology called photoinitiated olefin polymerization. Olefins are small organic molecules composed of carbon and hydrogen in which each carbon is bonded to another carbon through a conventional chemical bond, and another unique bond called a pi-bond. When this pi-bond is broken, a reactive molecule is created that can add to another olefin. This process can be repeated many times resulting in the formation of long chain macromolecules, commonly referred to as polymers or plastics. Plastics have benefited our society in numerous ways. In fact, plastics has helped aeronautics technology take giant steps forward over the past 70 years, including advancements in satellites, shuttles, aircraft, and missiles. In addition, the building and construction, electronics, packaging, and transportation industries have all benefited greatly from the use of plastics. In this research, olefin polymerizations will be initiated by light, in combination with acid and a metal species. The use of light in these polymerizations is advantageous because it causes cleavage of chemical bonds in non-invasive ways and is environmentally benign. Sophisticated studies will be conducted in order to mechanistically understand how the combination of these three components can be used to control the polymerization of olefins. These investigations are expected to provide insight into how plastics are produced with controlled length of polymer chains and architectures. If successful, the fundamental knowledge gained will enable the chemistry required for many advanced applications such as, for example, olefin-based 3D printable polymers. The research spans multiple disciplines, including polymer chemistry, polymer science, organometallic chemistry and engineering. Consequently, it will provide a cross-cutting educational opportunity for the students involved. The research team will also strive to recruit undergraduate students from underrepresented groups through the University of Tennessee-Knoxville SMaRT internship program, as well as Appalachian Students Promoting the Integration of Research and Education (ASPIRE) initiative. This research will focus on the use of photoacid generators to activate homogeneous metallocene and post-metallocene catalysts for the controlled polymerization of ethylene, propylene and higher α-olefins. To realize this important goal, the first objective will focus on detailed mechanistic and kinetic studies of photoinduced activation of dialkyl substituted zirconium and hafnium pre-catalysts. The designed strategy will intercept the precatalyst activation pathway by replacing a commonly used Bronsted acid activator with a photoacid generator (PAG). This PAG/ pre-catalyst mixture will be dormant in the absence of light, but upon irradiation will generate the open coordination site needed for the coordination-insertion polymerization of olefins. The second objective will apply the generated knowledge and principles to enable control over polyolefin tacticity and molecular weight distribution. Finally, in the last objective, heterogenous photoinduced initiation of olefin polymerization will be developed with a strong focus on controlling polyolefin film formation on surfaces using a gaseous feed of ethylene or propylene. If successful, the fundamental studies associated with this research will expand the library of light-based, 3D printable polymer types to include polyolefins. The knowledge gained from the mechanistic studies will be impactful to organometallic chemistry and catalysis field in general.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.