Yeo Hyunki, Akkiraju Siddhartha, Tan Ying, Tahir Hamas, Dilley Neil R, Savoie Brett M, Boudouris Bryan W
Charles D. Davidson School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States.
Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, United States.
ACS Polym Au. 2021 Nov 15;2(1):59-68. doi: 10.1021/acspolymersau.1c00026. eCollection 2022 Feb 9.
Nonconjugated radical polymers (i.e., macromolecules with aliphatic backbones that have stable open-shell sites along their pendant groups) have arisen as an intriguing complement to π-conjugated polymers in organic electronic devices and may prove to have superior properties in magneto-responsive applications. To date, however, the design of nonconjugated radical polymers has primarily focused on linear homopolymer, copolymer, and block polymer motifs even though conjugated dendritic macromolecules (i.e., polyradicals) have shown significant promise in terms of their response under applied magnetic fields. Here, we address this gap in creating a nonconjugated, three-arm radical macromolecule with nitroxide open-shell sites using a straightforward, single-step reaction, and we evaluated the electronic and magnetic properties of this material using a combined computational and experimental approach. The synthetic approach employed resulted in a high-purity macromolecule with a well-defined molecular weight and narrow molecular weight distribution. Moreover, epoxide-based units were implemented in the three-arm radical macromolecule design, and this resulted in a nonlinear radical macromolecule with a low (i.e., below room temperature) glass transition temperature and one that was an amorphous material in the solid state. These properties allowed thin films of the three-arm radical macromolecule to have electrical conductivity values on par with many linear radical polymers previously reported, and our computational efforts suggest the potential of higher generation open-shell dendrimers to achieve advanced electronic and magnetic properties. Importantly, the three-arm radical macromolecule also demonstrated antiferromagnetic exchange coupling between spins at temperatures < 10 K. In this way, this effort puts forward key structure-property relationships in nonlinear radical macromolecules and presents a clear path for the creation of next-generation macromolecules of this type.
非共轭自由基聚合物（即具有脂肪族主链且在其侧基上有稳定开壳位点的大分子）已成为有机电子器件中π共轭聚合物的一种有趣补充，并且在磁响应应用中可能具有优异性能。然而，迄今为止，非共轭自由基聚合物的设计主要集中在线性均聚物、共聚物和嵌段聚合物结构单元上，尽管共轭树枝状大分子（即多自由基）在施加磁场下的响应方面已显示出巨大潜力。在此，我们通过一种简单的单步反应填补了这一空白，制备了一种具有氮氧化物开壳位点的非共轭三臂自由基大分子，并使用计算和实验相结合的方法评估了该材料的电子和磁性性质。所采用的合成方法得到了一种具有明确分子量和窄分子量分布的高纯度大分子。此外，在三臂自由基大分子设计中引入了基于环氧化物的单元，这产生了一种具有低（即低于室温）玻璃化转变温度且为固态无定形材料的非线性自由基大分子。这些性质使得三臂自由基大分子薄膜的电导率值与先前报道的许多线性自由基聚合物相当，并且我们的计算结果表明更高代的开壳树枝状大分子具有实现先进电子和磁性性质的潜力。重要的是，三臂自由基大分子在温度<10 K时还表现出自旋间的反铁磁交换耦合。通过这种方式，这项工作提出了非线性自由基大分子中的关键结构 - 性质关系，并为创建此类下一代大分子提供了一条清晰的途径。
