Poly(iminoborane)s: An Elusive Class of Main Group Polymers

具有由无机元素组成的主链的聚合物通常显示出有用的性质和功能，这些性质和功能补充了现有技术的有机高分子材料。突出的例子是众所周知的有机硅，它现在被视为商品。聚（亚氨基硼烷）（PIB）构成一类具有交替的硼和氮原子的线性链的无机主族聚合物。相当大的理论兴趣一直致力于这些物种，因为它们是重要的半导体有机聚合物聚乙炔的形式BN类似物。然而，尽管大量的实验努力，聚（亚氨基硼烷）的从来没有被制备和令人信服的特点，迄今为止，本研究项目的目的是开发新的合成路线，使聚（亚氨基硼烷）的合成具有明确的微观结构的第一次。先前获得线性PIB的尝试的失败通常是由于潜在BN单体形成环状亚氨基硼烷三聚体（即，环硼氮烷，苯的BN类似物）代替。该项目侧重于两种策略，以防止在聚合过程中形成环。第一种方法的想法是通过烃桥连接主链的两个硼原子或两个氮原子。这提供了几何约束，使得不可能进行不希望的环化反应，形成环硼氮烷。聚（亚氨基硼烷）的目标组成的各种类型的杂环系统，可以是芳香族，非芳香族，或anti-aromatic。第二种方法的想法是开发新的链增长缩聚方法来获得聚（亚氨基硼烷）s。生成的增长的聚合物链在两个链端上应该具有相同种类的官能团。因此，在聚合过程的任何阶段都应该防止环状物质的竞争形成，这需要两个互补末端基团的存在。将开发新的、可能催化的B-N键形成方法，并探索它们在聚合过程中的适用性。（亚氨基硼烷）S可以是用于制造成形陶瓷如六方氮化硼的有价值的聚合物前体，与石墨/石墨烯等电子的理想绝缘体和热导体。富含硼的材料也可用于癌症的硼中子俘获疗法（BNCT）。此外，PIB嵌段共聚物的合成将与本项目一起进行。将研究所得材料的自组装在纳米科学中的应用。

Polymers with a backbone comprised of inorganic elements often show useful properties and functions that complement those of state-of-the-art organic macromolecular materials. Prominent examples are the well-known silicones, which are nowadays regarded as commodity products. Poly(iminoborane)s (PIBs) constitute a class of inorganic main group polymers with a linear chain of alternating boron and nitrogen atoms. Considerable theoretical interest has been devoted to these species, as they are formally BN analogs of the important semiconducting organic polymer polyacetylene. However, despite extensive experimental effort, poly(iminoborane)s have never been prepared and convincingly characterized thus far.The aim of this research project is to develop novel synthetic routes that enable the synthesis of poly(iminoborane)s with well-defined microstructure for the first time. The failure of previous attempts to obtain linear PIBs was generally due to the susceptibility of potential BN monomers to form cyclic iminoborane trimers (i.e., borazines, BN analogs of benzene) instead. This project focuses on two strategies to prevent ring formation during the polymerization process. The idea of the first approach is to link two boron or two nitrogen atoms of the backbone via a hydrocarbon bridge. This provides a geometrical constraint that makes the unwanted cyclization with formation of borazines impossible. Poly(iminoborane)s composed of various types of heterocyclic systems are targeted that may be aromatic, non-aromatic, or anti-aromatic.The idea of the second approach is to develop novel chain growth polycondensation processes to access poly(iminoborane)s. The growing polymer chain generated should have functional groups of the same kind on both chain ends. Consequently, the competing formation of cyclic species, which would require the presence of two complementary end groups, should be prevented at any stage of the polymerization process. Novel, possibly catalytic B-N bond formation methods will be developed and their applicability in polymerization procedures will be explored.Besides interesting electronic features anticipated to be associated with this novel class of macromolecules, solution-processable poly(iminoborane)s may be valuable polymeric precursors for the fabrication of shaped ceramics such as hexagonal boron nitride, a desirable insulator and thermal conductor that is isoelectronic with graphite/graphene. Boron-rich materials are also of interest for use in boron neutron capture therapy (BNCT) for cancer. Moreover, the synthesis of PIB block copolymers will be pursued with this project. Self-assembly of the resulting materials will be investigated for applications in nanoscience.