Preparation of Light and Moisture Stable Flexible and Rigid Asymmetrical Polystannanes
Theoretical calculations of polystannanes in an all trans-configuration possess a relatively small band gap (~2.8 eV). This is due to the extensive σ-σ overlap of the diffuse 5sp3 orbitals of Sn atoms in the conjugated Sn-Sn polymer backbone, which leads to a visible σ-σ* transition by UV-vis spectroscopy. The electronic properties of polystannanes suggests that these materials are candidates for semi-conducting intrinsic polymers. However, due to the weak bonding between Sn-Sn atoms and the Lewis acidic nature of Sn centers, polystannanes readily degrade with exposure to daylight and moist atmospheres. This project demonstrates clear synthetic pathways and designs to stabilize the Sn-Sn backbone. This was accomplished by incorporating functional ligands with Lewis basic heteroatoms such as oxygen or nitrogen moieties which can form a hypercoordinate interaction with the Sn center. Two major types of asymmetrical polystannane systems were investigated: 1) a flexible system where Sn centers are attached to a propyl chain containing either a bulky or small functional donor ligand and 2) a rigid system where the Sn center contain either a hypercoordinate benzyl methoxy ether (C,O) or benzyl dimethyl amine (C,N) ligand prepared using a direct approach. This thesis is broken into three different chapters. Chapter 1 and 3 include all synthetic pathways, characterization and stability testing of both flexible and rigid polystannanes. Chapter 2 describes a high molecular weight (Mw = 60 kDa) film forming, semi-crystalline (Tg = 49.3 °C and Tm = 110.1 °C) flexible asymmetrical polystannane containing a propylhydroxy ligand that displays exceptional stability to light and moisture (> 9 months). In addition, a tosyl containing polystannane that could function as a macromolecular intermediate was prepared. Substitution of model tosyl stannanes was demonstrated, and substitutions of the tosyl polystannane are ongoing.