Chapter 35
Synthesis and Properties of Polysilanes Prepared by Ring-Opening Polymerization 1
Downloaded via IOWA STATE UNIV on January 26, 2019 at 18:43:31 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
Eric Fossum and Krzysztof Matyjaszewski
Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213
A series of cyclotetrasilanes with varying numbers of methyl and phenyl substituents, Me Ph - Si , where n=3,4,5, and 6, have been prepared, characterized, and polymerized employing silyl cuprates. The polymerizations proceed with two inversions of configuration at both the attacked silicon atom and the newly formed reactive center and with some regioselectivety. The polymers have been analyzed by H, C, and S i NMR spectroscopy, along with UV spectroscopy. n
8
n
4
1
13
2 9
Polysilanes (polysilylenes) are a relatively new class of polymers with some unusual properties related to their intrinsic electronic and morphological stractures.(l3) The significant derealization of electrons in the Si-Si backbone leads to both intense UV absorptions and fluorescence emissions. The optoelectronic properties depend strongly on the structure of the substituents attached to the backbone, the chain conformation, and potential defects, such as siloxane linkages or branching. In a similar manner the morphology of polysilanes depends on the structure and symmetry of the substituents and their configurations, or microstructure. These factors control the overall morphology of the polymer chains. The establishment of structureproperty relationships for polysilanes requires well-defined polymers, as even small amounts of defects may strongly affect some properties and lead to erroneous correlations. Therefore, our continuous efforts are focused on the synthesis of welldefined polysilanes. Polysilanes are typically prepared by the reductive coupling of disubstituted dichlorosilanes with molten sodium. The resulting polymers have broad and uneven polymodal molecular weight distributions and unpredictable molecular weights. We have previously improved the synthesis of poly(methylphenylsilylene) by reducing the reaction temperature below 60 °C in the presence of ultrasound(4). Monomodal high polymers (M « 100,000) with relatively narrow molecular weight distributions (M /M
