Open Collections

From main group to transition metal-containing Brønsted acid initiators for the cationic polymerization of olefin monomers

University of British Columbia

This dissertation outlines the development of Brønsted acids and their application as single-component initiators for the cationic polymerization of olefins. Solid weighable Brønsted acids are of particular interest in the generation and stabilization of highly reactive cations. Weakly coordinating anions (WCAs) facilitate the isolation of Brønsted acids and play a critical role in the carbocationic polymerization of vinyl monomers. Chapter 1 gives an introduction to the mechanism of cationic polymerization and the challenges associated with it. The chapter also describes important initiator systems that are used in cationic polymerization and provides an overview of main group element-based WCAs that have been previously reported. Chapter 2 outlines the application of the known tris(tetrachlorobenzenediolato)phosphate,[P(1,2-O₂C₆Cl₄)₃] ̄, as a WCA in the stabilization of reactive cations. The isolated Brønsted acids H(L)₂[P(1,2-O₂C₆Cl₄)₃] (L = THF, DMF) were employed as effective single-component initiators for the cationic polymerization of n-butyl vinyl ether and p-methoxystyrene at various temperatures. Notably, high molecular weight poly(p-methoxystyrene) was obtained with an unexpected branched structure. Chapter 3 describes three potential routes to afford Hellwinkel’s salt, [P(C₁₂H₈)₂][P(C₁₂H₈)₃]. A pentavalent phosphorane, P(C₁₂H₈)₂(C₁₂H₉), and an unprecedented product, [P(C₁₂H₈)(C₂₄H₁₆)][P(C₁₂H₈)₃], were isolated and characterized. The cation [P(C₁₂H₈)(C₂₄H₁₆)]⁺ is formally derived from the insertion of an additional biphenyl unit into the known [P(C₁₂H₈)₂]⁺. Chapter 4 highlights the synthesis and characterization of several amine salts and an alkali metal salt featuring a hexacoordinate anion, [P(C₆H₄CO₂)₃] ̄. The basicity of [P(C₆H₄CO₂)₃] ̄ was examined using IR spectroscopy and found to be comparable to [ClO₄] ̄ and [N(SO₂CF₃)₂] ̄. Chapter 5 describes the synthesis and characterization of two different Brønsted acids with the cation moiety [H(OEt₂)₂]⁺. The Brønsted acids were employed as highly effective single-component initiators for the cationic polymerization of n-butyl vinyl ether, styrene, ⍺-methylstyrene and isoprene at different temperatures. Remarkably, high molecular weight polystyrene and poly(⍺-methylstyrene) were obtained. A predominantly rich syndiotactic poly(⍺-methylstyrene) (rr up to 90%) was isolated from a polymerization at –78 °C. Chapter 6 provides a summary of the thesis work and postulates future considerations in the field.

Text

2020-01-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/66536

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/