Dissertations, Theses, and Capstone Projects

Date of Degree

2-2019

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor

Qiao-Sheng Hu

Committee Members

Shengping Zheng

Probal Banerjee

Subject Categories

Chemistry | Physical Sciences and Mathematics | Polymer Chemistry

Keywords

Suzuki Cross-Coupling, Palladium(0), Polymerization, π-conjugated polymers, Controlled Polymerization, Aryl Dihalides

Abstract

The synthesis of well-defined and high molecular weight π-conjugated polymers under mild condition within short reaction time is a challenging and important task in both organic chemistry and polymer chemistry. As one of the most efficient and high tolerance to solvents and reaction conditions, palladium(0)-catalyzed cross-coupling reactions would give us a good chance to achieve the goal. Thus, my Ph. D dissertation research projects focused on developing Pd(0)-catalyzed Suzuki cross-coupling polymerization reactions including controlled ones.

My research first studied t-Bu3P-coordinated 2-phenylaniline-based palladacycle complex catalyzed Suzuki cross-coupling polymerization of aryl dibromides with aryldiboronic acids at room temperature. Based on our understanding of Pd(0)-catalyzed Suzuki cross-coupling polymerization process, I figured out the amount of the base used, and the solubility of the polymers were the mainly limitations of the growth of polymer chains. By adjusting the amounts of the base used in polymerization process, using different substituted monomers and changing the reaction conditions, I was able to achieve high molecular weight polymers at room temperature within one hour. Moreover, aryl diiodides were tested with the same reaction condition afforded promising results, which confirmed this palladium catalyst system is highly efficient for Suzuki cross-coupling polymerizations.

The high molecular weight π-conjugated polymers have better properties than low molecular weight polymers, including electrochemical stability, film-forming properties and so on. In order to make extremely high molecular weight polymers, a new polymerization reaction condition was studied and a combination of AA/BB approach and AB approach of the Pd(0)-catalyzed Suzuki cross-coupling polymerization reaction was proposed and demonstrated. Under the guidance of the new reaction mechanism, polymers with extremely high molecular weights have been produced, which we believed it would be a revolution of producing high molecular weight π-conjugated polymers under mild conditions. Since Br- and I- substituted aryl compounds were proved obtaining great reactivity for Suzuki cross-coupling polymerizations (SCCPs), further study of the polymerizations of Cl- substituted aryl compounds with tris(1-adamantyl) phosphine coordinated acetanilide-based palladacycle complex as the catalyst has been carried out. Less reactive aryl chlorides tend to be cheaper than aryl bromides or aryliodies, and many of them are commercially available. It was valuable that we employed aryl chlorides to SCCPs for synthesizing high molecular weight π-conjugated polymers. It widened the applicability of SCCPs.

The last part of my research explored robust initiators for controlled Pd(0)-catalyzed Suzuki cross-coupling polymerization of AB-type of monomers, affording polymers with unprecedentedly narrow PDIs and well-controlled functional end groups. The 31P NMR study was applied to check the initiation rate and efficiency of the precatalyst, which afforded a better understanding of the catalyst system to us.

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