I. Kinetic and mechanistic studies of dynamic alkyne metathesis and II. Towards regenerative thermosets using frontal ring-opening olefin metathesis polymerization

Greenlee, Andrew James

Permalink

https://hdl.handle.net/2142/121417 Copy

Description

Title

I. Kinetic and mechanistic studies of dynamic alkyne metathesis and II. Towards regenerative thermosets using frontal ring-opening olefin metathesis polymerization

Author(s)

Greenlee, Andrew James

Issue Date

2023-07-11

Director of Research (if dissertation) or Advisor (if thesis)

Moore, Jeffrey S

Doctoral Committee Chair(s)

• Moore, Jeffrey S
• Murphy, Catherine J

Committee Member(s)

• Guironnet, Damien S
• Appelhans, Leah N

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Alkyne
• Metathesis
• Dynamic
• Thermoset

Abstract

In recent years, dynamic covalent chemistry (DCC) has seen the synthesis of increasingly complex cyclooligomers, polymers, and diverse compound libraries. The reversible formation of covalent bonds characteristic of DCC reactions favors thermodynamic product distributions for simple unitopic reactions. Traditionally, it was also assumed that DCC self-assembly processes with multitopic precursors were also wholly governed by thermodynamic factors. However, evidence suggests that kinetic effects are increasingly influential in reactions of increasingly complex substrates. Part I of this Dissertation describes mechanistic investigations into dynamic alkyne metathesis (AM) with the aim of elucidating factors leading to pathway-dependency in AM self-assembly reactions. Kinetic studies reveal the kinetic regime occupied by AM and serve as the basis for a rule-based computational model of dynamic self-assembly. To explore the relationship between catalyst loading and assembly efficiency, we developed a pulsed addition technique to determine the kinetic profile of AM catalyst deactivation. We found that prototypical AM catalysts are deactivated in solution on a timescale comparable to that of a self-assembly reaction, potentially leading to inefficient thermodynamic error correction. In our exploration of more robust catalysts, we also established the orthogonality of dynamic imine exchange and AM. We hypothesized that tridentate AM “canopy” catalysts developed by Zhang, Fürstner, and Lee for AM would remain metathesis-active in the presence of Lewis basic moieties involved in other dynamic exchange reactions. Catalysts using a rigid trityl- derived ligand scaffold were found to successfully engender the metathesis of imine-bearing substrates, while catalysts using a relatively flexible triphenolsilane ligand were not. The former catalyst was found to be stable to imine moieties, but metathesis-inactive in the presence of basic ii amines, excess water, and Lewis acidic co-catalysts. Assembly and disassembly of a molecular ladder prepared via tandem DCC in one pot was demonstrated in the presence and absence of a Lewis acid catalyst. Part II of this Dissertation describes a novel approach to the design and manufacture of “regenerative” polymer thermosets and novel upcycling strategies for such species. While recent work has enabled the synthesis of thermosets with degradable linkages, current strategies for end-of-life management of these materials is still limited to upcycling strategies. Sustainability initiatives would benefit tremendously from the development of chemical strategies to regenerate polymer functionality through the restoration of the original polymerizable moieties, enabling reuse of degradation products in repeated polymerizations. We hypothesized that derivatives of dicyclopentadiene (DCPD) and its corresponding polymer possessing a potent dienophilic moiety, namely an enone motif, would be amenable to reactivation for ring opening metathesis polymerization (ROMP) by Diels-Alder reaction with cyclopentadiene. We found that a ketone- functionalized DCPD derivative forms persistent chelates in solution-phase ROMP, slowing the reaction. This diminished propagation rate, coupled with the crystallinity of the monomer, prohibited its application in frontal polymerization. Attempts at post-polymerization modification of oligo(oxaDCPD) via Diels-Alder reaction with cyclopentadiene failed to furnish the desired product, yielding instead chain end-functionalized oligomers as determined by advanced mass analysis. These data provide insight into the pitfalls of both monomer design and reactivation strategies for future regenerative thermosets.

Graduation Semester

2023-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Andrew James Greenlee

Owning Collections