Thermoset materials fabricated via frontal polymerization: Material properties and photoinitiation approaches

Stawiasz, Katherine Jean

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https://hdl.handle.net/2142/120482 Copy

Description

Title

Thermoset materials fabricated via frontal polymerization: Material properties and photoinitiation approaches

Author(s)

Stawiasz, Katherine Jean

Issue Date

2023-01-30

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

Moore, Jeffrey S.

Doctoral Committee Chair(s)

Moore, Jeffrey S.

Committee Member(s)

• Sottos, Nancy R.
• Zimmerman, Steven C.
• Guironnet, Damien

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• frontal polymerization
• olefin metathesis
• photo-initiated polymerization
• ring-opening metathesis polymerization
• polymers
• materials

Abstract

Frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene rapidly polymerizes strained cyclic olefin monomers into highly cross-linked thermosets. A localized thermal stimulus induces catalysis at the triggering site; the heat generated provides sufficient energy to catalyze additional polymerization events and results in a polymerization front with a well-defined monomer-to-polymer interface. Recent advances in FROMP have enabled the rapid and energy-efficient fabrication of high-performance and thermoset materials. The second-generation Grubbs catalyst (GC2) is the most exploited FROMP catalyst to date despite the availability of several other commercial variants. Changes in the nature of the catalytic species may provide potential advantages for controlling FROMP conditions, polymer microstructure, and monomer selectivities. In the second chapter of this thesis, nine catalysts are employed for the FROMP of dicyclopentadiene (DCPD) and ethylidene norbornene mixtures to generate copolymers, and the associated polymerization process parameters (front temperatures and velocities) are measured for each system. Dynamic mechanical analysis, differential scanning calorimetry (DSC), and quasistatic tensile testing reveal significant differences in the mechanical and material properties of the resultant polymers. The third chapter explores the use of light, instead of heat, as a triggering stimulus. We discovered that FROMP of DCPD could be initiated at room temperature, by using UV-light to induce ligand photo-dissociation of GC2. The resulting polymers exhibit identical properties to those prepared via thermally triggered FROMP. A series of DSC experiments support the hypothesis the polymerization results from a photo-excitation rather than adventitious heating. Furthermore, as will be discussed in chapter four, we found that a thermally latent bis-N-heterocyclic carbene complex efficiently catalyzes FROMP of DCPD after photo-activation; in this work 9-mesityl-10-phenylacridindium tetrafluoroborate was employed as a photoredox mediator to transform copper(II) triflate into an active transmetallation acceptor upon irradiation with 455 nm light. In this unique strategy, we initiate FROMP by inducing a photoredox event at the catalyst activator (i.e., Cu) rather than the catalyst itself. This catalyst provides resins resistant to background polymerization with extended pot lives. We observed that two-component systems were viable towards for FROMP for up to 5 days, a marked improvement of the 30 h working window demonstrated by GC2. Finally, chapter five will outline future opportunities for FROMP and give a sense of where the field is headed.

Graduation Semester

2023-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Katherine Stawiasz

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