Design and Synthesis of Monomers toward Sequence-Controlled Polymers
Restricted (Penn State Only)
- Author:
- Gerthoffer, Margaret
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 27, 2023
- Committee Members:
- Robert Rioux, Major Field Member
Elizabeth Elacqua, Chair & Dissertation Advisor
Raymond Schaak, Major Field Member
Philip Bevilacqua, Program Head/Chair
Robert Hickey, Outside Field Member
Vincent Crespi, Outside Unit Member - Keywords:
- Nanothreads
Ar/ArF Co-Crystals
ROMP
phenylene(arylene)vinylenes
cyclophanes
polymers - Abstract:
- Strategies to synthesize sequence-defined polymers remain limited for industrial-scale applications, often due to time consuming iterative addition or polymerization methods possessing low functional group tolerances. Throughout my PhD, I have utilized both ring-opening metathesis polymerization (ROMP) and pressure-induced polymerization to form sequence-defined polymers from deliberately designed A-B monomers. ROMP of electronically-biased paracyclophanedienes (pCpd) can form donor-acceptor poly(arylenevinylene)s. In addition, the pressure-induced polymerization of engineered aryl/perfluoroaryl (Ar/ArF) co-crystals translates into sequence-specific sp3-saturated copolymers known as nanothreads. Both polymerization methods form sequence-specific copolymers as dictated by the supramolecular monomer design. The ROMP of ring-strained pCpds containing dialkyloxybenzene donor and benzothiadiazole acceptor obtains well-defined polymers with ruthenium-based initiators. This design promotes favors sequence specificity between the electronically-activated dialkyloxybenzene and electronically-deficient benzothiadiazole that can guide the initiator homogenously during ring opening and polymerization events. During my PhD, I have discovered that the presence of sterically asymmetric alkyloxy groups (methoxy and octyloxy) on the donor further guides the polymerization process. I have elucidated that the steric effects of the alkyloxy donor group can further control the rate of well-defined donor-acceptor copolymer synthesis due to supramolecular interactions with ruthenium-based initiators. To expand on this, I targeted the synthesis of various alkyloxybenzene donor groups in both linear and branched substitutions to compare ROMP rate and polymer sequence definition with benzothiadiazole acceptors. The investigated pCpds formed well-defined polymers that did not prohibit ruthenium-catalyst attachment as confirmed by GPC and NMR spectroscopy. I have moreover been able to synthesize ladderane-like polymers known as nanothreads by the pressure-induced polymerization (23+ GPa) of alternating eclipsed stacks of aromatic cores in solid-state Ar/ArF co-crystals. I have designed monomer pairs through preorganization of Ar/ArF synthons with varied quadrupole, hydrogen, and halogen bonding to understand the design elements necessary to form substituted nanothreads at reduced pressure thresholds. For all co-crystals, supramolecular engineering has reduced polymerization pressures compared to individual components as confirmed through in situ Raman, NMR, and XRD spectroscopies under pressure. Phenol:pentafluorophenol illustrates strong hydrogen bonding that stabilizes interstack interactions under pressure to form nanothreads. However, I discovered that hydrogen bonding amongst external functionalities can prohibit facile compressibility if the direction aligns to the putative Ar/ArF thread axis. Direct intrastack hydrogen bonding can in fact increase the required pressure of polymerization (30 GPa+). Designing appropriate hydrogen bonding scaffolds in Ar/ArF co-crystals thus offers the ability to target sequence-controlled nanothread production at a reduced pressure.