| dc.description.abstract | The exposure that firefighters experience due to their occupation has recently been identified by the World Health Organization as a Group 1 carcinogen. One factor is colorless, odorless, toxic gases in “warm zones” near enough to fires where awareness and protection are lowered but the actual risks are still high. The current gas sensors available are based on metal oxides, and are bulky, inflexible, and costly to produce. By contrast, gas sensors based on conjugated polymers promise to be lightweight and flexible enough to weave directly into clothing and could be manufactured using low cost roll-to-roll printing. However, they require improvements in stability.
This work first establishes a baseline of stability for previously reported conjugated polymers. Common p-type dopant molecules are used to dope diketopyrrolopyrrole (DPP) copolymers, which are known for their stability. It was found that the longest the sensors could last was ~10 days.
Believing that the stability could be improved through increasing the energy level of the polymer’s Highest Occupied Molecular Orbital (HOMO), this thesis extends a recent report of a novel DPP-flanking group, methoxythiophene. The potential of methoxythiophene-flanking groups as a method to raise DPP polymer HOMO energy has several advantages. They are sterically small (only extending the length of the thiophene molecule by < 2.5 Å) and by using the flanking group to raise the HOMO, both the choice of solubilizing side chain and choice of comonomer remain free. A solubilizing side chain with thermally/chemically removable groups could therefore be used. The removal process could introduce stable pores, enhancing gas transport in and out of the polymer film. Likewise, a comonomer could be selected for its interaction with a target gas.
Three novel conjugated DPP-based copolymers were then synthesized, using methoxythiophene as a flanking group to the DPP unit. Two were produced through Stille coupling and one was produced through the more environmentally friendly Direct Arylation Polymerization (DArP).
As hypothesized, these copolymers show high HOMO levels, which are anticipated to grant them high stability once doped with common p-dopants. One, C8-EDOT shows conductivity stable in air over 2 months (~1%/day decrease in current) even without exogenous dopant, having been doped by trace HCl in chloroform used to coat films. The three polymers also show ultralow bandgaps, which could make them useful in Near Infrared detection or Organic Photovoltaic applications. | en |
