Elacqua Group Makes Strides in Overcoming Bottlenecks in Polymer Science

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21 May 2019


The Elacqua group—led by Dr. Beth Elacqua, Assistant Professor of Chemistry at Penn State—aims to use synthetic organic chemistry to address fundamental bottlenecks in polymer science and uses polymer science to circumvent challenges in synthetic organic chemistry. The group addressed one such bottleneck in a recent paper—the first they have published—entitled Poly(arylenevinylene)s through Ring‐Opening Metathesis Polymerization of an Unsymmetrical Donor‐Acceptor Cyclophane, which focuses on the synthesis of sequence-specific D/A polymers using ring-opening metathesis polymerization (ROMP).

“In the synthetic polymer community, a significant push continues to be made toward engineering well-defined sequence-specific materials in a manner analogous to nature,” Dr. Elacqua explains. One area of research wherein the dynamic interplay of structure and function is manifested prominently is in organic electronics, wherein the most desirable materials place electronically-donating species next to electronically-withdrawing species, enhancing communication along the entirety of the polymer chain.

For over a year, the Elacqua group worked to synthesize specific monomers that could serve as templates of donor-acceptor sequences within conjugated polymers. The polymers they developed feature structural elements that are generally efficient with electron conduction, making them ideal for use in organic light-emitting diodes (OLEDs). Many industries are moving away from inorganic products in favor of emerging organic materials. OLEDs are commonly used to create digital displays in devices like television screens, computer monitors, and smartphones; they emit visible light, meaning that tech manufacturers don’t have to build backlights into their products and can make their devices thinner and lighter.

To prepare their polymers, the Elacqua group synthesized and exploited a strained ring system to introduce an A/B (donor-acceptor) sequence with every monomer insertion into a growing polymer chain.  “We hypothesized that, by using stereoelectronics, we could bias the reactivity such that the monomer could only ring-open at one site, and if it opened at one site, it could systematically staple the same A/B sequence in each iteration to the growing polymer chain so as to generate ABABABABABABAB… and so on,” Dr. Elacqua says.

The group was able to confirm this hypothesis. “The combination of suitably placed steric bulk, and electronic influence allowed for the initiation and subsequent propagation events to occur such that on initiation, the active polymer chain always presents itself with the Ru-atom proximal to the deactivated benzothiadiazole species, as evidenced using NMR spectroscopy,” Dr. Elacqua explained, “We confirmed that this is present throughout the duration of the polymerization and we can make polymers exceeding molecular weights of 25,000, and also block copolymers using other ROMP monomers.” 

The success of the project was made possible in part by the contributions of recent Penn State graduate Maria Gregor, who worked to optimize much of the 8-step synthetic pathway. Gregor, who is the second author on the paper, joined the Elacqua group as an undergraduate researcher after becoming interested in Dr. Elacqua’s work with organic synthesis and polymer chemistry. The paper, which is Gregor’s first publication, is one example of the many important contributions undergraduates make to chemistry research at Penn State. Gregor is planning to pursue a career in the chemical industry.

In the future, the Elacqua group plans to continue with this project by using this monomer scaffold to develop modular synthetic approaches that provide access to a rich variety of donor-acceptor paracyclophanes, while possibly gaining mechanistic insights into ROMP along the way.  “Downstream, we are certainly interested in the properties of these polymers as it relates to electronic materials,” Dr. Elacqua adds, “which would involve collaborations with other departments here at Penn State.  Until then, we will continue to probe synthetic routes to afford target monomers and polymers.”

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