Chris Stubbs
Speaker's Institution
Colorado State University
Chemistry A101
Mixer Time
Mixer Time
Chemistry B101E
Calendar (ICS) Event
Additional Information

About the Seminar:

In the modern world, polymeric materials dominate both commercial and consumer materials. From car tires to drug delivery capsules, the applications of polymers are nearly limitless. As such, there has been significant interest in understanding the structure-property relationships for both theoretical and real polymers. In particular, the effect of chain ends on polymer structure and dynamics has received significant attention in an effort to access sophisticated nanostructures with targeted properties.
Given that chain ends can also influence polymer size and chain entanglement, there is significant merit in understanding polymers with and without chain ends.

Traditionally, the vast majority of non-tethered polymers contain two or more chain ends – these are classified as linear polymers. While linear polymer chains can possess more than two chain ends (star, comb, etc.), the absence of chain ends is impossible by definition. In contrast to linear polymers, topological polymers can have chains with zero (or more) chain ends. In the special case of a topological polymer possessing a ring architecture and zero chain ends, the polymer is termed a cyclic polymer. Due to their lack of chain ends, cyclic polymers have fundamentally different characteristics than their equivalent linear counterparts. These differences include chain dynamics, chain entanglement, radius of gyration, morphology, viscosity and more. While cyclic polymers have been studied since the mid-1960s, access to cyclic polymers with high purity and low dispersity has only been possible in recent years.

In this talk, I will examine a journal article which reports the synthesis and characterization of a conjugated cyclic polymer, cyclic polyacetylene (c-PA). Although polyacetylene has been previously shown to act as non-metallic semiconductor, its extreme insolubility and air sensitivity has made characterization greatly challenging. The work discussed in this talk addresses this insolubility by creating a temporarily soluble form of cyclic polyacetylene, allowing for unprecedented characterization of a cyclic bottlebrush polyacetylene. Additionally, while linear polyacetylene has been shown to strongly favor cis isomers, the c-PA synthesized here was determined to possesses ~99% trans double bonds. From these results, it is clear that cyclic polymers can possess very different properties than their linear counterparts – providing further motivation for continued research.

Lastly, I will present preliminary results from my own research on computational simulations of block copolymers via self-consistent field theory (SCFT). These computational simulations allow one to calculate the approximate energy for a given polymer morphology from an initial guess for a unit cell. The process of obtaining these results will be discussed, as well as the theoretical basis and shortcomings of polymer self-consistent field theory.

Miao, Z.; Gonsales, S. A.; Ehm, C.; Mentink-Vigier, F.; Bowers, C. R.; Sumerlin, B. S.; Veige, A. S. Cyclic Polyacetylene. Nat. Chem. 2021, 13 (8), 792–799.