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SUMMARY:Photoswitch Facilitated Depolymerization: Realizing Thermodynamics 
 as a Universal Approach Towards Enabling Polymer Chemical Circularity
LOCATION:Chemistry A101
TZID:America/Denver
DTSTART:20250331T160000
UID:2026-07-13-17-34-52@natsci.colostate.edu
DTSTAMP:20260713T173452
Description:About the Seminar:\n\nFor as long as we have understood the neg
 ative impacts of plastic waste on human health and the environment\, polym
 er chemists have been motivated to develop cost effective and industrially
  viable strategies to mitigate the historically unfortunate externalities 
 inherent to these essential materials. These efforts have resulted in an a
 rray of potential solutions\, one of the most compelling being the complet
 e depolymerization of used plastic back into its virgin monomer\, which es
 tablishes a closed-loop material life cycle. Traditionally\, selective dep
 olymerization relies on catalysis to lower the activation energy of active
  species generation and/or the ensuing depropagation. An alternative\, yet
  less explored\, strategy is to instead promote depolymerization via therm
 odynamic manipulation of the polymer mainchain. To better investigate the 
 potential of this unorthodox approach\, we propose the development of a mo
 del system centering on the incorporation of comonomers containing photosw
 itch moieties to strategically induce mainchain scission on demand through
  photoisomerization induced bond strain. Owing to the highly efficient rev
 ersible cis-trans photoisomerization of azobenzene compounds and their che
 mical similarity to styrene\, we propose polystyrene doped with styrenic a
 zobenzene dimers to be an ideal candidate for initial studies. Moreover\, 
 the easily modified benzene scaffold of the azobenzene containing comonome
 r may be judiciously derivatized to improve the polymer’s working state 
 orthogonality via manipulating the quantum yield of photoisomerization\, r
 aising the cis-trans vs. trans-cis interconversion excitation energy gap\,
  and suppressing thermally induced isomerization. We hypothesize that inco
 rporation of the cis form of the azobenzene comonomer will form a strained
  ring during polymerization\, which upon photoexcitation and the ensuing a
 vailability of interconversion to its trans isomer will promote regioselec
 tive cleavage of one of the enthalpically weakened mainchain [sp3-sp3] C-C
  single bonds between the dimerized styrenic repeat units. This cleavage w
 ill produce radicals capable of subsequently regenerating the original pho
 toswitch comonomer and monomeric styrene under depolymerization conditions
 . The propensity of this strategy to promote depolymerization and its ulti
 mate efficiency will be evaluated systematically through a series polystyr
 ene depolymerization studies designed to isolate the effects of the degree
  of photoswitch comonomer doping on the ultimate temperature required for 
 depolymerization\, selectivity for monomer regeneration\, and the apparent
  rate of depolymerization. Furthermore\, these runs will be contrasted to 
 identical metal oxide catalyzed depolymerizations to both assess the core 
 postulate of thermodynamically promoted depolymerization and to explore a 
 potential synergy in combining both approaches – ultimately seeking to l
 ower the energy requirement of depolymerization and improve monomer recove
 ry. Overall\, through the development and analysis of the proposed model s
 ystem\, this work aims to deepen our understanding of the chemical dynamic
 s of depolymerization and introduce a new branch of tunable depolymerizati
 on chemistry with the potential to enable a scalable circular materials ec
 onomy. 4:00 pm
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