Boron Dipyrromethene Photocages for Mild and Selective Light-Driven Polymer Chemistry

With the support of the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Dr. Zachariah A. Page of the University of Texas at Austin is developing light-selective boron containing dyes as catalysts for the synthesis of recyclable polymers.

The structure and reactivity of these dyes will first be optimized through systematic studies in order to understand their electronic and chemical properties. Successful candidates will then be used to prepare dynamic poly(urethane) networks using light. Poly(urethanes) are an important class of plastics which is extensively used to make coatings, adhesives and sealants.

The light that will connect individual building units into long polymer chains will also be used to disconnect them one at a time by simple changing its wavelength and intensity. Hence, this light-toggling will lead to recyclability. Studies associated with this research have the potential to provide fundamental chemistry knowledge associated with light controlled polymerization and how it can be used to efficiently prepare recyclable polymeric materials.

As such, chemistry emphasized in the proposed work also addresses the current and ongoing global issue of plastic waste accumulation. This research will provide new opportunities for undergraduate and graduate student training in polymer chemistry. Diversity seminars will be initiated, as well as development of a new course in undergraduate peer mentoring for organic chemistry.

Moreover, the work will also positively support public education and outreach. Dr. Page will create an interdisciplinary polymer teaching module on light as a tool in science to engage middle and high school students from institutions with disproportionate populations of minorities in STEM fields.

Outreach activities involving intercollegiate student interactions with North Carolina State University will also be established.

This research will focus on development of wavelength-selective boron dipyrromethene (BODIPY) photocages bearing benzyl sulfides as catalysts for controlled anionic photoredox polymerization. The underlying strategy uses mild reaction conditions and visible-to-NIR (near infrared) light to reversibly cleave BODIPY derivatives and generate strong nucleophiles (thiolate anions) that can initiate polymerization.

Specifically, the preparation of recyclable dynamic polymer networks bearing (di)thiourethane and imine/hydrazone/oxime functionality will be emphasized as soft materials that remain largely unexamined using light-driven approaches. Strong emphasis will be placed on the optimization of reactivities and kinetics through structural modification of BODIPY-based dyes in order to understand their electronic properties and responses to light with different wavelengths and intensities.

Proposed structure-reactivity studies could provide fundamental chemistry knowledge associated with the synthesis of recyclable polymers using photoredox initiated polymerization. The proposed ability to control the polymerization by different light intensities and wavelengths has the potential to permit the precise 2D-patterning and 3D-printing of polymeric materials, with long-term potential scientific impact upon tissue engineering, robotics, optical coatings and image sensing.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.