CAS: Harvesting Carbon Resources Locked in PVC and Polybutadiene Waste

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With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Professor Rebecca Braslau of the University of California – Santa Cruz (UCSC) will work to develop a chemical upcycling strategy for the commercial polymer, polyvinyl chloride (PVC). A series of chemical reactions will be used to transform this material from its non-recyclable form into value-added products using mild temperatures and ambient pressure. These transformations are aimed at producing 1,5-hexadiene, which can be collected or further transformed into other valuable alkane products. Use of waste plastic consisting of all-carbon backbones as a rich feedstock would provide a non-petrochemical source for useful organic chemicals, while mitigating part of the ecological catastrophe of persistent plastic waste in our environment and landfills. The impact of chemical upcycling of waste PVC would provide a significant environmental benefit. Utilizing PVC as a valued carbon-rich resource would give the carbon atoms in the polymer backbone new uses, and result in its diversion from landfills and reduce environmental contamination. The research experience will provide interdisciplinary training to graduate and undergraduate students in synthetic organic chemistry and materials science. UCSC is a Hispanic-Serving Institution; underrepresented undergraduates will experience meaningful, exciting research. Active outreach by presenting talks on plastics with hands-on experiments to local middle and high schools serving large, underrepresented populations will engage students from diverse backgrounds in science and provide role models for pursuing higher education. Polyvinyl chloride (PVC) is a commodity polymer that is notoriously difficult to reuse or recycle, hence the polymer often ends up in a landfill after use. This work will address this problem by developing an upcycling strategy for this commercial polymer. Elimination of HCl from the (CH2-CHCl) units of PVC to form polyenes followed by olefin metathesis with added small alkenes will form a variety of specific dienes as value-added products. Likewise, olefin metathesis to upcycle polybutadiene (and related polymers with olefin-containing repeat units) will allow the breakdown of synthetic rubbers and provide access to 1,5-hexadienes derived from polybutadiene fragments. These dienes, or their direct reduction products (devoid of E/Z isomers) have the long term potential of serving as feedstocks for the chemical industry with low supply chain energy investments and minimal greenhouse gas emissions. Development of reaction conditions that allow olefin formation in tandem with olefin metathesis will provide a powerful synthetic tool for targeted alkene harvesting from used/discarded polymer sources, but also for applications beyond plastics upcycling. Use of plastic waste as an untapped carbon resource provides an earth-friendly route to continued chemical innovation, without relying on petrochemical sources.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.