CAS: Self-amplifying depolymerizable polymers

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With funding from the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Professor John B. Matson of Virginia Tech is building synthetic polymers based on poly(thiourethanes) and poly(olefin sulfones) that fall apart (depolymerize) upon application on cue into gases that are both reactive and bioactive. Both classes of polymers are used in a wide variety of industrial applications, including foams, adhesives, building insulation, and even microcircuit fabrication. In this research, high molecular weight poly(thiourethanes) are prepared from building blocks designed using computational modelling. Chemical reactions are then developed to depolymerize these polymers into hydrogen sulfide, a vital biological gas present in all organs and systems in a human body. Hydrogen sulfide, in small doses, acts as a relaxant of smooth muscle and as a vasodilator and is also active in the brain, where it increases the response of some receptors and facilitates long term memory formation. In a related approach, a polymerization technique is developed to prepare well-defined poly(olefin sulfones) that are capable of depolymerizing back into the compounds that they are originally made from sulfur dioxide and small unsaturated hydrocarbons. Chemical approaches associated with this project are of relevance to the ongoing environmental problem of plastic recycling, and the results have the potential to advance the field of degradable polymers. The educational goals of this research focus on increasing enthusiasm for polymer science in elementary and middle school children in Appalachia. Outreach efforts are integrated with the Virginia Tech Youth Experiencing Science (YES) summer program that focuses on hands-on activities related to plastics.This research focuses on depolymerizable polymers, also called self-immolative polymers, that undergo end-to-end depolymerization in response to a specific stimulus. Synthetic methods are developed to make depolymerizable polymers in a controlled manner, which can unzip to generate gases that are both reactive and bioactive, in some cases enabling further depolymerization (self-amplification). A strong emphasis is placed on two types of polymers—poly(thiourethanes), which undergo depolymerization to generate carbonyl sulfide or hydrogen sulfide, and poly(olefin sulfones), which depolymerize to generate sulfur dioxide and alpha-olefins. In the case of poly(thiourethanes), computational methods are used to predict monomers with strong driving forces for polymerization, and their polymerization is carried out such that the resulting polymers contain various functional groups on the chain-end to trigger depolymerization. In addition, well-defined poly(olefin sulfones) are prepared using reversible-deactivation radical polymerization methods starting from alpha-olefins and sulfur dioxide. Polymer micelles are also developed that contain specific end groups that enable self-amplification of the depolymerization event. As a result, only a single triggering event on one polymer chain-end leads to depolymerization of an entire micelle core. This research has the potential to advance the development of degradable polymers or block copolymers with a degradable block. Generation of signaling gases such as sulfur dioxide and hydrogen sulfide during the depolymerization process is also of relevance to many biological applications.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.