Silyl Ether Metathesis for Universal Vitrimer Design

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NON-TECHNICAL SUMMARY:The main objective of this project is to develop a new method for producing dynamic materials made out of polymers that can combine excellent mechanical properties and chemical stability with good reprocessability and recyclability. Polymeric materials play an essential role in addressing many technological challenges including alternative energy, medical/health, and national security/competitiveness. Broadly defined, polymeric materials are classified into two large categories: thermosets and thermoplastics. Thermosets have their molecules permanently connected ("cross-linked") and as a result have excellent mechanical properties, dimensional stability, and resistance to chemicals and solvents. However, a critical limitation of thermosets is that they cannot be reshaped, reprocessed, or recycled since their molecules are permanently stitched together. In contrast, thermoplastic polymers can be reshaped and reprocessed, but they normally have lower mechanical strength, lower structural stability at elevated temperature, and poorer chemical/solvent resistances. This research presents a new chemical strategy that aims to combine the best attributes of both thermoplastics and thermosets. Specifically, a universal strategy will be explored to introduce plasticity, reprocessability and recyclability to various polymer networks and composites through a new silicon-oxygen exchange reaction. Successful demonstration of the proposed strategy could offer significant impact on new materials development, polymer recycling and sustainability, and modern processing technologies including additive manufacturing. This project will also provide extensive opportunities to train graduate and undergraduate students, including underrepresented groups in science. This project will also enable the PI to work with the UCI Mathematics, Engineering, Science Achievement (MESA) Program on a K-12 materials science/chemistry outreach effort with a module focusing on dynamic/self-healing polymers.TECHNICAL SUMMARY:The main objective of this research is to investigate silyl ether metathesis as a new, robust, and universal dynamic covalent chemistry for the design of dynamic polymeric materials. Permanently cross-linked polymers (i.e., thermosets) have excellent mechanical properties, creep resistance and dimensional stability, and chemical/solvent resistance. However, a critical limitation of thermosets is that they cannot be reshaped, reprocessed, or recycled by heat or with solvent. In contrast, thermoplastic polymers can be reshaped and reprocessed, but they normally have lower mechanical strength, lower structural stability at elevated temperature, and poorer chemical/solvent resistances. This project describes a new chemical strategy that aims to combine the excellent attributes of both thermoplastics (reprocessability, recyclability) and thermosets (mechanical strength, creep and solvent resistances). Specifically, a universal strategy is proposed to introduce plasticity, reprocessability and recyclability to various polymer networks and composites through a new silyl ether metathesis reaction. First, the general applicability of silyl ether metathesis will be investigated for vitrimers made of common commodity polymers (Aim 1). Aim 2 details plans for the synthesis of vitrimers from multiple polymers through dynamic reactive blending. This provides a simple way to tailor and improve vitrimer properties. The dynamic mechanical properties of the resulting vitrimers will be carefully investigated and correlated with the structures. Finally, the proposed strategy is extended to the design of inorganic/organic composite vitrimers through silyl ether metathesis between inorganic surfaces and organic polymer matrices (Aim 3). Similarly, structure-property studies will be conducted for the composite vitrimers. Successful demonstration of the proposed strategy could offer significant impact on new materials development, polymer recycling and sustainability, and modern technologies including additive manufacturing.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.