Decoding Mechanisms Governing Viscoelasticity of Dynamic Covalent Networks

About This Grant

Non-technical summary: Polymer based products penetrate all aspects of our life, from food packaging to energy and medical technologies. This wide use of polymeric materials and their poor recyclability (caused by strong covalent bonds) led to the explosive growth of plastic waste and raises the urgent need for creating recyclable polymers. One of the potential solutions is introducing a few reversible (dynamic) bonds. Polymers with reversible bonds traditionally called Dynamic Covalent Networks (DCNs) are not only easily recyclable but have many unique properties not achievable in traditional polymers, including self-healing and shape memory aspects. However, detailed quantitative understanding of mechanisms controlling properties of DCNs remains limited. This hinders development of novel functional materials with desired properties. The main goal of the research proposed here is to unravel the fundamental mechanisms controlling properties of DCNs. Several experimental techniques will be employed to study dynamics and structure of DCNs on different time and length scales. The proposed research will deepen fundamental understanding of mechanisms controlling properties of polymers with reversible bonds. This will be instrumental in a rational design of easily recyclable polymeric materials with unique viscoelastic and self-healing properties not achievable in traditional polymers. The proposed program will significantly impact the education of specialists for future science and engineering critical for the US competitiveness. Technical Summary: Dynamic Covalent Networks (DCNs) containing reversible (dynamic) bonds provide a solution for creating polymers recyclable by design. Moreover, DCNs are not only easily recyclable but have many unique macroscopic properties not achievable in traditional polymers, including self-healing, shape memory, and time programmable functions. However, detailed quantitative understanding of microscopic mechanisms controlling dynamics and viscoelastic properties of DCNs remains limited, due to additional complexity introduced by the reversible bonds. The goal of the proposed here research is to decode the fundamental mechanisms controlling dynamics and viscoelasticity of DCNs. The project focuses on three main objectives: (i) Bridge quantitatively the segmental and chain dynamics with bond rearrangement processes and viscoelasticity of DCNs with both dissociative and associative bonds; (ii) Develop a predictive understanding of the role of steric factor in bond rearrangement processes for both dissociative and associative mechanisms; and (iii) Unravel the mechanism of viscoelasticity in DCNs with microphase separation of reversible bonds. In the proposed work, the chain and segmental dynamics, bond dissociation and rearrangement, and viscoelastic properties of polymers will be studied by a combination of rheology, dielectric and light scattering spectroscopy, and differential scanning calorimetry. It will be complemented by analysis of structure using small angle X-ray and neutron scattering. The proposed experimental research will deepen fundamental understanding of microscopic parameters and mechanisms controlling macroscopic properties of polymers with reversible bonds. This will be instrumental for a rational design of easily recyclable polymeric materials with unique viscoelastic and self-healing properties which are critical for the sustainability. From a broader perspective, it might also have a strong impact on understanding of many biological materials where reversible bonding and interactions play a critical role. 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.