Materials from High Molecular Weight Cyclic Polymers: Insights on Properties and Dynamics

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NON-TECHNICAL SUMMARYPolymers are ubiquitous; these materials, made of long-chain molecules comprise all modern plastics, the fibers of textiles, and the key molecules of biology including proteins and DNA. This project will leverage a new method for creating large cyclic polymers to learn how connecting a long molecule into a ring influences the properties of materials generated from these cyclic structures. Cyclic polymers differ from linear polymers by just a single bond, but this minor chemical change influences how these molecules flow during processing, how they solidify and how they interact with their environment in ways that remain poorly understood. The planned research targets three specific aims. The first aim focuses on the generation of new classes of materials derived from cyclic polymers entrapped in cross-linked molecular networks to investigate how such an entangled cyclic chain influences the properties of the material. The second aim seeks to illuminate how cyclic molecules flow to gain a better understanding of how ring-like molecules entangle with one another and with linear chain molecules. The third aim focuses on the influence of a cyclic structure on the shapes that these large molecules adopt in the liquid and solid states. This project will suport and educate two graduate students, who will have the opportunity to collaborate with leading experts from foreign countries and at US National Labs. The Principal Investigator and the graduate students will engage in outreach programs at local schools to promote increased scientific understanding in the community at large. TECHNICAL SUMMARYThis research focuses on investigations of the conformation, properties, and applications of large cyclic polymers by leveraging previous advances in a new synthetic method for generating large cyclic chains. Zwitterionic ring opening polymerization (ZROP) produces large cyclic molecules by generating propagating chains that contain both a positively-charged end and a propagating negatively charged chain end. Three classes of polymers synthesized with this method will be used to achieve the above-stated goals. Water-soluble cyclic polyphosphoesters will be entrapped in three-dimensional, cross-linked hydrogel networks to investigate how the entrapped cyclic chains influence the properties of the resultant double-network hydrogels. These novel materials are anticipated to exhibit enhanced toughness relative to gels lacking the entrapped chains. The rheological behavior of high molecular-weight cyclic carbosiloxane polymers will be investigated to illuminate how cyclic molecules entangle. These materials are of a length approximately 125 times the entanglement molecular weight (Me) of the corresponding linear chains -- a molecular weight regime previously unattainable by any other synthetic method. These studies are aimed at investigating whether large cyclic chains can exhibit a plateau modulus that is typical of linear chain behavior. Neutron-scattering experiments of deuteriated high molecular weight cyclic polycaprolactones will be carried out to validate theoretical predictions that concentrated solutions of cyclic chains will exhibit collapsed conformations. The interdisciplinary nature of this project will provide an exceptional educational environment for students trained in polymer synthesis to interact with world experts in polymer rheology, polymer physics, neutron scattering, and modern chromatographic separations.