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PROGRAM | Materials Science & Engineering

Solution Self-Assembly of Semiflexible Amphiphilic Poly(D-glucose carbonate)s

By: Jee Young Lee Chair: Darrin Pochan

ABSTRACT

Motivated by the recent drive to replace petrochemical plastics for more renewable source-based materials, our efforts focus on designing and characterizing a next generation biomolecular-based polymer for solution assembly applications. Sugar-derived poly(D-glucose carbonate) (PGC) molecules are synthesized, and their solution chain dynamics and assembly behavior are analyzed in the production of nanoparticles. Unlike conventional vinyl-based polymers with flexible coil-like chains, the PGC system is characterized by its entire backbone composed of semiflexible, hydrophobic glucose monomers where its chain rigidity and local amphiphilicity created by the backbone compared to added side chains are expected to significantly impact both local and global solution chain behavior.

First, with a PGC-containing amphiphilic diblock copolymer system, we explored kinetically controlled assembly pathways by variation of solvent composition that led to the hierarchical assembly of ribbon-like fibers with features that do not follow the traditional BCP micellar-like packing. We show that while the stiffness of the PGC backbone impacts the local BCP chain conformation and chain packing within the assembled nanostructure, the backbone hydrophobicity drives the unidirectional hierarchical fibril growth by the formation of soft patchy precursor particles. Second, to understand how the chain behavior affects the final assembly morphology, the hydrophilic block equivalent homopolymers were studied using small-angle neutron scattering techniques to obtain polymer chain solution properties for a better understanding of the PGC block copolymer chains in similar solvent conditions. Lastly, to further fine-tune the BCP assembly and tie the BCP and homopolymer studies together, the PGC BCP assembly was explored with a variation in assembly conditions. Specifically, the change in solvent composition, pH or side chain chemistries led to an interesting deviation from the initial hierarchical fibril formation where network-like morphologies, twisty fibrils or no hierarchical assembly were observed, respectively.

These results suggest polymers with unconventional backbone chemistries, frequently found in natural carbohydrate-based molecules, can shed light on the effects of polymer backbone rigidity and hydrophobicity on the assembly pathway and final assembled structures while also presenting opportunities to better understand how other bio-inspired, green chemistries-based molecules can organize and assemble in various environment conditions.

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