Chemical and Biomolecular Engineering - Theses
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ItemAdvanced Star Polymers: From Synthetic Developments to Biomedical Applications( 2020)The developments in polymer synthesis and their applications over the last 100 years have had a profound effect on the world as we know it. While polymers abound in our everyday lives, significant advances continue to be made in the field of polymer chemistry. The first reversible deactivation radical polymerization (RDRP) method was discovered in the 1980s, enabling the synthesis of polymers with tailored molecular weights and advanced architectures. Reversible addition-fragmentation chain transfer (RAFT) polymerization is one type of RDRP that has shown exceptional promise for the synthesis of advanced materials, with recent developments in photo-mediated RAFT polymerization leading to unprecedented control of polymer size and architecture. Star polymers are one type of advanced architecture readily synthesized by RDRP and other techniques for a range of applications. Many of the recent advances in RAFT polymerization have yet to be applied in advanced architectures such as stars. Thus, the objective of this thesis is to investigate the synthesis of star polymers and their applications, with focus on stars synthesized by photo-mediated RAFT polymerization and N-carboxyanhydride ring-opening polymerization (NCA ROP). We first investigated the synthesis of star polymers via photoiniferter RAFT polymerization using a core-first approach. Multifunctional cores were synthesized for star synthesis via RAFT polymerization and early results demonstrated the highly “living” nature of the star polymers. This highly living nature allowed us to synthesize ultra-high molecular weight (UHMW) star polymers with molecular weights in excess of 20 MDa, the largest reported for any RDRP techniques to date. Although photoiniferter RAFT polymerization resulted in highly living stars, it does suffer from two significant limitations. The polymerizations are sensitive to oxygen and can only be mediated by a small portion of the electromagnetic spectrum. Photoinduced energy/electron transfer (PET)-RAFT polymerization can overcome these limitations by employing a photoredox catalyst or photosensitizer. We synthesized a novel self-assembled photocatalyst with broadband and near-infrared (NIR) absorbance, facilitating polymerization across the UV, visible light, and NIR regions. Using this photocatalyst we reported the first NIR-mediated RDRP in aqueous conditions and NIR-mediated star polymerization. Finally, the application of star polymers with degradable polypeptide segments was investigated for lysosomal escape of a model drug in vitro. Endo-lysosomal escape of therapeutics to reach their site of action remains a challenge in the field of nanoparticle drug delivery. Star polymers have exceptional potential in drug delivery stemming from their nanometer size and compact, unimolecular structure that allows for functionalization of distinct core, arm, and peripheral regions. Dye-loaded polypeptide star polymers with PEG-brush coronas were biocompatible, demonstrated successful internalization by cells, and allowed the dye to escape the lysosome due to enzymatic degradation of the polypeptide arms while a nondegradable control star accumulated in the lysosome, demonstrating the advantage of polypeptide stars for drug delivery. Together, these results mark exciting advances in the synthesis of star polymers and their applications. The versatility and exquisite control of photo-mediated RAFT polymerizations are demonstrated, while the advances reported in this thesis show great potential for numerous biomedical applications including biomaterials, cell surface modification, and drug delivery.