Synthesis of Protein-Polymer Hybrids by Aqueous Photo Atom Transfer Radical Polymerization

The development of protein-polymer hybrids (PPH) has emerged as a compelling avenue at the  intersection of biotechnology and materials science. By marrying the unique functionalities of proteins  with the versatility and tunability of polymers, PPH offer unprecedented opportunities to address  complex biomedical challenges and advance technological innovation. Photo-induced polymerizations, in particular photo-atom-transfer radical polymerization (photo-ATRP) has  revolutionized the field of PPH synthesis. Yet, significant enhancements and innovations are necessary  to fully harness this method for efficient high-throughput synthesis and automation.  

This thesis delves into the synthesis of protein-polymer hybrids (PPH) through aqueous photo-ATRP,  emphasizing the advancement of an oxygen-tolerant photo-ATRP technique facilitating benign  conditions for PPH synthesis. Moreover, these advancements have enabled the development of PPH  with tunable polymer architectures with tailored properties and enhanced performance characteristics.  

Chapter 1 introduces the fundamentals of reversible-deactivation radical polymerization  (RDRP) methods, particularly ATRP & RAFT, and explores polymer architectures achievable via  ATRP. It encompasses the synthesis, characterization, and applications of PPH through bio-relevant  ATRP, highlighting the role of polymer topology. 

Chapters 2-10 comprise research projects divided into two themes: (I) Aqueous photo-ATRP  for protein-polymer hybrids (Chapters 2-8), and (II) Solid-phase polymer synthesis and catalyst  immobilization (Chapters 9-10). 

Chapters 2-4 elucidate dual photo redox/copper catalysis facilitating open-air ATRP under  visible light. In Chapter 2, the demonstration of Eosin Y as an organic photoredox catalyst (PC) in  combination with a copper complex (X–CuII/L) leading to the synthesis of well-controlled  polymethacrylates has been discussed. Furthermore, a detailed comparison of photo-ATRP with PET- x RAFT polymerization revealed the superiority of dual photoredox/copper catalysis under biologically  relevant conditions. Chapter 3 expanded the method to synthesize hydrophilic polyacrylates using  CuII/Me6TREN (Me6TREN = tris[2-(diethylamino)ethyl]amine) and EY at ppm levels. The role of PC  was to trigger and drive the polymerization, while X–CuII/L acted as a deactivator, providing a well?controlled polymerization and allowed the synthesis of well-defined acrylate-based PPH using a  straightforward reaction setup without rigorous deoxygenation. Chapter 4 is a derivative project that  extends the technique to synthesize biotinylated fluorescent-dye copolymers that were conjugated to  antibody (Ab) or cell-wall binding domain (CBD), resulting in a highly fluorescent polymeric dye?binder complex that exhibited both enhanced fluorescence and selectivity for bioimaging of target  bacterium.  

Polymer topology significantly impacts polymer properties and applications. PPH comprising  of the branched polymer may show superior properties. Chapters 5-8 discuss the use of water-soluble  inibramers to induce branching during the copolymerization of various vinyl monomers in water under  benign conditions and its application to synthesis of PPH. The term “inibramer” refers to a monomer  that can initiate the branching process only after it is incorporated into the polymer chain. In Chapter  5, sodium 2-bromoacrylate, an ionic inibramer triggered branching during photo-ATRP of  methacrylate monomers in the open air resulting in well-defined branched polymers with controlled  molecular weights, degrees of branching, low dispersity values has been demonstrated. The technique  enabled synthesis of well controlled PPH and nucleic-acid polymer hybrids. Chapter 6 introduces  another water-soluble poly(ethylene glycol) (PEG)-based inibramer, oligo(ethylene oxide) methyl  ether 2-bromoacrylate (OEOBA), expanding the library of water-soluble inibramers for controlled  radical branching polymerization (CRBP) in water. This chapter discusses the contrast in the  copolymerization of OEOBA with acrylates vs methacrylates, resulting in hyperbranched polymers  and degradable polymer backbones respectively. In Chapter 7, photo-ATRP triggered by sodium  pyruvate has been employed to synthesize hyperbranched poly(meth)acrylic acids and  xi polyacrylamides. The branched PNIPAM showed lowering lower critical solution temperatures  (LCSTs) as a property of the degree of branching. Chapter 8 focuses on grafting-from ATRP for  synthesis and characterization of PPH with linear or branched polymer backbones and comparing the  molecular sieving behavior of PPH because of the topology of the grafted polymer.  

Chapters 9-10 (Theme II) focus on the application of poly(ethylene glycol) (PEG)-based resin,  ChemMatrix (CM) for solid-phase polymer synthesis and photocatalyst immobilization. In Chapter  9, CM resin has been functionalized with ATRP initiator and used for the grafting of well-defined  block copolymers in high yields. This approach was found to be highly attractive for sequence?controlled polymer synthesis, successfully synthesizing di-, tri-, ter-, and penta-block copolymers with  excellent control over molecular weight and dispersity in both aqueous and organic media. Later in chapter 10, the CM resin was covalently modified with photo redox dye EY and used for heterogenous  catalysis of fully-oxygen tolerant dual photo-redox ATRP. The remarkable swelling properties of CM  resin led to the efficient photocatalytic performance of CM-EY, as evidenced by rapid and well?controlled polymer synthesis, but also displayed excellent photostability, ensuring prolonged catalytic  activity over multiple cycles.  

Finally, Chapter 11 summarizes the development of aqueous photo-ATRP systems for  synthesizing bio-related hybrid materials, offering insights into future perspectives. Appendix 1. includes Chapter 12 which describes a project carried out in collaboration with Dr. Hironobu Murata  under the DTRA grant. Appendix 2. catalogs academic papers published or submitted during the Ph.D.  study, alongside group activities and related achievements.