ATRC PROCESSES AND ARCHITECTURES AS TOOLS FOR ADVANCING THE COMPLEXITY OF SINGLE-CHAIN POLYMERIC NANOPARTICLES
Date of Award
Program or Major
Doctor of Philosophy
Erik B Berda
Atom transfer radical coupling (ATRC) is gaining recognition for its utility in building complex polymeric architectures because it features efficiency, a wide range of compatible substrates, and a lack of byproducts. These qualities are especially desirable in applications requiring intramolecular cross-linking as in the synthesis single-chain nanoparticles (SCNP).
This dissertation aims to (I) provide motivation and context for developing ATRC technology for intramolecular cross-linking, (II) provide guidance into the impact of catalyst selection and substrate on reaction efficiency and morphology, and (III) demonstrate the possibility to sequence intrachain ATRC with ATRP to create advanced SCNP architectures.
Chapter II describes the preparation of SCNP from parent polymers containing alkyl or benzyl bromide ester pendants using ATRC catalyzed by copper halides complexes. Tri- or tetradentate alkyl or pyridyl amines (PMDETA, TPEN, and TPMA), which tune the redox potential of the Cu(I)/Cu(II) system, were directly compared. Coupling efficiency was positively correlated with the kATRP of the respective catalyst systems. However, PMDETA complexes afforded greater control as evidenced by lower polydispersity. In the case of alkyl halide pendants, selectivity for coupling over disproportionation systematically decreased under conditions designed to increase the concentration of CuI/L. Polymers with benzyl bromide pendants, which cannot disproportionate, tended to produce high molecular weight products, even in ultradilute solutions (0.25 –1.0 mg/mL).
Chapter III describes the preparation of SCNP from parent polymers capable of initiating intra-chain polymerization by ATRP under conditions favoring termination by coupling. Because of the wide variety of compatible monomers that have been well-established for ATRP systems, the ATRP/C framework both simplifies reaction procedures (one pot polymerization and coupling strategies are feasible) and imparts handles with which to control both architecture and functionality. To demonstrate this potential, model simple brushes and hyperbranched examples were prepared. SCNP with the hyperbranched motif were remarkably dense, a result which demonstrates the potential to facilitate more globular SCNP structures using modifications of intrachain polymerizations. Methacrylic brush arms, which are not non-ATRC active, could be induced to couple by adding 5 equivalents of styrene under the shared ATRP/C conditions. In addition, it was determined that hyperbranched SCNP retain “living” ω-ends which may be initiated to perform post-collapse polymerizations. A model styrene example is presented; despite occurring in an ultradilute solution, the polymerization maintains fidelity to pseudo-first order kinetics.
In sum, there is currently a great impetus for pushing the boundaries of structural and functional complexity that can be designed using the single-chain nanoparticle motif. Atom transfer radical chemistry is a particularly versatile example and it is my hope that this work facilitates the creation of new creative and functional designs.
Bright, Elizabeth, "ATRC PROCESSES AND ARCHITECTURES AS TOOLS FOR ADVANCING THE COMPLEXITY OF SINGLE-CHAIN
POLYMERIC NANOPARTICLES" (2019). Doctoral Dissertations. 2438.