Dr Nicole Hill
Thesis abstract:
This work focuses on the synthesis and full characterization of a novel bis-N-alkoxyamine for use in nitroxide-mediated radical polymerization. Chapter 1 details the advantages of nitroxide-mediated radical polymerization. A review of existing bi-directional initiators and low-temperature N-alkoxyamines is provided. A brief survey of some of the applications of telechelic polymers includes attachment to surfaces and biomolecules.
Chapter 2 details the synthetic challenges encountered during the synthesis of the bis-N-alkoxyamine. Highlights include a modified Ritter reaction and a thermal rearrangement of a bis-oxaziridine to a bis-nitrone compound. Once synthesized, the polymerization capabilities of this novel bi-directional initiator were explored in Chapter 3. Symmetrical ABA triblock copolymers were easily prepared in an “outside-in” manner. Cleavage experiments that entailed decomposition of the central bis-nitroxide verified bidirectional growth.
During the polymerization studies of the bis-N-alkoxyamine, it was observed that the initiator effected polymerization significantly faster than the parent mono-directional version. This prompted low-temperature polymerization studies as well as an investigation into the kinetic properties of the bis-N-alkoxyamine. With the use of EPR, the kd, EA and A values were determined in Chapter 4. Using 1H NMR kdec was investigated, however the rate of decomposition of the bis-N-alkoxyamine does not follow a first order relationship as α-hydrogen nitroxides can undergo two types of decomposition: β-hydrogen abstraction and disproportionation by single electron transfer. EPR of the bis-nitroxide revealed the existence of a half-field signal indicating an unusually strong spin-spin interaction. This suggests a novel delocalized mono-nitroxide as a key stabilized intermediate during polymerization.
Chapter 5 discusses the development of a number of functionalized mono-directional N-alkoxyamines. In Chapter 6, a yellow fluorescent protein was coupled to a carboxylic acid-functionalized bis-N-alkoxyamine and carried through a polymerization, highlighting the ability to prepare biomolecule/polymer hybrids under mild conditions.
Ph.D. 2007: Development of Novel Functionalized Bisnitroxide Initiators for the Preparation of Designed Polymers
2006 IBM Fellowship
BS Biotechnology, University of Delaware
Nicole is a Senior Research Chemist in Preformulation and Basic Pharmaceutical Sciences at Merck
Publications with the Braslau Group:
J. Ruehl, N. L. Hill, E. D. Walter, G. Millhauser, R. Braslau* “A Proximal Bisnitroxide Initiator: Studies in Low-temperature Nitroxide-Mediated Polymerizations” Macromolecules, 2008, 41, 1972-1982.doi: 10.1021/ma702358c http://tinyurl.com/cmbupv.
N. L. Hill, J. L. Jarvis, F. Pettersson, R. Braslau* "Synthesis of Thiol-Derivatized Initiators for Nitroxide-Mediated Radical Polymerization: Reversible Disulfide Formation" Reactive & Functional Polymers, 2008, 68, 361-368.
N. L. Hill; R. Braslau* “Synthesis of Arylethyl Functionalized N-Alkoxyamine Initiators and use in Nitroxide-Mediated Radical Polymerization” Journal of Polymer Science Part A: Polymer Chemistry, 2007, 45, 2341-2349.
N. Hill, R. Braslau* “Synthesis and Characterization of a Novel Bisnitroxide Initiator for Effecting “Outside-In” Polymerization” Macromolecules, 2005, 38, 9066-9074.
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Soon and Nicole, 2004
Nicole 2005
(dressed as Rebecca for Halloween!)
