Dr. Aaron Nilsen
This dissertation addresses the design, synthesis and testing of N-alkoxyamine initiators for nitroxide-mediated ‘living’ free radical polymerization. Chapter 1 comprises a general review of radical polymerization and an in depth review of nitroxide-mediated radical polymerization. It is believed that α-hydrogen nitroxides are good polymerization mediators because they decompose during the course of the polymerization maintaining a constant low concentration.
In Chapter 2, a postulated mechanism for the decomposition of the sterically hindered acyclic a-hydrogen nitroxide TIPNO is supported experimentally. In this mechanism, the structure of the intermediate dimer is proposed to be an ion pair formed by the disproportionation of the nitroxide via single electron transfer. An understanding of the mechanism of decomposition should allow the design of nitroxides that are more effective polymerization mediators. High temperature is required to give the rapid homolysis of the C-O bond between the growing polymer chain and mediating nitroxide that is necessary in a ‘living’ polymerization system. It has been shown that this homolysis temperature can be decreased by increasing the steric bulk around the N-O bond of the nitroxide and by stabilization of the nitroxide via intramolecular hydrogen bonding.
In Chapter 3, these approaches were used in the design and synthesis of novel N-alkoxyamine polymerization initiators. Also, N-alkoxyamines with ketone functional handles were synthesized, and the synthesis of an acid-functionalized N-alkoxyamine was explored.
In Chapter 4, a method for the synthesis of nitroxides from oxaziridine intermediates was developed.
In Chapter 5 nitroxide-mediated polymerization was used to prepare amphiphilic ABA triblock copolymers. A novel bidirectional N-alkoxyamine polymerization initiator was synthesized and used to prepare ABA triblock copolymers using a two step ‘inside out’ approach. The B block was first formed by adding hydrophobic monomer to both ends of the bidirectional initiator simultaneously. The A blocks were then formed in the same manner by addition of the hydrophilic monomer. Deprotection of the hydrophilic monomer provided the amphiphilic ABA triblock copolymer, which was shown to form vesicles in aqueous media.
Ph.D. 2005: The Design, Synthesis and Testing of N-Alkoxyamine
Initiators for Nitroxide-Mediated ‘Living’ Free Radical Polymerization
2003 University-wide Excellence in Teaching Award, UC Santa Cruz
2002 Departmental Excellence in Teaching Award UC Santa Cruz
2000-2001 Roche Bioscience Fellowship in Synthetic Organic Chemistry
2004 NSF Exchange at Mahidol University in Bangkok, Thailand, working
in the chemistry laboratory of Professor Vichai Reutrakul
B.S. Biochemistry, UC San Diego
Postdoc 1: UC San Francisco with Prof. Pamela England
Postdoc 2: UC San Francisco and Oregon Health & Science University with
Prof. Tom Scanlan
Visiting Assistant Professor Reed College, Portland OR 2012-13
Assistant Research Scientist at the Portland VA Research Foundation
Aaron is now Director, Medicinal Chemistry Core, Oregon Health & Science University
Publications with the Braslau Group:
G. O'Bryan, A. Nilsen, R. Braslau “Ketone Functionalized Nitroxides: Synthesis, Evaluation of N-Alkoxyamine Initiators, and Derivatization of Polymer Termini” Macromolecules, 2007, 40, 7848-7854.
J. Ruehl; A. Nilsen; S. Born; P. Thoniyot; L. Xu; S. Chen; R. Braslau* “Nitroxide-Mediated Polymerization to Form Symmetrical ABA Triblock Copolymers from a Bidirectional Alkoxyamine Initiator” Polymer 2007, 48(9), 2564-2571.
A. Nilsen, R. Braslau* "Nitroxide Decomposition," invited “Highlight” article for Journal of Polymer Science Part A: Polymer Chemistry, 2006, 44, 697-717. http://tinyurl.com/dbnr3m
R. Braslau,* G. O'Bryan, A. Nilsen, J. Henise, T. Thongpaisanwong, E. Murphy, L. Mueller, J. Ruehl “The Synthesis and Evaluation of New αll α-Hydrogen Nitroxides for "Living" Free Radical Polymerization” Synthesis, 2005, 9, 1496-1506. http://tinyurl.com/cm8ytr
R. Braslau,*V. Chaplinski, A. Nilsen, N. Arulsamy, “Stereochemical Studies Of Chiral Acyclic Nitroxides Coupling With A Prochiral Radical” Synthetic Communications, 2004, 34, 2433-2442.
Aaron and Elana
Aaron and Elana
Aaron and Soon