Dr Greg O'Bryan

Thesis abstract:

  The work presented in this dissertation details methods of preparing and utilizing chain end functionalized polymers prepared via nitroxide mediated polymerization (NMP).  Chapter 1 introduces concepts of polymer chemistry and analysis, and provides a review of controlled “living” radical polymerization focusing specifically on methods of polymer chain end functionalization.

The synthesis of a ketone functionalized N-alkoxyamine initiator is described in Chapter 2.  The ability to control polymerization of various monomers with this initiator was demonstrated by examination of the polymerization kinetics.  To confirm the “living” nature of this initiator, diblock copolymers were prepared from a macroinitiator.  Post-polymerization chain end functionalization was performed by preparation of the 2,4-dinitrophenylhydrazone derivative of the terminal ketone.  The amount of chain end functionalization was quantified by UV-visible spectroscopic analysis.

A method of chemically removing N-alkoxyamines as a post-polymerization functionalization reaction is developed in Chapter 3.  A mechanism for the oxidative cleavage of N-alkoxyamines with cerium (IV) ammonium nitrate (CAN) is proposed.  A variety of methods for polymer chain end functionalization were explored through oxidation of small molecule models.  Polymers prepared by NMP were functionalized using this oxidative cleavage method.  Chapter 4 extends the utility of the CAN oxidative functionalization method in the preparation of azide-alkyne α-ω hetero-telechelic polymers.  Hetero-telechelic polymers were treated with a copper catalyst under extremely dilute conditions to effect an intramolecular Huisgen 1,3-dipolar cycloaddition to produce macrocyclic polymers.  The amount of macrocyclization was determined by gel permeation chromatography and applying a multi-peak curve fitting analysis.  In summary, successful polymer chain end functionalization was performed by utilizing a ketone bearing N-alkoxyamine polymerization initiator and by post-polymerization modification of terminal N-alkoxyamines through oxidative cleavage.

Publications with the Braslau Group:

G. O'Bryan, N. Ningnuek, R. Braslau* “Cyclization of α, ω  Heterotelechelic Polystyrene Prepared by Nitroxide-Mediated Radical Polymerization” Polymer 2008, 49, 5241-5248. doi:10.1016/j.polymer.2008.09.035.

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.

G. O'Bryan, R. Braslau* “Terminal Functionalization of Polymers via Single Electron Oxidation of N-Alkoxyamines,” Macromolecules, 2006, 39, 9010-9017.

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

Hilary and Greg