The design, synthesis and testing of N-alkoxyamine initiators for nitroxide-mediated 'living' free radical polymerization.

摘要

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 alpha-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.