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A Proximal Bisnitroxide Initiator: Studies in Low-Temperature Nitroxide-Mediated Polymerizations
Jean Ruehl1, Nicole L Hill, Eric D Walter
1Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064.
Macromolecules
|September 28, 2011
Summary
A novel bisalkoxyamine enables controlled "living" radical polymerization of styrene, tert-butyl acrylate, and dimethylacrylamide. This method yields polymers with controlled length and narrow molecular weight distributions at elevated temperatures.
Area of Science:
- Polymer Chemistry
- Organic Synthesis
- Materials Science
Background:
- Nitroxide-mediated polymerization (NMP) is a controlled radical polymerization technique.
- Bisalkoxyamines offer potential advantages over monoalkoxyamines in NMP.
- Understanding alkoxyamine decomposition mechanisms is crucial for controlling polymerization.
Purpose of the Study:
- To synthesize and characterize a novel bisalkoxyamine for NMP.
- To investigate the polymerization behavior of the bisalkoxyamine with various monomers.
- To elucidate the decomposition kinetics and mechanisms of the bisalkoxyamine and its corresponding nitroxide.
Main Methods:
- Synthesis and characterization of bisalkoxyamine and monoalkoxyamine.
- Nitroxide-mediated polymerization of styrene, tert-butyl acrylate, and dimethylacrylamide.
- Electron paramagnetic resonance (EPR) spectroscopy to study alkoxyamine homolysis and nitroxide decomposition.
- Proton nuclear magnetic resonance ((1)H NMR) spectroscopy to investigate alkoxyamine decomposition.
Main Results:
- The bisalkoxyamine successfully mediated controlled polymerization of St, tBA, and DMA, producing polymers with narrow molecular weight distributions.
- EPR studies showed that the bisalkoxyamine homolysis rate constants were approximately twice those of the monoalkoxyamine.
- (1)H NMR and EPR decomposition studies indicated enhanced decomposition for the bisalkoxyamine and bisnitroxide compared to their monoalkoxyamine/mononitroxide counterparts.
- Low-temperature EPR revealed strong radical-radical interactions in the bisnitroxide, suggesting stabilization of the intermediate mononitroxide.
Conclusions:
- The novel bisalkoxyamine is an effective mediator for controlled "living" radical polymerization.
- The bisalkoxyamine exhibits faster decomposition and homolysis rates than the monoalkoxyamine.
- The enhanced stability of the intermediate mononitroxide, potentially due to radical-radical interactions and electron delocalization, contributes to the controlled polymerization process.
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