Poly(3-nitratomethyl-3-methyloxetane) (PNMMO) is a nitrate ester pre-polymer which can be cured with an isocyanate and utilised as a binder in solid rocket propellants; CH3 X[-H2C-C-CH2-0-]nY CH2ONO2 where X and Y are the end groups. Electrospray ionisation (ESI) mass spectra of untreated PNMMO show that it contains a series of low-mass cyclic and linear oligomers incorporating up to 22 monomer units. Oligomers of higher mass appear not to be detectable by ESI mass spectrometry. The relative abundances of the cyclic oligomer ions in the spectra are affected by various factors but the governing influence is the size of the alkali metal cation used to promote ionisation. The cyclic and linear oligomers can be separated from each other using column chromatography and the cyclic species can be individually characterised by ESI, size- exclusion chromatography (SEC) and 13C nuclear magnetic resonance (NMR) spectroscopy. Thermal degradation results in the gradual increase in intensity of two main new absorptions around 1729 and 1550 cm'1 in the solution infrared (IR) spectrum of PNMMO. The band at 1729 cm 1 is attributed to the carbonyl group in a formate ester and the formate proton and carbonyl carbon associated with this compound are clearly visible in the ‘H and l3C NMR spectrum at 8.1 and 162 ppm respectively and can be cross-correlated by 2-D NMR. The absorption at 1550 cm 1 is attributed to the asymmetric stretch of a nitro group attached to a tertiary carbon. We propose that this nitro species is formed by the recombination of NO2 following the loss of N02 and subsequent elimination of CH20 from the PNMMO side-chains. The assignment of this nitroalkane was confirmed by ESI and spectroscopic characterisation of a nearly pure sample of the tetrameric nitro species isolated from pyrolysed PNMMO using column chromatography. The thermal degradation pathways and products of polypropylene oxide) (PPO) were found to bear some similarities to those of PNMMO. ESI and matrix-assisted laser desorption ionisation (MALDI) mass spectra of thermally and photolytically degraded PPO show that oxidation occurs predominantly at the secondary carbon as opposed to the tertiary carbon.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:307970 |
| Date | January 1996 |
| Creators | Barton, Zachary M. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/109055/ |
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