The thermal degradation behaviour of poly-N-methyl-N-tertbutyl-aminoethyl methacrylate (PMTBAEM) has been studied using thermogravimetry, differential thermal analysis and thermal volatilisation analysis, with programmed heating at 10°C/min. Subambient TVA was used to separate the volatile degradation products, which were characterised by mass spectrometry and IR spectroscopy. The main volatile products were found to be isobutene and carbon dioxide. The less volatile liquid components of this product fraction were further separated by gas chromatography and identified by mass spectrometry: the main liquid product was tertbutylaziridine, while methanol and traces of methyl-terbutyl-aminoethyl methacrylate (MTBAEM) were also identified. The cold ring (tar/wax) fraction products, which formed the largest product fraction, were examined by IR spectroscopy and found to consist of modified oligomers of MTBAEM. It is concluded that the degradation mechanism involves two distinct type of side group decomposition together with fragmentation, mainly at higher temperatures, of the modified chains.