The present study employs a range of soft-ionisation mass spectrometry techniques to study the degradation of model compounds of poly(methyl methacrylate), poly(n-butyl acrylate) and poly(2-hydroxyethyl methacrylate) under conditions designed to simulate the worst-case scenario that would be experienced by a polymer used in a surface coating on a steel roof. Vinyl-terminated and saturated polymers were degraded for periods of up to 2 years under simulated solar radiation at a temperature of 95??C, temperature of 95 ??C in the dark, and simulated solar radiation at 35??C. Similar degradation mechanisms were observed under heat and UV radiation. The presence of UV radiation accelerated the degradation occurring at high temperature, and vice versa. The combination of heat and UV radiation is far more detrimental to the polymers than either of these conditions alone. Both vinyl-terminated and saturated pMMA degraded under UV radiation at 95??C, whereas under conditions of UV radiation alone or high temperature alone, the saturated polymer was found to be stable. The vinyl-terminated pMMA degrades in all cases via the formation of ethylene oXide-type end groups, which subsequently rearrange under the expulsion of formaldehyde and 2-oxo-propionic acid methyl ester. This is in contrast to all previous literature, in which pMMA degrades via depolymerisation and is stable at 95??C. Degradation of pBA included a degradation mechanism similar to that of pMMA in addition to other polymer fragments, some of which cannot be assigned. pBA (both saturated and vinyl-terminated) showed a tendency to crosslink under all degradation conditions in this study. Only saturated pHEMA was stable under thermal degradation. In all other cases, pHEMA showed some degradation, but displayed a much greater tendency to crosslink rapidly. Terminal vinyl bonds were shown in all cases to be a weak point in the polymer with respect to degradation. pMMA was found to be the least reactive of these polymers. pHEMA showed some small degradation but had a greater tendency to crosslink via the hydroxyethyl side groups. pBA does not have any such reactive groups, and its crosslinking reaction may be explained via the acrylate backbone, or the longer alkyl ester group.
| Identifer | oai:union.ndltd.org:ADTP/258675 |
| Date | January 2009 |
| Creators | Bennet, Francesca, Chemical Sciences & Engineering, Faculty of Engineering, UNSW |
| Publisher | Publisher:University of New South Wales. |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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