Kinetic Study of Stabilizing Effect of Oxygen on Thermal Degradation of Poly(methyl methacrylate)

Abstract

The thermal degradation of poly(methyl methacrylate) (PMMA) has been studied in both pure nitrogen and oxygen-containing atmospheres. The presence of oxygen increases the initial decomposition temperature by 70 °C. The stabilizing effect of oxygen may be explained by forming thermally stable radical species that suppress unzipping of the polymer. This assumption is supported by the experimental fact that introduction of NO into gaseous atmosphere increases the initial decomposition temperature by more than 100 °C. The model-free isoconversional method has been used to determine the dependence of the effective activation energy on the extent of degradation. The initial stages of the process show a dramatic difference in the activation energies that were found to be 60 and 220 kJ mol -1 for respective degradations in nitrogen and air.

The effect of boron-containing layered hydroxy salt (LHS) on the thermal stability and degradation kinetics of poly (methyl methacrylate)

“…The order reversed at higher conversions (145-140 kJ mol −1 in air and 175-190 kJ mol −1 in N2 for 40-70% conversion), with the transition being at about 35% conversion. This is consistent with the effect of oxygen on the degradation of PMMA; oxygen has been postulated to have a stabilizing effect on the first step and a destabilization effect on the second step [29]. The additive had the effect of increasing the activation energy of the first step of degradation, but did not have a significant effect on the Ea of the second step.…”

“…The Ea values obtained by Hu and Chen [48] agree qualitatively with those obtained in this work in that the first step has lower activation energy than the second step. The same general trend was also observed by Peterson et al who reported effective Ea values of 190 kJ mol −1 for the first step and 230 kJ mol −1 for the second step [29]. Hirata et al [28] did accessed by following the link in the citation at the bottom of the page.…”

“…The two steps in the degradation of PMMA have been attributed to scission at the vinyl terminated end and to random scission of the PMMA back bone respectively [27]. The initial stabilization of PMMA in air, although not very distinct in this work, has been reported elsewhere [28] and [29]. Hirata and core workers [28] have attributed the stabilization of PMMA at early stage to the modification of the terminal double bond in PMMA, by oxygen, which results in the suppression of the end initiation process.…”

“…Isoconversional methods do not suffer from that drawback and enables the determination of the dependency of Ea on the extent of reaction and are therefore favored over model-fitting methods [37], [38] and [39]. Both isothermal and non-isothermal methods have been used in the determination of kinetic parameters in the degradation of polymers [17], [29], [40], [41] and [42].…”

Thermolysis of RAFT-Synthesized Poly(Methyl Methacrylate)

“…We have performed thermogravimetric analysis of a PMMA of similar molecular weight (M n 3670) to that used by Xu et al [33] (M n 3600), and find it to be no less stable with respect to weight loss or end group elimination than higher molecular weight PMMA (onset temperature for degradation ∼190 • C for 5 • C min −1 under nitrogen). Air contamination of the nitrogen purge gas is expected make PMMA appear more stable [50] (oxygen traps PMMA propagating radicals interrupting the unzipping of chains) but would not prevent end group elimination. Factors which might lead to PMMA appearing less stable by TGA include the presence of residual initiator or metal contamination of the sample.…”