3.3.1. First stage
Fig. 8a shows the FTIR spectra of the evolved gases during
the thermal degradation of PMBeA, whereas Fig. 8b shows the
FTIR spectra corresponding to GrameSchmidt peaks (IR
spectra obtained at the maximum evolution rate for each decomposition
step). Spectra of evolved gases during the first
weight loss located at 265 C (which can be seen as monotonic
increment of the absorbance in the GrameSchmidt curve) do
not show any important band although noisy signals in the
3800e3500 and 1800e1400 cm1 regions were observed.
These signals can be attributed to some water molecules associated
with the COOH groups (which are removed by moderate
drying) as well as to some water molecules generated by
the reaction between two carboxylic groups to form anhydride
structures (this structures were detected in the partially degraded
material heated at 300 C). The presence of some water
molecules associated with carboxylic groups in the polymer
was confirmed by NMR analysis, as it was observed as a signal
structures. This observation supports the hypothesis that water
was released during the first stage of degradation yielding
some anhydride structures (in this case, benzoic anhydride).