These bands seem to indicate that two processes
take place simultaneously: decarboxylation of benzoic anhydrides
structures (associated with the presence of CO2) and release
of an ester derivative from benzoic acid (associated with
the carbonyl absorption bands), probably through depolymerization.
The emission of these structures suggests the formation
of glutaric anhydride type structures in the degrading
material. In agreement with these results, San Roma´n et al.
[23] reported the release of salicylic acid and the formation
of six-membered cyclic structures during thermal degradation
of poly(o-methacryloyloxy benzoic acid).
In PMBeA heated up to 390 C, the anhydrization process
is extended (see Fig. 9c) as shown by increased absorptions at
1807, 1762 and 1052 cm1, although a few ester groups still
survive (1737 cm1).