Gas Phase Oxygen Effect on Chain Scission and Monomer Content in Bulk Poly(Methyl Methacrylate) Degraded by External Thermal Radiation.
Gas Phase Oxygen Effect on Chain Scission and Monomer
Content in Bulk Poly(Methyl Methacrylate) Degraded by
External Thermal Radiation.
Brown, J. E.; Kashiwagi, T.
Polymer Degradation and Stability, Vol. 52, 1-10, 1996.
chain scission; decomposition; gasification; molecular
weight; polymethyl methacrylate; size exclusion
chromotography; thermal degradation; thermal oxidation;
The effect of the atmosphere oxygen on the thermal
decomposition of poly(methyl methacrylate), PMMA, in a
slab-like configuration was investigated. Blackbody
irradiation of 12 mm thick PMMA slabs on one side was
used to simulate the thermal decomposition and
gasification of the polymer in a fire environment.
Results are reported for chain scission number obtained
from molecular weight measurements and for residual
monomer content at various levels below the slab
surfaces irradiated at 17 and 30 kW/m2 in atmospheres
containing 0, 10, 21, and 41% oxygen in nitrogen. The
scission number and polydispersity of surface layers,
about 0.1 mm thick, were found to increase linearly with
the mole fraction of oxygen in nitrogen. Over this
range (0 to 41% O2) the scission number increased from
1.5 to 5.0 and the polydispersity increased from 3.6 to
11.3 when the PMMA was degraded at the lower flux, while
at the higher flux, the scission number increased from
5.0 to 14.4 with a concomitant polydispersity change
from 2.0 to 4.5. These results show that gas phase O2
reacts with the polymer chains, enhancing random
scissions and generating functional groups from which
depropagation is initiated. This enhanced decomposition
increases the transient gasification rate leading to
ignition and flame spread.