Y. Cohen et Z. Aizenshtat, ISOTHERMAL FLUIDIZED-BED STUDIES ON THE KINETICS AND PYRE-PRODUCTS OFLINEAR AND BRANCHED POLY(P-PHENYLENE SULFIDE) AND PROPOSED MECHANISMS, Journal of analytical and applied pyrolysis, 27(2), 1993, pp. 131-143
The isothermal kinetic behaviour under fluidized-bed conditions of lin
ear poly(p-phenylene sulfide) (LPPS) and the branched polymer (BPPS),
formed by curing at 340 degrees C, is presented. The FID monitoring of
the products volatilized at 575, 525 and 475 degrees C shows differen
t profiles for LPPS and BPPS and supports the concept that the thermal
stability of the poly(phenylene sulfide) (PPS) increases with an incr
ease in the degree of branching. This is also supported by differentia
l scanning calorimetry (DSC) and thermogravimetry results which indica
te that the weight loss on thermal degradation starts at 430 degrees C
. The pyro-products volatilized during pyrolysis were trapped, and GC
and GC/MS analyses for both LPPS and BPPS showed two families of compo
unds: (i) fragments of Ph-S unit structure; (ii) benzothiophenic struc
tures (mostly dibenzothiophenes). The ratios of products as well as ki
netic parameters lead us to conclude that: (A) the activation energy r
equired for the formation of type (ii) products is higher than for typ
e (i); (B) an increased degree of branching facilitates the formation
of dibenzothiophenes; (C) the activation energy required to form diben
zothiophenes of higher molecular weight pyre-products, e.g. 1,4-S-phen
yl-S'-2-dibenzothiophene benzenedithiol, is lower than that needed to
form smaller molecules, e.g. dibenzothiophene. Mechanistically, it is
proposed that ''low temperature'' pyrolysis is controlled by cleavage
of the phenyl-sulfur bond via free radicals which restructure to form
BPPS with small weight loss in the chain transfer processes. At higher
temperatures the free radicals may abstract hybrogen atoms from the p
olymer structure to form dibenzothiophenes and volatile pyre-products.
All changes are monitored quantitatively, and atomic ratio (H/C, S/C)
analyses of the residue are discussed.