A fixed bed reactor under argon flow was used to pyrolyse small samples of polypropylene (PP) and atactic polypropylene (APP). A special gas-phase sampling technique was used to determine the composition of products eluted from the reactor as a function of temperature and time. Capillary gas chromatography was used to determine the total volatile product evolution rate. The maximum volatile product evolution temperature was 420 C for APP and 425 C for PP. The recovery of carbon as an organic volatile product was determined and pyrolysis products were classified as a carbon number. The pyrolysis products were also identified with gas chromatography/mass spectrometry (GC/MS). Polypropylene (PP) and atactic polypropylene (APP) decomposed into a large number of aliphatic compounds without a residue. The variety of products was more complex than from polyethylene degradation. Due to the branched structure of PP and APP, also branched isomers are formed. 96 wt.% of carbon in PP and 97 wt.% of carbon in APP was converted to volatile organic compounds such as dienes, alkanes, and alkenes. Major compounds are for instance C compounds, like 2-methyl-4-octene, 2-methyl-2-octene, 2,6-dimethyl-2,4-heptadiene, 2,4-dimethyl-1-heptene, 2-methyl-1-octene. The thermal degradation of both PP and APP were investigated under non-isothermal conditions. The weight loss data have been analyzed by Flynn and Wall methods. The activation energies for overall degradation of PP and APP were determined. (C) 2002 Elsevier Science B.V. All rights reserved.