The mechanisms involved in polyethylene catalytic hydrocracking are investigated by monitoring temperature-dependent evolution profiles derived from mass spectra obtained while polymer/catalyst samples, were heated at a constant rate. Repetitive injection gas chromatography/mass spectrometry (GC/MS) results are used to identify class-specific fragment ions that represent paraffins, olefins, and alkyl aromatics. Class-specific ion signals are used to generate isoconversion-effective activation energy plots from which mechanistic comparisons are made. Studies using PtHZSM-5, PtHY, and PtHMCM-41 bifunctional solid acid catalysts in helium and hydrogen are reported. The effects of hydrogen on polyethylene cracking are dramatic and result in significant changes to isoconversion-effective activation energies. Catalytic cracking mechanisms for the three catalysts are compared and differences are explained by a combination of pore size and acidity effects. (C) 2004 Wiley Periodicals, Inc.