The thermal degradation behavior of head-to-head (H-H) and head-to-tail (H-T) polystyrenes and poly(vinylcyclohexane)s has been investigated by direct pyrolysis in a mass spectrometer. Both H-H and H-T isomers show only small differences in their initial temperatures of decomposition but remarkably different degradation processes. Whereas H-T polystyrene decomposes in accordance with earlier investigations mainly by a radicalic depolymerization into the monomer and yields only a small amount of dimer and trimer, the H-H polystyrene shows no unzipping and only a statistic degradation into oligomeric styrenes. The formation of stilbene is a diagnostic reaction of H-H polystyrene. The pyrolysi…