EPDM/PP model compounds were dynamically vulcanized by use of varying amounts of an organic peroxide and a trifunctional methacrylate to produce thermoplastic vulcanizates (TPV) materials with different properties. Tensile strength and ultimate elongation as well as compression set data of these materials are comparable to existing commercial TPV products. Although, crosslinking of the elastomer phase is the most important step during the production process, there is a lack of suitable test methods until now to determine the cross link density precisely. Therefore, a new test method, Temperature Scanning Stress Relaxation (TSSR) was examined to determine the crosslink density of the EPDM – phase. The results are in good agreement with results obtained from conventional swell measurements. The advantages of TSSR measurements over swell measurements are quite obvious. Whereas swelling measurements are very time consuming, TSSR tests are much easier and faster to perform. Additionally, information about the relaxation behavior and degradation of the PP ‐ phase was obtained from TSSR measurements.

Thermoplastic elastomers (TPEs) based on poly(styrene‐b‐ethylene/butylene‐b‐styrene) (SEBS), modified with poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE), were investigated by a new testing method. The development and characterization of TPEs with improved temperature and oil resistance is a current area of research to extend the applications of TPEs, especially in the automotive industry. Thermal scanning stress relaxation (TSSR) was used to investigate the relaxation behavior of compounds containing SEBS, blended with extender oil, various amounts of PPE and in some cases with a thermoplastic polymer. Polyamide 12 (PA12) or polypropylene (PP) were used as the thermoplastic component. TSSR measurements were applied to detect relaxation changes in the glass transition region of the polystyrene blocks mixed with PPE. It was shown that the glass transition temperature increased with addition of PPE to the compound up to a limit of approximately 150°C, which corresponded to a weight fraction of PPE in the polystyrene (PS)‐block of 0.5. The increased glass transition temperature lead to SEBS‐based thermoplastic elastomer compounds with improved upper service temperatures. Phase images obtained by atomic force microscopy showed that the addition of PPE results in an increase of hard phase dimension. The addition of a thermoplastic polymer improved the mechanical properties and temperature resistance, but naturally decreased the elasticity of the compounds. Compounds containing PA12 exhibited an improved oil resistance. POLYM. ENG. SCI., 45:1498–1507, 2005. © 2005 Society of Plastics Engineers