The Effect of Functionalized Ethylene Propylene Diene Rubber (EPDM) on the Kinetics of Sulfur Vulcanization of Normal Rubber/EPDM Blends Alex S. Sirqueira, Bluma G. Soares * Introduction Blends of natural rubber (NR) and ethylene propylene diene rubber (EPDM) were extensively studied in order to achieve more suitable elastomer materials which have a better ageing resistance. However, their thermodynamic behavior associated to the cure rate incompatibility normally results in poor mechanical properties. [1,2] Several approaches have been reported in the literature to solve this problem, including the addition of a low molar mass third component, such as transoctylene rubber (TOR), [3] the incorporation of an accelerator molecule on the EPDM backbone, [4] and the addition of anhydride-functionalized EPDM. [5–7] Our group has also recently reported on the efficiency of EPDM modified with mercapto group (EPDMSH) as a compatibilizing agent for this NR/EPDM blends. [8–11] The compatibilizer effect is based on the ability of mercapto groups to react with the double bond of the unsaturated rubber (natural rubber) which results in strong inter- actions between the components. The mercapto group when incorporated on ethylene–vinyl acetate copoly- Full Paper The effect of mercapto- and anhydride-functionalized ethylene propylene diene rubber (EPDM) or ethylene–vinyl acetate (EVA) copolymers on the vulcanization kinetics of natural rubber/EPDM blends was investigated using the oscillatory disk rheometer. The mercapto groups in both EPDM and EVA copolymers resulted in a significant decrease of the curing time. The Coran’s model was applied to set the kinetic constants within each distinct step of the vul- canization process. The high- est curing velocity was perceived in a blend containing 2.5 phr of mercapto-functionalized EVA. The functionalized EVA, especially that which was functionalized with anhydride groups, also displayed a lower solvent uptake on blending, which would imply an increase of the crosslink density as well a covulcanization phenomenon. A. S. Sirqueira, B. G. Soares Instituto de Macromole ´culas, Universidade Federal do Rio de Janeiro, Centro de Tecnologia, Bloco J, Ilha do Funda ˜o, 21945-970, Rio de Janeiro, RJ, Brasil P.O.Box 68525 E-mail: bluma@ima.ufrj.br 62 Macromol. Mater. Eng. 2007, 292, 62–69 ß 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/mame.200600332