Natural rubber grafted with poly(methyl methacrylate) (NR-g-PMMA) was prepared with a NR/MMA ratio of 90/10 by weight, and subsequently epoxidized in its latex state via in situ performic acid to create materials with epoxide contents of 10, 20 and 30 mol%. The grafting efficiency was 94.3% and the grafted PMMA content remained more or less unchanged after epoxidation. The changes of mate- rial polarity caused by the presence of epoxide groups at different levels in combination with the grafted PMMA clearly had effects on the thermal properties, wettability and swelling behaviors of the materials. The increase of polar functional groups and the presence of PMMA as ther- moplastic resulted in a higher glass transition temperature (Tg) and improved thermal stability. The shift in Tg and
decomposition temperatures were clearly observed by DSC and TGA, respectively. The introduction of epoxide groups onto the grafted PMMA further enhanced the inter- molecular interactions as additionally indicated by the increased plasticity and the decreased swelling ratio in ASTM oil No. 1 and IRM 903. The polarity changes also affected the wettability of the materials as demonstrated by the lower contact angles of water and diethylene glycol droplets on the polymer films. The modified rubbers con- taining both grafted PMMA and epoxide groups offer much better thermal stability and oil resistance, compared to virgin NR. Therefore, these functionalized rubbers can potentially be applied to various applications especially as compatibilizers in immiscible blends of NR with polar materials such as silica and nanoclay.