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 material
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 thermoplastic
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 intermolecular
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 containing
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.