Preparation and some properties of modified natural rubber bearing grafted poly(methyl methacrylate) and epoxide groups

• Modified NR having both grafted PMMA and epoxide groups was successfully prepared.
• Combined effect of both functional groups gives superior oil resistant material.
• Tg and thermal stability increase with increasing epoxide contents.
• Reduced contact angle clearly indicates their wettability by polar liquids.
• This modified NR shall benefit as potential compatibilizer or surface modifier.

Reactive double bonds of natural rubber (NR) enable several possibilities for chemical modification. This present study prepared novel modified NRs with both grafted poly(methyl methacrylate (PMMA) and epoxide groups on the molecules. NR was firstly grafted with PMMA using a NR/MMA ratio of 90/10 by weight, and cumene hydroperoxide/tetraethylene pentamine (CHP/TEPA) as a redox initiator. The grafted NR latex was subsequently modified by an in situ epoxidation reaction using performic acid and finally neutralized using an aqueous solution of ammonium hydroxide. The presence of grafted PMMA and epoxide groups on the modified rubbers was examined by Fourier-transform infrared (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy. The thermal properties were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The epoxidized NR-g-PMMA showed higher glass transition temperatures (Tg) when compared to NR-g-PMMA and virgin NR, and the Tg was shifted toward higher temperature with increasing epoxide contents. The thermal stability, wettability by water and diethylene glycol, rubber plasticity and oil resistance of the modified NRs increased after the introduction of PMMA grafted onto the NR chains, and were further enhanced by the presence of epoxide groups in the structures. The material consisting of 6 mol% of grafted PMMA and 30 mol% of epoxide groups showed superior thermal stability, wettability and swelling resistance compared to the modified rubber having only epoxide groups at the same level.

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