The effect of amount of oxidising agent and reaction time on the properties of hydroxyl terminated epoxidised natural rubber (HTENR) via oxidative degradation

Abstract

Hydroxyl terminated epoxidised natural rubber (HTENR) was synthesised via oxidative degradation method to produce a low molecular weight rubber. Epoxidised natural rubber (ENR) was depolymerised via chemical degradation method using cobalt (II) acetylacetonate (CAA) as the oxidising agent, followed by a treatment with sodium borohydride as a reducing agent to introduce hydroxyl (OH) functional group at both chain ends. The reaction times and the amount of oxidising agent tested were varied from one, three, five and twenty hours and 1to 5 wt% of CAA to obtain the low molecular weight of HTENR. The molecular weight of HTENR was determined using gel permeation chromatography (GPC). The lowest molecular weight of HTENR was achieved at 3 wt% of CAA after 5 h of reaction time at 60 °C where average number (Mn)and average weight (Mw) were 34,000 g/mol and 62,000 g/mol FTIR analysis confirmed that HTENR contained OH group with the appearance of a broad peak around 3,200 - 3,600 cm-1 after the reaction. The presence of OH end groups was verified by NMR analysis with the appearance of two peaks at 3.38 ppm and 3.88 ppm, corresponding to methylene proton adjacent to hydroxyl group in HOCH2CH2CH2 and methane proton adjacent to OH group in CH2CH2CH(OH)CH3.