Oxidation of natural rubber using a sodium tungstate/acetic acid/hydrogen peroxide catalytic system

Abstract A catalytic system based on Na 2 WO 4 /CH 3 COOH/H 2 O 2 effectively oxidizes natural rubber (NR) to prepare telechelic epoxidised liquid natural rubber (TELNR). The Na 2 WO 4 /CH 3 COOH/H 2 O 2 catalytic system possesses a much higher epoxidation efficiency than the traditional CH 3 COOH/H 2 O 2 system: the epoxidation degree ( X epoxy ) of products increases from merely 5.6% (CH 3 COOH/H 2 O 2 ) to values as high as 52.1% (Na 2 WO 4 /CH 3 COOH/H 2 O 2 ) by reacting for 24 h at 60 °C. Moreover, this catalytic system also induces hydrolytic degradation so that the weight average molecular weight ( M w ¯ ) of NR decreases, e.g., from 14.10 × 10 5 Da (NR) to 0.57 × 10 5 Da (TELNR) after reacting for 30 h. The catalytic process probably proceeds via a mononuclear tungsten peroxo-species with coordinated peracetyl/acetyl group, as suggested by ESI-MS measurements. During oxidation, the tungstic anion [W(CH 3 COOO)(O)(O 2 ) 2 ] − not only catalyzes NR epoxidation, but also induces a further oxidation of epoxy groups to form ketones and aldehydes.