Enhancement of molecular weight reduction of natural rubber in triphasic CO2/toluene/H2O systems with hydrogen peroxide for preparation of biobased polyurethanes

Abstract

Molecular weight reduction of natural rubber (NR) with hydrogen peroxide (H2O2) oxidizing agent is limited in biphasic water-toluene systems that is attributed to mass transfer. In this work, CO2 was applied to the (aqueous H2O2)-(toluene-NR) systems with the objective of improving reaction efficiency. Experiments were performed on the reaction system with CO2 at 12 MPa and at reaction temperatures and times of 60°C-80°C and 1 h-10 h to evaluate the reaction kinetics. CO2 could enhance the NR molecular weight reduction by lowering the activation energy (from 121 kJ·mol-1 to 38 kJ·mol-1). The role of CO2 in the reaction system seems to be the formation of oxidative peroxycarbonic acid intermediate and promotion of mass transport due to the reduction in the toluene-NR viscosity and interfacial tension. The epoxidized liquid NRs (Mn=4.9×103 g·mol-1) obtained from NR molecular weight reduction was further processed to prepare hydroxyl telechelic NR (Mn=1.0×103 g·mol-1) and biobased polyurethane.