EPOXIDATION OF NATURAL-RUBBER IN LATEX IN THE PRESENCE OF A REDUCING AGENT

The in situ epoxidation of natural rubber latex was successfully performed in chain-scissoring conditions. The chain-scissoring process could be carried out simultaneously or successively to the epoxidation, to a determined extent. The rate and the degree of epoxidation depend on temperature, pH, and H2O2/isoprene units ratio. The chain-scissoring reaction leads to a limited intrinsic viscosity range and, at pH 2-3, it was practically completed in 24-40 h. The gel content of epoxidized natural rubber (ENR) products are markedly reduced in the presence of reducing agent. Infrared spectra of ENR, thus prepared, are characterized by the presence of a typical weak band at 1550 cm-1, in addition to the other characteristic bands for normal ENR. At low pH and long-lasting reaction, the epoxide ring undergoes a ring-opening process, resulting in the formation of new OH, CO, ether groups, and slightly increased gel content. The Huggins constant, for a typical series of ENR obtained in redox conditions, was determined. (C) 1993 John Wiley & Sons, Inc.