Two-Phase Network Formation in Sulfur Crosslinking Reaction of Isoprene Rubber.

Synchrotron in situ zinc K-edge X-ray absorption near-edge structure measurements are conducted during sulfur crosslinking reactions of isoprene rubber at 140 °C. A two-phase network formation via two different reactions is revealed in a benzothiazolesulfenamide-accelerated curing system with zinc oxide and stearic acid. DSC measurements support this observation. The results are in good agreement with previous work using small-angle neutron scattering, where network domains of high network-chain density are proposed to be embedded in a mesh network. A formation of the mesh network is found to occur a little earlier than that of the network domains, and its fraction is unexpectedly observed to be larger than that calculated on the basis of a concentration of zinc stearate. The result is ascribable to amounts of zinc intermediates forming the mesh network. This study may be the first in situ evaluation for the inhomogeneous network formation during vulcanization. [ABSTRACT FROM AUTHOR]