Preparation and properties of phenyl-modified natural rubber

We prepared phenyl-modified natural rubber using a two-step process. In the first step, natural rubber was brominated using N-bromosuccinimide in a dichloromethane solution of natural rubber. The amount of N-bromosuccinimide controlled the bromine content. In the second step, a Suzuki-Miyaura cross-coupling reaction of the brominated natural rubber with phenyl boronic acid in the presence of a palladium catalyst replaced the bromine atoms with phenyl groups. H-1-nuclear magnetic resonance and C-13-nuclear magnetic resonance measurements characterized the products. The signals around 7ppm in the H-1-nuclear magnetic resonance spectra of the products were assigned to the phenyl protons, and based on the assigned signals, the estimated conversion of the cross-coupling reaction under mild conditions was more than 70mol%. The amount of phenyl groups present affected both the loss tangent and the glass transition temperature of natural rubber, which increases from -62 degrees C to -30 degrees C. Copyright (c) 2015 John Wiley & Sons, Ltd.