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. 1 H-nuclear magnetic resonance and 13 C-nuclear magnetic resonance measurements characterized the products. The signals around 7 ppm in the 1 H-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 70 mol%. The amount of phenyl groups present affected both the loss tangent and the glass transition temperature of natural rubber, which increases from À62°C to À30°C.

Phenyl‐modified natural rubber was prepared in latex stage by bromination of deproteinized natural rubber followed by Suzuki‐Miyaura cross‐coupling reaction. First, the bromination of natural rubber was carried out using N‐bromosuccinimide in latex stage. The bromine atom content increased as amount of N‐bromosuccinimide increased. Second, the allylic bromine atom was replaced with a phenyl group using phenyl boronic acid in the presence of a palladium catalyst, according to the Suzuki‐Miyaura cross‐coupling reaction in latex stage. The resulting products were characterized by nuclear magnetic resonance (NMR) spectroscopy. Signal at 7.13 ppm was assigned to the phenyl group of the product, while signals at 3.98, 4.14, and 4.44 ppm were assigned to the remaining allylic brominated cis‐1,4‐isoprene units. The estimated phenyl group content and the conversion of the Suzuki‐Miyaura cross‐coupling reaction were 1.32 and 23.7 mol%, respectively. Glass transition temperature (Tg) of deproteinized natural rubber increased from −62°C to −46.7°C, when the phenyl group was introduced into the rubber.