1. Introduction
Natural rubber (NR) is a renewable material with unique and special properties, including high resilience, strength and fatigue resistance. It has been used in a wide range of engineering applications, e.g. tires, rubber springs, vibration mounts etc. However, NR is sensitive to heat and oxidation due to its unsaturated nature as well as having poor oil resistance because of its hydrophobic character. These inherent drawbacks of NR limit its use for many applications in industry. In an effort to extend its use, various methods have been developed to modify its properties through both physical and chemical means. Among the chemical modifications of NR which have been attempted are epoxidation, hydrogenation, maleinization, and graft copolymerization [1].