A series of segmented block copolymers was prepared by the chain extension of hydroxyl terminated liquid natural rubber (HTNR) with polyurethane oligomers derived from toluene diisocyanate (TDI) and 1,3-butane diol at varying NCO/OH ratio. The previously reported two-step method of synthesis was modified to get improved products. This was done by optimizing the formation of polyurethane oligomers in the first step of the synthesis. All the samples were characterized by solubility testing, DSC, tensile testing, etching studies, and SEM. The data obtained were correlated to the structural features of the block copolymers. It was found that NCO/OH ratio played an important role in determining the structural variations in the block copolymers.