This research synthesized polybutadiene nanoparticles and investigated the induction time for their nucleation under different supersaturations and their cross-linking to be utilized in an asymmetric membrane synthesis. Purchased (bulk) polybutadiene was dissolved in toluene and then ethanol was added dropwise to the solution as an antisolvent. The induction time, i.e., the time interval between adding the last drop of ethanol till appearance of a turbidity due to polybutadiene nucleation, was determined. The nucleation mechanism was investigated. Dependence of the induction time on supersaturation suggests that the mechanism of nucleation is primary. The correlation coefficient was obtained as 0.986. After formation, the nanoparticles were cross-linked with sodium persulfate as initiator and divinylbenzene as cross-linking agent. The SEM photos showed the formation of nanoparticles as well as their cross-linking. Such a finely porous layer can act as an effective support for active non-porous layers in applications such as gas separation. Also, based on the practical results, it was determined that for pressure equal 7 bar, temperature of 70 °C, membrane thickness of 1.15 mm and polybutadiene to divinyl benzene ratio of 1.5, the relative separation will be 93.58.