A series of hydroxyl terminated polybutadiene (HTPB) based polyurethanes (PU) were synthesized by solution polymerization with different kinds of polyols and diisocyanates, hard segment contents, NCO/OH value, polymerization methods and annealing time. The segregation between hard and soft segments was manifested by incompatibility between hard and soft segment, steric hindrance of urethane groups and the extent of interchain hydrogen bonding. Hydrogen bonding index (HBI) measured by FTIR was employed to show the extent of interchain hydrogen bonding, which affects the segregation and hence gas permeability of the prepared membranes. Membranes with high HBI were seen to have low segregation and hence low gas permeability. Membranes with mixed diisocyanates of polar 4,4’-diphenylmethane diisocyanate (MDI) and nonpolar isophorone diisocyanate (IPDI), lower hard segment content and NCO/OH value, and one-stage polymerization methods exhibit higher gas permeability.