Various polyurethane-based SMPUs were synthesized using five types of polyols as soft segments and two different diisocyanates as hard segments. The effects of diisocyanate concentration on material properties such as crystallinity, transition temperature, shape-memory effect and tensile strength were investigated. SMPUs with a maximum strain near 1 000%, recovery rate up to ≈98%, fixity up to ≈90% and Tgs of 35–45 °C were obtained. A high MDI content results in SMPUs with better shape-memory effect, whereas increasing IPDI content leads to a weaker shape-memory effect. High IPDI concentration seems to prevent or restrict chemical reactions and crosslinks between the polyols and the hard segments, leading to large phase separation and coexistence of soft and hard segments in the macrophases.