Segmented polyurethane (PUR) elastomers with different soft segments (polyether，polyester，polysiloxane) and molecularly uniform hard segments，based on 1，5-naphthalene diisocyanate (NDI) and1，4-butanediol (BDO)，were synthesized.They served as model elastomers for detailed investigations of the structureproperties- relations of the hard segment phase of technologically relevant NDI based elastomers.The amount of microphase separation and with that the melting points and heats of fusion rose with increasing hard segment length and decreasing strength of the hydrogen bonds between the urethane NH groups and the soft segment O atoms in the order polyester，polyether and polysiloxane.Multipeak behaviour at the melting of the hard segments indicated the formation of semi- crystalline NDI/BDO hard domain regions，which transformed into better ordered crystalline domains on annealing.At temperatures above180℃，decomposition reactions of the NDI/ BDO hard segments were initiated by breaking the hydrogen bonds.This process began in the badly ordered areas of the semi-crystalline hard segment domains.Rapid decomposition occurred at temperatures above250℃. The dynamic mechanical behaviour of the NDI based polyether elastomers showed a higher hard domain stability than elastomers based on other diisocyanates.They showed also in the service temperature range the highest storage modulus value G′over the broadest temperature range.This indicated a higher and less temperature dependent stiffness as well as a stronger effect as an active filler of the NDI/BDO hard segments.