In order to investigate the effects of strong and well-defined hydrogen bonding on the properties ofthermoplastic elastomers (TPEs), we have applied two distinct and strongly dimerizing 2-ureido-4-[1H]-pyrimidinone (UPy) quadruple hydrogen bonding units as physical crosslinker. While the UPy-groupsconsequently serve as the 'hard phase' or 'hard block' in these TPEs, an amorphous polyester has been used as the 'soft phase' or 'soft block'. The UPy-unit has been flanked with either a sterically demandingisophorone spacer or a linear hexamethylene, where these spacers have been derived from isophoronediisocyanate (IPDI) or hexamethylene diisocyanate (HDI), respectively. This difference on a molecularlevel leads to a homogeneous amorphous material in the IPDI-case (polymer 1) and to a nanophaseseparatedmaterial in the HDI-case (polymer 2) as revealed by AFM and DSC experiments. Apart fromthis distinctive difference in morphology and nanoscopic organization, the macroscopic properties ofboth materials are also fundamentally different. In linear stress-strain and DMTA experiments, thehomogeneous IPDI-material 1 shows rubber-like behavior at room temperature, while the mechanicalproperties are strongly temperature dependent. The nanophase-separated HDI-material 2 shows acombination of rubber and plastic behavior and displays a clear rubber-plateau between 0 °C and 50 °Cwith little temperature dependence. The apparent activation-energy of flow for the latter material,determined by multi-frequency DMTA, is 135 kJ mol–1.