Poly(propylene oxide) based polyether(ester-amide)s (PEEA) with non-crystallisable amide segments were synthesized and their structure-property relations studied. These model segmented block copolymers were used to gain insight in the structure-property relations of block copolymers with liquid-liquid demixed morphologies, also present in segmented polyurethanes. The poly(propylene oxide) used had a molecular weight of 2300 g/mol and was end capped with 20 wt% ethylene oxide. The non-crystallisable amide segments are based on an amorphous polyamide: poly(m-xylylene isophthalamide) and the repetitive length (x) of the amide segment was varied from 1 to 10. Phase separation in these PEEA's occurred by liquid-liquid demixing when the length (x) of the non-crystallisable amide segment was higher than 2 (x > 2). TEM experiments showed spherical structures at two size scales, 5-10 nm domains (nano-domains) and 30-500 nm domains (sub-micron domains), both dispersed in a polyether matrix. The size and volume fraction of these spherical domains were found to increase with increasing the amide segment length. The modulus of the materials increased moderately with increasing amide segment content (increasing amide segment length x). The compression and tensile sets values of these PEEA's were found to decrease with increasing amide segment length, thus these PEEA's behave also more elastic at longer amide contents (thus also at higher modulus). Giving time these liquid-liquid demixed segmented block copolymers recovered completely. © 2005 Elsevier Ltd. All rights reserved.