SynopsisSegmented copoly(ether ester) based on poly(ethy1ene terephthalate) and poly(oxytetramethylene) suffers from having a rather low rate of crystallization. "he crystallization behavior of this elastomer can be influenced by cocondensation of selected diols and addition of nucleating agents and plasticizers. Changes of the crystallinity and morphology are studied by differential scanning calorimetry and dynamic-mechanical analysis, respectively. Mechanical properties in relation to the different crystallinites obtained are reported.