Thermoplastic elastomers of the poly[ester-b-ether] copolymer type (PEE) comprising a hard block of poly(butylene terephthalate) (PBT) and oligoether soft segments, differing in the molecular weight of the oligoether [α, ω-dihydroxy poly(oxytetramethylene) (PTMO);Mn= 650, 1000, and 2900 g/mol] were synthesized and analyzed. Synthesized PEEs were modified by a dimer fatty acid (DFA,Mn= 570 g/mol) as a component of the soft segments. Each copolymer (consisting of one hard-segment component and two components of the soft segments) was obtained in a two-stage process involving transesterification and polycondensation in the melt. Elastomer series were prepared with a constant PBT mass ratio of 50; the content of PTMO and DFA segments was changed. Differential scanning colorimetry results showed a single glass transition temperature for the mixed PTMO-DFA soft phase, which indicates that ether and aliphatic units are able to create a homogenous amorphous phase.