Segmented copolymers with crystallizable uniform p-phenyleneterephthalamide ester units and soft poly(tetramethyleneoxide) (PTMO) segments were synthesized by polycondensation. Long PTMO (>1000 g/mol) segments are known to crystallize around room temperature which reduces the low temperature flexibility of the copolymers. The PTMO crystallization was reduced by incorporating chemical irregularity. PTMO1000-9000 segments having a reduced tendency to crystallize are formed by extending PTMO650 or PTMO1000 with dimethyl terephthalate or dimethyl isophthalate. Furthermore modified PTMO segments (PTMOm: 15 wt% of methyl side groups) were used. The thermal and dynamic mechanical properties of the copolymers were studied with DSC and DMA, respectively. In addition, the PTMO crystallization was studied with synchrotron WAXS measurements. PTMOm segments melt about 20 degreesC lower than PTMO. PTMO1000, DMT and DMI extended PTMO1000 and PTMOm strain crystallize reversibly, while PTMO1400 and longer strain crystallize irreversibly. Reversible strain-induced crystallization of the PTMO phase gives the polymers a relatively high tensile strength combined with a good recovery from tensile deformation. The glass transition temperature of the polymers is not increased by incorporation of the stiff terephthalic or isophthalic units in the PTMO phase. The p-phenyleneterephthalamide ester units crystallize fast and nearly completely due to their uniform length. Even at a concentration of only 3 wt% of p-phenyleneterephthalamide ester units dimensionally stable polymers with a relatively high melting temperature were formed.