A series of di-polyester diamides was synthesized via a nucleophilic ring opening polymerization process. FTIR investigations revealed the spectral characteristics evidencing the newly formed chemical bonds as well as the changes in the relative intensity of the characteristic peaks, due to the increasing side-block lengths of the different members of the series. 1H-NMR analysis of the described materials confirmed the chemical structures seen by FTIR analysis. The side segment length of the different di-polyester diamides was calculated from the integration ratios in the NMR spectra. The molecular weight results exhibited relatively small deviations from the stoichiometrically calculated values. All the members of the triblock series, with side blocks of up to 120 lactoyl units, were essentially amorphous and glassy at room temperature. The presence of two separate glass transitions indicated a segmented and microphase separated morphology. It was deducted that the amorphous nature of the relatively long poly(lactic acid) side blocks occurs due to the dominance of the hydrogen-bonded central segment. Synthesis of a di-polyester diamide containing a reduced number of hydrogen-bond-forming groups in the central segment yielded a partial side-block crystallization. The di-polyester diamide with 120 lactoyl unit-long side blocks was eventually able to crystallize in solid state, following thermal treatment during thermal analysis. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012