Dispersity under Scrutiny: Phase Behavior Differences between Disperse and Discrete Low Molecular Weight Block Co-Oligomers.

An experimental study is presented in which we compare the bulk phase behavior of discrete and (partially) disperse diblock co-oligomers (BCOs) with high χ-low . To this end, oligomers of dimethylsiloxane (DMS) and lactic acid (LA) were synthesized, each having either a discrete number of repeat units or a variable block length. Ligation of the blocks resulted in DMS-LA BCOs with dispersities ranging from <1.00001 to 1.09, as revealed by mass spectroscopy and size exclusion chromatography. The phase behavior of all BCOs was investigated by differential scanning calorimetry and small-angle X-ray scattering. Compared to the well-organized lamellae formed by discrete DMS-LA, we observe that an increase in the dispersity of these BCOs results in (1) an increase of the of the microphase-segregated state, (2) a decrease of the overall , and (3) an increase of the .