Consequences of Dispersity on the Self-Assembly of ABA-Type Amphiphilic Block Co-Oligomers

Intriguingly, little is known about the impact of dispersity on the crystallization driven self-assembly (CDSA) of amphiphilic block copolymers in aqueous media. Here, we investigate the influence of dispersity on the CDSA of ABA-type amphiphilic block co-oligomers (ABCOs). Two pairs of ABCOs are synthesized comprising discrete (D = 1.00) or disperse (D = 1.20) isotactic L-lactic acid 16-mers as the semicrystalline hydrophobic block and either oligo(ethylene glycol) methyl ether (MeOoEG) or oligo (tetraethylene glycol succinate) (oTEGSuc) as the discrete hydrophilic block. Self-assembly studies in water with 10% THE reveal uniform nanofibers/2D sheets for the discrete oligomers, but such structural regularity is largely compromised in the disperse oligomers. The results are corroborated by sharp melting transitions in both solution and bulk for the discrete ABCOs, unlike their disperse analogues that show a lack of crystallization. Interestingly, the discrete MeOoEG-LLA oligomer reveals crystallization driven gelation, illustrating the contrasting differences between the discrete oligomers and their disperse counterparts.