Effects of crystallinity and dispersity on the self-assembly behavior of block co-oligomers in water

Self-assembly of block copolymers in solution is a topic of great interest in polymer science due to the potential for applications as a drug carrier system. In bulk, fully discrete polymers have been shown to self-assemble in extremely well-defined structures, but the effect of full discreteness on self-assembly in solution is less known. Furthermore, little is known about the effect of molar mass dispersity on crystallization driven self-assembly. Here, we investigate both the effects of dispersity and crystallinity on the self-assembly behavior of low molecular weight poly(lactic acid)-poly(ethylene glycol) block co-oligomers (BCOs) in solution. The results show that the introduction of dispersity and/or crystallinity does not significantly affect spherical and cylindrical morphologies, but vesicular structures are affected. The introduction of dispersity in amorphous vesicle forming BCOs lowers the reproducibility of preparations in solution. For crystalline BCOs, the introduction of dispersity leads to a clear decrease of ordering in bulk and it prevents crystallization of the lLA block in solution. This all arises already at a low dispersity (D <= 1.06), highlighting the effect of dispersity on assemblies of low MW BCOs. It also underlines the need to take dispersity into account when aiming for homogeneous well-defined structures in solution.