Controlling the morphology of poly(ethylene glycol)-b-poly(lactide) (PEG-PLA) self-assemblies in solution: Interplay of homopolymer additive and kinetic traps

Abstract Block copolymer (BCP) self-assembly involves various components in the system interacting in diverse and intricate ways to result in a final state. This paper explores the how homopolymer additives and kinetic traps can be used to control the morphology of self-assembly of poly(ethylene glycol)-b-poly(lactide) (PEG-PLA) nanostructures in water. By kinetically trapping PEG-PLA nanostructures formed in the presence of a non-adsorbing PEG homopolymer, we reveal how different concentrations and molecular weights of the added PEG was found to be able to induce micelle-to-vesicle transitions. This phenomenon was ascribed to a change in the molecular geometry of the underlying BCP induced by the added PEG homopolymer due largely to excluded volume screening effects. In addition, we demonstrated the reverse vesicle-to-micelle transition upon homopolymer removal, and the kinetic nature of the system rendered the transition effect time and temperature dependent. Analysis of the intermediate transition structures reinforces our proposed mechanism involving the change in the underlying molecular geometry of the PEG-PLA BCP. As proof of concept, we showed how our understanding of the PEG-PLA system allowed us successfully utilize the PEG-PLA vesicles thermoresposive delivery systems. We showed how the vesicles was able to retain dye at low temperature (4℃) and the release can be triggered upon heating (37℃). Overall, the work here introduces a novel means of regulating the morphology and behavior of BCP nanostructures, which can have important downstream applications.