How Does Cross-Linking Affect the Stability of Block Copolymer Vesicles in the Presence of Surfactant?

Block copolymer vesicles are conveniently prepared directly in water at relatively high solids by polymerization-induced self-assembly using an aqueous dispersion polymerization formulation based on 2-hydroxypropyl methacrylate. However, dynamic light scattering studies clearly demonstrate that addition of small molecule surfactants to such linear copolymer vesicles disrupts the vesicular membrane. This causes rapid vesicle dissolution in the case of ionic surfactants, with nonionic surfactants proving somewhat less destructive. To address this problem, glycidyl methacrylate can be copolymerized with 2-hydroxypropyl methacrylate and the resulting epoxy-functional block copolymer vesicles are readily cross-linked in aqueous solution using cheap commercially available polymeric diamines. Such epoxy-amine chemistry confers exceptional surfactant tolerance on the cross-linked vesicles and also leads to a distinctive change in their morphology, as judged by transmission electron microscopy. Moreover, pendent unreacted amine groups confer cationic character on these cross-linked vesicles and offer further opportunities for functionalization

Thiol-Functionalized Block Copolymer Vesicles

Thiol-functionalized block copolymer vesicles are readily prepared via RAFT-mediated polymerization-induced self-assembly (PISA). More specifically, a disulfide-functionalized poly­(glycerol monomethacrylate) macro-CTA is chain-extended using 2-hydroxypropyl methacrylate): the growing water-insoluble poly­(2-hydroxypropyl methacrylate) chains drive in situ self-assembly to produce diblock copolymer vesicles in concentrated aqueous solution. The disulfide bonds in the poly­(glycerol monomethacrylate) stabilizer chains are reductively cleaved in situ using either tributyl phosphine or tris­(2-carboxyethyl)­phosphine to generate thiol groups, which react immediately with either a quaternary acrylate to introduce cationic character or with rhodamine B acrylate or rhodamine B isothiocyanate to confer a convenient fluorescent tag. In addition to such facile derivatization, such thiol-functionalized vesicles may offer some potential for drug delivery applications, because enhanced muco-adhesion is anticipated for these nano-objects