Nanoporous Vesicular Membranes of Amphiphilic Polymers Containing Trans/Cis Isomers

Nanoporous membranes and vesicles are interesting systems with potential in applications offering channels for material exchange. Herein, nanoporous membranes and polymersomes are developed by self-assembly of trans- and cis-stereoisomers of amphiphilic polymers. Two polymers, PEG550-TPE-Chol and PEG550-SS-TPE-SS-Chol, containing a central tetraphenylethene (TPE), a cholesterol (Choi), and a poly(ethylene glycol) (PEG550) are studied. Their difference resides in the spacers connecting the TPE to the Chol and to PEG, where PEG550-SS-TPE-SS-Chol contains disulfide bonds (-SS-) with two longer and more flexible spacers compared to PEG550-TPE-Chol. For PEG550-TPE-Chol, a progressive transformation from standard vesicles to porous vesicles, networks, and cylindrical micelles is shown as the trans/cis ratio increases. A local, hexagonal structure of nanopores is observed in the membrane of PEG550-TPE-Chol (trans/cis = 50/50), while a two-dimensional crystalline hexagonal structure of nanopores with long-range order is obtained in that of PEG550-SS-TPE-SS-Chol (trans/cis = 50/50). This self-assembly is likely driven by the microphase separation between vesicle-forming trans-isomers and micelle-forming cis-isomers, where both kinetic effects and free energy minimization play important roles. The hexagonal pore organization is facilitated by higher molecular mobility due to the softer and longer spacers or higher temperature. All nanostructures exhibit cyan aggregation-induced emission fluorescence. Moreover, PEG550-SS-TPE-SS-Chol polymersomes can be destroyed using reducing agents, which may be useful for controlled release.