CO₂-responsive polyacrylamide copolymer vesicles with acid-sensitive morpholine moieties and large hydrophobic RAFT end-group

Sequential Reversible Addition Fragmentation Chain Transfer (RAFT) polymerizations using 2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044) and 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) were used to give amphiphilic polyacrylamide block copolymers containing N-(2-morpholin-4-ylethyl)acrylamide (MEA), where the morpholine moieties are CO₂-responsive. The order in which monomers were polymerized determined the placement of the large hydrophobic RAFT end group with more complex ABA′ type self-assembly (e.g. patterned and large worm-like vesicles, large compound micelles) obtained when the dodecyl trithiocarbonate end-group was attached to the hydrophilic poly(MEA) block. Cleaving the hydrophobic end group reverts self-assembly to simpler spherical vesicles observed in the triblock of the same chemical composition, but with the RAFT end group attached to the hydrophobic poly(tert-butyl acrylamide) block. Ionization of the hydrophilic poly(MEA) block through flushing with CO₂ irreversibly shifts self-assembly towards lower order morphologies with spherical micelles being more favoured than vesicles.