Morphological transitions of cationic PISA particles by salt, triflate ions and temperature; comparison of three polycations

Three strong polycation stabilizers, poly((vinylbenzyl) trimethylammonium chloride), PVBTMAC, poly((2-(methacryloyloxy)ethyl)trimethylammonium chloride), PMOTAC, and poly((3-acrylamidopropyl) trimethylammonium chloride), PAMPTMAC have been synthesized with reversible addition-fragmentation chain transfer, RAFT, reactions. Solubilities of the polycations change with hydrophobic counterions such as triflate. PVBTMAC undergoes a thermal phase transition with a low amount of triflate, whereas PMOTAC or PAMPTMAC do not. These three cationic macro chain transfer agents were chain extended with a hydrophobic core forming monomer diacetone acrylamide, DAAM, in polymerization-induced self-assembly (PISA) processes. In aqueous sodium chloride solutions, the obtained particles show morphological transitions from spheres to aggregated structures and to vesicles with increasing the ionic ratio (salt concentration). With either increasing the DP of the PVBTMAC block or using other polycations, the particle morphologies change to raspberry-like ones at high salt or solids concentration. When PVBTMACs were used as stabilizers in aqueous LiOTf dispersions at elevated temperatures, spherical particles fused together. Upon cooling, the particles either aggregated or formed worm-like structures. On the other hand, no morphological changes were observed when other two polycations were used as CTAs. The results show how changes in the chemical structure and hydrophilicity of the polycation affect the morphologies of the particles. Particle morphologies may be further tuned with hydrophobic counterions, with which also thermoresponsive morphological changes can be induced.