Poly(diallyldimethylammonium) based poly(ionic liquid) di- and triblock copolymers by PISA as matrices for ionogel membranes†
The synthesis of poly(diallyldimethylammonium)-b-polystyrene di- and triblock ABA copolymers was investigated by Macromolecular Design by Interchange of Xanthate/Reversible-Addition Fragmentation Transfer (MADIX/RAFT) using Polymerization-Induced Self-Assembly (PISA) conditions. A diallyldimethylammonium chloride (DADMAC) monomer was firstly polymerized in water using a mono- or difunctional MADIX agent at 60 °C with a water-soluble azo initiator. Then, PISA was implemented using poly(diallyldimethylammonium chloride) as a cationic macromolecular chain transfer agent and styrene for the emulsion phase, leading to latexes made of di- or triblock copolymers. After anion exchange between the chloride and bis(trifluoromethanesulfonyl)imide, the corresponding poly(ionic liquid)-b-polystyrene copolymers were obtained. The block copolymers were mixed with an ionic liquid electrolyte commonly used in sodium batteries composed of a mixture of a propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid and a sodium bis(fluorosulfonyl)imide salt. After casting, self-standing ionogel membranes were obtained. Compared to diblock copolymers, triblock copolymers showed the best self-standing properties, which may be related to the physical cross-linking of the two external polystyrene blocks. Interestingly, the ionogels based on triblock copolymers showed superior ionic conductivity values to previous electrolytes using homopoly(ionic liquid) matrices.