Insights into Structure‐Properties Relationship of Cationic Copolymers with Quaternary Ammonium Moieties via RAFT Polymerization as Potential Binders for Lithium–Sulfur Batteries

In this work, the synthesis and structure/properties relationship of well-defined linear and branched copolymers composed of vinylbenzyl trimethylammonium chloride (VBTMA-C) and 2-(acryloyloxy)ethyl trimethylammonium chloride (AETMA-C) was investigated. Copolymers were obtained via reversible addition-fragmentation chain transfer (RAFT) polymerization in aqueous media at 70°C. Subsequently, chloride counterions were substituted by bis(trifluoromethanesulfonyl)imide (TFSI), and copolymers were characterized. Infrared (IR) and nuclear magnetic resonance (NMR) spectra confirm the chemical structure, while size exclusion chromatography (SEC) and rheological measurements highlight the influence of PAETMA moieties in electrostatic and inter-intramolecular interactions of copolymers. Thermogravimetric analysis (TGA) points out the thermal stability of materials. In addition, copolymers with TFSI exhibit a glass transition temperature (T_g) between 50°C and 87°C. X-ray diffraction tests demonstrate a physical rearrangement of amorphous copolymers contained TFSI. Mechanical behavior of copolymers was evaluated, and results demonstrated high modulus (8.406 GPa), tensile strength (25.035 MPa), and toughness (0.214 MJm^-3) of synthesized materials compared to values of polyvinylidene fluoride (PVDF) with modulus (0.605 GPa), tensile strength (1.10 MPa), and toughness (0.021 MJm^-3), respectively. These results confirm physicochemical features and great mechanical properties of the synthesized copolymers, opening the way for their uses as binders in cathodes for lithium-sulfur batteries.