The activities performed during these few months focused on the controlled synthesis of PDADMA (poly(diallyldimethylammonium chloride)), which will then serve for both PIL and PIL-PEO based electrolytes. The motivation behind the use of a controlled polymerization process is the need for a polymer with precisely controlled molecular weight that could be compared with the commercially available PDADMA, with analogous general structure but no control over the length of polymer chains and their distribution. Reversible addition-fragmentation chain-transfer (RAFT) polymerization was selected based on literature report from the group of Barner-Kowollik and others (Macromolecules 2007, 40, 3907-3913), using a xanthate chain transfer agent: O-ethyl-S-(1-methoxycarbonyl) ethyl-dithiocarbonate. The latter was synthesized according to a reported procedure (RSC Adv. 2015, 5, 91225-91234). Then, the RAFT agent was employed for the synthesis of PDADMA-Cl starting from DADMA-Cl, via RAFT/MADIX (macromolecular design by interchange of xanthates) polymerization in water. The polymerization was attempted at 2 different temperatures, 60 and 80 °C, and using the following conditions: [DADMA-Cl]:[RAFT agent]:[initiator] = 100:1:0.1. These conditions would enable to reach a target degree of polymerization of 100 in case of quantitative monomer conversion, and thus a molecular weight of PDADMA-Cl of ca. 16000 Da. Both polymerizations reached ca. 80% conversion after 20 h (overnight), however the one at lower temperature produced a polymer with molecular weight closer to the theoretical value (13200 Da from gel permeation chromatography analysis) and narrower distribution of molecular weight (dispersity of 1.1).
The remaining steps toward the formation of electrolytes (i.e. polymer mixing with Mg and Al salts) and their comparison with commercial polymers were not yet performed.
In addition, the Fellow was trained on the use of broadband electron spectroscopy (BES), which is the most important technique for the study of ion transport in solid electrolytes. In particular, we took advantage of samples of solid electrolytes of a different kind available in the laboratory and we tested their conductivities over a wide range of frequencies and temperatures (10 mHz-10 MHz, -80 - +160 °C). Each sample was sandwiched between two circular Pt electrodes kept apart by a separator comprised of optical fibres inside a sealed cylindrical Teflon cell closed in a glove box filled with Ar. BES measurements enabled to identify polarisation (σ) and dielectric relaxations in the systems (f). The polarisation events are related to the formation of cationic and anionic nanoclusters with different permittivity.
