Synthesis of an Original Fluorinated triethylene glycol methacrylate Monomer and its Radical Copolymerisation with Vinylidene Fluoride. Application as Polymer Electrolyte Gel for Li‐Ion Batteries
Résumé
The synthesis and characterisation of novel poly[VDF‐g‐oligo(EO)] graft copolymers (where VDF and EO stand for vinylidene fluoride
and ethylene oxide, respectively) are presented. First, 2‐trifluoromethyl oligo(EO) acrylate, MAFTEG, was prepared by esterification of
triethylene glycol monomethyl ether (TEG) with 2‐trifluoromethacrylic acid (MAF) catalyzed by methanesulfonic acid, in 50% yields. Then, various radical copolymerisations of such MAFTEG with VDF from different feeds (VDF ranging from 85 to 95 mol.%) led to
random poly[VDF‐co‐MAFTEG] copolymers that bore oligo(OE) side‐chains in satisfactory yields (60‐70%). These original graft
copolymers were characterised by 1H and 19F NMR spectroscopy. Their molar masses reached ca. 7,000 g∙mol‐1 and their thermal
properties were investigated while their glass transition temperatures ranged between ‐31 and ‐19 °C. Their thermogravimetric
analyses under air showed decomposition temperatures from 235 to 325 °C with 10 % weight loss (Td,10%). Gel polymer electrolytes
were achieved at room temperature by blending ionic liquid electrolyte (RTIL), poly[VDF‐g‐oligo(EO)] graft copolymers, and silica
nanoparticles, the ionic liquid being made of 1‐propyl‐1‐methyl pyrrolidinium bis(fluorosulfonyl)imide (PyrFSI) dissolving lithium
bis(trifluoromethanesulfonyl)imide (LiTFSI). These novel copolymers are of potential interest as gel polymer electrolytes in lithium ion
batteries, showing competitive ambient conductivities of 0.2 mS.cm‐1 that increased up to 0.5 mS.cm‐1 with a content of silica
nanoparticles at 20 wt%. In addition, the electrolyte gel appeared to be electrochemically stable in a wide range of potentials varying
from 1.5 V to 4.1 V vs. Li+/Li, compatible with 4 V class lithium ion batteries.