Polymer Electrolytes and Hydrogels from Polyethylene Glycols Cross-Linked with a Hydrophobic Polyisocyanate

Abstract

Solvent free polymer electrolytes have been extensively researched in recent years because of their potential as thin-film ion-conducting materials in high energy density batteries and electrochromic devices.^1-3 Our work in this area has been chiefly concerned with the morphology and conducting properties of salt-containing comb-like poly(methacrylate)s and polysiloxanes endowed with oligo-oxyethylene side chains.^4–5 Ion transport in such systems largely occurs by a free volume mechanism. This is facilitated when the polymeric component has a minimum of crystallinity and a low glass transition temperature. The presence of ion-chelating or polar additives can also have spectacular effects on the conductivity, since they can function as plasticizers or cause the dielectric constant of the material to increase. In this report the synthesis and conducting properties of lithium perchlorate and lithium triflate-containing networks of polyethylene glycols cross-linked with a hydrophobic tri- or tetrafunctional isocyanate are described. The cross-linking agents are well defined hydrosilylation products of ?,?-dimethyl-meta-isopropenylbenzylisocyanate(m-TMI). With added propylene carbonate, the elastomeric sdids have conductivities exceeding 10^-3S cm^-1 at 25 °C and reach values close to 10^-2S cm^-1 at 90°C. The salt free networks when swollen in water exhibit a strong affinity for a variety of hydrophobic molecules. The latter apparently are bound to the large hydrophobic cross-linking sites. Preliminary results of the properties of these hydrogels are also discussed.