PREPARATION AND PROPERTIES OF SOLID ELECTROLYTES ON THE BASIS OF ALKALI-METAL SALTS AND POLY(2,2-DIMETHYLTRIMETHYLENE CARBONATE)-BLOCK-POLY(ETHYLENE OXIDE)-BLOCK-POLY(2,2-DIMETHYLTRIMETHYLENE CARBONATE)

The dissolution of alkali metal salts, e.g. LiClO4, LiCF3SO3, NaSCN, N aI, NaCF3SO3 and KSCN in poly(2,2-dimethyltrimethylene carbonate)-bloc k-poly(ethylene oxide)-block-poly(2,2-dimethyltrimethyle carbonate) (P DTC-b-PEO-b-PDTC) results in solid polymeric electrolytes. Depending o n the nature of the salt, differential scanning calorimetry (d.s.c.) m easurements of the polymer/salt systems reveal that crystalline comple xes are obtained with NaI, NaSCN, and LiCF3SO3. These complexes exhibi t characteristic infra-red (i.r.) bands, e.g. at 1106 and 1080 cm(-1) for the complex with NaI. X-ray powder diagrams of the polymer/salt co mplexes show that the original patterns of the salt and the crystallin e PEO phase have disappeared in favour of a new pattern for the comple x; however, reflections attributed to the crystalline PDTC phase are f ound to be unchanged. Complexation takes place mainly with the PEO seg ments of the block copolymer, thus causing a change in the secondary s tructure of the original PEO helix. The stoichiometry of the polymer/s alt complexes is 3/1 (EO repeating units/metal cation). The highest va lue of the alternating current conductivity was obtained for LiCF3SO3 as the salt component, with values of sigma = 10(-4) at 60 degrees C b eing obtained at concentrations of 5 to 10 mol% (based on the EO repea t units). From temperature dependent conductivity measurements it was concluded that above the glass transition temperature the ionic conduc tivity of the sodium salt systems follows an Arrhenius behaviour, whil e the lithium and potassium salt systems follow a Vogel-Tammann-Fulche r behaviour. Copyright (C) 1996 Elsevier Science Ltd.