The absence of entanglements, the more compact structure and the faster diffusion in melts of cyclic poly(ethylene oxide) (PEO) chains have consequences on their crystallization behavior at the lamellar and spherulitic length scales. Rings with molecular weight below the entanglement molecular weight (M < M), attain the equilibrium configuration composed from twice-folded chains with a lamellar periodicity that is half of the corresponding linear chains. Rings with M > M undergo distinct step-like conformational changes to a crystalline lamellar with the equilibrium configuration. Rings melt from this configuration in the absence of crystal thickening in sharp contrast to linear chains. In general, rings more easily attain their extended equilibrium configuration due to strained segments and the absence of entanglements. In addition, rings have a higher equilibrium melting temperature. At the level of the spherulitic superstructure, growth rates are much faster for rings reflecting the faster diffusion and more compact structure. With respect to the segmental dynamics in their semi-crystalline state, ring PEOs with a steepness index of ∼34 form some of the "strongest" glasses.

The phase state, local structure, local mobility, and viscoelastic response have been studied in the archetypal polymer electrolyte (PEO) x LiCF 3 SO 3 with ether oxygen to lithium ion ratio of 2 ≤ [EO]/[Li] ≤12 over a broad temperature range in an effort to explore the factors controlling ionic conduction. We confirm that the crystal structure of the complex is identical to the (PEO) 3 LiCF 3 SO 3 polymer electrolyte independent of the [EO]:[Li] content. Heating the nonstoichiometric compositions result in progressive melting of the complex, whereas the complex formed at or near the stoichiometric composition remains stable up to the liquidus temperature. The temperature dependence of dc conductivity is neither Arrhenius nor VFT. Its temperature dependence is more complex reflecting the underlying structural changes. Surprisingly, ionic conduction takes place both within the crystalline complex and in the amorphous phase with the latter having the major contribution. The (PEO) 12 LiCF 3 SO 3 polymer electrolyte is the one with the highest conductivity at all temperatures investigated. The linear viscoelastic properties were studied as a function of temperature at two compositions. The different phases have distinct viscoelastic signatures. The complex formed at or near stoichiometric composition has a predominantly elastic response, whereas the more dilute compositions (consisting of the crystalline complex and an ion-containing amorphous phase) have a viscoelastic response and an ultraslow relaxation. Local polymer relaxation and ionic mobility are completely coupled. It is suggested that local ion jumps at subsegmental level are responsible for the measured conductivity.

Densely grafted poly­(ethylene oxide) (PEO) brushes on a poly­(hydroxyl­styrene) (PHOS) backbone (PHOS-g-PEO) as well as block copolymers with polystyrene (PS) (PS-b-(PHOS-g-PEO)) are designed as model systems for Li ion transport. This macromolecular design suppresses the propensity of PEO chains for complex crystal formation with LiTf as well as for crystallization. Li ion conductivities similar or even exceeding those in the archetypal electrolyte poly­(ethylene oxide)/lithium triflate (PEO/LiCF3SO3 (LiTf)) are obtained for a range of temperatures and LiTf compositions. At the same time, PHOS-g-PEO and PS-b-(PHOS-g-PEO) show improved mechanical stability. Typically, at 333 K, the ionic conductivity is ∼6 × 10–5 S/cm and the modulus at ∼2 × 106 Pa for a [EO]:[Li+] = 8:1 composition. In the endeavor for suitable solid polymer electrolytes macromolecular architecture seems to play a decisive role.

Diblock copolymers of poly(styrene-b-ethylene oxide), PS-b-PEO, are employed together with lithium triflate (CF 3 SO 3 Li, LiTf) at several [EO]: [Li] ratios as solid polymer electrolytes. Their thermodynamic state, self-assembly, and viscoelastic properties are discussed in conjunction with the ionic conductivity. PS-b-PEO/LiTf differs from the wellinvestigated PS-b-PEO/LiTFSI system in that the electrolyte in the former binds intramolecularly to PEO chains. Microscopic and macroscopic parameters affecting ion transport are discussed. From a microscopic point of view different parameters were considered as potential regulators of ion transport: the characteristic domain spacing, d, the interfacial thickness, Δ, and the ratio of Δ/d. By comparing two block copolymer electrolytes (PS-b-PEO and PI-b-PEO) bearing the same conducting block (PEO) and the same electrolyte (LiTf) but in the presence of different interactions, among the microscopic parameters it is the domain spacing that appears to have the most decisive role in ionic conductivity. Ion conductivity in PS-b-PEO/LiTf exhibits a molecular weight dependence similar to that reported for the PS-b-PEO/LiTFSI system, however, with somewhat lower values reflecting anion size effects. Among the macroscopic factors that limit ionic conductivity, the possible preferential wetting of the electrodes by either of the constituent phases can lead to an orientation that effectively blocks ion transport. The viscoelastic properties of the block copolymer electrolytes differ substantially from the neat block copolymers. Li-ion coordination affects not only the PEO segments but also, surprisingly, the PS segments. An increase in PS glass temperature by ∼10 K is reported. In addition, the viscoelastic properties suggest the formation of transient structures in the molten complex.

The Bjerrum length is approached in a low polarity solvent by encapsulating, both, a borate anion and a phosphonium cation in a rigid lipophilic dendrimer shell. In addition the cation size is varied by 34-fold. We thus obtain superweak ions with potential applications in catalytic processes.