A series of 12-, 13-, and 14-membered crown ether rings bearing polymerisable side-chains has been synthesised. The crown ethers were attached to a methacrylate or acrylate polymerisable group either via a short link (Ring-CH(_2)-O-Polymer) or via a spacer group. Both hydrocarbon and ethylene oxide spacer groups were used, giving structures of the form (Ring-CH(_2)-O-(CH(_2))(_6)-O-Polymer) and (Ring-CH(_2)-O-((CH(_2)CH(_2))(_2)O)-Polymer). The ethylene oxide chain can potentially bind to a Li(^+) dopant ion. The relative Li(+) binding affinity of 12-, 13-, and 14-membered mono- and disubstituted crown ethers has been assessed by variable temperature (^13)c and (^7)Li NMR. The crown ether bearing monomers were polymerised using standard free-radical polymerisation methods to yield amorphous materials whose glass transition temperature (T(_g)) was controlled principally by the nature of the spacer group. On doping with lithium triflate (LiCF(_3)SO(_3)), the polymers exhibit high ionic conductivity. The conductivity was primarily dependent on polymer T(_g), but was also found to be higher for 12-crown-4 based systems than for 13-crown-4 and 14-crown-4 based analogues. This behaviour was consistent with the results of the NMR studies, which showed that Li(^+) exchange occurs more readily between 12-crown-4 rings than 13- or 14-crown-4 rings. The NMR studies also showed that 12-crown-4 systems have a higher tendency to form 2:1 (ring : Li(^+)) complexes. Within a polymer matrix, the presence of 2:1 complexes allows Li(^+) migration via an association-disassociation mechanism, avoiding the high energy intermediate state of a free or weakly bound Li(^+) ion. The greater encapsulation provided by 2:1 complexation may also aid in ion pair separation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:295482 |
| Date | January 1995 |
| Creators | Collie, Luke E. |
| Publisher | Durham University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://etheses.dur.ac.uk/5196/ |
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