Polyphosphazenes with novel architectures: Influence on physical properties and behavior as solid polymer electrolytes

Three types of polyphosphazenes with different architectures have been synthesized and characterized. The influence of the polymer architecture on solid ionic conductivity was of particular interest. The first type includes linear oligo- and polyphosphazenes with the general formula [N=P(OCH2CH2OCH2CH2OCH3)(2)](n) (MEEP) with different chain lengths. The second type consists of a series of triarmed star-branched polyphosphazenes with the general formula N{CH2CH2NH(CF3CH2O)2P[N=P(OCH2CH2OCH2CH2OCH3)(2)](n)}(3) with different arm lengths. These were synthesized via the reaction of the tridentate initiator [N{CH2CH2NH(CF3CH2O)(2)P=N-PCl3+}(3)][PCl6-](3) with the phosphoranimine Cl3P=NSiMe3 in CH2Cl2 followed by halogen replacement with sodium (methoxyethoxy)ethoxide. The molecular weights in this system were carefully controlled by variation of the monomer-to-initiator ratios, and the effect of polymer molecular weight on solid ionic conductivity was examined. The third polymer system was designed to examine the effect of complex branching on ionic conductivity. Thus, a highly branched polymer containing five branches from a cyclotriphosphazene pendent side group (with 26 ethyleneoxy units per repeat unit) was synthesized. The conductivity of this polymer in the presence of three different salts has been measured and compared to the behavior of MEEP with a corresponding molecular weight. The mechanism of ion transport in these systems is discussed.