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Comprehensive investigation of lithium ion complexation with 15N-labeled polyphosphazenes 15 N-poly[bis(2-(2-methoxyethoxy)ethoxy)phosphazene] (15 N-MEEP) and 15 N-poly-[((2-allylphenoxy)0.12(4-methoxyphenoxy)1.02(2-(2-methoxyethoxy)ethoxy)0.86)phosphazene] (15 N-HPP)was performed by NMR, IR, and Raman spectroscopies. Previous studies characterized the ionic transport through the polymer matrix in terms of “jumps” between neighboring polymer strands utilizing the electron lone pairs of the etherial oxygen nuclei with the nitrogen nuclei on the polyphosphazene backbone not involved. However, noteworthy changes were observed in the NMR, IR, and Raman spectra with the addition of lithium trifluoromethanesulfonate (LiOTf) to the polyphosphazenes. The data indicate that the preferred association for the lithium ion with the polymer is with the nitrogen nuclei, resulting in the formation of a “pocket” with the pendant groups folding around the backbone. NMR temperature-dependent spin−lattice relaxation (T 1) studies (13C, 31P, and 15N) indicate significant lithium ion interaction with the backbone nitrogen nuclei. These studies are in agreement with molecular dynamics simulations investigating lithium ion movement within the polyphosphazene matrix.

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We report in this article an improved procedure to isolate and purify representative water-soluble polyphosphazenes that dramatically reduces the time and equipment involved, while maintaining or exceeding the yields and purity reported in the literature for these polymers obtained using dialysis methods. This technique takes advantage of the phase transition behavior exhibited by some hydrophilic polymers, namely that associated with the lower critical solubility temperature (LCST). The polymers used in this study were poly[bis-(2-(2-methoxyethoxy)ethoxy)phosphazene], MEEP (1), and two new water-soluble polymers. These polymers are similar to MEEP, yet they contain a small percentage of a crosslinkable pendant group; either 2-hydroxyethyl allyl ether (2), or o-allyl phenol (3). The observed behavior was quite different for these two polymers than that found for MEEP, and is a direct consequence of the pendant group substitution patterns. Although the homopolymer MEEP yielded a single sharp LCST point, the two heteropolymers exhibited this phase transition over a broader temperature range. Further, fractionation of polymer 3, based on pendant group speciation, was possible due to the more hydrophobic nature of the phenol.