Di-ureasil ormolytes doped with Mg2+ ions.: Part 2.: Cationic and anionic environments

Fourier Transform mid-infrared and Raman (FT-IR and FT-Raman, respectively) spectroscopies were used to investigate the cation/polymer, cation/cross-link, cation/anion and hydrogen bonding interactions in sol-gel derived ormolytes doped with magnesium triflate (Mg(CF3SO3)(2)). The framework of these xerogels (di-ureasils) contains poly(oxyethylene) (POE) segments with about 40.5 repeat units bonded at both ends to a siliceous backbone through urea cross-links. Materials with compositions infinity > n >= 1 (where n is the ratio of oxyethylene moieties per Mg2+ ion) were studied. FT-IR data revealed that, while the urea carbonyl oxygen atoms bond to the cations in all the compounds analyzed, the POE chains complex the Mg2+ ions only at high salt content. Although the beginning of the POE/Mg2+ interaction was detected spectroscopically at n = 10, thermal data obtained in Part 1 of this series of papers suggest that this threshold composition is probably located at lower salt content. Bonding of the Mg2+ ions to the ether oxygen atoms of the POE chains is accompanied by the destruction of the urea/POE hydrogen-bonded aggregates formed in the d-U(2000) medium. Proofs of the existence of a crystalline POE/Mg(CF3SO3)(2) complex in samples with n <= 10 were found. "Free" and weakly coordinated CF3SO3 ions, present in all the samples examined, appear to be the main charge carriers of the conductivity maximum of this family of ormolytes (i.e., d-U(2000)(20)Mg(CF3SO3)(2)). At n <= 40, along with those anionic species, another anionic configuration, attributed to contact ion pairs, emerges. Higher ionic aggregates are formed in di-ureasils with n <= 5. (c) 2005 Elsevier B.V. All rights reserved.