FT-IR and Raman spectroscopic study of di-urea cross-linked poly (oxyethylene)/siloxane ormolytes doped with Zn2+ ions


The interactions occurring in di-urea (-NHC(=O)NH-) cross-linked poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils) doped with zinc triflate (Zn(CF3SO3)(2)) were investigated by Fourier Transform infrared (Fr-IR) and Raman (Fr-Raman) spectroscopies. Bonding of the Zn2+ ions to the urea carbonyl oxygen atoms occurs in the entire range of compositions studied (infinity > n >= 1, where n, salt content, is the molar ratio of oxyethylene moieties per Zn2+ ion). At n > 20 the incorporation of the guest cations progressively reduces the number of free C=O groups. At n = 20 the saturation of the urea cross-links is attained and the Zn2+ ions start to coordinate to the POE chains giving rise to the formation of a crystalline POE/Zn(CF3SO3)(2) complex. The latter process occurs at the expense of the destruction of the hydrogen-bonded POE/urea structures of the host di-ureasil structure. New hydrogen-bonded associations, more ordered than the urea-urea aggregates present in the non-doped matrix and including Zn2+center dot center dot center dot O=C coordination, emerge in parallel. "Free" and weakly coordinated CF3SO3- ions, present in all the xerogels studied, appear to be the main charge carriers of the conductivity maximum of this family of ormolytes located at n = 60 at 30 degrees C. In materials with n <= 20 contact ion pairs, "cross-link separated" ions pairs and higher ionic aggregates appear. The data reported demonstrate that the behaviour of the di-ureasils doped with triflate salts depends on the type of cation. (c) 2005 Elsevier B.V. All rights reserved.



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Chemistry; Spectroscopy


Nunes, SC; Bermudez, VD; Ostrovskii, D; Carlos, LD

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