FT-IR and Raman spectroscopic study of di-urea cross-linked poly(oxyethylene)/siloxane ormolytes doped with Zn 2+ ions

Abstract

The interactions occurring in di-urea ( NHC( O)NH ) cross-linked poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils) doped with zinc triflate (Zn(CF 3SO 3) 2) were investigated by Fourier Transform infrared (FT-IR) and Raman (FT-Raman) spectroscopies. Bonding of the Zn 2+ ions to the urea carbonyl oxygen atoms occurs in the entire range of compositions studied (∞ > n ≥ 1, where n, salt content, is the molar ratio of oxyethylene moieties per Zn 2+ 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 Zn 2+ ions start to coordinate to the POE chains giving rise to the formation of a crystalline POE/Zn(CF 3SO 3) 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 Zn 2+⋯O C coordination, emerge in parallel. “Free” and weakly coordinated CF 3SO 3 − 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 °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.