Urethane cross-linked poly(oxyethylene)/siliceous nanohybrids doped with Eu3+ ions Part 1. Coordinating ability of the host matrix

Abstract

Fourier transform mid-IR and Raman spectroscopies were extensively used to examine cation/polymer and cation/cross-link interactions, as well as hydrogen bonding, in Eu³⁺-doped sol–gel derived organic/inorganic materials (monourethanesils). The hybrid framework of these xerogels contains short methyl end capped polyether segments covalently bonded to a siliceous backbone through urethane groups. The cations were incorporated as europium triflate, Eu(CF₃SO₃)₃. Samples with compositions ∞ > n ≥ 10 (where n indicates the ratio of (OCH₂CH₂) moieties per lanthanide ion) were investigated. The spectral data obtained provided unequivocal evidence that the cations coordinate exclusively to the urethane carbonyl oxygen atoms in compounds with 400 ≥ n ≥ 50. The participation of the ether oxygen atoms of the polymer chains in the Eu³⁺ complexation process is initiated at n = 30. The presence of a crystalline phase was detected at n = 10. The variation of the glass transition temperature of the monourethanesils studied with salt concentration is in perfect agreement with these claims. The beginning of the Eu³⁺–polyether interaction is accompanied by a breakdown of the hydrogen bonded aggregates of the matrix, as confirmed by photoluminescence spectroscopy.