Study of ionic conductivity and microstructure of a cross-linked polyurethane acrylate electrolyte

A cross-linked polyurethane acrylate (PUA) was synthesized by end capping 4 ,4'-methylene bis(cyclohexyl isocyanate), H12MDI/poly(ethylene glycol), PEG based prepolymer with hydroxy ethyl acrylate (HEA). Significant interactio ns of the Li+ ions with the soft and hard segments of the host polymer have been observed for the PUA complexed with lithium perchlorate (LiClO4) by m eans of differential scanning calorimetry (I)SQ, Fourier transform infra-re d (FTIR) spectroscopy, li magic angle spinning (MAS) NMR measurements and t hermogravimetric analysis (TGA). The li MAS NMR investigation of the PUA in dicates the presence of at least three distinct Li+ sites at lower temperat ure, which merge to a single one at higher temperature in similar line with uncross-linked polyurethane. The results of TGA, DSC and FTIR spectroscopy support the formation of different types of complexes by the interaction o f the Li+ ions with different coordination sites of PUA. No detectable inte ractions could be observed between Li+ ions and groups in HEA. The DSC data indicates the fort-nation of transient cross-links with the ether oxygens of the soft segment and mixing of soft and hard phases induced by the Li+ i ons. In addition, a Vogel-Tamman-Fulcher (VTF) like temperature dependence of ionic conductivity implies coupling of the ion movement with the segment al motion of the polymer chains in the cross-linked environment. Predominan t formation of contact ion pairs of LiClO4 has been consistently observed t hrough AC conductivity, DSC and NMR spectroscopic results. Swelling measure ments of PUA with plasticizers reveal the improved dimensional stability fo r these cross-linked PUA in comparison with uncross-linked polyurethane. (C ) 2001 Elsevier Science Ltd. All rights reserved.