Transition metal ion-modified polyurethanes: Spectroscopic and thermal studies on polyesterurethane/chromium metallopolymers

Polyesterurethane/chromium(III) metallopolymers (PUCr) having chromium contents below 1% were prepared by using different initial molar ratios urethane groups/chromium ions. PUCr were characterized in comparison with the parent polyurethane (PU) by AAS, UV-Vis absorption spectroscopy, FTIR spectroscopy, DSC, DMA and TGA. Chromium ions form coordination complexes with the urethane nitrogen atoms, the intermolecular complexation bringing about the crosslinking of the hard segments. As a result, disturbance of the hydrogen bonding and modifications in the crystallinity of the hard-segment domains take place. PUCr exhibit higher values of soft-segment glass transition and storage modulus than PU, revealing the reinforcing effect of chromium ions on the polyurethane matrix. As compared with PU, PUCr present lower initial thermal stability, a strongly catalyzed final stage of the thermal decomposition process and more thermally stable intermediate decomposition products.