Poly(vinylamine) complexes with f-block salts from the lanthanide series that exhibit significant glass-transition temperature enhancement

Abstract

Six f-block salts from the lanthanide series form complexes with poly(vinyl amine) and increase the glass-transition temperature of the polymer. Results for poly(vinylamine) complexes with EuCl3(H2O)6 and TbCl3(H2O)6 surpass those for d7 cobalt complexes that were studied previously. The glass-transition temperature increases by 49 °C per mol % Eu3+ and 50 °C per mol % Tb3+, up to 2 mol % of the f-block cations. At 5 mol % Eu3+, Tg is slightly higher than 250 °C with no visual evidence of thermal degradation of either component in the complex. This corresponds to a Tg enhancement of almost 200 °C with respect to the undiluted polymer. The increases in Tg for these lanthanide complexes with poly(vinylamine) obey the following trend: up to 2 mol % of the f-block cation. With the exception of Gd(CH3COO)3, which contains different anionic ligands than all of the other trichlorides, this trend correlates inversely with the highest dehydration/dehydrochlorination temperature of each undiluted lanthanide salt, as measured via calorimetry above the melting point and verified by thermogravimetry. Waters of hydration and amino sidegroups undergo ligand substitution in the coordination sphere of the lanthanides. Since lanthanide cations are classified as hard acids, it is not unreasonable that they form complexes with the nitrogen lone pair in the amino sidegroup of the polymer, which is classified as a hard base. Micro-clustering of several amino side groups reduces chain mobility significantly in the vicinity of each metal center, produces coordination crosslinks, and increases Tg. Complementary solution studies reveal that hydrogels form with swelling ratios between 20 and 50 at Eu3+ mole fractions between 0.01 and 0.05 with respect to poly(vinylamine). Infrared spectroscopic observations suggest that the amino nitrogen lone pair in poly(vinylamine) interacts with these lanthanide metal centers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1931–1938, 2000