Formation of inorganic protonic-acid polymer via inorganic-organic hybridization: Synthesis and characterization of polymerizable olefinic organosilyl derivatives of mono-lacunary Dawson polyoxometalate

A novel polymerizable organosilyl-modified Dawson-type polyoxometalate (POM) [alpha(2)-P2W17O61{CH2=C(CH3) COO(CH2)(3)Si}(2)O](6-) (1) was synthesized as both Me2NH2+ salt (Me2NH2-1) and H+ form (H-1). They were characterized with complete elemental analysis, thermogravimetric and differential thermal analysis (TG/DTA), FTIR, (H-1, C-13, Si-29, P-31 and W-183) NMR and n-butylamine titration method. H-1 was immobilized to a polymer network through free radical copolymerization with methyl methacrylate (MMA). The acidities of H-1 and hybrid copolymer (H-1-co-MMA) were evaluated using the Hammett indicators (dicinnamalacetone and benzalacetophenone; pK(a) values of the protonated indicators are -3.0 and -5.6, respectively). The pK(a) value of H-1 was estimated as that between -3.0 and -5.6 in CH3CN solution and H-1 was immobilized in H-1-co-MMA with the original acidity being retained. Glass transition point (T-g) and molecular weight distribution of H-1-co-MMA were affected by the used amount of H-1 because of the cross-linking effect of H-1. (C) 2007 Elsevier B.V. All rights reserved.