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) [α2-P2W17O61{CH2C(CH3)COO(CH2)3Si}2O]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, (1H, 13C, 29Si, 31P and 183W) 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; pKa values of the protonated indicators are −3.0 and −5.6, respectively). The pKa 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 (Tg) 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.

Graphical abstractThe inorganic–organic hybrid polyoxometalate [α2-P2W17O61{CH2C(CH3)COO(CH2)3Si}2O]6− (1) is prepared as Me2NH2+ salt and H+ form. The free-acid form of 1 is immobilized to polymer network through free radical polymerization with methyl methacrylate.Figure optionsDownload full-size imageDownload as PowerPoint slide