Composite Xerogels Based on Poly(methacrylic acid) and High Concentrations of LTA Zeolite: Solid-State NMR Investigations

Enhanced Linde Type A (LTA) zeolite-poly(methacrylic acid) (PMAA) composites are synthesized by incorporating high concentrations of LTA zeolite (35-52 mass%) into the PMAA hydrogel network. PMAA, LTA zeolite-PMAA composites in xerogel structure, and LTA zeolite are investigated by ¹³C, ²⁷Al, and ²⁹Si solid-state NMR. The interactions between LTA zeolite and PMAA in the xerogel structure are confirmed. Regularly aligned acid dimers with the carboxylic acids hydrogen-bonded to each other in LTA zeolite-PMAA composites are revealed. The ²⁹Si MAS NMR reveals the prevalent tetrahedral coordination of silicon atoms in composites and the presence of the hydrogen-bearing amorphous species. The ²⁷Al MAS NMR spectra of LTA zeolite and composites confirm predominant tetrahedrally coordinated aluminum atoms in a typical LTA zeolite framework and the presence of extraframework octahedral aluminum in composites.