SI-29 NMR-STUDIES OF TETRAALKYLAMMONIUM SILICATE SOLUTIONS - 2 - POLYMERIZATION KINETICS

The kinetics of formation of the silicate cubic octamer, Q(8)(3), in a queous tetramethylammonium (TMA) silicate solutions was investigated b y Si-29 NMR. The rate equation for solutions at pH 13.2-13.6 is d[Q(8) (3)]/dt = k(f) H+](1.6+/-0.1)[TMA(+)](0.36+/-0.08)[Si](0.8+/-0.3) wher e k(f) = (2.2 +/- 0.8) x 10(16) mol(-1.8) kg(1.8) s(-1) at 296 K. The findings prove unequivocally that alkylammonium cations participate di rectly in the formation and subsequent stabilization of cagelike polys ilicate anions. This implies a radically different mechanistic role th an ''templating'' for alkylammonium cations in the synthesis of molecu lar sieves.