(Fig. 10) signals occurred at 38 ppm, 8 ppm
and 14 ppm, which were assigned to aluminates in different AleO
coordination: AlO4, AlO5 and AlO6, respectively. The peak observed at
38 ppm, which is dominant, is the typical signal for aluminium
phosphate AlPO4. The shape of the signals suggests the amorphous
nature of those structures, which most probably form a network. In
this combination residue formation was very poor and none of the
formed aluminates was able to form a sufficient protection barrier.
The 27Al NMR signal ratios changed when additional components
were added. Additionally, the shape of the signals was narrower,
suggesting that the structure was more ordered, similar to
crystalline structures. To better distinguish all signals and to estimate
distances between various Al atoms in different structural
units to the surrounding P atoms, 27Al(31P) REDOR NMR was used
(Fig. 11). The REDOR difference spectrum (DS) between the spectrum
with 31P pulses switched off (S) and switched on (S0) clearly
showed that for both TPE-S/AlPi/MH (Fig. 11a) and TPE-S/AlPi/ZB/
PPO (Fig. 11b) signals at 40 ppm were coming from aluminates
that have phosphorus nearby. The resonances coming from aluminates
in five- and six-fold co-ordination were also partially
phosphonated, but for both potentially synergistic systems the
signal for AlPO4 was dominant. It was concluded that for both
systems the formation of aluminium phosphates was independent