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Case Studies - Thermal
Analysis
Thermal Stability of Silica Gel
One of the strengths of silica bound scavengers and reagents is
the high level of thermal stability. While not every reaction requires
high temperature the increasing use of microwave technology means
that many more reactions are being run albeit briefly at extremely
high temperatures. For polymer bound scavengers and reagents this
poses a major problem while the reactivity of the material may not
be affected physically the beads will melt or breakdown making filtration
and other manipulations difficult or impossible.
Using scanning electron
microscopy we can monitor the effect of temperature on silica and
polystyrene. Both were stirred in Toluene at 110 °C
and sampled after 1hr the effect on the polymer was so profound (figure
1) we decided to test it at lower temperatures 90 and 50 °C (figures
2 & 3). Meanwhile the silica was unchanged after 4 hrs at 110 °C
in toluene (figure 4). Figure 5 shows silica that has not been heated
for a point of reference.
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| Figure 1: |
| Polystyrene stirred in toluene at 110°C for one hour most
of the spheres have fragmented making filtration impossible without
stirring the particle would probably agglomerate. |
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| Figure 2: |
| Polystyrene stirred in toluene at 90°C
for one hour degradation of the polymer spheres is visible. Again
without stirring the particles would probably agglomerate. |
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| Figure 3: |
| Polystyrene stirred in toluene at 50°C
for one hour. The polymer is unchanged this may be the thermal
limit for working with polystyrene scavengers and regents. |
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| Figure 4: |
| Silica stirred in toluene at 110°C for
four hours. The silica is unchanged. |
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| Figure 5: |
| Silica that has not been heated. |
Silica bound scavengers and reagents have a much higher level of
thermal stability making them more versatile and durable.
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