Page 183 - Academic Press Encyclopedia of Physical Science and Technology 3rd Polymer

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Polymers, Inorganic and Organometallic 691

ions replace Si(IV) in the lattice. Examples of 2D sheet
aluminosilicates are clays, micas, and talc. Feldspar and
zeolites (molecular sieves) are 3D network structures in
which AlO 4 and SiO 4 units share tetrahedral vertices. The
cavities created in these network polymers are accommo-
dated by cations such as Na and K . Depending on the
+
+
size of the cavity, these cations can be displaced by other
cations, hence their use as ion exchange materials. More-
over, by synthetically controlling the size and shape of
the cavity, small molecules like water, methanol, or gases
FIGURE 34 Poly(aluminosiloxane) ladder polymer. can be selectively trapped. Thus these materials are used
in laboratory and industrial separations and purification
processes (Table V).
If a trifunctional silane is used, the Si:Al ratio is larger
than 7 and a soluble polymer, believed to have a ladder
3. Tin-Containing Polymers
structure, is obtained (Fig. 34).
The aluminosilicates are anionic polymers that are Polystannanes as analogs to polysilanes were mentioned
present in natural and synthetic minerals where Al(III) earlier. There are also a number of heteroatom polymers of

FIGURE 35 Heteroatom tin-containing polymers.