Page 482 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Inorganic Polymers 445

O O O
– – – – – –
Ph C–C–CMe Ph C–C–CPh + Ph C–CPh + Me C–C–C–Me + Me C–CMe 3 (12.35)
3
3
3
3
3
3
3
3
3
A B C D
Employing a single zeolite that selectively accommodates the Me C radical results in a preferen-
3
tial formation of D and little C because of preferential diffusion of the Me C radical as it is formed
3
with the other radicals being “washed” past. The use of two zeolites in conjunction, one preferen-
tially accepting the Me C radical and the second accepting the Ph C radical results in the preferen-
3 3
tial formation of B and D.
An additional consideration involves matching the so-called “hardness” or flexibility of the confi ned

space. Zeolites offer hard or infl exible confined spaces whereas liquid crystals and some other polymer

media offer softer confined spaces. While the zeolites offer a “safe haven” for selected species enabling
the hosted species a relatively long existence, they do not allow for ready movement and mixing. By
comparison, a more flexible container such as especially designed polyethylenes allow a more fl exible

environment that allows for variations in the product sizes and shapes and some assembling to occur
within the more fl exible confines. Thus, the reaction of 1-naphthyl esters was carried out in an appro-

priate zeolite and appropriate polyethylene. In solution, eight products are formed. In the zeolite, only
one product, the result of a specific geminate-pair recombination, is formed. In the polyethylene, several

products are formed primarily the isomeric products of geminate-pair recombinations.
12.26 SUMMARY
1. Inorganic polymers are widely employed in the construction and building businesses, as abra-
sives and cutting materials, as fi bers in composites, as coatings and lubricants, and as catalysts.
They also serve as the basis of rocks and soils.
2. Portland cement is the least expensive, most widely used synthetic polymer. It has a complex
(short-range order and long-range disorder; average structure), three-dimensional structure.
3. There are many specialty cements, including reinforced concrete, light-weight concrete, pre-
stressed concrete, gypsium, and heavy glass.
4. Silicates are among the most widely found materials on the face of the earth. They form the
basis for much of the soil, sand, and rocks with most of this being of the crystalline variety of
silicates. As amorphous materials they are found as the fiber material in fiberglass, as window

glass, and a whole host of specialty glasses, including safety glass, borosilicate glasses, lead (or
heavy) glasses, colored glasses, and glazes. Glass can be shaped by drawing, pressing, casting,
and blowing. Most of these glasses have the approximate structure of SiO or silicon dioxide.
2
Many of the rocks are present in crystalline silicate forms as quartz and feldspar. Today, the sol-
gel technique is important in making many materials, including aerogels, among the least-dense
solids known today. In nature, silicates are found as polymeric sheets such as asbestos, three-
dimensional materials such as the zeolites, and linear materials.
5. There are many widely used carbon polymers. These include the hardest known material, dia-
mond, graphite a sheet material with little strength holding together the sheets, carbon fi bers used
in high-strength composites, CNTs one of the most important new materials for the twenty-fi rst
century, bitumens used in asphalt, and carbon black widely used as a fi ller material. Diamonds
structurally have a carbon at the center of a tetrahedron composed of four other carbon atoms.
They can be industrially synthesized and used for cutting and shaping. Graphite occurs as sheets
of hexagonally fused benzene rings. The bonds holding the fused benzene rings together are
covalent bonds while the bonding between the sheets results from the weaker overlapping of
pi-electron orbitals. Thus, many of the properties of graphite are anisotropic. The weak forces
holding the sheets together are responsible for its “slipperiness.” Graphite is commercially made
from charcoal or coke.

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