Page 436 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Organometallic and Inorganic–Organic Polymers 399

The third reason for interest in boron polymers involves the ability of many boron compounds
to form cocoons about objects allowing a ready method for coating wires and fibers. Thus boron-

containing polymers and monomers have been employed to form a surface layer of intumescent

protective char that acts as a barrier to oxygen protecting the wires and fibers from ready oxidation.

These coatings also provide flame retardancy to the coated materials. Recently, boron-containing
units have been incorporated into polymers, resulting in materials that have added fl ame resistance
through char formation. Somewhat related to this is the use of boron-containing polymers in form-

ing high-strength fibers and whiskers for use in composites. Finally, boron has a high capture ability
of neutrons so effort had gone into using this nuclear characteristic.
Today there exist a wide variety of boron-containing polymers, including ring systems such as
borazines (11.45), boroxines (11.46), and triphosphatoborins (11.47),

R R R

R 1 B R 1 B R 1 B R 1
N N O O P P
B B B B B B
R N R R O R R P R
R 1 R 1
Borazine Boroxine Triphosphatoborin
(11.45) (11.46) (11.47)

as well as metal, metalloid, ferrocene, and so on containing polymers each offering their own poten-
tial for exhibiting desired properties.

11.6 ION-EXCHANGE RESINS
Just as calcium ions form an insoluble compound through reaction with the carbonate ion (calcium
carbonate) so also does it complex with a carbonyl functional group on a polymer. This concept
forms the basis for many analyses, separations, and concentration techniques. Many of these tech-
niques are based on organic resins, silicon dioxide intense compounds such as the zeolites, and on
carbohydrate-related compounds such as dextran-based resins. The functional groups include typi-
cally fully charged sulfates, sulfonates, and acids and noncharges groups such as amines, imines,
and hydroxyls. The functional groups are normally located on the surface of somewhat spherical
beads. The use of negatively charged functional groups to preferentially capture cations is referred
to as cation exchange. Amines are often protonated forming cations that attract anions and are
called anion-exchange resins. The combinations of reactions generally are simple Lewis acid–base
reactions.
While acid groups attract cations, the neutralized acid groups, salts, are more effective. The
tendency of coordination is related to the size of the cation and the charge on the cation. In gen-
+2
+2
eral, multiple-charged cations such as Ca , Mg , and Fe +3,+2 are more strongly coordinated than
+1
+1
single-charged cations as Na and K . This difference in tendency to coordinate is widely used in
ion-exchange resin applications.
When two or more coordinations occur with a single cation, it is called chelation after the Greek
word for the claw of a crab.

Applications of cation and anion resins are varied and include the purification of sugar, identifi -
cation of drugs and biomacromolecules, concentration of uranium, calcium therapy to help increase
the amount of calcium in our bones (that is, increase the bone density), and use as therapeutic agents
for the control of bile acid and gastric acidity. In the latter use, a solid polyamide (Colestid) is diluted
and taken with orange juice to help in the body’s removal of bile acids. Removal of the bile acids

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