Chemistry Reference
In-Depth Information
The polymer can be spun into an elastic yarn of very fine denier. It is also claimed to exhibit good
mechanical properties for molding and compares favorably with commercial polyesters and nylons.
Also, polycaprolactone was reported to be used in some medical applications in biodegradable
surgical sutures and postoperative support pins and splints [
39
]. Similar uses are also found for two
other polyesters, poly(lactic acid) and poly-(glycolic acid) [
40
]. The two polymers form from their
cyclic dimers by cationic ring opening polymerizations with the aid of Lewis acids:
O
O
O
O
O
n
O
O
O
O
O
O
O
7.3 Polyamides
The family of synthetic polymeric materials with amide linkages in their backbones is large. It
includes synthetic linear aliphatic polyamides, which carry the generic name of
, aromatic
polyamides, and fatty polyamides used in adhesives and coatings. In addition to the synthetic
materials, there is also a large family of naturally occurring polymers of
nylon
a
-amino acids, called
proteins
. The latter ones are discussed in Chap.
8
with the rest of the naturally occurring polymers.
The nylons include polyamides produced by ring opening polymerizations of lactams and condensa-
tion products of diamines with dicarboxylic acids.
7.3.1 Nylons
The nylons are named by the number of carbon atoms in the repeat units. The materials formed by
ring opening polymerizations of lactams, therefore, carry only one number in their names, like, for
instance, nylon 6 that is formed from caprolactam. By the same method of nomenclature, a nylon
prepared by condensing a diamine with a dicarboxylic acid, like, for example, hexamethylene
diamine with adipic acid, is called nylon 6,6. It is customary for the first number to represent the
number of carbons in the diamine and the second number to represent the number of carbons in the
diacid. A discussion of various individual nylons follows. Not all of them are industrially important.
At present, we only know how to prepare
Nylon 1
by anionic polymerization of isocyanates. This
R
NaCN
R
n
NO
n
DMF
O
