Chemistry Reference
In-Depth Information
The mixture of the two isomers is synthesized from isophorone according to the following scheme:
[H]
O
[O]
O
O
O
OH
OH
+
HO
HO
O
O
The mixture of the isomers of trimethyl adipic acids is treated with ammonia, converted to amides,
dehydrated to nitriles, and reduced to amines:
NH
3
Trimethyl adipic acid isomers
N
+
N
N
N
NH
2
[H]
NH
2
+
H
2
N
H
2
N
This polyamide is prepared somewhat differently. Salts of the diamine isomers with terephthalic
acid are only partially polycondensed and the reaction is completed during extrusion [
71
], because the
melt viscosity of the polymer is very high. The product is amorphous and exhibits greater light
trasmittancy. It melts at 200
C and is sold under the trade name of Trogamid T.
Many commercial nylon copolymers are also formed by melt mixing different nylons. Amide
interchange reactions occur at melt conditions. At first block copolymers form, but prolonged heating
and stirring results in formation of random copolymers. Nylon copolymers are also best prepared
directly from mixed monomers.
Nylon polymers generally exhibit high-impact strength, toughness, good flexibility, and abrasion
resistance. The principal structural differences between many nylons are in the length of the aliphatic
segments between the amide linkages. As a result, the differences in properties depend mainly upon
the amount of hydrogen bonding that is possible between the functional groups and on the amount of
crystallinity. Also, due to high cohesive energy, nylons are soluble in only a few solvent. The melt
viscosity of these materials, however, is generally low
In any one series of melting points of polyamides, polymers that contain even numbers of
methylene groups between amide linkages fall on a higher curve than those that contain odd ones
do [
72
]. This is due to the crystalline arrangement of the polymeric chains [
72
,
73
]. A zigzag
planar configuration of polymers with even number of methylene linkages allows only 50% of the
functional groups to form hydrogen bonds. This same configuration, however, allows polymers
with odd numbers of methylene linkages to form 100% hydrogen bonding [
72
,
73
]. Polyamides,
like nylon 6,6 or nylon 6,10, arrange themselves in pleated sheets during crystallization and
hydrogen bonds form between N-H group of one molecule and the C
ΒΌ
O moieties from a
neighboring one.
