Chemistry Reference
In-Depth Information
prepolymers and the chemical and mechanical properties of the final polymeric
structures will vary with the choice of ingredients and reaction conditions.
H
H
O
O
+
(BF
3
· NCH
2
CH
3
)
-
BF
3
· NH
2
-CH
2
CH
3
+ CH
2
CH
CH
2
CH
H
(BF
3
· NCH
2
CH
3
)
-
O
H
H
CH
2
H
(BF
3
· NCH
2
CH
3
)
-
+ CH
C
H
HOCH
CO
+
CH
(1-10)
O
+
CH
2
CH
H
H
CH
2
(BF
3
· NCH
2
CH
3
)
-
H
OCH
2
CO
+
n
CH
1.4
Why Are Synthetic Polymers Useful?
[3]
The primary valence bonds and intermolecular forces in polymer samples are
exactly the same as those in any other chemical species, but polymers form strong
plastics, fibers, rubbers, coatings, and adhesives, whereas conventional chemical
compounds are useless for the same applications. For example, n-hexatriacontone
(molecular weight 437), which was mentioned earlier as an oligomer of polyethyl-
ene, forms weak, friable crystals but the chemically identical material polyethy
(1-3) can be used to make strong films, pipe, cable jackets, bottles, and so on,
provided the polymer molecular weight is at least about 20,000. Polymers are use-
ful materials mainly because their molecules are very large.
The intermolecular forces in hexatriacontane and in polyethylene are essen-
tially van der Waals attractions. When the molecules are very large, as in a poly-
mer, there are so many intermolecular contacts that the sum of the forces holding
each molecule to its neighbors is appreciable. It becomes difficult to break a poly-
meric material since this involves separating the constituent molecules.
Deformation of a polymeric structure requires that the molecules move past each
other, and this too requires more force as the macromolecules become larger.
