Chemistry Reference
In-Depth Information
Fig. 8.1
Compounds that
occur in various woods and
might, perhaps, participate
in formation of lignin
OH
O
O
O
OH
O
O
O
OH
Charidol
Coniferyl alcohol
Safrole
Isosafrole
8.4 Polyisoprene
Natural rubber is polyisoprene [
21
]. It is produced commercially from the sap of trees called
Hevea
brasilensis
and sometimes referred to as
Hevea rubber
. These trees yield a latex containing
approximately 35% rubber hydrocarbon and 5% nonrubber solids, like proteins, lipids, and inorganic
salts. The remaining 60% of the latex is water. The hydrocarbon polymer consists of 97%
cis
-1,4
units, 1%
-1,4 units, and 2% 3,4 units, in a head to tail structure. Molecular weights of naturally
occurring polyisoprene range from 200,000 to 500,000. A verity of shrubs and small plants, including
some weeds, like dandelion and milkweed also contain polyisoprene in their sap. The
guayule
shrub,
which grows in Mexico and in southern United States, is a good potential source of natural rubber.
Work is now going on in various places to cultivate this shrub for potential rubber production.
An almost all
trans
-1,4 polymer called
trans
gutta-percha
is found in the exudations of various trees of
the genus
Palaquium, Sapotaceae, and Habit
.
The molecular weights of these polymers range from
Balata
and
chicle
, also mainly
trans
42,000 to 100,000.
-1,4-polyisoprenes, are found in saps of some
plants in West Indies, Mexico, and South America.
Chapter
9
deals with various reactions of polymers including those of natural and synthetic rubber.
That includes vulcanization of rubber. While there are very many commercial applications of the
cis
isomer,
gutta-percha
utilization is limited to wire coatings, impregnation of textile belting, and as a
component of some varnishes. Its use is limited, because it is considerably harder than natural rubber.
8.5 Proteins
These materials are building blocks of animal tissues [
22
,
26
,
28
,
31
]. To a lesser extent they are also
found in vegetable sources. Because the major constituents of animal bodies, including skins, hairs,
and blood, are proteins, they are of much greater interest to the biochemists. Nevertheless, some
proteins are important commercial materials. These include animal glues, silk, and wool. It is beyond
the scope of this topic, however, to render a thorough discussion of the proteins. For that reason, only
some basic principles are presented here.
Proteins are naturally occurring polyamides, polymer of
-amino acids. The structure can be
a
illustrated as follows:
R
N
n
