Chemistry Reference
In-Depth Information
is evidently the repeating unit of poly(vinyl alcohol):
H
H
H
H
~ CH
2
C
CH
2
C
CH
2
C
CH
2
C
CH
2
~
OH
OH
OH
OH
1-8
The ostensible precursor for this polymer is vinyl alcohol,
H
CH
2
C
OH
1-9
which does not exist (it is the unstable tautomer of acetaldehyde). Poly(vinyl alco-
hol), which is widely used as a water-soluble packaging film and suspension agent
and as an insolubilized fiber, is instead made by linking units of vinyl acetate,
H
CH
2
COC
CH
3
,
O
1-10
and subsequently subjecting the poly(vinyl acetate) polymer to alcoholysis with
ethanol or methanol.
Similarly, protein fibers such as silk are degradable to mixtures of amino acids,
but a direct synthesis of silk has not yet been accomplished. Another polymer for
which there is no current synthetic method is cellulose, which is composed of
β
-1,4-linked
D
-glucopyranose units:
CH
2
OH
HO
O
O
OH
HO
O
OH
CH
2
OH
O
O
1-11
The concept of an identifiable simple repeating unit loses some of its utility
with polymers that are highly branched, with species that consist of intercon-
nected branches, or with those macromolecules that are synthesized from more
than a few different smaller precursor monomers. Similar difficulties arise when
the final polymeric structure is built up by linking different smaller polymers.
