Chemistry Reference
In-Depth Information
7.2. SOME BASIC CHEMISTRY OF POLYMERIC SURFACTANT
SYNTHESIS
As noted above, many classes of water-soluble and water-insoluble polymers can be
functionalized to increase their hydrophobicity or hydrophilicity, as needed. In
some cases the resulting materials will be statistically random modifications,
while in other cases the distribution of the relevant functional modifications will
be more regular or uniform.
7.2.1. Modification of Natural Cellulosics, Gums, and Proteins
Natural product polymers such as cellulose, starches, gums, and proteins have been
employed in a wide variety of applications for centuries. In many cases, particularly
in the cases of gums and some proteins, the natural product is amphiphilic as
isolated and can be used directly. While such ''natural'' amphiphilic materials have
found wide use in the food, cosmetic, and pharmaceutical industries, as well as
in industrial process applications, more stringent environmental, regulatory, and
end-use requirements of modern products often require new modified products
that, in some minds at least, take them out of the ''natural'' category. Semantic
nit picking aside, modified natural polymers have a number of inherent advantages,
including their generally lower environmental load in manufacture, their enhanced
biodegradability because of their sources, and the theoretically renewable nature of
their sources.
The modification of natural polymers to introduce or modify their amphiphilic
character can take two general approaches: (1) degradation processes such as hydro-
lysis to reduce molecular weights or break crosslinking bonds to increase water
solubility in normally insoluble materials such as cellulose; (2) chemical modifica-
tion through the addition of molecular components that alter the nature of the mole-
cules, usually involving esterification, amination, oxidation, etherification, or
similar reactions; and (3) enzymatic modifications.
A classical example of such functionalization is the carboxymethylation of
cellulose to produce carboxymethylcellulose (CMC), used in a wide variety of
applications as a thickener, stabilizer, binder, or other agent. The functional char-
acteristics of such materials can be controlled with some exactness by controlling
the degree of functionalization and the molecular weight of the base polymer. Simi-
lar classes of materials can be prepared by the hydrolysis of proteins or the use of
various reactions well known to the organic chemist.
7.2.2. Synthetic Polymeric Surfactants
Synthetic polymers can be equally useful as bases for the preparation of poly-
meric amphiphilc materials. A common example of the functionalization of a
water-insoluble material is the sulfonation of polystyrene
C
6
H
4
SO
3
P
C
6
H
5
þ
SO
3
!
P
