Introduction and Nomenclature - Principles of Polymer Chemistry - page 2

was correctly assigned in 1860, and the concept of extending the structure to very large molecular
weights by continued condensation was understood [ 4 - 6 ].
At approximately the same time, poly(methacrylic acid), which we now know to be a linear molecule

COOH COOH COOH

was prepared in 1880 [ 7 ]. But, here too, a cyclic structure was assigned which was believed to be
attached to other cyclic structures by “partial valences,” thereby forming gels. What is more
noteworthy is that Emil Fischer and his coworkers studied many natural polymers, such as rubber,
starch, polypeptides, cellulose, and lignin. His work probably entitles him to be called the spiritual
father of polymer chemistry. During that period, Willst

€ atter worked on the synthesis of

polysaccharides, and studied lignin and enzymes [ 8 ].
One should also acknowledge the fact that in spite of ignorance of structure, many inventors
developed ways to convert cellulose into cellulose acetate and then to use the products to form fibers,
films, and coatings. Cellulose was also converted to cellulose nitrate and was used to prepare
explosives and other products. At the turn of the century, Baekeland formed a hard resin by
condensing phenol with formaldehyde [ 9 ],
The evolvement of our present-day understanding of polymeric structures occurred in the early
1920s. Thus, Staudinger et al. firmly established the existence of macromolecules [ 10 - 15 ]. Others, by
X-ray analyses and careful use of molecular weight determinations, confirmed his findings [ 16 ]. In
1929, a series of outstanding investigations were carried out by Carothers on other polymeric
materials. This resulted in much of today's knowledge and understanding [ 17 ].
Now, we know that a typical molecule such as polyethylene can have a contour length of 25,000 ˚ ,
but a diameter of only 4.9 ˚ . Such a molecule can be compared in dimensions to a long, snarled
clothesline, 75 ft long and 1 in. in diameter. Furthermore, work with naturally occurring
macromolecules, such as nucleic acids, for instance, revealed even more startling dimensions.
When molecules of virus dinucleic acids were tritium-labeled (whose nuclear emission is less than
1 m long [ 18 ].

Such length would signify a molecular weight of 100 million. Similar work carried out on dinucleic
acids of bacteria revealed molecular weights of approximately 200 million.
The above figures are, of course, extremes in molecular dimensions. Typical synthetic polymers
will range in molecular weights anywhere from ten to several hundred thousand, although synthetic
polymers in molecular weight ranges of several million are well known and some are used commer-
cially. Interestingly enough, many of these polymers are prepared through the use of organic reactions
that have been known for a long time. Also, new reactions and catalysts are still being discovered and
applied to polymer syntheses. It is probably safe to predict that this situation will undoubtedly
continue into the distant future.

m m) and then autoradiographs prepared, these showed molecules that were about 50 m

1.2 Definitions

The word polymer is commonly understood to mean a large molecule composed of repeating units, or
mers (from the Greek word meros —part), connected by covalent bonds. Such units may be connected
in a variety of ways. The simplest is a linear polymer, or a polymer in which the units are connected to