Page 358 - Carrahers_Polymer_Chemistry,_Eighth_Edition

10 Naturally Occurring

Polymers—Animals

One of the strongest, most rapidly growing areas of science and polymers is that involving natural
polymers. Our bodies are largely composed of polymers: DNA, ribonucleic acid (RNA), proteins,
and polycarbonates. Aging, awareness, mobility, strength, and so on, that is, all the characteristics
of being alive, are related to the “health” of these polymers. Many medical, health, and biological
projects focus on polymers. There is an increasing emphasis on such natural polymers. The empha-
sis on the human genome and relationships between genes, proteins, and our health underlies much
of this movement. Thus, an understanding of polymeric principles is advantageous to those desiring
to pursue a career related to their natural environment, be it medicine, biomedical, biological, bio-
engineering, and so forth.
Physically, there is no difference in the behavior, study, or testing of natural and synthetic poly-
mers. Techniques suitable for application to synthetic polymers are equally applicable to the study
and behavior of natural polymers.
Proteins and nucleic acids typically act as individual units, the nanoworld in action, while many
other natural polymers and synthetic polymers act in concert with one another. This is not entirely
true since proteins and nucleic acids, while acting as individual units, act with other essential bio-
logically important units to carry out their tasks. Synthetic polymers generally act as groups of
chains through chain entanglement and connected crystalline units giving the overall aggregate
such desired properties as strength. In a real sense, the behavior of branched natural polymers such
as amylopectin is similar to the branched low-density polyethylene while the behavior of linear
amylose is similar to that of the largely linear high-density polyethylene.

While the specific chemistry and physics dealing with synthetic polymer is complicated, the
chemistry and physics of natural polymers is even more complex because of a number of related
factors, including (1) the fact that many natural polymers are composed of different, often similar
but not identical, repeat units; (2) a greater dependency on the exact natural polymer environment;
(3) the question of real structure of many natural polymers in their natural environment is still not
well known for many natural polymers; and (4) the fact that polymer shape and size are even more
important and complex in natural polymers than in synthetic polymers.
Biological polymers represent successful strategies that are being studied by scientists as ave-
nues to different and better polymers and polymer structure control. Sample “design rules” and
approaches that are emerging include the following:

• Identification of mer sequences that give materials with particular properties

• Identification of mer sequences that cause certain structural changes
• Formation of a broad range of materials with a wide variety of general/specifi c properties
and function (such as proteins/enzymes) through a controlled sequence assembly from a

fixed number of feedstock molecules (proteins—about 20 different amino acids; fi ve bases
for nucleic acids and two sugar units)
• Integrated, in situ (in cells) polymer productions with precise nanoscale control
• Repetitive use of proven strategies with seemingly minor structural differences but result-
ing in quite divergent results (protein for skin, hair, and muscle)
• Control of polymerizing conditions that allow steady-state production far from
equilibrium

321

9/14/2010 3:41:06 PM
K10478.indb 321
K10478.indb 321 9/14/2010 3:41:06 PM