The Nobel Prize in Chemistry 1974
Paul J. Flory
15 October 1974
The Royal Swedish
Academy of Sciences has decided to award the 1974 Nobel Prize
in Chemistry to
Professor Paul J. Flory, Stanford
University, Stanford, CA, USA
for his fundamental achievements, both theoretical and
experimental, in the physical chemistry of macromolecules
THE CHEMISTRY OF PLASTICS
This year's Nobel Laureate in Chemistry, Paul J. Flory, has done
epoch making research in the field of the physical chemistry of
macromolecules. Among the substance which are made up of
macromolecules we find our most common plastics - polymers - but
also a great number of very important biological compounds, e.g.
proteins, nucleic acids, cellulose and rubber. Flory's early
research concerned polymers of the nylon type, polystyrene. Their
molecules are built up of long chains of atoms and can be
compared to strings of beads where the atoms are represented by
the beads. These strings can be very long and contain thousands
of atoms - beads - in the chain. These chains are also very
flexible and can assume the most varying shapes. Stretched
molecules - chains - are found in fibres such as nylon. In solid
plastics the molecules are rolled into balls. In solvents the
molecules assume more or less ballshaped structures.
It was very difficult to find a satisfactory theory of how these
molecules behaved. On the one hand, the statistical treatment of
the shape of chains is very complicated and, on the other hand,
it is difficult theoretically to define quantities so that the
properties of polymer chains can be compared with different
chemical properties.
The Flory temperature
Flory has solved both these problems. He has introduced a new
concept, theta temperature and theta point properties. A
simplified description is as follows: If a polymer molecule is
dissolved in a good solvent agent then the chain is somewhat
stretched out as the attraction forces between the chain and the
solvent molecules are stronger than those between the different
links in the chain. If the temperature is lowered, the solvent
agent deteriorates and the attractive forces between the
molecules of the solvent agent and the chain become weaker
whereas the attraction forces between the links of the chain
strengthen. Consequently, the molecules of the chain draw closer
together and it decreases in size. It becomes increasingly
compact and finally becomes insoluble. There must then exist a
certain intermediate temperature - theta temperature - where both
these different attraction forces balance each other. At this
temperature, now called the Flory temperature, the polymer
molecule assumes a kind of ideal state. The Flory temperature
varies for different types of polymers and for different solvent
agents, but by using their respective Flory temperatures it is
possible to make useful comparisons.
Flory has also succeeded in working out quantitative terms
describing the extension of polymer chains when the temperature
is raised above the Flory temperature. He has demonstrated that
the chain in solid polymers has the same extension as it has in
polymers in solution at the Flory temperature. This has been of
vital importance for the development of polymer chemistry.
Universal constant
Flory has also demonstrated how quantities used in the theory can
be determined experimentally by measurements of viscosity, light
dispersion, ultra centrifugation and diffusion. By skilful
analysis Flory has shown that it is possible to find a universal
constant which quantitatively summarizes all the properties of
polymer solutions. This constant is now known as Flory's
Universal Constant. It can be said to be analogous to the
universal gas constant.
Flory has done pioneer research in elucidating the formation of
polymer molecules. This takes place by the addition or
condensation of small molecules which then link up into long
chains. Flory was the first scientist to demonstrate the
theoretical connection between the lengths of formed chain
molecules and reaction conditions. He also discoverer a very
important, entirely new type of reaction, the so-called chain
transmission. A growing chain can transmit its growing power to
another molecule and itself stop growing.
Has remained in the lead
In recent years Flory has increasingly turned his attention to
polymers of biological origin, both in solutions and in gells. He
has carried out important studies - both experimental and
theoretical - in this field.
During the nearly 40 years Flory has been active as a research
scientist the chemistry of macromolecules has developed from what
was, theoretically speaking, a primitive discipline, to the
highly advanced science of today. This progress has been made
thanks to the great achievements of various groups of research
scientists at universities and research laboratories. All this
time, Flory has remained the leading researcher in this field and
this demonstrates his exceptional standing as a scientist. This
is largely due to his ability to find essentially simple
solutions to fundamental problems. At the same time he has an
outstanding ability to extract the necessary experimental
findings from well-planned, but often simple experiments, which
he carries out with a comparatively small research team.
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