Paul Flory

Paul John Flory (June 19 1910 – September 9 1985) was an American chemist who was known for his prodigious volume of work in the field of polymers, or macromolecules. He was a leading pioneer in understanding the behavior of polymers in solution.

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Biography

Early life

After graduating from Elgin High School in Elgin, Illinois in 1927, Flory received a bachelor's degree from Manchester College in 1931 and a Ph.D. from the Ohio State University in 1934. His first position was at DuPont with Wallace Carothers. (Morris p. 70-73)

Polymer science

Flory's earliest work in polymer science was in the area of polymerization kinetics at the DuPont Experimental station. In condensation polymerization, he challenged the assumption that the reactivity of the end group decreased as the macromolecule grew, and by arguing that the reactivity was independent of the size, he was able to derive the result that the number of chains present decreased with size exponentially. In addition polymerization he introduced the important concept of chain transfer to improve the kinetic equations and remove some difficulties in understanding the polymer size distribution.

In 1938, after Carothers' death, he moved to the Basic Science Research Laboratory at the University of Cincinnati. Here he developed a mathematical theory for the polymerization of compounds with more than two functional groups and the theory of polymer networks or gels.

In 1940 he joined the Linden, NJ laboratory of the Standard Oil Development Company where he developed a statistical mechanical theory for polymer mixtures. In 1943 he left to join the research laboratories of Goodyear as head of a group on polymer fundamentals. In the Spring of 1948 Peter Debye, then chairman of the chemistry department at Cornell University, invited Flory to give the annual Baker Lectures. He then was offered a position with the faculty in the Fall of the same year. Here he elaborated and refined his Baker Lectures into his magnum opus, Principles of Polymer Chemistry which was published in 1953 by Cornell University Press. This quickly became a standard text for all workers in the field of polymers, and is still widely used to this day.

Flory introduced the concept of excluded volume, introduced by Werner Kuhn in 1934, to polymers. Excluded volume refers to the idea that one part of a long chain molecule can not occupy space that is already occupied by another part of the same molecule. Excluded volume causes the ends of a polymer chain in a solution to be further apart (on average) than they would be were there no excluded volume. The recognition that excluded volume was an important factor in analyzing long-chain molecules in solutions provided an important conceptual breakthrough, and led to the explanation of several puzzling experimental results of the day. It also led to the concept of the theta point, the set of conditions at which an experiment can be conducted that causes the excluded volume effect to be neutralized. At the theta point, the chain reverts to ideal chain characteristics - the long-range interactions arising from excluded volume are eliminated, allowing the experimenter to more easily measure short-range features such as structural geometry, bond rotation potentials, and steric interactions between near-neighboring groups. Flory correctly identified that the chain dimension in polymer melts would have the size computed for a chain in ideal solution if excluded volume interactions were neutralized by experimenting at the theta point.

Among his accomplishments are an original method for computing the probable size of a polymer in good solution, the Flory-Huggins Solution Theory, and the derivation of the Flory exponent, which helps characterize the movement of polymers in solution.

The Flory convention

see Flory convention for details.

In modeling the position vectors of atoms in macromolecules it is often necessary to convert from Cartesian coordinates (x,y,z) to generalized coordinates. The Flory convention for defining the variables involved is usually employed. For an example, a peptide bond can be described by the x,y,z positions of every atom in this bond or the Flory convention can be used. Here one must know the bond lengths l_i, bond angles θ_i, and the dihedral angles φ_i. Applying a vector conversion from the Cartesian coordinates to the generalized coordinates will describe the same three-dimensional structure using the Flory convention.

Later years

He accepted a professorship at Stanford University in 1961, became the Jackson-Wood Professor there in 1966 and retired from there in 1975. He was awarded the Nobel Prize in Chemistry in 1974 "for his fundamental achievements, both theoretical and experimental, in the physical chemistry of macromolecules." He remained active after his retirement, and consulted for IBM for some years. He and his wife Emily Catherine Tabor had three children, all of whom enjoyed careers in the physical sciences. He died of a heart attack in Big Sur, California in 1985.

Books

• (1953) Principles of Polymer Chemistry. Cornell University Press. ISBN 0-8014-0134-8.
• (1969) Statistical Mechanics of Chain Molecules. Interscience. ISBN 0-470-26495-0. Reissued 1989. ISBN 1-56990-019-1.
• (1985) Selected Works of Paul J. Flory. Stanford Univ Press. ISBN 0-8047-1277-8.

References

• Morris, Peter J. T. Polymer Pioneers: A Popular History of the Science and Technology of Large Molecules Center for History of Chemistry, Philadelphia (1986).