Paul Flory

**Paul John Flory** (June 19, 1910 – September 9, 1985) was an American chemist and Nobel laureate. He worked in the field of polymers, or macromolecules.  He was a leading pioneer in understanding how polymers dissolve in solutions. He won the Nobel Prize in Chemistry in 1974 "for his fundamental achievements, both theoretical and experimental, in the physical chemistry of macromolecules."

### Early life

He graduated from Elgin High School in Elgin, Illinois in 1927. Flory received a bachelor's degree from Manchester College (Indiana) in 1931 and a Ph.D. from the Ohio State University in 1934.  His first position was at DuPont with Wallace Carothers.

### Polymer science

Flory's earliest work in polymer science was in the area of polymerization kinetics at the DuPont Experimental station.  Most chemists studying condensation polymerization believed that the reactivity of the end group decreased as the macromolecule grew.  Flory argued  that the reactivity was independent of the polymer's size. He showed that the number of polymer chains present decreased with size exponentially.

Flory introduced the important concept of chain transfer to the study of addition polymerization. This improved chemists' understanding of the kinetic equations. It also helped chemists to understand the distribution of the polymer sizes.

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

In 1940, he joined the Linden, NJ laboratory of the Standard Oil Development Company. He developed a statistical mechanical theory for polymer mixtures there.

In 1943, he left to join the research laboratories of Goodyear Tire and Rubber Company 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.  At Cornell, Flory expanded and refined his Baker Lectures into his best work (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 to polymers. (Werner Kuhn had already invented the term in 1934 for molecules in general.) "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. Excluded volume explained several puzzling experimental results of that time. 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 coming from the excluded volume are eliminated. This allows experimenters to more easily measure short-range features such as structural geometry, bond rotation potentials, and steric interactions between near-neighboring groups. Flory taught another advantage of performing the experiment at the theta point: the chain dimension in polymer melts would have the size computed for a chain in ideal solution. This works because excluded volume interactions are neutralized at the theta point.

He also invented an original method for computing the probable size of a polymer in good solution. He invented the Flory-Huggins Solution Theory. He derived the Flory exponent, which helps characterize the movement of polymers in solution.

Flory won the Perkin Medal and the Priestley Medal.

### The Flory convention

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 , bond angles , and the dihedral angles . A three-dimensional structure can be described using the Flory convention by applying a vector conversion from the Cartesian coordinates to the generalized coordinates.

### Later years

He became a professor at Stanford University in 1961. He became the Jackson-Wood Professor there in 1966. He retired from Stanford 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 (now dead) had three children, Susan, Melinda and John.  Susan has two children, Elizabeth and Mary.  Elizabeth has three children, Katy Greer, Margaret Greer, and Sam Greer.  Paul J Flory died of a heart attack in Big Sur, California in 1985.

## Bibliography

- Flory, Paul. (1953) _Principles of Polymer Chemistry_. Cornell University Press. .
- Flory, Paul. (1969) _Statistical Mechanics of Chain Molecules_. Interscience. . Reissued 1989. .
- Flory, Paul. (1985) _Selected Works of Paul J. Flory_. Stanford Univ Press. .

## Other websites

- A short autobiography of Paul Flory
- Nobel lecture by Paul Flory

## Infobox (scientist)

- **name**: Paul John Flory
- **image**: Paul Flory 1973.jpg
- **caption**: Flory in 1973
- **birth place**: Sterling, Illinois
- **death place**: Big Sur, California
- **nationality**: United States
- **field**: Physical chemistry
- **work institution**: DuPont, Stanford University, Carnegie Mellon University, Cornell University
- **alma mater**: Manchester College (Indiana) and Ohio State University
- **doctoral advisor**: Herrick L. Johnston
- **known for**: Polymers
- **prizes**: Nobel Prize for Chemistry (1974)
Priestley Medal (1974)
Perkin Medal (1977)
Elliott Cresson Medal (1971)