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."
Biography
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.