Presentation Speech by Professor Stig Claesson of the Royal Academy of Sciences

Translation from the Swedish text

Your Majesty, Your Royal Highnesses, Ladies and Gentlemen,

This year’s Nobel prize in chemistry has been awarded to Professor Paul Flory for his fundamental contributions to the physical chemistry of macromolecules.

Macromolecules include biologically important materials such as cellulose, albumins and nucleic acids, and all of our plastics and synthetic fibers.

Macromolecules are often referred to as chain molecules and can be compared to a pearl necklace. They consist of long chains of atoms which, when magnified one hundred million times, appear as a pearl necklace. The pearls represent the atoms in the chain. One should realize that this chain is much longer than the necklaces being worn here this evening. To obtain a representative model of a macromolecule all of the necklaces here in this hall should be connected together in a single long chain.

One can readily appreciate that the development of a theory for these molecules presented considerable difficulties. The forms of the chain itself, whether extended or coiled, represents a property difficult to rationalize.

A statistical description is of necessity required, and Professor Flory has made major contributions to the development of such a theory. The problem is more difficult, however. How can one compare different molecules in different solvents?

When chain molecules are dissolved in different solvents they become coiled to different degrees, depending on the interaction between repulsive and attractive forces in the solution. In a good solvent the chain molecules are extended. In a poor solvent, in contrast, the chain molecules assume a highly coiled form.

Professor Flory showed that if one takes a solution of extended chain molecules in a good solvent, and slowly cools the solution, then the molecules become progressively more coiled until they are no longer soluble.

Thus, there must be an intermediate temperature where the attractive and repulsive forces are balanced. At this temperature the molecules assume a kind of standard condition that can be used, generally, to characterize their properties.

This temperature Professor Flory named the theta temperature. A corresponding temperature exists for real gases at which they follow the ideal gas law. This temperature is called the Boyle temperature after Robert Boyle who discovered the gas laws. By analogy, the theta temperature for macromolecules is often referred to as the Flory temperature.

Professor Flory showed also that it was possible to define a constant for chain molecules, now called Flory’s universal constant, which can be compared in significance to the gas constant.

When one, in retrospect, reads about an important scientific discovery, one often feels that the work was remarkably simple. This actually indicates, however, that it was brilliant insight in a new and until then unexplored research area. This is highly characteristic of Professor Flory’s scientific discoveries, not only those concerned with the Flory temperature and Flory’s universal constant but also many of his other important research studies. Further examples are found in his investigation of the relationship between the reaction mechanism and the length of the chains formed when chain molecules are prepared synthetically, as well as his important contribution to the theory of crystallization and rubber elasticity. These achievements have been of major importance for technological developments in the plastics industry.

In recent years Professor Flory has investigated, both theoretically and experimentally, the relation between rotational characteristics of the chain links and the form of the chain molecules. This is of fundamental significance for the understanding of both biological macromolecules and synthetic chain molecules.

During the time Professor Flory has been active as a scientist, macromolecular chemistry has been transformed from primitive semi-empirical observations into a highly developed science. This evolution has come about through major contributions by research groups from both universities and many of the world’s largest industrial laboratories. Professor Flory has remained a leading researcher in the area during this entire period, giving further evidence of his unique position as a scientist.

Professor Flory,

I have tried to describe briefly the fundamental importance of your many contributions to macromolecular chemistry and in particular those concepts introduced by you and now referred to as the Flory-temperature and the Flory universal constant.

On behalf of the Royal Academy of Sciences I wish to convey to you our warmest congratulations and I now ask you to receive your prize from the hands of His Majesty the King.