How was Paul J. Flory awarded the Noble Prize?

Name: Paul J. Flory. 
Country: California, U.S.
Date of Birth: 19 June 1910.
Date of Death: 9 September 1985.
The subject of Study: Macromolecule.
Noble Prize Year: Nobel Prize for Chemistry in 1974 for is work fundamental achievements, both theoretical and experimental, in the physical chemistry of macromolecules.