Julian Hill received his Ph.D. from the Massachusetts Institute of Technology in 1928. He joined DuPont shortly thereafter and began working under Carothers in 1929. Hill's most important contribution took place long before nylon was invented, and involved the synthesis of polyester 3-16. He was the first person to use a molecular still for polymerizations. This still allows reactions to take place under extreme vacuum conditions. This proved to be the key to making polyester 3-16 with high molecular weights. The feat went a long way toward proving Hermann Staudinger's macromolecular theory, which proposed that polymers materials were made from giant macromolecules.

When Hill made polyester 3-16, he also proved the viability of Carothers' step-growth polymerization theory. While not directly involved in making nylon, Hill's accomplishments were of great scientific value, and this provided Carothers with a good deal of satisfaction.

Hill was also involved with the research on cyclic polymerization byproducts that led to the creation of the first synthetic musks. It was while researching these cyclic compounds that Edgar W. Spanagel first prepared the polyester called poly(ethylene terephthalate).

Julian Hill and his wife Polly Butcher Hill were friends of Carothers. They often gathered with Carothers to listen to records of classical music. Like Carothers, Hill loved music and played violin in the Wilmington Symphony. Hill was the best man when Carothers married Helen Sweetman in 1936. He died in 1996 at the age of 91.