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John Rex Whinfield CBE (16 February 1901 in Sutton, Surrey, England – 6 July 1966 in Dorking, Surrey) was a British chemist. Together with James Tennant Dickson, Whinfield investigated polyesters and produced and patented the first polyester fibre in 1941, which they named Terylene (also known as Dacron) equal to or surpassing nylon in toughness and resilience. He was born in Accrington, but moved out of town before the age of 4.
He worked initially as an assistant to Charles Frederick Cross and Edward John Bevan, who had done earlier work on viscose rayon in 1892. In 1924 he was employed as a research chemist by the Calico Printers' Association based in Manchester.
During the late 1930s, the hunt was on for new synthetic fibres to rival Wallace H. Carothers' nylon. Whinfield and his assistant James Tennant Dickson investigated other types of polymers with textile fibre potential. Whinfield and Dickson discovered how to condense terephthalic acid and ethylene glycol to yield a new polymer which could be drawn into a fibre. Whinfield and Dickson patented their invention in July 1941, but due to wartime secrecy restrictions, it was not made public until 1946. ICI (Terylene) and DuPont (Dacron) went on to produce their own versions of the fibre.
- Commander of the Order of the British Empire (1954) 
- Honorary fellowship of the Textile Institute (1955)
- Perkin Medal of the Society of Dyers and Colourists (1956)
- "World of Chemistry". Thomson Gale. 2005. Retrieved 1 November 2009.
- Allen, P C (1967). "Obituary". Chemistry in Britain.
- Frank Greenaway, ‘Whinfield, John Rex (1901–1966)’, rev. Oxford Dictionary of National Biography, Oxford University Press, 2004 accessed 20 June 2011
- "Department of Chemistry Library". University of York. Retrieved 22 May 2016.