Possibly, but not necessarily true. The DuPont patent was for the product referred to as "Freon" and several other manufacturers made CFC refrigerants. Atofina Chemicals (formerly Elf Atochem), Ineos Fluor (formerly ICI Klea) and Honeywell (formerly Allied Chemical and Allied-Signal) were all major vendors of R-12.As to the demise of R 12 do you suppose that had anything to do with the fact that the patent ran out on it and China was starting to import it really cheap.
DuPont comes out with R134 convinces congress to outlaw R12 and now they get 11 bucks for a small can of it. HOW CONVENIENT.
Given that patents are good for 20 years and the original patents were issued in 1931 through 1934 to various individuals for versions of CFC refrigerants, the patents would have expired in the 50's.
The trade mark "Freon" was granted to Kinetic Chemicals, Inc. of Wilmington, Delaware in 1931. Kinetic Chemicals became E. I. du Pont De Nemours and Company.
The Allied Chemical R12 product was sold starting in 1946 and in 1951 they were awarded the trademark "Genetron" for their CFC's.
The fact that four major manufacturers were competing with CFC's is probably the only thing that kept DuPont from ripping the public in those years.