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Some discoveries start with a broken experiment. In 1938 Roy Plunkett opened a valve on a gas cylinder and nothing came out. The cylinder was not empty, though, and what he did next turned a failed experiment into a new material. This post tells the story from the Science History Institute's records and Plunkett's own patent, and works through the numbers he reported.
Who was Roy Plunkett?
The Science History Institute's biography gives his dates as 1910 to 1994. He grew up on a farm in Ohio during the Depression and studied at Manchester College in Indiana, where for a time he shared a room with Paul Flory, who later won the 1974 Nobel Prize in Chemistry for polymer theory. Both went on to doctorates at Ohio State University and were hired by DuPont. Plunkett spent his whole career there.
What happened in the cylinder?
At DuPont's Jackson Laboratory, Plunkett's first job was to research new chlorofluorocarbon refrigerants. The institute's account says he made about a hundred pounds of tetrafluoroethylene gas, CF₂=CF₂, and stored it in small cylinders kept at dry-ice temperature. When he and his helper prepared one cylinder for use, no gas came out, yet the cylinder weighed the same as before. They opened it and found a white powder.
The weight was the clue. If the gas had leaked, the cylinder would have been lighter. Mass had been conserved, so the gas had to still be inside in another form. Plunkett concluded that the tetrafluoroethylene had polymerised, joining into long chains:
n CF₂=CF₂ → (–CF₂–CF₂–)ₙ
According to the institute, this went against what polymer science of the day predicted.
The Science History Institute's oral history interview with Plunkett, recorded in 1986, covers the same events in his own words, including "the plugged gas cylinder and his recognition of the unusual properties of the polymer".
What did the patent claim?
Plunkett filed for a patent on 1 July 1939, and US Patent No. 2,230,654, "Tetrafluoroethylene Polymers", was granted on 4 February 1941, assigned to Kinetic Chemicals. It opens by noting that there were no satisfactory materials for handling corrosive agents such as hydrofluoric acid, whose fumes attack even glass goggles. It describes the polymers as white or brown powders or jellies, insoluble in the usual solvents and inert to the usual chemical reagents.
Worked example: checking the patent's yields
The patent lists experiments with the yield of polymer. You can check them with one formula: percentage yield = mass of polymer ÷ mass of monomer × 100.
Example I: 8.5 parts of tetrafluoroethylene under pressure at 25 °C for 10 days gave 0.6 part of polymer. Yield = 0.6 ÷ 8.5 × 100 ≈ 7.1%. The patent reports 7.1%, "or a polymerization rate of 0.71% per day", and 7.1 ÷ 10 = 0.71.
Example VI: 7 parts with 0.1 part of silver nitrate as catalyst, 21 days at 25 °C, gave 2.3 parts. Yield = 2.3 ÷ 7 × 100 ≈ 32.9%, reported as 33%.
The repeat unit: C₂F₄ has a molar mass of 2 × 12.01 + 4 × 19.00 = 100.0 g/mol, so a chain of 10,000 units would weigh about 1,000,000 g/mol.
In addition polymerisation nothing is lost, so the polymer's mass equals the mass of monomer that reacted. A common mistake is to think a 33% yield means mass was destroyed. It means two-thirds of the monomer had not yet reacted.
What happened to the material?
The institute's biography says Plunkett was soon moved to another division, while DuPont's polymer specialists developed the substance. It was expensive at first. Its first use was in the Manhattan Project's gaseous diffusion plant, which needed materials that resisted fluorine compounds. Non-stick cookware came years later. When Plunkett received Philadelphia's Scott Medal in 1951, every guest went home with a Teflon-coated muffin tin.
For other polymers made on purpose rather than by accident, see our posts on Wallace Carothers and nylon and Ziegler, Natta and polymer catalysts.
What can a student take from Plunkett's way of working?
Measure before you discard. Weighing the cylinder is what showed something had happened.
Test the new thing for what it is. He checked heat resistance, inertness and friction rather than only asking whether it was a good refrigerant.
A prepared mind helps. As the institute notes, he often told students that his training let him recognise novelty.
If addition polymers and yield calculations still blur together, the Fermi Problem Library has worked problems with a step-by-step solver that explains the reasoning rather than printing an answer.
Try it now: work out the yield in the patent's Example X, where 8.8 parts gave 0.05 part of polymer.
