Plastics and polymers were first being produced, whether on accident or on purpose, in the early 1930s. Dupont's Teflon, or PTFE, is probably the most widely known polymer because of its uses in cooking as a non-stick coating for pots and pans. While there are lots of other polymers out there, there are only a few that have as many uses as PTFE, one of which is Parylene.
Parylene was developed by a chemist named Michael Szwarc while he was running experiments on chemical bonds between carbon and benzene rings. While heating para-xylene, he discovered a precipitate in his equipment that turned out to be small and tube-like. He correctly identified these tubes as the polymerization of p-xylene. After a brief period known as Szwarcite, Parylene soon found uses in the medical field as an excellent hydrophobic barrier, but has been found to have plenty of other uses in electronics; metal, rubber, and surface protection from corrosion and outside elements; and as a friction reducing coating especially with needles.
PTFE's discovery, on the other hand, was purely accidental. While working with gasses for refrigeration in the Dupont laboratories, Dr. Roy Plunkett thought that a canister containing TFE was not working. After cutting the canister in half, he discovered a white flake that had developed in the tank and correctly guessed that the flake was a polymer. After conducting several tests on the flakes, since TFE was widely thought to be impossible to polymerize, Plunkett discovered that it was insoluble in anything he tried, as well as being completely inert. The first applications for PTFE were on the seals for the atomic bomb, but it also worked as the nosecone for proximity bombs because it is transparent on a radar and resists electricity.
Parylene was the first vapor deposited polymer ever discovered, and because of the vapor deposits and the fact that no solvent or catalyst is used to cause the polymerization it has a one hundred percent yield, which makes it an extremely efficient polymer to manufacture. Because it is hydrophobic and biostable, parylene has been used extremely effectively as a coating for medical tools, instruments, and hoses. It's strong resistance to corrosion make it an excellent metal coating for scalpels, hypodermic needles, and other metallic tools. It also works as a micro barrier since its surface is impermeable above thicknesses of 1.4 nanometers. Its uniformity helps it adhere to sharp edges and points, again pointing to its widespread use in the medical field.
Unfortunately, because of its formation, it cannot be applied through a solvent. This means that the only way to coat an object in parylene is during the production of the polymer which occurs in a vacuum. While the object to be coated remains near room temperature, which aids in the safety of the process, and the coating is universal and uniform, it does mean that the polymer cannot be put into an aerosol can or produced en mass for consumer use.
PTFE can be made in one of two ways, each resulting in a different looking product, but by and large the same end result. With suspension, TFE is polymerized in water and results in the PTFE forming grains, whereas dispersion causes the PTFE to form as a milky paste. Both the paste and grain are processed and used to coat various products. Although PTFE itself is non-toxic, some of the byproducts of the manufacture process are toxic and at high heats the PTFE itself can emit toxic gasses.