Canadian Plastics

Polycarbonate: what can happen when the good stuff is already patented

Let's face it: "engineering" resins aren't called that because engineers like them or use them. That handle means one thing: expensive. But what do you call a polymer that went to the moon as space su...

November 1, 2003   By Jim Anderton,technical editor



Let’s face it: “engineering” resins aren’t called that because engineers like them or use them. That handle means one thing: expensive. But what do you call a polymer that went to the moon as space suit helmets, but can be purchased at any Home Depot to replace your broken basement window? Or an engineering thermoplastic that’s consumed at a rate of two million tonnes annually around the world? It’s polycarbonate, and like so many resins that we mold every day in this industry, it has a history and properties that you’d never imagine when looking at a pair of sunglasses or a compact disc.

Who invented polycarbonate? It depends upon whom you talk to. At General Electric, it was Dr. Daniel W. Fox and across the Atlantic, Bayer’s Dr. Hermann Schnell.

What is polycarbonate?

Regular readers who remember polymers as long chains of carbon atoms (polyethylene) or long chains of carbon with little hanging carbon atoms like charms on a bracelet (polypropylene) will find the molecular “repeat unit” of polycarbonate a Frankenstein image right out of Hollywood. It’s made of two main components: “bisphenol A”, a relatively harmless compound (phenols are popular sore throat remedies), and phosgene, a gas made popular by killing thousands during World War I. The stuff reacts in a mixture of solvents that are evaporated away, leaving a polycarbonate film.

Bayer’s first application was the balloons at Schnell’s 1953 laboratory Christmas party, made by using bottles as molds. Returning to the lab in the New Year, sober reflection (literally) and flaccid balloons on the floor suggested that a new production process was needed. Schnell’s team immediately began to work on a melt polymerization process, like that used for commodity resins, in an effort to eliminate the dissolving, washing, kneading and general beating up that it took to mass-produce polycarbonate. But which process was the best way to go: solution or melt polymerization? Bayer went both ways, with parallel plant development, while Schnell noted with amazement that no one in the U.S. or Japan appeared to be developing competitive resins. In 1957, Bayer’s P.R. team proudly announced the new thermoplastic, which would be named Makrolon.

In a classic irony, at the same time, General Electric announced that it had developed polycarbonate, calling its material Lexan. Lexan was the product of the laboratory of GE’s Dr. Daniel Fox, who invented polycarbonate in, you guessed it, 1953. As a result, both firms held valid patents and by 1973, General Electric had the dominant position by sales, while Bayer licensed some production technology to GE.

Is it possible that two research teams could develop the same sophisticated thermoplastic technology at the same time without knowledge of the other? Schnell’s notes reveal that it was coincidental, but perhaps not surprising because of another significant aspect of the development of polycarbonate. It may have been only 1953, but the days of stumbling over some goop at the bottom of a test tube were definitely over. Polycarbonate chemistry was the result of extensive patent searches that blocked Bayer’s entry into polyamides, since DuPont was that market leader, while Dr. Karl Ziegler had patented the process that led to mass-produced HDPE. If you were looking for a polyester derivative that wasn’t already on the market or at the patent office, polycarbonate was a logical place to investigate. By 1953, happy accidents were already history.


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