Students should come up with a variety of examples. The instructor can provide the example of Dupont’s Teflon. Dupont patented the chemical discovery, polymerized tetrafluoroethylene (PTFE) in 1941, and registered the trademark Teflon. Initially only Dupont could produce Teflon (wholly proprietary), but soon it began licensing the product to be used in other applications (limited to moderate licensing). The patent on polymerized tetraflouroethylene eventually expired (but the trademark remained intact) so other companies began producing polymerized tetraflouroethylene under different names such as Silverstone or T-Fal (mostly open). Notably, the EPA is now investigating the potentially harmful effects of PTFE products to the environment and human health. After more than 60 years of popularity, a decision is expected to be made in 2004 about whether the product should be withdrawn from the market.