Plastics and Ziegler-Natta polymerization In the early 1950s a new process for synthesizing polymers was discovered that made a lot of common plastics possible, including high-density polyethylene and polypropylene. Karl Ziegler (1898–1973) and Giulio Natta (1903–1979) were just two of several scientists who independently developed the process. Robert Banks (1921–1989) and J. Paul Hogan (1919– ) of Phillips Petroleum had actually discovered the same process about a year earlier, but this wasn’t sorted out until the 1980s, and by then the name Ziegler-Natta polymerization had already stuck.