Answer
High-density polymers are produced by a process called Ziegler–Natta polymerization, which was developed by Karl Ziegler and Giulio Natta in the 1950s. This process involves the use of Ziegler–Natta catalysts, which are complexes of transition metals such as titanium and aluminum with organometallic compounds. These catalysts allow for the production of polymers with high molecular weights and narrow molecular weight distributions.