plastics are made up from tightly packed polymers, which are extremely long chains of atoms formed by joining small units of carbon-containing chemicals repeatedly end to end. Early methods for attaching these smaller monomer units together were unpredictable in that the resulting chains also contained random branches of chemicals, like a frayed rope, which affected characteristics like the strength of the final product. Karl Ziegler was testing possible new catalysts that could drive reactions to create neater chains, when he accidentally discovered that compounds containing aluminium and carbon in the presence of trace amounts of a transition metal element could achieve the task. Acting upon his fortuitous observation, Ziegler systematically tested a range of related compounds, until he arrived at a combination that could link together the small chemical monomer ethylene to form polyethylene chains that were longer and had fewer branches, and crucially could achieve this under less intense temperatures and pressures than the methods used at the time.