1. Staudinger H, Heuer W (1930) Highly polymerized compounds XXXIII. A relation between the viscosity and the molecular weight of polystyrenes. Ber dtsch Chem Ges B 63:222–234
2. Ziegler K, Holzkamp E, Breil H, Martin H (1955) Angew Chem 67:426–541
3. Haenel M (2008) Historical sites of chemistry. Karl Ziegler. Max Planck Institute for Coal Research, Mülheim an der Ruhr
4. Hogan JP, Banks RL (1958) US patent 2,825,721
5. Hogan JP, Banks RL (1986) History of crystalline polypropylene. In: Seymour RB, Cheng T (eds) History of polyolefins. D Reidel, Dordrecht, pp 103–115