Preparation of olefin polymers, e.g. polyethylene, for producing pressure pipes for transport of gas and wastewater, by polymerization of alpha-olefin(s) with hybrid catalyst to produce higher and lower molecular weight polymer components

Preparation of olefin polymers comprises polymerization of alpha -olefin(s) in the presence of a hybrid catalyst to produce a polymer comprising a higher molecular weight polymer component and a lower molecular weight polymer component in the presence of 2-100 mol ppm water and/or 2-100 mol ppm carbon dioxide. Independent claims are also included for: (1) a method of controlling the ratio of a higher molecular weight polymer component to a lower molecular weight polymer component in an olefin polymer; (2) a method of regulating the ratio of a higher molecular weight polymer component to a lower molecular weight polymer component in an olefin polymer using the control method; (3) use of carbon dioxide for decreasing the ratio of a higher molecular weight component to a lower molecular weight component in an olefin polymer; and (4) use of water for increasing the ratio of a higher molecular weight component to a lower molecular weight component in an olefin polymer.