Process for the polymerization of olefins and block (co)polymers derived from at least one olefin

A process for the polymerization of at least one olefin, which is a suspension process employing a hydrocarbon diluent such that at least 70% of the polymer formed is insoluble therein, and which employs at least two polymerization reactors, including a first reactor and a second reactor, comprising:

• (a) introducing a first portion of the at least one olefin and a catalyst into the first reactor, the catalyst comprising bis(cyclopentadienyl)chromium, which may be substituted, supported on an inorganic oxide support;
• (b) polymerizing the at least one olefin in the first reactor to provide a first composition comprising a polymer and the catalyst;
• (c) drawing off the first composition from the first reactor and introducing the first composition and another portion of the at least one olefin into the second reactor;
• and
• (d) polymerizing the another portion of the at least one olefin in the second reactor in the presence of the first composition,
• wherein hydrogen is introduced into at least one of the reactors at a partial pressure ranging from 0.01 to 0.50 MPa, the ratio of the hydrogen to olefin partial pressure in this reactor ranging from 0.01 to 3,
• wherein the catalyst is supplied solely into the first reactor,
• wherein the olefin partial pressure in the at least two reactors ranges from atmospheric pressure to 5 Mpa, and
• wherein the polymerization in the at least two reactors is carried out at a temperature ranging from 50.degree. to 100 .degree. C.