Abstract: This invention discloses a process for the preparation of polyolefins having a bi-or multimodal molecular weight distribution comprising the steps of: (i) contacting olefin monomer and a first co-reactant with a catalyst system in a first continuously stirred reactor under first polymerisation conditions to produce a product comprising a first polyolefin having a first molecular weight distribution; and (ii) contacting olefin monomer and a second co-reactant with a catalyst system in a second continuously stirred reactor under second polymerisation conditions to produce a product comprising a second polyolefin having a second molecular weight distribution that is different from the first molecular weight distribution; wherein the first and second continuously stirred reactors are connected in series, and the first and second polyolefins are mixed together, and wherein one of the co-reactants is hydrogen and the other is a comonomer, and wherein each catalyst system comprises (a) a bisindenyl catalyst componen