A process for preparation of a polymer product comprising the steps of i) feeding an aqueous mixture comprising a monoethylenically unsaturated monomer or a mixture of monoethylenically unsaturated monomers into a first reactor device (2) through at least one inlet; ii) partially polymerising the monomer or monomers and transferring the polymerising monomer or mixture of monomers from the inlet to an outlet (3) of the first reactor device (2) to provide a partially polymerised product; iii) flowing the partially polymerised product out of the outlet (3), in which no more than 60% of the monomer or mixture of monomers has been polymerised in the partially polymerised product as it exits the outlet (3) of first reactor device (2), and transferring it to a further reactor device (5), in which the further reactor device (5) has an inlet and an outlet (6); iv) continuing the polymerisation in the further reactor device (5) and removing the polymer product from the outlet (6) of the further reactor device (5), characterised in that the first reactor device (2) comprises a positive displacement pump.