The invention relates to a process of producing polymers of a N-vinyl carboxamide comprising the steps of flowing a reaction mixture comprising an aqueous liquid containing at least one polymerisationinitiator, N-vinyl carboxamide monomer or a monomer mixture which comprises N-vinyl carboxamide into a reactor system, polymerising the monomer or monomer mixture to produce the polymer of a N-vinylcarboxamide, in which the reactor system comprises a series of reactor units comprising a combination of at least one mixed flow reactor and at least one single pass tubular reactor, wherein i) the atleast one mixed flow reactor comprises at least one vessel containing internal and/or external means of mixing; and ii) the at least one single pass tubular reactor comprises a tubular section disposed between two ends, at least one inlet and at least one outlet in which the reaction mixture flows through the single pass tubular reactor only once, wherein substantially none of the reaction mixture exits the single pass tubular reactor less than 0.5 of the mean residence time of the reaction mixture in a single pass tubular reactor. The polymers resulting therefrom may be hydrolysed to providepolymers containing vinyl amine units. Also provided are the apparatus suitable for producing said polymers.