Preparation of N-vinyl carboxamides in a series of reactor units

A process for producing a polymer of an N-vinyl carboxamide, the process comprising:

• flowing a reaction mixture comprising an aqueous liquid comprising at least one polymerisation initiator, N-vinyl carboxamide monomer or a monomer mixture comprising N-vinyl carboxamide into a reactor system;
• and
• polymerising the monomer or monomer mixture to produce the polymer of N-vinyl carboxamide,
• wherein:
• 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, in which
• i) the at least one mixed flow reactor comprises at least one vessel comprising an internal mixer, an external mixer, or both, 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;
• and
• substantially none of the reaction mixture exits the single pass tubular reactor less than 50% of a mean residence time of the reaction mixture in the single pass tubular reactor.