A study is presented of the polymerization of lauryl lactam and the copolymerization of lauryl lactam and caprolactam in a modular co-rotating twin screw extruder: Lauryl lactam had not been previously polymerized in a twin screw extruder: It was found possible to do this to high molecular weights. Generally, lower screw speeds result in longer residence times and higher conversions and molecular weights. The copolymers produced have broad melting transitions and their melting temperatures and heats of fusion exhibit minima as a function of comonomer composition.