The synthesis of polyetheramide, containing poly(tetramethylene ether) (PTMEG) as the soft segment phase and polylactams as the hard phase was carried out in a Leistritz modular intermeshing counter-rotating twin-screw extruder in a one-step, solvent-free process. No by-product such as carbon dioxide or H2O is formed during the reaction procedure. Isocyanate-terminated telechelic PTMEG was premixed with caprolactam, and these were fed into the twin-screw extruder to form the polyetheramide triblock copolymer. This triblock copolymer has not been previously polymerized in a twin-screw extruder or continuous mixer. Subsequent to polymerization, the copolymer and PA6 homopolymer were also melt-spun into fibers. Molecular weights and molecular weight distributions were determined by GPC on trifluroacerylated samples. Thermal, rheological, mechanical, and structural properties were investigated. It appears that phase separation (arising from immiscibility between the polyether segment and the polyamide segment as the reaction proceeds) did not hinder the chemical reaction between the two reactants because of the intense mixing in the twin-screw extruder. The new triblock copolymer should have application as a rubber-toughened thermoplastic or thermoplastic elastomer depending upon the elastomer content.