LAUSR

The practical application of polyamide 6 (PA6) in structural engineering is hindered by its limited toughness and weak interfacial interaction with reinforcing fillers. Carbon nanotubes (CNTs) have been widely explored to overcome these deficiencies, yet their strong tendency to agglomerate and poor compatibility with PA6 restrict efficient load transfer. Herein, we propose a solvent‐free one‐pot in situ polymerization strategy that simultaneously functionalizes carboxylated CNTs with bis(3‐aminopropyl)‐terminated polydimethylsiloxane (APDMS) and integrates them into PA6 during ε‐caprolactam polymerization. Compared with neat PA6, the nanocomposites exhibited increases of 16.1% in tensile strength, 21.9% in flexural strength, and 10.3% in notched impact strength. These improvements originate from a chemically bridged siloxane interphase, in which APDMS provides dual amino groups for covalent coupling and a flexible backbone for interfacial stress dissipation. The proposed approach eliminates the need for organic solvents and multi‐step procedures, providing an environmentally friendly and scalable route to tailor interfacial structures. This work not only demonstrates a balanced enhancement in stiffness, strength, and toughness, but also provides mechanistic insights into interphase engineering for advanced thermoplastic nanocomposites.