In this study, flexible nylon 6 was reinforced by the following rigid-chain aromatic polyamides: poly( m-phenylene isophthalamide) (PmIA), poly(4,4 -diphenylsulfone terephthalamide) (PSA), poly( p-diphenyloxide terephthalamide) (POA), and poly( p-diphenylmethane terephthalamide) (PMA). Various high-molecular-weight block copolyamides were synthesized by solution polymerization using p-aminophenylacetic acid (p-APA) as a coupling agent. Their thermal properties have shown that the block copolyamides exhibit higher T g and T m and better thermal stability than those of nylon 6, especially PmIA-modified nylon 6. The order of their thermal properties of aromatic modified nylon 6 copolyamides is PmIA ΓΊ PMA ΓΊ POA ΓΊ PSA. Besides, the T g and T m of multiblock copolyamides are higher than those of triblock copolyamides. From the wide-angle X-ray diffraction pattern, it is found that the triblock copolyamides have two diffraction peaks (i.e., 2u Γ
20.5 and 24Π). However, the multiblock has only one at 2u Γ
20Π, indicating a different crystal structure for multiblock copolyamides. This can be further confirmed from scanning electron microscopy. It shows that the triblock copolyamides are a dispersed phase structure, although the multiblock copolyamides exhibit a homogeneous texture rather than an aggregated one. For the mechanical properties, it is found that the multiblock copolyamides have a more significant reinforcing effect than the triblock copolyamides. Also, the order of their physical properties of aromatic modified nylon 6 copolyamides, such as tensile strength, is PmIA ΓΊ PMA ΓΊ POA ΓΊ PSA; but for the elongation, the order is PSA ΓΊ POA ΓΊ PMA ΓΊ PmIA.