In this research, a series of amorphous nylons 6 were prepared by introducing adipic acid and different structure amines into the copolymerization with caprolactam. The effects including thermal properties, crystallinity, dynamic mechanical properties, optical properties, and water absorption of different copolymerization structure and copolymerization ratio on the properties of nylon 6 were investigated. The results show the melting point and thermal cracking temperature Td 5 of nylon 6 are, respectively, between 179[Formula: see text]C and 217[Formula: see text]C and 278[Formula: see text]C to 336[Formula: see text]C. Nylon 6 structure introducing a methyl side chain is more effective than a meta-benzene ring, a meta-cycloalkyl, and bicycloalkyl groups, so CAMM and CAI have the lowest crystallinity.