Structural studies on 6–66 and 6–68 copolyamides

The effect of irregularity of chemical structure on melting points, densities and crystal structures was studied for 6–66 and 6–68 copolyamides. All copolyamides showed V‐shaped melting point vs. composition curves. The densities, corrected for the difference in molecular weights between comonomers, also showed a minimum at similar compositions with respect to melting points. X‐ray diffraction angles of the two main reflections, (200) and (202/002) in polyamide 6, and (100) and (110/010) in polyamides 66 and 68, respectively, approached in the copolymers. In melt‐crystallized 6–66 copolyamides, the approach of the reflections was especially prominent, and the crystal structure of the copolyamide containing 30 mole‐% of the 66 monomer was rather close to pseudo‐hexagonal. The crystallites are transformed easily to the α from by annealing in boiling water.