Polyurethane and Nylon 6 block copolymers were prepared by the anionic polymerization of ε-caprolactam in bulk. Polyurethane segment was composed of the reaction product of poly(propylene glycol) (PPG) and 4,4'-diphenylmethane diisocyanate (MDI) to form an isocyanate-terminated PU prepolymer. The PU prepolymer was reacted with ε-caprolactam to give a caprolactam-terminated polyurethane prepolymer which was used as an initiator in the anionic polymerization of ε-caprolactam.
Caprolactam magnesium bromide was used as a catalyst. The reactants were mixed at 100℃ and transferred into a preheated mold. The reaction was performed at 145℃ for about 10 hours.
The molecular weight of the polyurethane segment was 2,500 and 7,500 and that of Nylon6 segment was varied from 5,833 to 67,500. The polyurethane compositions in block copolymers were varied from 10% to 30%.
$T_g$, $T_m$ behavior and % crystallinity of the Nylon6 segment and the dynamic mechanical properties were observed by DSC and DMA. The block copolymers showed two separate $T_g$'s of the component polymers, the Nylon6 segment $T_g$ being shifted towards higher temperature as the polyurethane composition was increased. But $T_m$ of the Nylon6 block showed gradual change from 215℃ to around 195℃ as the PU composition was increased to 30%.
Mechanical properties such as tensile strength and impact strength were also observed. As the PU composition was decreased to 30%, impact strength and \% elongation were increased and tensile strength was decreased. In edition, shore D hardness, water absorption and density were measured.
