ABA block copolymers, where A and B represent nylon 6 and polyurethane respectively, were prepared by anionic polymerization of ε-caprolactam in bulk. Isocyanate-terminated polyurethane prepolymers which were prepared from poly(tetramethylene glycol) (PTMG) and excess of hexamethylene diisocyanate (HDI) were reacted with ε-caprolactam to give caprolactam-terminated polyurethane prepolymers. Those prepolymers had N-acyllactam end groups showing the best initiator efficiencies and are called 'macroactivator' or 'macroinitiator'.
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 6 hrs. The molar ratios of MDI to PTMG (m.w. = 986) were 2:1, 3:2, 4:3, 5:4. The polyurethane compositions in block copolymer were varied from 10% to 40%.
Tg, Tm behavior, % crystallinity of nylon 6 segment and dynamic mechanical properties were observed through DSC and DMA. Shore D Hardness, water absorption and other mechanical properties such as tensile strength and impact strength were also observed.