Improved mechanical properties of shape-memory polyurethane block copolymers through the control of the soft-segment arrangement

High-performance shape-memory polyurethane block copolymers, prepared with two types of poly(tetramethylene glycol) (PTMG) used as soft segments, were investigated for their mechanical properties. Copolymers with a random or block soft-segment arrangement had higher stresses at break and elongations at break than those with only one kind of PTMG. Random copolymers with fewer interchain interactions showed higher elongation than block copolymers. All the copolymers had shape-recovery ratios higher than 80%. In dynamic mechanical testing, the glass-transition behavior clearly depended on the soft-segment arrangement: random copolymers had only one glass-transition peak, whereas block copolymers showed two separate glass-transition peaks. Overall, the control of the soft-segment arrangement plays a vital role in the development of high-performance shape-memory polyurethane. (C) 2004 Wiley Periodicals, Inc.