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Development of high performance shape memory polyurethane by cross-linking pp.727-754 $100.00
Authors:  (Yong-Chan Chung, Byoung Chul Chun, Department of Chemistry, The University of Suwon, Hwasung, Korea, and others)
Effect of various cross-linking agents such as glycerol and pentaerythritol on the
shape memory property of polyurethane block copolymer is investigated. The copolymer
was composed of MDI, PTMG-2000, 1,4-butanediol (BD), and cross-linking agent. In
addition to the conventional cross-linking method, shape memory polyurethane (SMPU)
was laterally cross-linked by a polyethyleneglycol (PEG) spacer to remain flexible after
cross-linking, where PEG connected the hydroxyl groups of two polyurethane chains via
MDI as a connecting agent. Phase separation of hard and soft segment is dependent on
cross-linking and hard segment content. Hydrogen bonding and dipole-dipole interaction
between hard segments provides strong interaction between copolymer chains in addition
to chemical cross-linking. As the hard segment content increases, the copolymer shows
better tensile mechanical properties and higher melting temperature of soft segment (Tm).
Effect of glycerol cross-linking on mechanical properties and Tm of soft segment is low
compared to hard segment effect. Significant increase in shape recovery in the case of 30
wt% hard segment copolymer is observed after glycerol cross-linking. The four-way
cross-linking by pentaerythritol also improved the mechanical properties and showed a
very high shape recovery (94%), where the interaction between hard segments is mainly
responsible for the very high shape recovery rate. In the case of flexible cross-linking,
significant increase in maximum stress compared to linear polymer was attained without
any sacrifice in strain. Especially, it is shown in the stress-strain curve that the flexibly
cross-linked SMPU shows similar behavior and superior tensile mechanical properties to
natural rubber. Excellent shape recovery (96.8%) was found and shape recovery time was
3 times faster than linear polymer. The drastic change of the properties of polyurethane
block copolymer is discussed in the point of copolymer chain interaction. 

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Development of high performance shape memory polyurethane by cross-linking pp.727-754