Shape memory polyurethane (PU) block copolymers composed of 4,4′-methylenebis-(phenylisocyanate), poly(tetramethylene glycol), and 1,4-butanediol as a chain extender were synthesized by a two-step process. FT-IR spectra showed that carbonyl peak appearing at 1700 cm -1 increased with higher hard segment content, whereas another carbonyl peak at 1730 cm -1 decreased. It suggests that hard segments get more aggregated to form domains in the PU block copolymer as hard segment content increases. Such domain formation has a significant influence on the mechanical and thermomechanical properties of PU, such as maximum stress, tensile modulus, and elongation at break. Especially, maximum stress, tensile modulus, and elongation at break increased significantly at 30 wt % of hard segment content, and the highest loss tangent was observed at the same composition. Heat of crystallization as measured by differential scanning calorimetry is also dependent on the hard segment content. Finally, 80-95% of shape recovery was obtained at 30-45 wt % of hard segment content, and the control of hard segment content in PU block copolymers is very important in determining their physical properties.

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A series of polyurethane (PU) polymers cross-linked laterally by pentaerythritol and polyethyleneglycol (PEG) spacers were compared with linear PU. The PU was composed of 4,4 0 -methylenebis(phenylisocyanate) (MDI), poly(tetramethyleneglycol), 1,4-butanediol (BD), pentaerythritol, and PEG-200 as a spacer. PEG-200 connected the pentaerythritol hydroxyl groups of two PU chains with MDI as a connecting agent. The phase separation between hard and soft segments was disrupted by the PEG crosslinking, and T m did not change with an increase in cross-linking content. Instead, the cross-link density increased with an increase of pentaerythritol content. A significant increase in maximum stress compared with linear PU was attained, together with an increase in strain. The combination of both pentaerythritol and PEG-200 in the PU resulted in the improvement of both stress and strain, unlike in the conventional cross-linking method. The shape recovery increased to 90% and did not decrease after three test cycles.

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Water vapor permeable fabrics were prepared by coating shape-memory polyurethane (PU), which was synthesized from poly(tetramethylene glycol), 4,4Ј-methylene bis(phenylisocyanate), and 1,4-butanediol, onto polyester woven fabrics. Water vapor permeability and mechanical properties were investigated as a function of PU hard-segment content or polymer concentration of the coating solution. Water vapor permeability of PU-coated fabrics decreased dramatically with increased concentration of coating solution, whereas only a slight change was observed with the control of PU hard-segment content. The coated fabric showed the clear appearance of a nonporous PU surface according to SEM measurements. Attainment of high water permeability in PU-coated fabrics is considered to arise from the smart permeability characteristics of PU.Mechanical properties of coated fabrics, although there was some variation depending on the concentration of coating solution, were primarily affected by PU hard-segment content. Fabrics coated with PU hard-segment content of 40% showed the lowest breaking stress and modulus as well as the highest breaking elongation, which could be interpreted in terms of the dependency of mechanical properties of coated fabrics on PU hard-segment content and the yarn mobility arising from a difference in penetrating degree of coating solution into the fabric.

Dimethyl terephthalate (DMT) and ethylene glycol (EG) were used for the preparation of poly(ethylene terephthalate) (PET), and poly(ethylene glycol) (PEG) was added as a soft segment to prepare a PET-PEG copolymer with a shape-memory function. MWs of the PEG used were 200, 400, 600, and 1000 g/mol, and various molar ratios of EG and PEG were tried. Their tensile and shape-memory properties were compared at various points. The glass-transition and melting temperatures of PET-PEG copolymers decreased with increasing PEG molecular weight and content. A tensile test showed that the most ideal mechanical properties were obtained when the molar ratio of EG and PEG was set to 80:20 with 200 g/mol of PEG. The shape memory of the copolymer with maleic anhydride (MAH) as a crosslinking agent was also tested in terms of shape retention and shape recovery rate. The amount of MAH added was between 0.5 and 2.5 mol % with respect to DMT, and tensile properties and shape retention and recovery rate generally improved with increasing MAH.

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The arrangements, whether block or random type, of the soft segments of polyurethane block copolymers prepared with MDI and two kinds of poly(tetramethylene glycol) (PTMG; MW of 1000 or 2000) in various ratios were compared for possible effects on the physical properties of the copolymers. A long soft segment, PTMG-2000, was superior in all mechanical properties (strain, stress, and modulus) because a long chain length could provide more motional freedom than a short one (PTMG-1000) could and therefore was helpful in forming strong interchain attractions among hard segments. Inclusion of more PTMG-2000 led to a lower T g and a peak shift in infrared spectra. The arrangement of two soft segments in a block-type copolymer, a key finding in this study, was controlled by separately synthesizing two prepolymers, each with a different chain length, and connecting two prepolymers in a second step. Random-type copolymers prepared for purposes of comparison were allowed to react with two PTMGs in one step. Two types of copolymers were compared, and the reason for the differences in the shape memory property are discussed.