Flexible Cross-Linking by Both Pentaerythritol and Polyethyleneglycol Spacer and its Impact on the Mechanical Properties and the Shape Memory Effects of Polyurethane

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'-methylenebis(phenylisocyanate) (MDI), poly(tetramethyleneglycol), 1,4-butane-diol (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 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. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2800-2808,2009