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‐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 Tm 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.