Castor oil and PEG-based shape memory polyurethane films: effect of chain extender amount on some polymer properties and performance

A series of polyurethane (PU) films were synthesized via one-shot bulk polymerization with polyethylene glycol, castor oil, hexamethylene diisocyanate, and 1,4-butanediol (BD) at three different chain extender ratios. Since it was found in our previous study that hard segment content is more effective on shape memory property than soft segment length (Bonfil, M., Sirkecioglu, A., Bingol-Ozakpinar, O., Uras, F., Güner, F. S. J. Appl. Polym. Sci. 2014, 131, 1–12), in this study the effects of BD amount on some physical properties, thermal properties, and shape memory performance of the films were investigated. Shape fixity and shape recovery were achieved under two different cooling/heating regimes. The amount of BD is an important parameter affecting the physical properties, chemical structure, and thus shape memory performance. Decreasing the BD amount increased the crystallinity and the films, being of relatively high crystallinity, showed the highest shape recovery ratio. Increasing BD amount in PU films increases the hydrogen-bonded structure and the films having a relatively high degree of hydrogen-bonded structure showed the highest shape fixity ratio. The samples showed higher shape memory performance at high cooling and heating rates.