Abstract
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., Guner, 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.
Highlights
Since the first shape memory polyurethanes were discovered in 1988 by Mitsubishi Heavy Industry, the research area has developed rapidly
The correlation between the intensity of the C = O peak, hard segment content, and effective phase separation is reported in the literature. 17,18 This correlation was investigated for the samples prepared in this study, since hard segment content and H-bonding affect shape memory polyurethane
10 In this study, we focused on the effect of chain extender ratio on shape memory performance for polyurethane films prepared from polyethylene glycol (PEG) and castor oil (CO), since the chain extender directly affects hard segment content
Summary
Since the first shape memory polyurethanes were discovered in 1988 by Mitsubishi Heavy Industry, the research area has developed rapidly. Polyurethane (PU) is a special polymer composed of soft and hard segments in its structure. Hard segments consist of diisocyanate and chain extender. 1 Due to the aggregation of hard segments via hydrogen bonds to form hard segment domains, which disperse in the soft segment matrix, a segmented structure and microphase separation occur. 2,3 Interactions between the molecules of hard segments increase the phase separation between soft and hard segments and enhance the shape memory properties of polyurethanes. 4 Since soft segments show a thermal transition at transition temperature and they work like a reversible molecular switch point, the molecular weight and the amount of polyol in the polymer are important parameters. The type and the amount of chain extender, which is an indispensable component of the hard segments, are important parameters, since hard segments are responsible for the original shape
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