Polyurethane with an ionic liquid crosslinker: a new class of super shape memory-like polymers. Issue 31 (20th July 2018)

• Record Type: Journal Article
• Authors: Behera, Prasanta Kumar; Mondal, Prantik; Singha, Nikhil K.
• Is Part Of: Polymer chemistry. Volume 9:Issue 31(2018)
• Page Start: 4205
• Page End: 4217
• Publication Date: 2018-07-20
• Subjects: Polymers -- Periodicals; Macromolecules -- Periodicals; Polymerization -- Periodicals; 547.705
• DOI: 10.1039/c8py00549d
• Languages: English
• ISSNs: 1759-9954

Abstract

Abstract : Polyurethane (PU) with an ionic liquid crosslinker (with a unique double network having a combination of covalent as well as ionic crosslinking) showed excellent shape-recovery as well as excellent shape-fixity properties compared to linear PU and non-ionic crosslinked PU. The non-ionic crosslinker resulted in hard and soft phases intermixing, whereas the ionic interaction in ionic liquid crosslinked PU kept the phase separation intact. Abstract : This investigation reports on the synthesis of a new class of ionic liquid crosslinked shape-memory polyurethane (PU-IL) based on polycaprolactone diol and 4, 4′-methylenebis(phenyl isocyanate) (MDI), which can overcome the major drawbacks of conventional shape-memory polyurethanes. In this case, the ionic liquid crosslinker in PU-IL exhibited not only a higher shape-recovery ratio (98%), but also showed excellent shape-fixity (98%). In the second cycle of the cyclic tensile test, PU-IL showed almost complete shape recovery while maintaining excellent shape fixity. The higher shape-fixity value in PU-IL was also supported by its higher crystallization and melting enthalpy, as evidenced by DSC analysis. The properties of this PU-IL were compared with those of conventional linear PU having 1, 4 butanediol (BDO) as a chain extender as well as of non-ionic crosslinked PU using trimethylolpropane (TMP). Ionic liquid as a crosslinker reduced the glass transition temperature ( T g ), whereas the non-ionic crosslinker increased the T g . Interestingly, the soft segment crystallinity as well as melting enthalpy of PU-IL is higher than that of PU-BDO, whereas no melting or crystallization peak was observed in the DSC thermograms of PU-TMP. The DSC results were supported by DMA analysis. The higher T g and the absence of a soft domain melting transition indicated complete intermixing of hard and soft phases in PU-TMP, but the ionic interaction in PU-IL restricted this. Inter-domain mixing in PU-TMP was also supported by the absence of a scattering peak in SAXS analysis. FT-IR spectroscopy showed stronger hydrogen bonding in PU-BDO followed by PU-TMP and PU-IL.