The effects of hydrogen bonding on the liquid crystalline behavior of semiflexible poly(urethaneester)s |
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| Authors: | Michele Laus Annino Sante Angeloni Oriano Francescangeli Giancarlo Galli Emo Chiellini |
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| Institution: | 1. Dipartimento di Chimica Industriale e dei Materiali, Università di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy;2. Dipartimento di Scienze dei Materiali e della Terra, Università di Ancona, Via Brecce Bianche, 60131 Ancona, Italy;3. Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126 Pisa, Italy |
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| Abstract: | The peculiar liquid crystalline behavior of two poly(urethane-ester)s TDI-C6C4 and TDI-C6C8 is reported. Evidence is provided of the formation of two nematic mesophases, a cybotactic nematic and a conventional nematic mesophase, in TDI-C6C8 and of one cybotactic nematic mesophase in TDI-C6C4. IR spectroscopy indicates that different hydrogen bonded and non-bonded structures occur with varying temperature. The transition from the nematic cybotactic mesophase to the nematic mesophase, or to the isotropic phase, is accompanied by a substantial decrease of the strength of the hydrogen bonds. This is also reflected in the dynamic-mechanical behavior of these poly(urethane-ester)s which is similar to the one of slightly crosslinked thermoreversible networks. |
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