An overview on 12-polyurethane: Synthesis, structure and crystallization |
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Authors: | CE Fernández RM Versteegen GJ Vancso |
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Institution: | a Departament d’Enginyeria Química, Universitat Politècnica de Catalunya, ETSEIB, Diagonal 647, Barcelona 08028, Spain b Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands c Department of Materials Science and Technology of Polymers, University of Twente, 7500 AE Enschede, The Netherlands |
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Abstract: | The knowledge on linear aliphatic polyurethanes n-PUR has increased significantly due to a series of works made in these last years and published in recent literature. An overview of 12-polyurethane (12-PUR) embracing its synthesis, thermal properties, crystal structure and crystallization is given in this paper. The purpose is to provide a representative example able to reflect comprehensively the state of the art reached for the whole family. The synthesis of 12-PUR was accomplished in good yield and with acceptable molecular weight from 12-amino-1-dodecanol by applying a two-step method without isolation of the isocyanate alcohol precursor. 12-PUR is a semicrystalline polymer with an equilibrium melting temperature of 157 °C. It adopts a layered crystal structure similar to the α-form of nylons with chains in fully-extended conformation and arranged in hydrogen-bonded sheets in the antiparallel mode. This structure is thermally stable up to melting and is unable to undergo Brill transition. 12-PUR crystallized from dilute solution affording well-shaped lamellar crystals with a thickness of 8-9 nm and from the melt yielding either banded or fibrillar spherulitic textures displaying negative birefringence. Isothermal crystallization of 12-PUR from the melt took place with heterogeneous nucleation, while both crystallization rate and the finally attained crystallinity degree were highly depending on crystallization temperature. |
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Keywords: | Polyurethanes Structure-properties relationship Polymer crystal structure Polymer crystal morphology |
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